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aP IRRIGATION .ENGINEERING BY

(. R. SHARMA P.

s. E. Class I ; C. E. tHons). (Roorkee) ; M. I. Eo P. W. D. Irdgation East PDnjab.

VOLUME I

INDIA PRINTERS,. BOOKSELLERS $: PUBl.ISHERS. ,

'

TRAINING COLLEGE ROAD. JULlUNDUR. INDIA

Printed by Sh: Kahan Chand at the Steao Press, Putligllar, .A.MRITSAR. Published by It. R. Sharma, P. S. E., Cla.ss I; C. E. (Hons). (Roorkee); M. I. E. (India), Punj~b Irrigation. '

AmrI&IJar Agen1s:. Jaswant Rai Gyani & CO., Hall Bazar, AMRIrSAR.

FOREWORD. By A.M.B.

Montagu,

IS. F •• C.I.E" M.l C.E .• A.C.GJ. Chief Engineer, Irrigation works, Punjab. I look upon' it as a great privilege to write the foreword to Mr. Sharma's comprehensive work on Irrigation. I have known Mr. Sharma and his work for a number of years and have always been impressed by his keen interest in the physical foundation of irrigation practice. But he does not confine himself merely to prinf'ip\es of hydraulics lllvolved in the art and practice of irrigation He has made a prfllonged study of all mc:.tters that can be said to touch upon irrigation in general. Even the revenue side received his careful and zealous attention. In many respects. Funjab irrigation leads the world. Without irrigation, the Punjab would still consist of a few strips of land contiguous to the rivers, upon which the anxious cultivator would sow a crop uncertain whether or not it would reach malurity. Today, by virtue of its canal systems, the Punjab is the granary of India. Valuab e crop are now grown in areas which were originally arid waste whereon nothing was found t ut thorn and the camel which throve upon it. During the last few years, no less than 14 milllOn acres of crops have been matured by irrigation water from the fiftt::en separate canal systems of the Province. The actual distributinn of the available water tf'tween the canal systems has necessiated the construction of feeder canals which convey surplus waters of one river to a river in deficit Distrihution nmong the iJl(livldual channels of a canal system IS a relatively simple matter. Far more difficult is the o'stributi()n among the Individual cultivators. In the Punjab, the greatest athntion is concentrated 11pon this di.strihution. Where thi, distribution Is faulty, cultivators promptly bring facts to notice. The individual irrigation officer is concerned not only with distributiorJ by existing known methorls, hut in many cases utilizes his scanty lei~ure in endeavours to secure fresh forms of outlets which will still further improve and stabilize the distribution to the cultivator's watercourses. Among the~e energetic and enquiring gentlemen, Mr. Sharma occupies a high place. His work on outlets is well known. His activities in other directions have not perhaps received all the attention they deserve. This book is a compendium of all knowled!!e aVd.ilable to him on the suhject ano will unquestionably prove of the greatest value n'1t only to the practising irrigation Engineer but al"o to the student who is preparing himself to serve in that great service, the Irrigation Rranch of the public Works Department, Punjab It is but natural that many of the views put forwarrl I,y t e ~uthol are coloured bv his Punjab experience. Reailers foreign to the Punjab may concludt' lha,t unone weight is laid upon the Punjab practice ard Punjab views. The ans\\er to any ~uch implied criticism lies in the fact that the Punjab is very confident of its c::tDacity to design. construct and arlministff irrigation systems of the largest size. In many w"},!;, such as distrihution of water already mentioned, the des;ign of major works on the shifting sands of rivers, the economical design and m~tnan(e of relative Iv minor structurei, the Punjab Engineer may justifiably h(lld that he is to the fore front modren practice and knowledge. In other directions, the Punjab Engineering is first to recognize that he can l,..arn not only from other countries of the world. but also from other provinces in India It is probable that the construction of high cams will snon occupv the attention of the Punjab. E xpf'rien 'e ill this field is negligible and we turn to other Countries notably the United States of America for instruction and gUluancc! III thi~ field. The Punjab is behind other countries in the use of machinery, but it is probable that post war development will impose an advance in this direction also. S

nf

ii In many ways, the advance of kn'lNledge in our relatively restricted field, is phenomenal. For example. in the mltter of pl ll)iag water ton the su~-soil water resevoir by means of tUbe-wells, it is p.)ssibla tnat the praGtij;e described in \1r Sharma's book may have advanced by the time these VOlll:n~S are in th.e huh of the public, but for many years to come the student of i,rigation engineuing may turn with cJilfirljnGe to the3e pages for a useful and comprehensi're gtlide to irrigatiJn puctice. with spe~ial reference to the Punjab. Lahore, 15th January 1945.

; A.M.R. Montagtt.

PREFACE TO 1st EDIITON.

The science of Irrigatio) Engineering in India has developed by leaps and bounds during the last two decades. Th:ltrrigation Works of India, especially of the Punjab, oc.upy a prominent place in the world, both from the point of view of the academic interest as a science and of the successful results of large irrigation engineering projects. Since the epic books 'Irri~ation 'vVork5' by Bligh, 1907, and Irrigation Pf'cket Book. by Buekley, 1911. were written, the development of the Science in India is confined to the technical papers co ntribted by the eminelllt Engineers available in the proceedings of the various Engineering Sccieties, such as the Punjab Engineering Congress, Lahore, tht' Institution (If Engineers India, Cenrral Boaro of Irrigation, Bombay Engineering Congress, the departmental technical papers of P. W. 0, Punjab and Bombay and the research publications of the Punjab Irrigation Institute and Central Hydro-Dynlmical Research station Poona, Bombay. The purpose of this hook is to present the science and the practice of Irrig::ltion Engineering in a concise form comprising practically all the modern developments. The book is essentially ment to be used as a Text RO'Qk for the students preparing for the Engin~ering Degree Examinations of the various universities in India and otRer c0mpetitive examinations of the Central GOVErnm"nt. Selected examination qU!3stions usually set in Degree Examinations of the various universities in india are giv=n at the end of each Chapter. Some examples of the typical design .. of irrigation Works have reen worked out for the guidance of the students. Since irrigation Engineering (distinct from HJdraulics) is not a suhject taught in the British or other European unive 'sities, no text booh dealing with the subject are available. This book is intended, therefore' to meet a lqng standing need of the student comm~nity in Tndia The book also deals with the actual practIce of science in the field and is meant to be used as a refel ence book I ha ye, therefore, attempted to cover the require men ts of the students in the examination que .. ti0ns (covering the syllabus of the v:'lrious universities in India and the competitive examinations of the Fedral public Services Commission). In th~ Chapters which are considered beyond the scope of the studen's, no questions are given at the end The subject of Irrigation EngiKeering has developed mathematically so much that it g~es beyond the capacity of an average stu<~ent or a practiC::lI Enginee, to cram up all the formulae. In aI, accompanying volume, the diagrame gen' nlly used in Irrigation practice are given which can be used by the students and practical Engilleers. for solving the problems relating to the design of Irriga!ion Works. . The book i" devided into six parts and forty four cha.pters. The first part, comprising two chapters, deals with Lift Irrigation, the s~cond comprising 20 chapters deals with Flow Irrigation, the third ?ompri~jng six ch_apte~s deal; ~ith Ta.nk . !rrjg~tiQn the fourt~ ?omprising f our chapters deals WIth DraInage Engmeenng-, the fIfth ccmprtsmg SIX chapters dealsrivlth Ground Water Eugineering [water· logging] and the last part camprising six chapters deals with general informa.tion usually required in engineering practice. The fourth ::Ind fifth parts comprise the subject which is usually definer{ as Hydrology in American practice Obviou>ly the whole of such a comprehensive book cannot be original Detailed references to Ihe publications cOIisulted have been mentiond in the text. The list of author~ is SO large that it is not possihle to acknowledge gratefully the help and the U8e of their work by naming to them individu 11ly. Similarly the refences to the proceedings of various Eagineering Societies, referred to in the text are gratfful 1y acknowledged. The help rpndered in compiling. editing anti improving this Book by the following Irrigation Engineers of the Punjab is thankfully acknowledged: [lJ R::Ii Bahadur B. N, Singh' T. S, E., retired Chief Eng-ineer, punjab Irrigation. [2J Rai Bahadur D. K. Khanna I.S.E. Superintmding Engineer [now Chh~f Engineer Irrigation Works.] [3J Rai B::Ihadur B 1.. Uppal I.S E., retirerl. Superinteding Engin Eer Punjab Jrril!ation. [4J Rai Behadur Kanwar Sain I.S.E, Superintending E~ginee~ [5J Rai Eaha?ur B,~. Kap~r, Director ~rrigati:n Resear.ch, Lahore. [6] Rai Bahadur Hakim Rat, I.S.E. Snpenntenrlmg Engmeer [7[ ]atIDder Smgh, ASSIstant Engin~er. ~uld [8] K.S. Pdthak Assistant Engineer

iv

J

The author is '-'extremely grateful to the Honourable Minister of Public Works Department (now premier of the Punjab) Malik Khizar Hayat khan Tiwana and the Honourable Member of Revenue in-charge of Irrigation Department, the late Sirdar Bhadur Sir ?undar Singh Majithia, for se lectillg the author to do spade -work of Civil Engineering teaching In the Punjab as the first professor and the h .. ad of the Civil Engineering Department at the Maclagan Engineering College, Lahore. The author availed of this opportunity to study the, subject as a whole and to compile his lectures in the form of this Book. He is also grateful for the encouragement received from the Honourable Minister of Kevenue, Rao Bahadur Chaudhri Sir Chhob) Ram. The author's thanks are also due to A. M. R. Montagu, Esquire., C.LE., ChIef Engineer, Irrigation, for the trouble of going through the whole Book and then writing the foreword. Extremely useful and valuable suggestions to improve the Book were kindly supplied by him. . Last' but not the least. the Author is specialy indebted to E.S. Crump, I.S.E; C.I.E Retired Superintending Engineer.under whose guidance, the author carried out experimental research work for more than 5 years. K. R Sharma, Amritsar, 27th May, H:l44. Preface to 2nd Edition. Part III of this book dealing with the Storages and Dams [Tank Irrigation] has been . revised and enlarged. It comprises now six chapters instead of four in the 1st edition. . Design diagrams' are bound 1D volume III. These are intended to be used by the students 1D the class room and could be issued to the students in the Examination Hall for the soluticD of the problems dealing with practical designs. . The help rendered by Dr. J. K Malohtra, Ma.thematical officer Irrigation Research Instttute East Punjab in editing the 2nd edition of this booN is gratefully acknowledged. Amritsar. 1st. Decem ':ler, 1948.

K. R. SHARMA.

NOTA nONS (A) Hydraulics.

USE~ :rHE BOOK' -

,

Steady flow is tbat state of flo'.v in a stream where the discharge across any defined section of the stream remains constant in respect of time. . . (Tni'orm flow. Uniform flow is steady flow in a stream when the depth does not vary wIth constant d;~ch
Constants. C

Arbitrary or experimental co-efficients. Lacey's "silt factor" g The gravity constant. K Theoretical constant in the "free fall" discharge formula K=-vg-(iJ 3 /!=3.0888. N The co-efficient of rugosity of a channel. . Na Lacey's co -efficien t of Roughness in a channel. w The weight of 1 cubic ft. of water=62'S Ibs. W .~otal weight. Discharges. Q The dis~harge in cubic feet per second (cusecsl of a channel or work. q The discharge in cusecs per foot width of a channel or work. Energy. E The total energy expressed in feet head of water above a fixed datum. When plotted, this depicts the "total energy line". The 'energy of flow' expressed in feet head of water above the bed. When the total energy line has been plotted. the "energy of flow" is depicted by the intercept betw.een the bed line and the total energy line. (In hydraulic books, the term specific energy of flow is llsed instead). Ec Energy of flow in critical conditions of flow. fL

h

H

Ha ha

Hw

The head or energy required to produce a velocity h

==~

Depth on crest including velocity of approach head:s:G+ha Afflux bead The hea? or energy equivalent to a velocity of approach Va The. aval1abl" working head, i. e. the difference in total energy levels between two sectlons. The minimum working head required between two point

vi Hl

The head lost between two points, due to aU cayses e1l1Cept destruction in a standing wave. The head or energy distroyed in a Hydraulie jump.

HL

Velocities. The mean velocity in feet per second of a stream at any section. The mean "velocity of approach" The mean velocity of normal [Neutral] flow corresponding to Dn . The mean velocity of regime flow corrpsponding to Br . . The velocity of flow, at a section with critical flow. Kennedy's standard silt-charge velocity Vo =0.84 Dg·64 x

= ~ =critical velocity ratio [Kennedy's] Vo

Dimensions. L The length of a channel or work measured along the line parallel to the direction of flow between two points. Lt Tl.l.e length of parallel sides of the throat of a weh:. flume. etc. B The length of a channel bed transverse to the direction of flow. i. e. the width. Bt The width of the throat of a weir, flume etc. D Th@ depth below the surface of a strpam ber! at a stated point. Dn The normal depth of a stream corresponding to Vn • Dr The regime depth of a stream corre!'ponding to Vr. Dc Critical depth corresponding to Ve. A The cross sectional area of a stream at a stated point. Pw The wetted perimeter of a cheRnel. Bs The top or surface width of a stream. R

The hydraulic mean depth of a

stream=-~. Pw

Miscellaneous. S The actual slope of the total energy line at any given point. Sw The aetual slope of the water surface at any given point. . Sh The actual slope of the bed of a channel at any given point . .")0 The slope of the total energy line in the case of normal flow. Sr The slope of the total energy line in the case of ngime flow. f Co-efficient of friction s The side of at rapezoidal channel. G The gauge rpading: Zero of gauge must be specified. p \.:fV· The total pressure on a cross section of a stream. p The intensity of pressure at a stated point. The instantaneous radius of cnrvature at a point in general, aDa lor thtn_ r •t streams ......... of the bed; exectly ......... the mean radius of curvature of all the filamen~. in a stream, (B} Hydrology

Areas in square miles:A

Ae Ao

As Ah Ag

Total area of a catchment, Effective area of a catchment. That a.rea for which dispersion is uuity or thlt ateawllldh can be Wholly eovered by . a storm with unvariable intensity of storm. . . Area covered by a particular storm, Area between two isohyetals. Area of in1 1uence assigned to a. rain-gange station,

yii

P Pa Pm

Pt

Ps Ph

R Ra Rm 'Ra,

Q Qs Qo q

T t

st

o Ba Om

L B E D I Im S F

R?1infall or precipitation in inches:, Mean annual total rainfall over a catch ment. Total annual rainfall over a catchment for any year. Total monthly rainfall over a catchment fur any month. Tetal rainfall during an interval 't'. Total rainfall of a particular storm as recorded at a rain-gauge. Mean annual precipitation between two isohyetals. Run-off [for volumetric studies} in inehes:Mean annual total run-off from a catchmeBt. Total annual 'run off from a catchment for any year. _ Total monthly run-off from a catchment for any month: Total run-off of a particular storm. Discharge for [intensity stt~dies] in cusecs:Maximum discharge from a catchmeNt. Maximum diseharge from a catchment on account of a particular stOl:'m, Maximum discharge from a catchment Ao. JJi5charge per square milt: of catdllnent. Time in hours:Inlet time. An interval of time. Duration of storm. Temperature in d~grees [Fahrenheitj:Temp~rature

in degrees Fahrenheit. Mean annual temperature over a catchment. Mean monthly temperature over a catchment. M is,ellaneous;·Distance in feet 01 watershed from the stream along the line of flow. Absorption into the soil in inches of depth per hour. Evaporation in in~ 01 depth per hour. Total loss in inches per hour=E+ B. Intensity of rainfall. Maximum inten;ity of rainfall. Maximum slope of catchment from watershed to the dlainage. Reduction in, inches due to rain initially held by trees, crops and undergrowth.

To determine mean annual rainfall of a catchment:Exmapels, (a) Isohyetal method;p=~ Ph.Ah =;;S Ph.Ah ;;S Ah A (h) Weightage method:-

Extra notation. 1 't ~ .::'".; 1" ;Pg Precipitation at any rain ..gaug8!~tation~·" , :,

< I .'

P=~ Pg.Ag _:2 Pg.Ag ~Ag A

('e) The straight average method {ior a large plain area} ~'In '.. p A1Pl+A 2 P2+ Al+A 2 +

, .

.'

An~

An

viii q

Uld Pl ,

Note,-The total area is divided into n sub-divisions, Pa• Pn represent the average rainfall Run off formulae (volume)

':.i ...

Al , A2 .............. An for eaeh sub-division.

(a) Vermeule formula:-R::::P- (11 +O.29P, (0.358--0.65) (b) Khosla's formula:-R=P- {} +C 2 Extra notation

. :J:J

.,

C=A constant which allows for catchment characteristics humidity' glacier contribution

etc, but

not

for absorption, evaporation and transpiration covered by the

e

tempera.ture factor 2'

MaximHm discharge from a catchment (int;nsif/l): (a) Inglis formu1a:-

Q= ?~OOA for fan-shaped catchments 'vA+-i

And Q=7000,/A- -'Z40 (A-lOO) for an etongated catchment. (b) Khungar and Gulllatj's formula:Q=645AoZ;:nax - F C Ae T Ao

m Zmax

t

Index of disper~ion, Maximum height of a theoretical hydrogra.ph for a rainfall of ma.ximum possible intensity in the catchment,

(e) Flow of water through sub-soil under weirs and dames.

Symbols:

H P

Pc G GE t p

fl

Head in feet or difference in water levels upstream and downstream of a work [Percolation head]. ' Pressure head in feet in a pressure observation pipe measured above the downstream water level. Pressure head at point C. Gradient, or rate of change of head. Exit gradient. Temprature in-degrees Fahrenheit. Density of fluid. Viscosity= '47-1~~~O?k~()f+~000682 t 2 t'IC · K merna

Q

. 't y= VISCOSl

flp

The discharge in cusecs of a channel or work.

q// The discharge in cusecs per foot of width of a channel or work.

p pressure head expressed as a percen tage of the total head = -Ir- X 100.

Determination of exit gradient:(a) Floo], with pile at downstream end:-

JX

d b

Extra notations, Depth of pile line below floor surface. length of impervious floor. b

=(i

l+V-I~

2

GE

H • '~ ... 1 A. =EXl't gra d'lt'n t =(1

-

(h) Floor with pile at downstream end with step:-Depth of pile line belo,"" upstream impervious flolr. Depth of pile line below downstream pervious floor. Length of impervious floor upstream.

H

--~c----

[d1 -d 2hl

K A.

•

.

l-K'

where K is given by the equation

Cos- 1 K= . ?t~_ d 1 -d 2 Pressures at different points one pile line or depressed (laor:-: d1 Depth of pile line below upstream floor. Depth of pile line below downstream floor. d2 bl Length of impervious floor upstream. b2 Length of impervious floor downstream. b bl+b a ~E q, at junction of upstream floo~ pile line. ,pD q, at bottom of pile line. q, at junction of downstream floor and pile line. Mutual interference of piles:-.

V

l-K2 K

+c

C-19 d_2~ d1 +d, vb' ' - b C b' d, dl h

the correction to be applied as percentage of head. the distance between the two piles. the depth of pile whose influence has to be determined on the neighbouring pile of depth d i . depth of pile on which the effect of pile d 2 is sought to be determined total floor len~th,

x

(DJ Dimensional Formulae.

2

Geome ricai quantities. Length (any linear dimension) Depth Head .

r

4

ft.

L

I

R

I

pwJ

.

A V

Area

Volume . . Kinemalical quantities.

(ft.)1

a

v

g fL

=ILp

Discharge Dynamical quantities. Mass. . Surface tt n~ion Viscosity . • Pre'sure (unit stress). Modulus of elasticity. :--.hearinp; morlulu$ Density Momentum Force Weight

1'~

locii

:ool!

Q

i"

i, !;~f'\ ~~

T '."'.

lIT

Tlrs

LIT LIP

LIP

ft.'/sec.

L2JT

ft a/sec.

vJr

M

Mass

M

v

to./ft.

Hi. X ~ec,{ft.2

M/T' MILT

lb./ft.'

M/LT'

Mass/ft. 3 Mass x ft./sec,

M/L3 ML/f

(-l

, BI

~'-i ,~"

second Radians/Sec. Radians/Sec.1 ft/sec. ft./sec.' ft./sec. 3

1i!

•

Vt I.V'

(ftoll!

T

ime • Angular velocity . Angular acceleration • .Velocity • Acceleration due to gravity Lacey's silt factor Kinematic Viscosity •

3

~l

H I d }-

Diameter . Raf1ius . Hydraulic mean df!pth Wetted Perin.eter

Dimensional formull in terms of mass, length and time.

Common English Unit

Symbol.

Name of quantity,

p e es p

1 J

ill

F)

Wr

11>

ML/P

J

Torque

Pq

1

E lEwJ

Energy Wo1'.l&

(E) 0:

Alpba

13 Beta 'Y

Gamma

a LI Deft::!.

i

Epsilon Theta iota

iT

Kappa

E.

/J

MVII

ft.x lD.

-rs

Greek Alphabets.

Laulbada fl Men

Upsilon

,{

1.1

t!-:

t Xi 1] Eta ...l. Zeta

(Jw

7\

Neu Omicron Pi

p Rho ~ Sigma T Tau

x

ChHki)

(j!)

Omega

¢ V.

Phi Psi

Author's other Technical Papers. 1.

2. 3. 4. 5. 6.

7. 8.

9. \0.

Underpinning Satghara Rest House, L.J.C., Paper No. 143. Punjab Engineering Congress, 1931. Remodelling of' Mithalak Distributary, Paper No. 154 Punjab Engineering Congress, 1932. Effect of outlets on the Regime of a channel. "Indian Engineering" Calcutta October and November 1932. Silt conduction by Irrigation Outlets. Paper No. 168 punjah Engineering Congress, 1933. Design of an A.P.M. Paper No. 176 PunJab Engineering Congress. 1934, Design of irrigar.ion channels paper read in "Institution of Engineers India" in 1935 and copiE's placed in the Punjab Irrigation Libraries received vide Superintending Engineer U J.C. No. 962 dated ~8th July 1937. Silt selective Distributary Head Regulators. Paper No. 189 Punjab Engineerin5 Congress 1936. Design of R.C. Extensible Bridges i0r Drains, August 1936. printed copies placed in the Punjab Irrigation Libraries vide Chief Engineer':> No. 386, dated 29th January 1937. Standing Wdve or Hydrauiic Jump, "Indian Engineering, Calcutta" October 1936. Indian Engineenng. Calcutta Determinat.ion of water profIles over Hydraulic Works. 19l~.

11.

12. 13. U. 15. 16.

17.

18. 19. 2U. 21. 22.

23. 24 25.

,26. 27. 28. 29. 30.

Experiments in Spepage Losses from canals. Paper No. 209 Punjab Engineering Congress, 1938. Automatic Silt extractors without loss of water. Indian Engineering, Calcutta, February 1938. Cross Darin'lge Work (Auto-Suction Weirs) Indian Engineering, Calcutta. Febru:try 1938. Improved adj ustable proportional modules and open flume outlets. Punjab Engineering Congrflss 1940. Model Experiments to determine suitable length/of skimmig platforms on models of the Head Regulator at Rasul, Punjab Engineers' jo\unal, May 1939, Lahore. . Theory anti physics of seepage flow from canals. Paper No. 231 punjab Engineering Congress, 1940. Use ot P0rtable Flumes for water course discharge Measurements. February 1940 Punjab Engineers' Joumal, Lahore. Minimum M )dular Hea.d 1M. M. H ) for an Adjustable Proportional Module, January ~940 Punjab Engineeri' Journal, Lahore. EXDeriments to determine" frue Basic Sub-soil Pressure at R. D. 299,000 U. C. C (W. l. R. Bib 16). Metf'r experiments to determine Losses in Mangtanwala Feeder (W. I. R. Bib 5). Tank Exp.erim"nts to determine laws of seepage losses at R. D. 348,000 U. C. C.· (W. I.R. Bib 71. Determination of Seepage Los;es in U. J C. from Rashidpur to Shadiwah from meter discharges. (W. I. R. Bib 14). Trough experiments to determine Seepage Losses by Point Method in U. J. C. (W. I. R. Bib 44). Sub-soil con(litions in adjoining fields of Thur anG cultivation. Determination of losses in Low.:r Chenab Canal by taking Seepage Discharge Observations in a closure (W. r. B Bib 21) Determination of losses in Uoper Cenab Canal by taking Seepage Discharge Observations in closure. (W. I. R. Bib 21) B. S P. Experiments at Khanki to detllrminp. B. S. p. costours in a complicated case of sources and sink and to oetermine True Soil Pressures in River. (W. 1. R. Bib 17). Report on Seppa~e Los,es of U. C. C. & L. C. C. (years calculated and actual compared by months). (W. 1. R. Bib 31. "Hump" Investigations unoer c'lnal. Point Method Apparatus and its use on L.C.C. Distys: to determine their losses.

X

.. ,;

Plotting and analysis of 39 Daily B.~.P. Stations (W l.R. Bib 43). Plotting and analysis of B.S.P. PIpes along canals calculations of losses by using observed S.LC. (W.I.R. Bib 18). 33. Capillary fringe and soil evaporation st1ldies with Hydmdynamic soil Pressure Observations (W.I R. Bib 42,. (a, Containing fore ward by Mr. Blench. (b) Detinitions. (c) Note dated 5-6-39, 15-12-39 on ,- Hydrodyna:nic Soil Pressure observations at Lahore. (d) Note dated 8-6-39 on "Experiments at R,D. 180,000 L.C.C. to measure evapora_tion from the .bed of a pit. (e) Note dated 15-9--39 on "Capillary fringe and Rise of water level in Bore Holes at R O. 1S0,00a L.C.C:," (f) Note dated 20-9-39 on "Soil Pressure Observations· to determine evaporation gradient by Progressing Lowering of ben of pit at RD. !80,OOO L.C.C." (g) Note dated 16-11-39 on "Hydrodynamic Soil Pressure Observations and Capillary Fringe studies at RD.' 150,000 LC.C. (hI Note dated 25-'7-40 on "Hydrodynamic Soil Pressure observati()Ds and capillary' fringe studies opposite RD. 46,000 Chichokim~llian Distributary." . (i) Note dated 2-1-40 on "Technique of Hydrodynamic Soil Pressure observations below' the effective saturation line." (j) Note dated 25-3·40 on "Capillary Fringe studies at Hudiara Nala." (kl Note dated 26-340 on "Hydrodynamic Soil Pressure observations at Sheikhupura site. 34. "Division of the Punjab" by an engineer. June 1947. . 31,

32.

IRRIGA~~ION RNGIN~ERING.

Volume •. Table of Contents Foreword by A.M.R. Montagu C.LE , I.S.E., M.LC.E., A.C.G.I., Chief Engineer, Irrigation Works Punjab, Preface by the Author List of other Technical Papers by the author Table of contents Introdu;ti0n

Page iv IX

iii xi 1

PART I-LIFT IRRIGATION Chapter i-Open Well I r r i g a t i o n . , 3 Definition. S:.lUr~e of Water Supply,location of w~!l" d.scharge of Irrigation Wells, suitability of well water for crops, classes of wells, construction aud sinking of wells, methods of raiSing water, duty alJd delta of well wat"er. cost of Well Irrigation, Well Irrigation versus Canal !rrigataion. Questions. Chapter ll-Tube well Irrigation 13 Tube wells and their object, water bearing or non-water bearing formation, water dividing, History of tube well practice for Irri;.:ac;on, Boring of tube "'ell and different methodS, percussIOn rope. bv
PART. II-CANAL IRRIGATION. Chapter I--Classification of Canals. 42 Irrigation and navigation canals. classes of Irrigation Canals, fin~ classifiication. receipts from irrigatirn canals, parts of canals, Punjab Canals, distribution of river supplies to the Punjab Canals Functions of Canals, Questions. Chapter H--Principal crops and Assessment. 49 Introductory. Soil conditions in the Punjab, rainfall, principal crops in the Punjab, fertilizers and manures, crop diseases and their cure, aconomy of water. Snb-Irrigation Internal distribution, Units of Measurement of areas, asses"ment metbods, record of irrigation, special charges, Miscellaneous Reccipts Duty of Canal Water, Efficiency, Questions. Chapter III--Hydraulics and Control of Large Rivers. 62 Introductory, Major Divisions of River Channel, torrents and streams, river regime Theories by Molloy Oldham etc. meandering and avulsions of rivers and their extent, erosion, swirls. silt and velocities, in Punjab rivers, reclamation works, spurs and groynes (Denhy's). object of guide banks (Bell's Bund) an':! extent of narrowing, their desigr. and construction, retired embankments. marginal Bunds an 1 ;;purs, pitched islands, I" yout of river embankments. cross sections of emba'lkments, Question. Chapter IV-Head Works. 87 Introductory, selection of site, layout, types of weirs, afflux. ponil level, waterway for weir, effect of weirs on the' regime of river, undersluices. divide wall, fish ladder, head regulator, silt control at head works, guide banks and marginal bunds. moveable weir crests and shutters. Gate lifting arrangements. Chapte. V-Design of Weirs on Permeable Foundations 115 Introductory, Theory of design and its development, parctical weir design", determination of uplift pressures (Khosla's theory), theory of exit gradient, curtain walls, and sheet piles, Khosla's design of modern weirs, wing wall design, examples of weir design, Questions. Chapter VI-Design of Irrigation Channels. 151 Introductory, Hydraulic formal
xiv flume, author's design of meter flume and calculations, examination questions. Chapter XI-Silt Excluders and Ejectors 268. Intr\9duction, definition, approach channel to a silt extractor, escape discharge above extractor, approach design of the extractor. tunnels and their design, extractors C',m meters, effe-:t on canal regime, efficiency of silt extractors, tYl'ical design and its calculations, Author's automatic silt extractor without loss of water, examinat;on qupstions, Chapter XH-Fluming and Headless Meters 282 Definition, cla,sification ot flumes, hed profile de~ign, upstream approa"h design, theory of departure or expansion, Burkitt's method of expao:-;ien, athor's method of downstream splay, examples with calculationr and desi~n of flumed acqueduct, flumed bridges, contraction with depressed floor, Burkitt's Headless Meter Flumes, Author's improved and economical headless meter flumes. weir cum spillway, syphon flume, surge tar,k" <11,d chambers and rigi,i tOP flumes, Chapter XIII - Syphon Spillways and Hydratomats 303 Introducticn, discharge formula of syphon spillways, types of spillways, priming methods and their comparison, de"ign vf syphon spillways for High Dam£. graphical method of desIgn. effect of splllw&\'s on dams, ice trouble in sp.llways Hvdratomats, six example cf design of various, ype.; of ~yphons with calculations. Chapter XIV-Di,trioLtary Head Regulators and Distributors . ... ... 329 introduction undershot distributary head regulators, over-shot regulator, (Wood's rising cill gates), Cribb's d:stributary Head Regulator, King's "ilt vanes, head with skImming platform, Cantilpvered skimmer,;. Author's Slit sE'lective distnbutory Head Regulators, Ex,mple of de·ign of SIlt ~elective Hedd Regulators, proportional di,tributors, field tPsts of silt excluding devIces, examination questions. Chapter XV - Outlets and Tail Clusters 340 Tvpe of modules, ctefin,tion, modular heRri, non-morlular outlets, tilted pipe outlets, Kennedy's Gauge Outlets, Harvey Stoddard improved outlets, Kirkpatnrk module (Jamrao type). Crump's adjustable proportional module. Author's improved '. P. M (submerged semmJf)duh oTJflce outlet S. S. 0 0.), Crump's open flume outlet, ~ utnor's weIr flume and n.rrow opE'n flume OUI Jets, Pipc-cum-semi-me:>dule (double module outlets), rigid modules (Kent Glbb Khanna and GhHffur), tail clusters, watpr-course discharge observat,ons, Cipollette "elr and Author's detachable and protable flumes, outlet chaks, examiloation qestions. Chapter XVI-Irrigation Projects 361 Introduction, prellmina. y survpvs, surveys ano alignment, location and layont of Headworks, longitudinal sections ",nd cross "eeti"ns of mian can. Is," land plans, Inca' ion and alIgnment of distributaries, area, command and draw-off scatments, chak plans and alignment of water-courses, masonry works, estimating and rules of preparation of project estimat" and construction, direct and indirect receipts and financial outturn, plans· required in Ir·rig-ation Projects, examination questions. Chapter XVII--Remcdelling Channels, 482 IntroductIOn, necesslty of remodelling channels, hench marks and hydraulic surveys, history .of channels di3.gnosis of troubles, ch'tnnel sectin'J~, outlets, head regulotor, drowned bridges, J,-,wering of channels, eontrol paints and metprs, strengthening banks, silt clearance and berm cutting, watching channel after remoaelling, H_ registers and characteristic curves, examinatio.\ questions. Chapter XITIII--Inundation Canals _ 391 Introduction charcteri'tics, ~ilting canal head re"ch, changes in head reaches, selpction of off-take subsidiary tu a'is "unns at h"ads, miscellaneou< works. P. cl"xton's theory of Inundation canals, concluslOllS, examinati 1\ quest om,. Chapter X,X--Discharge Observations anc. Regulation 400 Intro
Volume II. PART III-TANK IRRIGATION (STORAGES & DAMS) Chapter I-Storage Reservoirs or Tanks. lntroduction, Definition, Catchment discharge from rainfall and snow melt, preliminary investigations and survey, final investigations. choice of site, capacity of reservoirs, irrigation capacity of tanks, capacity for water supply to towns, abwrption and avaporation lossps from tanks, silting of reservoirs and their remedies, auxiliary re,erVOIrs and supply channels, flood absorptiv ... capacity of tanks, reservoir flood routing, floud control leservoirs, leservoir ope,ations, sptllway di,charge capacity of reservolrs, spillway tuniJels, emcrgency spillways, biblography, examination questior.s. Chapter II. Earth Dams. Introduction, definitions:- Foundation of earth dams, Material of construction of Earth Dam, Practical Criteria for th ... safety of earth dams. safety agalDst oven, pping, seepage flow net and seepage flow under dams, Method of dealin~· with excessive seepage through Eanh lams, Prec3.utions to guard against free passage of weter thlough darns, Remldies to be appled to reduce excessive flow under the dams, Stability of Hydrauhc fill lams. foundation of earth dams Elastic theory of shearing Stre~ses in earth dams, :Slip Circle net hod of testing earth dams Taylor's "tability numbers, construction detaIls of ear:h ~ ams

xv construction of Hydraulic-fill-dams, observations and studies to watch safety of dams after construction, Waste weirs, Tower and outlets, Maintenance and repairs of earth dams, failures of earth dams, Examination questions. Biblography. Chapter III. Rock Fill dams 59 Introduction, definitions :-T)'pical cross-sections of Rock fill Dams, Foundation charactenstics of a Rock tiiIl Dam, Design of rock fill dams and its parts. Settlement of rock fiJI dams, Core wall type of Rock Fill dams, Composite type of rock fill dam, Earth Core type of Rock fill dam, hand packed Rock fill dams, Biblography. Chapter IV. Gravity Dams (Masonry or Concrete). 69 Introduction. definitions :-Advantages of masonry dams, disarlvantages of masonry dams, Examination of site, Forces acting on a gravity dam, Silt pressure, ice pre~sure, Earthquake forces Uplift, Wind pressure, Wave pressure, Requisites for stability of Gravity dams, Design of If)w gravity dams, Profile of a low gravity dam, DeSign of high dams with Example, method of mf)ments for testing stability, graphical mf'th"d of testing stability, Haes~ler's graphical method of testing stability, Vertical shear and the Ellipse oistresses in the body of the dam (solved example). Constructions details of masonry dams, Construction details of concrete dams, Temperature control in dam~, Failures of masonry dams, Temperature stresses in dams, EXamination questions, Biblography. Chapter V. Arch and Multiple Arch Dams. 104 Introduction, definition, Arch Dam types, Masonry arch dams, shell theorey of arch dam design, Ela~tic theory of Arch Dam design, Trial and load analysis of arch dams, Design proceedure of Arch dams, Loads on arch dams, Investigations of arch dams, Model tests of Arch dams, Failure of Arch dams, Multiple arch dams, Design of Multiple arch dams, Rib-shortening, Professor Cain's formula, F. H. Fowler's Diagrarus, F. A. Noetzli's formula, Diagram of working stress intensities, Design of the buttress, Failure of multiple arch dams, Comparative cost of a Multiple arch dam with othtr types of dams, Example ofaxisting Multiple Arch dam, Biblography Chapter VI. Buttress aDd Reinforced Concrete Dams. ~ 126 Introduction, definition :-Forceb against buttresses, Earthquake loading for buttr<ssed dams, Spacing of buttresses, Design of buttresses, Upstream face of buttress dams, Shrinkage cracks in buttresses. Masonry buttress, demand example of design, Shrinkage cracks in buttresses, Masonry buttress dam and example of design, Slab buttress dams and their various types. columnar buttress dam, Truss buttress dam, Cantilever deck dam, Round head buttress dam, Diamond head buttress dam, steel buttress dam, Connection of facing & foundation, Buttress dams on soft foundation, Reinforced concrete dams, Reinforced concrete Dome Dams, columnar and slab design of Buttress Dams, Biblography.

PART IV-DRAINAGE ENGINEERING Chapter I. Rain Fall and Run off ... 139 Introduction, hydrology, rainfall phenomenon, definitions, effect of climate, variability of the annual rainfall, measurements of rain fall, intensity curves, spacing of rain gauge stations, factors affecting run off, IUn off estimate in a small catchment. hydrograph, combination of hydrographs of various areas Gullati and Khungar's analysis, run off from large catr.hment. run off from very large catchment areas, examination questions. Chapter II. Surface Drainage (Open Drains or Ditches) ...... \. 160 Introduction, classification of drains, alignment, capaCity of drains, drain section design, cr
PART V-GROUND WATER ENGINEERING Chapter I. Soil Physics ... 191 Introduction, soil and its textures, soil cJas8ification, physical properties of soil, soil water, soil characteristics, other soil constants and equilibrium limits, swelling and shrinkage of soil, stability of 50ils, properties of clay and collOids, distribution of wat€f in soil crust, soil temperatures, soil atmosphere, soil sampling and 3.nalysis. Chapter 11. Surface Evaporation, Soil Evaporation, Transpiration 212 Definitions, effect of temprature on surface evaporation, effect of Manometric pressure, effect of Relative Humidity. effect of wind, effect of depth of water, measurement. of surface evaporation. soil evaporation, factors affecting soil evaporation, measurements of soil evaporation, transpiration, factors affecting transpiration, amount of transpiration. Chapter III. Grouud Water Reservoir Movements. 222 Introduction. general configuration of the ground water reservoir, definitions, experimental evidence of ·B. S. P. conception, well observations, water equivalent of well rise, sub soil flow (Darcy and Hazen). Author's '" , 8ub soil flow formula, and its use in the field, well Versus B. S. P. observations, water table in a soil crust, capillary fringe in a soil crust, fluctuations of wells in water logged areas, effect of barometric pr€ssure on B. S. P. level, yearly cycle of rise and fall of grounds water reservoir, hump in water table under the canals. Chapter IV. Theory and Physics of Seepage Flow from Canals ... .., 249 Introduction, history of the development of the subject, Wilsdon experiments, Author's experiments, temperature correction, moisture variation below canal bed in three phases, pressures and gradients below bed in saturated and unsaturated phase, conditions of losses in three pha~es, Haigh's formula of absorption losses; reasons for the unsaturated phase not causing any addition to the water table, method of assessing .seepage

xvi losses, discharge observation method, flume ob,ervation method, evaluation of percolation intensity co-efficient from seepage discharges in cloures, point method (point method apparatu5 and trough methGd), statistical methed, Dr. Yaidianathan's method by observing seepage profile, examination questions.

Chapter V. Water Logging and Antiwater LoggIng Measures ...... 274 Defil'lition, factors responsible, the infertihty ~f water 10liged lands, water requiremenb. for crops in water logged aleas, causes of water le>:ging, ri,e of water table in various Doabs in the Punjab, the cure of water logging and anti-w6ter logging measur~;;, lowerinR of water table in Bist D0ab and, its remedies, stable water table near the "nd of Rechna noab and water inventory in R,chna Doab; examination questions. ;;hapter VI. Reelamatiol'l of Thur and 5"", Land '" ••• 284 Introduction, salt in the soil crust, formation of Rukkar ~oils by base exchange in the salts, soil clalisification for purpose of reclamation, Telia Kallar Lanrl5, re~lamation methods, reclamation opelations, permanency ol reclamation by leaching, Immunity of Kallar trouble iu well irrigated areas, reclamation of Sem lands, adjoining fields of Kallar and good culturable lands, eXamination que5tions.

PART V[-GENERAL SECTION Cltapter I. Soll StablJization .,. 2&3 Introduction, properties of ~oi), ideal soil lor bl'st stabilization,clay percentages,<:>ptimum moistures content density of soil, soil compactiem at optimum moisture in large works, various methods of soil sta.bilization, detrimental salts in soii, use of soil s'abilization ill road eU/iineering, use of stablilized soil base for aeroplane landing !!roundo, soil stabilization in water logged areas Cllapter II Design of Bridges and Culverts 309 Introdu~t!On, I. R, C, Standard loading reinforced C?'1crete bridges, masonry arched bridges timber bnd>:es amd ublll8 of design. Cbapter III, Technique of Hydrollynamic Sub-SoiJ Pressure Observation 321 Introduction, design of appalalus I'nri its working, design of pressur6 tapping pOint, theO£y of bellzine. differential manometer, temperatu"e errors, design of P.T. pipe in stiff soil crust, record of pressure unaffected by temperature, diaphragm manometer, use of Chattock Micro manometer, use of hydrodynamic pressure ob~eryation to measure height of capillary fringe, measurt:ment of Darcey's K or a.uthor·s (P,r.C), soil evaportion, flow into the water table, effect of drains .. nd canal_, ground water flow down the Doal;) and transpiration. Chapter IV. Hydraullc Jump and Water Proll.les 336 Notations. general equation of floW' in open Channels, critical conditions of flQW with various prdpertie~, standing wave, hydrauliC jump on a level flow, jump on a glacis,' jump with lTough drowned, determinatioa of position of jump, back water f'qu Hions in different cl!Jndltions, backwatet function~, determination of water profiles, examination qu<'stions Chapter V. Iiydraulles applied to Iniga tloR 3S() Introduction, hrdro~tatlc~, Bernhouilli's theorem. flow through small orifices, small an
Volume III Diagram used in designs of Irrigation

works-Plat~

No.1 to XXII

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xViii

•

IRRIGATION ENGINEERING

!1nh,oduction RRIGA TION is the art and practice of causing water to flow and spread over land with the oJject of nourishing the growth of plants. Plants may be agricultural crops, fr'uit trees From the point of view of art, it is a branch of in gardens, or trees in fortsts. Engineering and fro.n that, of actual practice it is one of Agriculture.

ll

Plants require for their growth proper weather conditions of heat, light and moisture In irrigating countries situated chielJy in tropical and sUJ-tropical regions, the first two are a'oundant and do not need to be supplenented. The last na
(d) DRAINAGE ENGINEERING-Drainage Engineering inclUdes Hydrology and deals with the science of measuring and analysing the flow of precipitation of water (rainfall) evaporation and analogous phenomenan to provide the correct basis for estimation of the supplies availaole for irrigation purposes from the natural drains such as rivers. This further deals with the artificial channels known as surface drains or sua-surface drains, which are designed and constructed to drain

2

off surplus rain water.. ~h~ w.ater from such drains is irrigation purposes, by hft Ifngatl9~>' , .....

sometimes used

for

(t) GROUND WATER ENGINEERIl-<"lG+Tbis deals with the science of water occuring telow the surface of the earth, its distribution and movcment. This further deals ~ith the dynamics of water ta ,Ie mowments as infl.uenced lJy rainfall, irrigation and other factors. 'Vater percolates to the undergrcund reservoir from the canals, from other su)siqiary irrigatiol} ,Ehannels, and from the irrigation fields. Irrigation results in excessive additions of watcr . to the water ta 'Jle which gradually rises under ground. The lands are said to J e waterlogged when water ta.Je rises so near the natural surface, as to di~inish the proc:.uce of the crops. The works required to reduce and prevent water-logging, necessarily pertain to that branch of engineering which deals with irrigation. ,.,

.

_, The o'Jject of .thiS book is essentially tc deal with' ;.trtificia.'l irrigation involving works of • the nve types as enumerated a·cove. This Dook. 4eals with the techniqu of the Cfj)llstruction f and maintenance of works relating to all of these five branches of irrigation engineeriI4:i with a view to equip the student with su'ficient practical and theoretical aspect of the projlems relating. to them. A large number of solved examples of. the. design of irrigation works are given. Selected examination, questions ar{) given at the end of chapters, important for the ·:sfudents preparing for the Degree Examinations of the various Engineering ,Univetsities in India . .' Italy' I~ay wen ce considered as the parent country in the science of distribution of . water. It was the first country to .take up large schemes involving large irrigation works. The' Italian storage reservoirs !ln~ aqeducts have served as a guide to irrigation engineers in other countries. Indian Irrigatian no dou')t followed the foot steps of Italian practice. The first large canal was constructed more than a century ago in the enited Provinces in India. The Ganges Canal is still a great engineering success, and was followed by large canals in the Punjab. The Punjab canals are first-class examples of the development of the science of irrigation engineering. The .reyenue return from the Punjab canals is the highest and the efficiency of their working surpasses all irrigation works in the world. It is a well known fact that the Egypti.arirrigation system is founded on the Indian system. The science of Irrigation engineering:,independently developed at great strides in. the United States of America.' Large irrigation schemes both in the forms of tank and canal irrigation have teen successfully constructed there. . The ,Al!1erican practice undoubtedly now leads the world in the teChnique o,f .the design and construction of high dams. ,

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PART

I

LIFT IRRIGATION Chapter I

iRRIGATlt)N FROM UPEN' WELLS' '''

1.

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Definition. , Wells are merely holes in the ground t(!{tap·.the underground water. They may be entirely unprotected, partially protected or entirely protected by means of lining ofbr~c~,milsonary. They are called open wells as distingui.shed from the tu .. e wells:" ,A~~,~~.;.... , 2. Source of Water SUllply. The source of water supply for open wells is the sheet of water found under the gro~nd. This underground reservoir of water commonly called the water ta·.lle is fed 'by .rainfall which, soaked into the soil, permeates under the grclUnd. Water is 'held thera by the ;~ncec of the impervious stratum below this sheet of WaLer. The retent;ve SU0stratum is no~hihg but the consolidated sodiu n clay hardened by the 'heat in the interior of the earth glaDe which increases towards the centre. The laws relating to the flow of the sub scil ground water are dealt with at length in pa~t V of this volume. There is only slight lateral flow in the sui) soil reservoir towards the mam drainages, i. e., rivers; and as the country slopes from the foot of hills to the confluence of the rivers, the main underground flow occurs along the slope of the ~?untry. The underground water is available in three forms :(a) Rock hollows. (b) Artesian basins. •. ' (c) Ground reservoir.

Rock hollows filled with water are found in the hills, they are generally small and cannot be used for irrigation. The artesian Dasins are found near the foot of the hills. The rainfall permeating in the hills reappears on the natural surface on, account of the high pressure gradient and the presence of the i:nperviou5 soil consisting of coarSe sand'a_I!d gIavel a"ail
<

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The- average discharge from an irrigation well, water'r eing lifted by Pe~sian Wl:e~ls, ha5 1een found to be 0'137 cusec (page 253 Farm Accounts 1933-34 Punja1:l). The dIscharge IS more than this in the case of mot or charas. The discharge require:nent of a well is never going to b(t more than 0'15 cusec. The discharge formula to estimate the discharge. from an open well may te used in the following form:Q=4/3 a AH where Q=Discharge in cusecs. A=Area of the well in sq : ft.

,

H=Infilteration Head or Depression Head (Percolation Head) .. a=Percolation !ntensity co-efficient in cUsecs per unit area per units head. The constant ','3 represents ratio of the actual area A' ?f the safe cavity fOffiled to the area A of the well as shown In Fig. 2. The usual value of a for tte Punjab soil of t~e water i earing strata is .75 X 10- 4 which gives a corrcs~ondig value of the Transmission constant of about '00023 In the Darcy formula of viscous flo N throgh the soil. •

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EXAMPLE •

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Find the diameter of a wall to give a discharge of 0'15 Cs with an infilterati~n head of 12'0 feet.

Let percolation intensity co-effcient per sq : foot='75 X 10- 4 Let the diameter of the well=d feet. d2 Area of the well = - 7T 4-sq: ft.

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= 12'8 say 13 ft.

For an average sand of 16/1000 inch average diameter in the Punjab, the optimum velocity

~f .005 it./Sec has teen found to move the finest soil particles in the experiments carried out out

the Irrigation Research Institute, Lahore (vide page 228, Paper No: 248 punjab Engineering Congress) . .

III

The actual velocity of flow in the above quoted exampl{(==

0009 ft jSec. which allows approximately a factor of safety of 5. A factor of safety of at least 3 should always be allowed to provice for the years of draught when the well has to be \\'orked under the worst conditons.

5. Suitability of we:l water

fOf

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All sub ~oil waters are !lot suitable f~r irril$atiori J?ut'poses, ~~ter. of the well shoul.d be" tested to e.xamlne the amount of salt contamed 1n solutIOn. The lrngatlOn Rllsearch InstItute, Lahore has cevcloped a technique in evolving an expression to which the name of Salt IndeJi

5

is giveri. T.his is a measure of the quality of irrigation water in relation to the soils. The sodiu'll salts nre,ent in tlle Irrigation Water cause l'ase reaction to take place in the soil with its consequent deterioration. If calciull salts are present in the irrigation water, the reaction is opposed and delayed some what . . Salt Index=(Total Na -24'5) - (Total ('a-Ca in Ca C0 3) 4'85. When the e'{nression is np.gative, the water is suita'-.le for irrigation of the crops, and when Dositive it is unsuitahle. The brackish water as found in the Western Punjab is unsuita~)le fOf irrigation, while the sweet water of the Jullundur, Hoslliarpur, Amritsar, Gurdaspur and Sialkot distr:cts is very good fOr irrigation. . ~ 6. Classes of wells. ra) ImpervIous lined weIls. These are the only type., of wells userl for irrigation purvo5es. They are usually of tyoo shown in Vig. 2. The de3i~n anti the Df0CeSS of sinking such wells is descrihed in detail in the su"sequent paragraTlhs. When the botto'1l of the well is in san~y soil, it is usual to provide ipverted filters at its rott'1'1l so that a dangePJJ., cavity is___nill_for:nerl during t"'e years of draught. TIie"luverfen filter simply consists of alaver of eoarse sand aHheO-oUom, a layer of fine gravel in the micldle anrl a layer of bajri of a'~out i" to t"SiZe at the top. These layers are a!~out one foot thick each. (b) P'JfV:OllS Unei Wells. A QQl~ is dug in the ground.kthe water table and dry brick or stone lining_is then laid on.a well £ur~} l!p._!.9- a h~igm0f8 or 10lecl:lhe soIl InsIde IS scooped and ~eH can Fe sulik easl1Y~ feet }-~]Q"".J:lle spring leveI."WIiile sinking is done, the sandWiIlno dou',t flow out from the joints: -This will ;"e very mu:cn reduced, if brick ballast of size 1" to 1" is filled around the lining, so th8.t it may sink along side the lining. Such wells are~conomIcal III the case of ,small devths. And when the discharge required is not much, water percolates from the sides also. They are quite successful when the arrangement for lifting 'Water is Rati or Denkli. I, () Kacha Wells. t This supposes that clay stratum is available from the natural surface down to a few fee~ below the spring J&yel.an.4.!hat the soil is stf()I!K_tlllough to_stand_witho:ui. tlw_ ht:1p of_th,e lining. -. Such wells are used for low lifts up to 10 to 12 ft. by means of Rati or Denkli. 7. Linei Or Pacca Wells. .- ~. ..--All open wells used for irrigation are circular. The thickness of the lining or steinins is usually 2 bricks i. e. 1'5 ft. for depths up to 40 or 50 ft. For depths up to one hundred

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, feet, the thickness of lining sho~l~ ie2t tricks, i, ~." ;t~;k RPWL:''?:tlN~ for~eR~~s. ~?\q~,e;lifol,~

100 it. are never built, Leca~se hftmg of wa~e.r bewme-J V«x:Y ,~neyp~?mlFaL , 1~~ hnmg ~s PUllt in lime mortar of proportlOn 1 : 2 (one h!ne ,and 2 ,S,\lT~Jq qr ~fl.11c;l)~ Qr, sei~J,C
t'

The well curb' is a continuous tent team in cetween the tie rods supporting the triangular wedge of masonry of isosceles shape with angle 45 when the masonry IS in Ce'l!-ent mortar, and with angle 60 when the masonry is in: muLi or lime mortar. fhc lengtas of tne rods should be at least double the height of the weight triangle of masonry. fne tie rods are anchored at the top in a circular plate iron f' to i" thick anu about 6" wide. The section of the wooden well cur,) can l"e designed according to the formula;0

,

0

M= ~-- or d2=M2/Z where d=dept~ in inches . . . 2 -V2~ M=cendmg moment lO lOch tons.

It is supposed in deriving this formula that

'-

"the sale tensile stress in wood is ! ton/sq. inch and that the section is triangular with top width 12". R. C. section of a curu can easily D,e calculated' , considering it to ce a Learn of triangular section carrying a weuge load in ;__etwcen tne rods as shown in Fig. 3. (c).

B.

Construction and sinking of welJ,:;. (a) A circular pit is dug in the ground up to the water taole or up to the bottom of the clay str';ita, which ever is higher. Tile pIt snould De sujicient -in circuinference to allow a space of at least 2 ft. around tile lining. In clay the sides 6t the pit can usually stand vertical. (b) The well curb is laid when soft soil or water table is

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(cl Masonry of the required thickness is, then, built on the well- cu~h 'to it height of about 8 to 10ft. a Jove the ground level. ;', ,(d) Then a temporary platform is made on the top of:linjng to ~1.)-pport t~e weight of gunny bags filled with earth ,to facilitate its sinking. 'The lO,
ot

r.

(I} If is necessary to see th,
The o1:lstruction may te in the form of roots of a _ tree or pieces of stone. If tl'ere is no such obstruction, it is then a case of the unequal soil friction against He lining. The weights on the platform are the1] shifted to the siee which is sinking slowly. If unequal loading cannot cope with unequal skin friction, then the soil behind the lining should "te wetted by using water jet under pressure. (g) The c1igging of the insi£ie soil by men is usually possible up to five or six feet j elow the spring level by cootinuously bailing out water. When the ingress of water is more than the removal, then digging by means of kassies cannot proceed. FurPler digging is done by a jham which is a large kassi. A diver dives and fills thc jham with soil, which is lifted by the pulley arrangement. This is no doubt a slow process. Wells have j een successfully sunk from 20 to 25 ft. below the sDring level by this method. The modern dredgers like the Bull's dredger clench the soil by weight of tl':e' blades and when the chains are pulled, the blades autO'natically close with the soil filled in t1ce drcdger. The digging of soil under water is very much facilitated by this method. (h) When the curb with steining has thus been sunk to the required level, the space around the lining is filled with good clay earth consolidating it by ramming and watering in successive iayers of a'Gout a foot de" tho (i) Finally the top parapets are built on the top of the steining to suit the water lifting arrangement which is usually a Persian Wheel.

9. ,Methods of RaiSing Water. c>'

The following water lifts are more or less in general use in India :__:;,"

1.

Rati or pulley block arrangement for small garden plots.

2.

Denkli or lever for small gardens and vegetable plots.

3.

Charas or mot or leather bag for agricultural crops.

4.

Persian Wheel for agricultural crops.

These arrangements are shown in Fig. 4 (a to d). "

1N6. DIN,,"

hg. 4 a.

Fig. 4 b.

.

/.1FT IRR~TION - TNI. tNUlt1/1

Fig. 4 c.

Fig. 4 d. In very few cases, the water lifting arrangements have been modernised in the form of

chain pumps, ordinary suction pumps worked by bullocks. and modern pumps worked by the electric motors or the oil engines. The e;nciency of different water lifting arrangements was tested in experiments by Captain Cliooorn given in Roorkee Treatise on Irrigation Works Vol: 1, reproduced below: Class of lift.

No.

Rati Denkli Chain Pump Chams Persian Wheel

1 2

:J 4

5

Lift in feet

Labour

17

Man

15'4 15'0 320 30'0

" Cattle "

Foot tons per hour per head 32'26 21'99 30'55 588 57'1

A ton of water raised one foot ton.

10. Duty

of

well water.

The duty of a well cannot ce defined in terms of acres per cusec discha:tg~ because there is no fixed and continuous discharge. ... --.. ~ Area to which a well gives protection in the case of draught is d.efined as t1M tiuty of the well. It is thus the average area irrigated from a well per annuIn.

9'

The experimcnts carriei out in following figures:No.

t~Je

Unitcd

Provinc'~5

by

~IL

Lift

Class ot lift

Anthony

gave the

Duty in acres per annum

-~~----~-~-------,

I. 2,

3. 4,

Charns w.th cattle Charlls WJth men Denkli Pati

25 28

3'91

IS 18

')1

27f) '8

This is a very poor show, but in the Punja~, the usual duty of a well worked by chams or Fersian Wheel is 25 to 30 acres. Csually there are three shareholders having an area of eight t) ten acres each. The higher duty for the Punjab wells is due to the following causes : ~ (i) In the Pun:ab the wells are generally fitted with Persian wheels which are suita~le for lifts of 20' to 50'. (ii) The cattle and men in the Punja') are hardy and, therefore, capa~le of putting in strenuous effort. (Hi) Holdings in the Punja~ are small and, therefore, water is used economically. 11.

Delta of Well Irrigltion. Delta is defined to be depth of water required in feet to mature a crop. The usual depth of first watering fro.n a well is three inche3 in a pbugled field and the suosequent waterings are of 2" depth each. The average depth of watering from statenellt No. 1. Farm Account 1933-34. Punjao Agriculture Pu.)lication No. 46 works out to be '193 ft. or 2'33 inches. Pro:)aJle deltas for various crops in the Central Punjab with average rainfall of .20" per annum (IS" in monsoon months of July and August) is given in the table below from personal 00servations : ' No. 1. ')

3. 4. S.

6 7. 8.

~o.

Crop.

of waterings.

4 5 to 6

\V"e it Cq·to 1 "Vegei..a.b:e:i Pet~t )es

",

I ler 'T'H)S Chari. Ma.ze dn I'Senjl S;,ahal Ber,elffi S'lgarcane Maize

6 8

"

p

'"

"~ d

-...

~

,•

',.n "

3

Velta in feel.

-----_._--

~dO

~'>ll

10 '!'1 l··t)

f:v.

-6

G

1'2

8 to 10

1'8

5 to 6

},O

A comparison of weI} delta with the canal irrigation figures in Part II ' Chapter II will show that a')out i water is used in well irrigation as co:npared with canal irrigation. The yield of crops from well irrigation is usually somewhat better than that from canal irrigated crops on account of timely waterings and Jetter manuring facilities. The reasons for low delta in the casa of well irrigation are ;.(i) The cultivator is aware of the cost and the la')our e:nployed by him to lift water and, therefore, he uses it very economically by resorting to small kiareis in his fields. Well water-courses are usually well maintained and there is no wastage from iii) breaches and overflows. ( iii) Well water-courses are always kept clear of all jungle and grass and are often well consolidatad and plastered with mud to reduce absorption losses. (iv) Water is lifted according to the requirements of crops at the will of the zamindar. He has not to wait for his turn as in the case of canal irrigation.

16

12.

Cost of Well Irrigation.

ilhe cost of well irrigation from Persian Wheel is worked out on page 253, Ac-co1&at ]933-34 Publication No. 46 of the Punjab Agriculture Department. Cost of well Area cropped A verage number of irriga.tors Time taken to irrigate OIle acre

Fan.

Rs.774/17'4 acres .(

2'84 days

COST PER AORE Rs .. a. p. 11 13 0 11 4 0

Overhead charges Bullock labour Manual labour

... 11 12

Total Rs.

0

... 34 },3 D per a.cre.

Cost excluding manuallabour=23jl say Rs. 231The manual labour does not cost a cultivator anything as he or his children usually supply the requisite labour. The overhea.d charges for the cost of a well etc., are also very excessive. Bullocks will also te used for ploughing and cartage and other miscellaneous work. The well irrigation is definitely many tim(!s more expensive than the canal irrigation. The Irrigation Research Institute, Lahore, has also worked out the expenditure and income of one family in Jullundur District possessing ten acres of land on a well with one third share in the well. The gross receipts in a year work out to Rs. 741/- while his actual expel'l$itnre is Rs,,383/- for paying land J:evenue, casual labour, bullocks, share of well and Persian Wheel, seed and kamin and nliscellaneous expenditure. His net income is about Rs. 358/- per annum. 13, Well Irrigation Versus Canal Irrigation. Well irrigation has got a definite advantage over canal irrigation, I:;ecause a cultivator . can raise water when it pleases and suits him. In certain tracts, well water is more beneficial to the crops as in the Bist Doab in the Punjab. The well irrigation should te encouraged parallel to the canal irrigation as it is an effective antiwaterlogging measure and serves to keep the water table low. Well irrigated tracts should 1:e debarred from canal irrigation when new irrigation is extended to a tract, so thllt wells may not tecome extinct. Canal water should be given to about 50 Yo intensity of tke irrigable ar.ea so that the well irrigation should also develop. The canal irrigation in the Punjab has a definite advantage over the well irrigation in the manuring value of the canal water ca.rrying fine silt and clay in susr;ension. All canals take off from alluvial rivers, .

<"

11

14.

Examination Questions. 1.

2. 3. 4.

5. 6.

(a) Define duty of a well. (b) What factors govern the delta irrigation from 6pen wells? (c) Why is delta for open well irrigation the lowest as compared to the delta f
in

14

irrigate finally 17389 acres. 20 tube wells are at present installed and are wofking. . (e) Ganges Canal Hydro-Electric SC;1eme was conc~ived and carried out by Sir William Staml;e E /::.I.E .. Chief Engineer, United P lOvmces, India. The energy has Leen developed from the low head falls on tte Ganges Canal. The complete scheme envisages the generation cf 30,000 Kilowatts of which more than 24,000 are from canal falk The bulk of tl'e power is useJ to energise 1500 state operated tube wells wilh an everage c1isc:large of l'S causes each. It is meant to irrigate 1300 square miles area Tubt! wells are e.-nerted to run for about 3000 hours per annum. This sc\e:ne has proved a financial success and the returns are very promising. This is the biggest undertaking in india for Irrigation from tube' wells. i. Borln~ of tube wells (An extract is given from Bi"J. 28). A. choice of site for boring. (A) Wate,: divining.·-Considera·le di'ficulty often arises in determining a suitable si.te for a boring. Eut for locating springs or flowing water near the surface there are often other indicatioJ.s which may prove valuable. Water divining has receJ.tly received much attention' and there is a')undant proof available to show bat Le art of "doNsing" is a fairly reliable means of detecting the presence of flowing water near ground level. Many theories have been formulate to explain the p"henOil1enOn '. ut no prcof is yet availa~le. (,:::i.). 1.) There are indications which may lead t6 the discovery of springs or water near ground level, in cases wl~ere nothing would a?pear, to t':lose unaccustomed to observations of natural phenomena to induce a Lelief in their existence. The following are· some of the simplest. (Bib. 1.) In the early part of the year, if the grass assumes a brighter colour in one particular part of a field than in the remainder, or, when the latter is ploughed, if a part is darker (or damper) than the rest, it may te suspected that water will l::e found beneath it. In summer, the gnats hover in a column, an,i re'llain always at a certain height ahove the ground, over the spots w:le~'e springs are concealed. In all seasons of the year, more dense vapours aris~ from those portions of t'~e eartYs surface w;lic3, o,'{iag to Le pre ;e~lC'~ of subterranean springs. are more damp especially in the morning or in the evening. In selecting sites for wells to tap 1'1e u;)per layer of su')-s')il water it is aha ne{:e'is1.ry to study the phnt life in t'1c locality. It is CO'11mon knoNleolgc tlat certain tree:> thrive "ell where the su ,-soLI water is more plentiful or nearer to ground level. . Tl:ese rules apply generally to springs near the surface. WilCre the source is lONer these are rarely su ficient. It is clai:ned that with the aid of a "divining rod" or electrical instruments springs several hundred feet ~elow ground level can i~e located fairly accurately. For further information on t'iis su ject a reference may te made to "The Physics of the Divining ~od," by Maby and FrankLn. pu·.)lished by Bell and Sons Ltd., London, S. W. 2. But expenence with these instru:nents has not Leen very encouraging and the only safe guide for correctly detcrmining deep sub-soil aquifers is a trial coring. (B) Boring for W dIs.- The diameter of boring tu':es is measured on the outside as against ordinary pipes which are measured on the inside, Lecause in the former case we areconce.rnd wi.th the size of the bore made. This point should be taken note of when orden~g J:;ormg-tubes from foreign countries In practice coth the methods of measurement are Lemg used by the borers almost indiscriminately; and in India generally inside diameter is. measured, forthe sizes of boring tools strainers, pipes, etc., have to be adapted to the inside dIameter of the boring-tu1:es A safe course is to mention the outside diameter as also the thickness of the loring tu':es when placing an order for these. Another point, about which there is a good deal of confusion is regarding the nomenclature of casing pipes, blind pipes, blank pipes, plain pipes, solid pipes, etc., and these words are used indiscriminately and in different senses by different borers. The generally accepted practice which is adopted in this book is as below. It is very successfull so far.

15 All pipes and tub(s used for boring have leen described as "boring-pipes" and "boring-tubes," or 'casing-pipes" and "casing-tules." . ' . 1A..ll pipes used for the tube-well itself (whether between stramer as m a stramer well, or in c.ontinuat:on 'with a slotted or perforated pipe as in the case of slotted tu':e-wel~s and perforated pipe-wells, or in cavity wells where "boring pipes" are not used) are descnbed as "plain pipes" or merely as "tubes" The small length of plain pipe (generally 4 to 5 feet) used at the bottom f nri. of a strainer or slotted _tube-well and having a cap or bail-plug fixed to it is described as ·blind-pipe." In the case of cO'l1pound wells the larger diameter plain pipe on top, in which the bore-hole pump bowls are housed is sorr,etimes descri~~ed as "housing pipe." . The use of the words "blank pipes" and "solid pipes" has been done away with as it is confusing. Though boring requires skill and care, yet in principle it is extremely simple The operation consists, as its name implies. in boring a hole of a dia'l1eter varying according to circumstances, and in a vertical direction. Many syste:ns have teen and are now follO\yed in carrying out this Jdnd of work. (C) Ior:ng system3.-Boring systems may te BOA1D7HRSlilJS TIJ.aNINC}/ divided into three' .main clas,es. viz, 'percussion boring, by which a hole is made into tte ground by recucing the strata to powder, water jet boring which makes a bore by washing out the strata, and rotary boring by which a hole is drilled into the strata and a solid core obtained. The percussion system is suitable for ordinary sand or gravel strata, :) Oflt£T JOYIT . while hard tenacious clay is better penetrated with OltlIJTNIl.EaD.s)"O ANINCN a water-jet plant and the rotary system of boring with core drills is adapted in the case of firm and hard strata. The driven tube is the simplest form of tore hole. This method is rarely employed for larger wells. (i) (a) Pe;'cussion rope boring -H.e old system 5W£I.I.£.DIiND CR£.sSED of well boring is the original Chinese rope boring 8 ()/t1D TH.Il£IWS 70 nil/NCR system which is described in the beginning of this book and is of great antiquity. The present method of rope coring is described below: A pit is dllg at the site where toring is to l-e done, about 6 to 8 feet in diameter and about 15 to 20 feet in depth, and the boring·tn e is lowered into it with a cutter shoe fitted to the f:;ottom of FLUSH ,JOINT it. These cutter shoes can be "slip shoes" or "screw shces" and are of slightly bigger diameter than the boring-tube itself so that they may BDIUN6 SHoeS provide a clear passag.e for borbg-tub~s as hey
a

D

o S

\:B\jtj:)1 ~~

''-. '/1-'1:'..

.

~I ,<;~ /

S

16,

Scm:e extent while the tute is being withdrawn. On the other hand the screw-shoe is. screwed to the 1 ottom end on tr.e tore tul:e and comes out with the tube when it is withdrawn. In this case as tte screw-shoe has to be withdrawn with the 'oring-tu':~e there is no extra clearance left while withdra\~ing. Therefore a screw-shoe is chiefly used for sandy soils. Screw-shoe are generally good for the average size tuee wells in India and with experience this practice has been estaDlished here. There should be female threads to the shoes to receive the screwfd end of the toring-tube which should fit in butt t.J Dutt with the shoe. In the case of very deep borings, or Dorings in clayey strata, the bore is started with a larger dia'l~eter Doring-tu1:e and carried down till the friction on its outer surface makes it difficult to carryon the coring any further without damage to the tu~es. A slightly smaller size roring tu 'e is then lowered inside the larger siz, tu ,e. The boring' is next continued with the s:naller size tu JC which is free froTI any frictional resistance to the hottom of the larger size ture. If necessary a still smaller size of f~oring-tu::e is lowered inside the inner tu~e when the friction on the latter also recomes excessive aft<:r carrying on the Doring lower down. Thus the diameter of the tore-hole is successively r :duced as the conditions demand, All th' tu es should however extend right up to ground level or aJove the bed level of the pit in ,which the bore is made, so that they may all be ex:tracted with jacks when required. This system of lowering boring-tu"es one inside the other to distribute and overcome frictional resistance in the su )-soil strata is known as "telescopic boring." Care has to be taken to select the size of the various soring tu',es in such a way that the inside diameter of the innermost tu'~e, reaching the bottom of the bore, is su"ftciently large to allow the lowering of tu' e-well pipes and strainers inside the finished bore. The boring-tu:es are ste 1 tubes with the following types of joints :(1) Flush joints. (2) Swelled and cressed joints. (3) Socketed joints. These are shown in Fig. 1. The flush joint is the best for ease in lowering and with,'rawal "ut t~ese tu' c<; hay!) tf) . n flicker elan socketed pipes or swelled and cressed' pipes to ha';e su ;';cient strengtil at the joints. After eeing lm'"f!reri in t:~e pit _a<; ,',:scri'Jed above, the boring-tUDes are clamped in position Wit'l woo 'C:l cla'llps, a'1'l ,yutly fille·j with water. Water is necessary for Doring o,:eratiollS ::tnd must :~e poured from Le top of c:1sing pl'Je u,til W:1t'~r i<; stnEk in Ete t--ore-hol~ it<;~lf, T f! adm.l ,. oring is done with a tool known as a "shll;ger' or "san.l pu;np '. TI,is imple;nel1t is a steel pi~ce of a',out 1/4" t1-tickn~<;s, varying in lengt'l aa.t dia1l'!tcr according to the size of well to 'e ·,ore'1. It is aJout 2" IC3s in diamet,:r t lan the casing pipe and its length varies from 8 feet to 12 feet for ;;orings from b inc';es tu 16 ine~les in diameter. A cutting shoe of "hard steel" or tungsten steel, is riveted to the sand sludger at its lower end. The cutting shoe is tapered out slightly at the 'I;ottom to give it a clearance in cutting the material at the bottom of the 'core. A flap or ball valv~ is fitted inside the sludger pipe just above Le cutting shee. The sludger is suspended hy a wire rope from a pully on a tri1)od. The legs of the tripod are to L e 'curied a,:out two feet under ground to prevent their sliping or tilting. The ___ . leg opposite the craJ-winch has to : e securely buried and anc.'JOred so that the tripod will not turn over when su ject to a pull fro'll the winch, The sludger comes centrally over the boring-tute and can work smoothly inside it. When the sludger is worked vertically up and down by manuallaJour, or an engine with cranking arrange:nent, etc., a circular motion is also automatically imparted to it by the torsion in the wire rope. On the downward stroke of the sludger the flap valve is force j open and the loose material pounded at the bottom of the bore-hole enters into the sludger pipe As the ul-stroke tegins the flap valve closes thus retaining the loose material inside the slur:ger pipe, At the same time the upstroke creates a momentary vacuu"YI at the l:ottom of tr.e t;ore as the sand sludger is lifted upwards. Owing to this vacuum or suct;on the pounded loose material in the bore is sucked up and gets eetter mixed with the water at the bottom of the 'Dare, The loose material thus pulled up and remaining suspended in the water enters into the sludger pump on the next

17

downward stroke oHhe sludge~ and is retained by the, <JIve. At the enrl of th downward stroke the cutting shoe cuts some more of tht matl~rial at the bottom' of the hore which is pulled up and enters tte sludger in suiJsequcnt strokes. After about 30 to 40 stJ;"okes the sludger is taken out and the loose material retained inside it is empt;ed out. This material is carefully examined as it is a sample of the stratum at the cottom of t1:.e Loring where the sludger has been working at that time. A change in the characteristics of this material is an indication that tr.e stratu'1l is changing and a careful record of the nature and c'.cpth of these strata is ke]:lt. The samples of ~he excavated material arc also preserved. Ttc c0ring-tute is clampci-l with sleepers at some convenient point a'~ove ground level and over the clamps a pliJ.tform is made which can 1 e loaded with su f;cicnt weight to' overcome the surface ad;1es:on on the 'Doring pipe and force it down as the sludger excavates a hole l:elow it. Thus boring progresse, and one casing pipe after another is s.;rewed on and lowered till the required depth of ;)orc is reached. (01 An1her~1l(jlt methoil of leading blring-pipes.,-A convenient and more efficient method of applying load to the boring-pipes is the "Anchor-bolt" methGd. The anchor-bolts consist of two mild ste.el rods H inches or more in diameter and a:oout 16 feet in length. Both the1e rods are threaded with square threads for aJout 2! feet length at one end and aJout 1 foot af the othe'r end. If tlwse rods are not availa')le in one length two rods 8 feet in length each may be used to form one anchor :001t by cou?ling the two pieces together tightly with a solid coupling. To each of these rods, on the end having thr,~ads for about one foot length only, are baIted together two rail pieces, R. S. Joists or channels about 6' x 4" in section and about 4 fect in length to form tIre anchor. For this purpose holes about 1i inches iJ;l diameter are drilled in the centres of the,se pieces and the anchor DOltS are passed through these and tpe two pieces ooIted to the rod. A pit about 5 feet in diameter and 7 feet in depth is dug at the site where a boring is to be made, and the boring-pipe with the cutting shoe at its bottom end is placed vertically in the centre of this pit. The two anchor-'Dolts with the channel anchors fitted at their bottom ends are placed on either side of the boring-pipe and ~ept about 4 inches away from it. The channel anchors are placed in a cross fonn. The pit is then filled with earth and well rammed taking care that the boring-pipe and the anchor-bolts remain in their correct position. A wood'en clamp is made from two pieces of sleepers 10" X 10" by 5 feet long. Each of these two sleepers has a semicircular hole in the centre so that wh'~n clamped together they form a circular hole slightly larger in diameter than the outside diameter of the boring pipes. On either side of this hole and about 4" away from it the clamp has two smaller holes about Ii inches in diameter into whichA:he anchor-.bolts are loosly fitted. These two wooden sleepers ·are clamped together with four mUd steel bolts It inches diameter and a ')out 21; feet long. This loose clamp is fitted acr0SS the boring pipe and the tcp of the an::hor bolts and the two halves are clamped together with the four-tightening bolts described a'bove. The loose clamp is held in position and prevented from moving up or slipping down by nuts and washers screwed into the top threads of the anchor-bolts on Doth sides of clamp. ' A second wooden clamp similar to the loose clamp described above but with the central hole tightly fitting to the outside of the boring pipe is also required. When clamped together its central hole must grip the borin:~-pipe tightly. It is fixed to the boring-pipe below lc()se clamp at such a point that the vertical distance between the two clamps is just sufficient to put in two jacks with their caps fully screwed in On top of these caps iron plates are placed to act as bearing surfaces when the jacks are worked. This second clamp is fixed to the boring-pipe as de,cribed aJove and the jacks (20 to 40 tons capacity each) an~ put in position. The sludger pump is now worked and the jacks are put into operation by unscrewing them, this exerts a pressure on the loose clamp. But as it can not move up the pressure reacts on the bottom tight clamp itself. " Tht; bottom, clamp is thus pushed down and drags the boring pipe with it. When the jacks have compeleted their travel they are screwed in and taken out, and the verticility of the boring pipe check(>q and

18

set right if necessary. Tb.e tight clamp is loosoned and raised up, and again fixed celow the ~op loose clamp at a P?int j?,st .low ~nou~h to accommodate the screwed in jacks. The process IS repeated till the Lonng pIpe IS dnven m. Both the clamps are then taken out and a new boring pipe screll cd to the bottom pipe and the operations repeated till the required depth of boring is reached, Another convenient method of applying load to the boring-tube is to use a weighting frame mac'e up of duplicate R. S. Joists assemoled around the tu::e and resting on the ground. A pair of winches are bolted to the joists of the weighting fram~, and a pair of pulley sheaves to a clamp fastened on the boring-tube at convenient point above ground level. A!" dia:netcr rope with one end tied to the weighting frame passes over these pulleys and is wound over the winch drums. As the winches arc operated F,e load of the weighting frame and winches comes on to the clamp on t:1C casing pip'~ whic'1 is thm pulle i d:) va and enters the bore mac.e by the sludger. But n.e weighting frame is sufficiently loac'ed so that it is never lifted off the ground and always rests on it, Thus there is no risk of its slipping down and injuring the workmen operating it. This arrangement is also used for extracting horing tu es. For this purpose the clamp with pulley shave, is fastened to the boring tul:::e a little below ground level The rest of the operation remains the salLe as tefore and th tu')e gets pulled up. The pipe with the weight on it, supported over a clamped platform, is, at times, rotat~ ed with manual labour to help its sinking down. In this case it is necessary to watch the movement of the pip~ going into the bars, If the pipe goes in all of a sndden, i.e, if it slips, • it will take along with it the sorrounding earth which will jam the pipe, and it will be difficult to move it either up or down Hence it is necessary that the pipe should be held back with a rope and a cra'J, and only allowed to go in slowly. A careful record of the boring progress and the strata samples met with as also of the morning and evening spring water levels inside the bore is to be maintained. When a hard stratum is met with the sludger is replac d with different tools such as chisols underreamers, auger, spring-rimor, etc., to pierce through it. (c) "Morninr," "Evening" and "Working" water level.-(Indications they give with a "Lailor-test" regarding the water contcnts of a stratum.) The excavated material coming to the surface with the sludger will indicate what type of stratum is being passed through at the bottom of the. bore. The existence of watercearing strata is indicated by tr.c presence o~ fine, medium or coarse sand, gravel, boulder, or round-edged kankar etc. while clayey strata are generally non-water cearing. An indication of the pressure at which water is fio~ ing in a particular stratum is given by the level to which water rises in the toring-tub~ wtcn it is passing through total stratum, It is clear that when the bore passes through a non-water bearing stratum the water level inside the boring-tu: e will 1e very low for there is no water coming into it from the non-water bearing stratum at the bottom of tte bore. But as soon as a water bearing stratum is reached water will rush into the tu'. e. The pressure of water in the water tearing stratum, as indicated by the level to which water rises in U.e boring tn e, should ce carefully observed toth in the morning, I::efore starting work and also Guring the progress of the work in the day time. The former gives the static pressure of water III the core proviced no boring has been doneat night and the watet has had tirr.e to attain its natural level; and the latter indicates the working pressure. n.e working pressure is generally lower than the static pressure, for as tLe sludgcr is taken out to ttc surfacc to cmpty It of tLe excavated materiaL SOlLe of tae water also comes with it and thus throughout the day water is f eing tailed out from the tore. Hence the working ani cycn;,ng water levels are effected by this continious bailing out of II'ater. The working wat~r level also gives an indication of tte fiow of water in the stratum, and if it is not appre-:ia'oly lower than the static water level it may be safely assumed that t Le fiow of water in tLc stratum is satisfactory ann that it will give a good yield. A record of morning water levels observed before starting work and of evening water levels taken after stopping \\ ork s'1oukl \:;e carefully maintained. As a matter of fact it is desirable to \~onr1uct a "Oailer lest' as each individual water-oearing stratum is met with while boring, so ihat sun,l: infom:ation regan:ing tt.e probable yield hom the stratum may be had by

19 observing the difference between the static water lcve 1 and the lowered water level in t 11J stratum after a "bailer test." In carrying out this test the slucger with its flap valve is used as a bucket to oail out water. If the level of water insic'e the tuce-well remains steady even after ,Jailing Ollt water, for say a couple of hours (apprc.ximately 80 'bails of 6" to 8" diameter and 8 feet height in the case of 8" to 10" diameter torings), the stratum may te considered satisLlctory for location of strainers, or for further cevelopment and gauging in the case of a cavity well. (ii) Rod. boring. - Another system of boring is the rod boring system. This is similar to rope boring except that rods e \ tend from ground level to the boring tool instead of a rope. The rod boring system is used for very deep borings or borings in very hard strata. The rods are of ash weoel ~ith the metal male 'and fe:nale screws spliced on to their ends, or steel rods with screws (in length from 3 feet to 20 feet and fro:n 1 inch to 3 inches tJ_ick). Boringrigs are constructed either of wood or wrought iron tubes, with a head-puIley-DIeck over which a wire rOFe is passed to support the boring rods and tools. The other end of the rare passes to the wind-fass in the hand-power-rigs or to the winch or winding drum in a steam driven plant. • In order to obviate the jarring e 'Cect of the great length of rods, particularly in very deep borings, a tr~p link is introduced 20 to 30 feet a'.::ove the tool as it is dangerous to exerci~e a percussive actlon of such power which will expose the lower rods to the danger of breaking. The method usually adopted is to employ a form of sltding joint, on one of the rods, 20 or 30 feet above the tool. This is based on an lllvention of Oeuyenhamen. It consists of a slide joint of two parts which are aole to slide upon one another for a distance of a')out on foot, and so arranged that during the descent one Leco:nes detached from the other. The upper part is balanced by a counter-weight suspended to a lever, and the lower one only allowed to act by percus~ion, Certain adaptations of this joint in the form of jar-bars and other sliding joints are now generally used. Square rods with taper joints are sametimes used for shallow borings. In this method earth auger, cross chisels, flat chisels, Dull-nose auger, etc., are used as boring tools. The square rods are rotated with drill, and the auger is allowed to penetrate in the earth about one foot and then withdrawn. The earth is removed from the auger and the clear tool is again inserted into the bore. The above process is repeated till the boring is made to the required depth. In Gujrat bores up to 150 feet are sunk with this method and with manualla'bour. For shallow borings this method is generally more expeditious than ropeboring. (iii) B)ring by HydrauliC Wash or Water-Jet-llorlng.-At places where su 1icient water is availade for working a water-jet plant, the hydraulic washing system is a very convenient m~thod .of boring t~lrough. hard and tenacious soluble days in w~ich progress .of boring WIth ordmary perCUSSIOn iJormg sets would be very slow. Hollow oonng rods or pIpeS, with a s",:ive~-he~d at the top a,nd conn?cted to a. chisel at their bottom end, are used and a rotary mohon IS glVen to these oy rotatmg the water-tu:Jes from ground level. A sIaN rotary motion is given to the boring-pipes aha to e {pedite their sinking. For 8 to 12-inch diameter borings going to depths of 3 to 4 hundred feet, ordinary W. I. pipes a'')out 4 inches in diameter are used as hallow boring rods. These are sus:_Jeade,j fro:n a pulley in the derrick of the oaring rig with an adjustable length of wire rope, and pass inside the boring tube. At its bottom end the water-tu e is fitted with a chisel having two nozzle orifices, one on either side of the chisel, The nozzles are kept at about 9' aJove the bottom of the bore. A suitable connexion with an electric or oil-engine power pump is made (at the upper end of the pipe) by means of a flaxi'Dle hose pipe, and water is pumped ..into the tu:;e. The capacity of the pump silOuld not ordinarily te less than 15,000 gallons per hour and it should be capable of working up to heads of 200 feet. The water which is pumped through the tube to the bottom of the bore-hol~ shoots out through the nozzles and rises in the annular space ,etween the water-tui;e and' the casing pipe carrying with it any comminuted material and overflows into the settling tanks at ground le,:el. The vel~city of water in this annular space should be su ncient to carry all tte commmuted materIal with it. This velocity can be regulated by controlling the discharge from the pamp. After settlement and clari'ication in U.e settling tanks this water ean be used again for boring purposes.

20

Although this method has proved efficient it is not very widely used owing to the difficulty of obtainin through whic':l water, with clay in suspension, is sent under pressure The fluid mixes with the cuttings and carries them up to the surface in the annular space eetween the drill pipe and the bore hole. The clay that is held in suspension in the water "muds up" the walls of the hole, prevents caving, and causes the pipe to turn more rapidly as there is practically no friction tetween the boring pipe and the silles of the bore hole. The muddy fluid, cecause of its greater density, also trings to the s~rface cuttings which could not te lifted by water alone. A derrick like that of the standard rig is used, tut machinery and tools are unlike those of a percussion outfit. A pump with proper pipe connections is provided for feeding a constant stream of the mud flush to the tools when drilling. Usually a second pump is kept ready for use as a stand by. Thin mud or slush plays an important part in drilling. A slush pit, an essential accessory. is usually dug near the derrick a'1out 40 feet long. 15 feet wide, and 3 to 4 feet deep. A ditch where sand may settle out of the mud is cut from the well circuitously to the slush pit from which hose or pipes lead to the pumps. A machine called the rotary, is used f~r rotary ho~i~lg. This rotates the drill pipes and at the same time permits th'~ir b,;ing lo.verc l..in be :)Or0 as re:ruire-i. The chief parts of a rotary are a rigid base and a turn-ta.)le rotated ny a system of gears actuated by means Qf a a: chain drive sprocked. The drill pipe is held by a ca )le, which passes over the crown pulley ;(ttached to the Doring rig and around the. drUll shaft
21 do not justify the use of this machinery. But this syste n is largly used for oil borings when great depths are atiained for rock boring. In rock sand-stone, trap, slate, granite, etc., the rotary core drill with shot bits is found most effici~nt. The ordinary core drill consists of a tool called a ('crown" which is a short piece of cast steel tute, into one end of which a number of "black diamonds" are fixed circumferentially. ' Black diamonds are an amorphous variety of diamond usually called caroons and are only valuable on account of their extreme hardness. Chilled steel shots are now generally used in ,place of dia'11orids, The upper end of this crown is screwed to steel pipes of the rotary drill. Machinery on the ground surface causes the pipes and the crown to rotate aJ explained in the case of rotary boring. and the crown cuts through the strata causing a "core" to rise up the hollow tu~e into a core barrel. Lead balls or some gravel a')out !" to i' in dia'1leter are then injected with water in the bore so that these balls or gravel rr:ay act as a wedge between the core and the crown. If the tool is now rotated fro;n. top tre core gets sheard 0'1 at the bottom and breaks. The tool is then raised and take:l out and broken core comes out along with it. The crown, when it has been taken out, is given strokes with a copper hammer and this makes the core drop out'from it. Fro:n time to time the core is broken 0'1, the tOClls raised, and the core extracted. Water is pU'11ped down the hollow rod as in hydraullc washing and rot lry boring and enters into the bore hole acting and enters into the bore hole acting as a IUJricaht to the drill and carries off loose deJris when returning to ground surface through the annular space between the drill and the bore hole. (vi) Cllifornia or strove-pipe method of boring-This is a method of boring used for wells of 6 to 30 inches in diameter. The casing consists of short sheet-iron cylinders, forced down by large hydraulic jacks and perforated in place by a special tool. Materials within the casing are excavated Dy a sand bucket (sludger pump). This method is chiefly used far unconsolidated alluvial depoists and is known as Calisornia method, as it was originally developed there.. It is also called stove pipe method on account of its special casing. The casing is made of lap riveted or welded cylinders of sheetiron or steel, usually of 10 to 14 gauge, 24 inches long, and 6 to 30 inches in' diameter. Two sizes are used one of which just fits within the other, so that the joints of one may be adjusted to fall midway ;:etween jojnts of. the other. Sections are added one at a time as sinking proceeds, each 2 feet section adding 1 foot to the length of the casing. Outer and inner sections are united simply Ly centing with a pick; and the casing is watertight. Casing may te started from a prorerly recessed steel drive shoe and. drive pipe. Casing is us,l,lally sunk by two or more hydraulic jacks iJuried in the ground. and pulling at a casing yoke placed on top of the casing pir::e. PI. sand pump is used for horing as in the case of rercussion rope boring described before. A strata chart is carefully kept, as usual and after the well has ceen sunk. to the required depth a cutting, knife is lowered inside the casing anJ vertical slits cut in the casing in sclec:ed "ater-', caring strata. Revolving cutter used is such that it punches five hc1es at eacl reVolution of the wheel. Vertical slits are of a form and size that do not clog reaqily. For best results in fine material, a' natural strain.J' is forn ed surrounding the casing hy re;noving the finer materials adjacent to the pipe by pumping tl e v.ell as low as possi'le for several days. It is seldom necessary to reperforate a well casing. The yield of an old well may often be increased by using compressed air for back-blowing or' by heavJ pumping, thus loosening the surrounding sand and gravel. (Bib. 2) 6. Tube-well pipe.' (An extract is taken from Bib. 28.) (a) Tnreads on boring-pipe.-from American practice it has found that the ~ threads pipe (i.e. 8 threads to an inch) lacks strength, owing to the deeper cut required for the thread. It was found that the pipe often broke in the thread when subjected to strain. BesiC'es, the 10 thread pipe proved more consistently watertight and less liablE to admit particles of sand and grit, which would bind the thread and destroy it in unscrewing, The Americans strongly recommend use of 10 thread pipe' (Bib 33). It is howover eXFerienced that when casing pipes with 10 threads to an inch art ,jacked out, during the process of extraction from a bore, they at times slip from the joints

22 .pecially if the threads are partly worn out. Casing pipes with 8 threads to an inch a~e better in this resj::ect tecause their threads are. cut deeper and ~herefore they do not S~IP ;0 easily. But greater depth of threads necessitate~ that the thIckness of pIpes should l!e correspondingly greater so that ~hey I?ay ~ot lack m strength. and may not part (Dreak) at the joints. Generally speakmg pIpes WIt~ 10 t~reads .to an ~nch are preferable where the thickne~s of pipes is less .than 1/4th of an m~h, lJut wIth thIcknesse~ cetween 1/4th and 3/Sth of an inch pires wIth 8 threads to an mch are preferred espeCIally when used for boring purposes. (b) Collar-bound pipe.-Boring pires if socketecl sometimes become "collar-bound" in a hole. In such an event the pipe can be worked for about the length of a single joint, but will not pull above a certain point. This is caused by mud loading heavily upon the collars, and by a mud-laden collar, usually the 'r:ottom one, coming in contact with a tight place in the hole. The condition may te aggr~vated .by the .sand filtering in :'lnd ,findinl? a resting place upon the mud-laden collar, (That IS why It IS advIsable to hav,~ tonng pIpes wIth tlush joints, fig. 1, where tte collar at tl'e joints are disrensed with), In such cases, it is necessuy to keep the pipe m constant movement until it will pull freely pass the point of o:)struction and pass easily down through the same place; otlcerwise, such a contiition is sure to cause the pipe to 'freeze' rapidly, The expre,sion "frozen pipe" is applied to toring tutes rendered immovable in a bore by muri, sand, limestone cuttings, and other gritty substances, settling nound the outside of the tube. When a pipe is collar-';_lound, too powerful an effort to pull it through the tight place in the hole will often cause it to become lodged so that it will neither pull nor fall back to the bottom, a common occurrence in the Vijapur area of the B:uoda State. This condition should, if possible, 1:e obviated by the exercise of patience in keeping the pipe in ~onstant movement. Usually a collar-bound pipe, if worked patiently up and down the ';)ore, the collar 1eing pulled gently into the tight place and then lowered i'efore the pipe gets lodged, will clear itself sufEciently of the sand and mud gathered upon the collars to permit free movement, Unless great care is exercised in controlling the ripp, it may be injured in dropping, because a pipe thus lodged drops with a tremendous force under H.e impetus of its own weight when once starteo. Therefore a free fall of even a few inches may result in serious damage if the pipe is allowed to strike the bottom. Sometime dynamite is used to give jerks to the pipe and thus to loosen a jammed pipe from the surrounding earth. The vibrations taking place at the time of exploding the dynamite shake the whol\.' length of the boring-pipe and also give vibrations to the surroundi.lg ;oil. Due to these vibrations the ~oil round the pipe which has stuck to its sides is likely to get loose and the boring-pipes tecome free. This process was tried in Padra (Baroda State) )oring for the extraction of the jammed casing pipes with considerable success. (e) Bad pipes i,e. pipes in a siRte of partial collapse, or split up, while l;oring.--A pipe :emaining in a bore for some time will frequently "go j'ad". This expression refers to a pipe that has become dented from a stone bruise, etc, and is in a state of partial collapse from outside wall Fessure or is perhaps split and partly flattened, The pulling of such a pipe for the purpose of replacing the damaged joints is often inadvisable tecause of the danger of breakiug t.he pipe at the "bad place" and leaving the lower part of the string of pipes in the bore, Such a pipe is oftenJrozen, and attempts to free it by applying too much force would ~ause the weakened joints to part. "Bad pipe" is usually first detected ty the tailed or sludger hesitating in its drop as it is let down the bore. This hesitation if recurring continuously at the same place, leads the borer to suspect that the pipe is giving way at that place. One of the remedies for a bad pipe is "swaging". The 'swage' is a heavy piece of steel, oval in shape, with a small groove cut into the steel as a watercourse. At its greatest diameter, the swage should be a fraction of an inch smaller than the diameter of the boring pipe through which it has to pass, Thus a boring pipe with a 10 inch inside diameter should permit the. entrance of a swage 91 inches in diameter. The common method is to drive a swage of a small diameter through the bad place first. This swage is then withdrawn and a swage of a larger iiameter is used. This procedure is repeated until a swage of maximum permissible diameier

23

is driven through the impared pipe. The swage is rua below the stem with long stroke jan and tools working Lnmediately a Jove thc swagc. The operation of driving thc swage down through the bad pipc and jarring it back throug:.1 the sa'1lC place should be repeatcd un till the swage will pull frccly through the impairc,l pipe, It can then be safely assu l1cd that the pipe has i cen extendcd to its normal size. If a swage has 'teen driven through a spilt joint of casing, and cavings are falling into thc pipe through the split portion, great care s:10uld 'J:e taken to prevent the cav;ngs froTI wcdging the sNage in the pipe, the swage bcins so nearly flush with the pipe, tJ.at any hard obstacle, may causc it to wcJge. 7. Sand hIowln~ cI.·,e during boring. (An extract from Bib, 28,) While boring is in progress there may be encountered a stratum of fine sand, or sand and clay etc., which rus'les up the bormg pipe to a consUerable length and thus hampers the progress of further boring. This sand is generally very fine (with or without clay) and dry. It would appear that this particular sand stratum is sandwiched between two strata and is under considerable pressurc, It may also be that it is in an arc 1led condition, all the while, betw€en the two strata aJOVc an,t below it. When t'lis stratu'll i3 struck during boring its stability is disturbed and thc iJoring pipe provide.> an opening for the release of its pressure. The sudden release of pressure causes the sand to blow up ins:de the boring pipe to considerable heights, In one well in Okha, Baroda State, sand was blowing up everyday from a depth 01 680 feet below ground level to 140 feet, i c., to a height of 540 feet. The di,licultya'lout sand bloNing is that when the hore is very nearly cleared of all the sand and the '00ttO:n end of the boring tu',le is reached, the sta:jlity of the sand underneath is again distur'jed and it blows into the pipe up to the old level and during this blowing up the drillus tools, etc" may get struck up or jammed or damaged in the rushing sand; and i1 provides a di'1icult pro:)lem to deal with. The simplest mdhod is to release the clamp which is holding the boring pipe so thai the pipe may sink down under its own weight whenever suticient sand has been cleared from inside the bore. All the while the sand is teing cleared out, the boring pipe should be kept full of water right to the top, which will keep th) sand under pressure and prevent it from rushing up, specially when the pipe is being cleared near its bottom. As the boring pipe is unclamped it will sink down by its own weight when the sanl is cleared beloN the cutteI shoe. In some cascs it may becoTIe necessary to e:den,l tIle ;)oring tu')e a'Jove ground lev31 by adding another piece on top of the tU'Je, and filling it wit~ WJ.t~r to increase the head of water over the rushing sand. This process of watcring cleeming, ani sinking is followed u].til the stratum has been crossed by the :;oring pipe If the thickness of the stratum is great and the pressure of sand high it may not be possiole to pic ~ce tllfough the stratu 11 in one day. In such cases even though the pip.: is kept full of water during the night it may not be a')le to prevent the sand from rushing in durin~ the closure hours. The well at Okha, referrei to above. is an exa'1lpl of such sand blowing. Every mornin~ the driller had to spend a')out 5 hours in cleaning the sand before he could commence further sinking of the boring pipe. The principle followcd in the above method is to line the bore while at the sa'1lt time taking out the sand, whic',l is prevented from rus\ing in iJY keeping it under pressure of water. It is o'lVious that if this pressure of water on the sand coulrl be maintained there would be a lesser chancc of the sand pus':ling its way tllfoug'l and blowing in even during the clOSUie hours. This is achieved by the use of '·aquajel." "Aquajd" is a powder of the colour of cel1cnt and hcavier than clay, Wh~n mixed with water it forms a jelly which is very tenacious and whic\ d0e, n'Jt m:x with sand. So w:le.:1 t'le trou')le of sand blowing is encounte:-ei 'aquajel' is addcd fro n the top of thc boring pipe It, being heavier than water, sinks b tl.C botto n, W:lere the Joring to)l is wC)rking. By the action of any solid boring tool (not a sludger w:lich will tend to collect t1)e 'aquajel' inside it and bring it up with it when the sludger is lifted up) the 'aquajel' will get mixed with water and a jelliy will be formed whic'1 will stick to the side, of the bore as a plaster and will bind the sand and keep it in place near the bottom of the boring-tu'Je. The boring operation can then be stopped, and the layer of 'aquajel' will form a sort of bur) at the botto'll of the boring-tuhf and prevent sand fro.l1 blo Ning in during closure hours,

24 If the rushing sand is coarse it indicates good water bearing stratum provided its iydrostatic pressure is high. When such a stratum is struck water will rush in the boring cube and along with it may bring in sand also. But "this sand do;;s not rise so high as the lry fine sand referred to above. It is easier to penetrate through such water bearing stratum ind a sand pu,:np su"tices for this purpose as the sand docs not rush in so often or as high. ' ~. Fishing t~ols. (An extract is taken from Bib. 28.) Wh')u sludger or other tools re:nain imide a boring pipe due to the snapping ()f a wire rope there are different types of fishing tooh which can be used to fish out the )ludger. etc. fro:n the bore. For a detciled description of these, "oil gas and water weUs'_' by Lucy Manufacturing Corporation Ne\v York, or other' Looks on this sui ject may be referred to Bi') 6. The handbook on oil wells, published by the Gil Well SUPFly Co., Fittscurg, U. S. A. ane also the handbook pu lished by the National Tools Supply Corporation, Oho, U. S. A., He good refrence books on this sU'Jject. A borer should keep a log t)ook in which he should keep measurements of length and diameter of each tool, their thickness at various points, length of threaced parts, numi:er of threads per inch in the various tools, etc. These constitute 'important information for a borer~ for in case of an accident he will have full information to prepare fishing tools, of the correct size easily, to ena~le him to fish out the broken parts of tools left inside a bore. 9. Types of tube-wells. (An extract from Bib. 28.) Tu'pe-wells generally comprise the following types : (1) Strainer wells (including radial wells). (2) Cavity tube wells. ' (3) Slotted-tubewells (including shrouded wells). (4) Perforated pipe tupe wells. (S) Artesian tu',)e wells. In a tube·well we can draw water not only from the water L-earing stratum nearest to the surface of earth but also from one or -more of the water tearing strata lower down, and this makes it possible to ,draw out a larger quantity 6f watar fom a tu'ce-well as compared to to an open well. The water bparing stratttrr1 nearest the ground suface is not. however, tapped in the case of larger tube-wells in order to avoid interference with the supplies of the adjacent open wells and prevent their getting depleted. Open wells generally get their supplies from the first water-' earing stratum When we start boring from ground level we reach the' uppermost water' tearing stratum in which water stands at we call "spring water level" or "static water level" and it is this stratum which feeds most of the open wells. If we continue boring we pass through imf:ermeable ,trata of clay, conglomerate or stone alternating with other water~'~earing strata lower down. in the case of tube-wells we tap one or more of these lower water-bearing strata. Radial wells and ground water collecters.-In some cases it is found that vertical ,trainer wells need replacement very frequently owing to 'rapid incrustation,. of the strainers. ft is generally 'relieved that the incrustation occurs from the lil eration 'of dissolved car",on dioxide as a result of the release of pressure or change of temperature due to the tapping of underground water from aquifers at diferent depths. The loss of CO 2 decrl/ases the solvent power of water and causes precipitation of the minerals on the vertical well strainers. As an improvement. radial wells, with radially driven strainers, have i:;~e;n constructed. These strainers are driven radially in a horizontal plane in the same water-teanng stratum and are thus at all times under the same water pressure and temperature. A shaft of suitable diameter (12 feet or more) is sunk down to the water bearing stratum to be tapI=ed. " ' The shaft is constructed of rein£orced sections (air-applied concerete and sheet steel sections) each a: out 10 feet long. At the Lottom there are tr.eble-walled steel sections comprising the cutting shoe, the intermediate and port hole sections. These are all welded together with the annular spaCE reinforced and filled with concrete. Through the port hole section the slotted screen pipes about 10 inches in diameter (with a pointed driving end are driven to about 200 feet length horizontally with specially

25 constructed sliding hyraulic packer. The screen pipes are made from i" Copper b~aring steel plate punched with 11" x 1" slots. There are about 36 screens driven radially from one shaft ~nd kept just above the' clay ted underneath. (For London Water-works Installation, thl)se screens were kept one foot above the clay bed.) The open ends of these screen pipes project inside the central shaft and are fitted with sluice valves and vert:cal back-wash pipes which extend to ground level, and can be operated from there. All these s:reens are backwashe.d and properly developed. The sand thus taken out averages about 3 c. ft. per lineal foot of screen pipe projected. The water from all these screen tu·. es flows under gravity into the central shaft and ispumped out with deep well vertical motor driven pumps. The yield from one such radial well is of the order of 7,O;)() g.p.m. with a drawdown of about 7 feet." Cavity wells are tube-wells, which, being without strainers, draw their supplies from', one acquifer or water- oearing stratum only. 10.

Suitability of the Tract lor Tu1:e Well IrrIgation.

(a)

Geolo~lcal

strata.

Below the soil crust in the ground water reservoir, there should be available ~ 6 coarse sand stratum from 100" to 150 deep to locate the strainer of a tu')e well. Geological conditions in the Punja~) are suc':l that unfortunately such a water bearing strata are not available everywhere. Trial bores are ab;olutely essential to ensure suitable strata for every individual tube well. Water bearing strata are often separated by clay or kankar bed layers which are only partially pervious and yield muddy water. The trial bores indicate the position of such layers.. If ~he strainers have to pass through such layers, the portions should te closed by putting blmd pipes.

The Geological conditions In Northern India:"There are three crests of the crustal warpings or underground rock ridges sweeping across the Northern India as shown in the map of the Punja~ Plate I, Vol. III. One major and a number of minor crustal warps, run transversely across the three main crests. These ridges of rock, varying in dep.ths'fro~, at least 2,000 feet to surface outcrops, have an important bearing on the flow of SUb~SOll water. "The middle one of the three main crustal warps, is of vital importance to the Punjab and United Provinces. It runs from Sargodha, through to Delhi and thence to Allahabad, Bhagalpur, and ShiJong. The major transverse crustal warp appears to run from the head waters of the JlJ,mna river, via Delhi and Ahmadabad to. BomJay. The northern portion of this warp follows, very approximately, the boundry line of the Punjab and the United Provincess The rocky floor, of which these crustal warps are an integral part. is covered by.alluvial deposites of th~ Indo-Gangetic 'pl~in. .The entire str~tch from Karachi to Calcutta IS of the same geolog1cal type, but W1thm th1S type there 1S marked difference of detail. In that area of the United Provinces covered by the upper waters of the Jumna and the Ganges, the. alluvial sub-soil i<> lenticular in formation. Ltmticles 01 clay are contained in a matrix of sand. East of the line LucknowJ~awnDore, the clay becomes predominent and the characteristic tends to reverse. In the Punjab, west of the major transverse warping below the Jumna, already referred to, the characteristic change! sharply. The clay appears ir: beds or layers, of varying thickness and very varying extent. In some instances the sub-senl water appears under pressure between two clay bends and acquires artesian propertie~. In the Unite? Pro,,:"inces the gener~l d~rection of the subsoil flow is that of the Ju'nma and Gange3 flvers, m an easterly dlrectlOn roughly parallel to the main crustal warps. So far as the3e crustal warps are concerned therefore, the flow is unimpeded in t~1e United Provinces though obstruction is probable in Bengal, between Jal Paiguri and the Ganges river. But in the Punjab, the direction of the sub-soil flow is roug'oly normal to the main crustal warps and is impeded by the second on the San;olha Delhi line." RY GKVK UAS LIBRA >

'

11\\1\111\\111\\\111\1 \111 1\\1

1135

26 (b) !oll. The soil survey should be carried out hy taking samples for every 100 acres of the proposed area for tube well irrigation. The pH value should be from 7 to 9. The significance of the so called pH value is explained in Part II Chapter II. (c) SuitabilIty of the Pumped Water.

It is determined by working out the Salt Index as explained in tho previous chapter on well irrigation. Tho Salt Index should be negative for suitability of the water for irrigation purposes. (d) Source of Water Supply. The source of water supply should be such that the yield of the tube well does not deteriorate in course of tirr:e. The yield is effected in two ways; firstly by the choking of the slrainar and secondly by insufficient inflow to replace the depletion when the soil is not suffciently rervious. The first factor can generally be controlled by an engineer by a suitable design of the strainer, but the second one is often beyond the control of the engineer due to the irregular presence of the clay lenticles which are only partially pervious. 11. Tube Well Chaks.

(a) Size of Chak.

The size of chak depends on the discharge of the tube well and the delta or the depth of the water required by the crops which will be raised. There is yet very little information on the delta performance of the tube well irrigation in the Punjab. This cannot be compared to the United Provinces irrigation from the tube well because the average rainfall of the tracts ~rrigated in that province is from 30" to 40' per aAlnum, while even half of that is not availahle 'In the Punjab plains. In the PunjaD canal irrigation is fully developed and the delta: ~tatistics of this are availahle. The average figures of delta for the canal irrigation are given III Part II Chapter II. The delta performance of tube well irrigation is likely to be about three fourth of canal irrigated depths of waterings to mature a crop. The Karol tube well irrigation scheme has teen based on an average Rabi delta of 1'1 ft. and an average Kharif delta of 1'7 ft., while the adjoining Shalamar Disty., of the Upper Bari Doab Canal has an average of 1'57 f1. in Rabi and Z·57 ft. in Kharif. Assuming that the pump will work for 5000' hours a year, it willI e able to deliver annually acout 420 foot acres per cusec of the pump supply. Allowing th depths of watering as stated a! ove and assuming tte discharge of a tube well to be 1'5 cusecs, the Rabi area is likely to ·[·e 190 acres and Kharif area 1.20 acres. With irrigation intensity of 75% an average chak works out to be 424 acres. (b) Suitable discharge for a tube well. Excessive discharge for an individual tube well results in wastage from breacheo on water-ccurses and excessive depths in the fields. Too little discharge needs a extra number of wells and results in wastage in the fields by taking relatively longer time to fill a field. A discharge of 1'5 cusecs is considered to be suitable for a tube-well chak. Depth .0£ first watering is likely to te 4 inches and that of the subsequent waterings 3", which are very nearly the same as for the canal flow irrigation, but the major economy of water is likely to result from lining of the water course, and from division of the fields into small kiaries, because in this case a cultivator has to pay for the energy or the volume of water used. (c) Location of Tube Wells and Water-courses. A tube well should t e located near the centre of the area to be irrigated, so that the radiating water-courses are not more than one mile in length in any direction. It should be situated at the highest place in the chak so that the water-courses do not run in embankment. The depressions or drains should form the boundary of the chak. Main water-courses should be aligned in such a way that no field is more than half a mile from the Government water-course. In designing water courses the usual practice is to provide a field command of '2 ft., a slope of 1 in 3000 in tte subsidiary ( zamindary) water-courses and a slope of 1 in 5000 in main (Government water-courses}.

27

. It is de.>irable to line the main water-courses to save absorption or percolation losses. Tiles one and a half inches thick laid in cement mortar 1 : 4 will serve as a useful non-erodable lining, while the sodium caroonate, lining is liable to be easily damaged and subject to cracking on drying, . 12. Selectio:l of Pump Sets. An extract is given from the Punjab Engineering Congress (1941) paper No. 248 by Messrs. H. L. Vadhcra and A. R. Talwar. "Selection of a sllitable type of pump is of primary importance in any tube-well scheme. Before making the final choice, different kinds of pumps and headgears installed in the United Provinces and elsewhere were examined." "Centrifugll pumps with horizental spindles are usually installed at the nor.nal lowest level of the sub soil water table to ensure constant priming. Due to the occasional rise of water-tahle during the mOJ.soon season, When the demand is slack, the installation is in danger of being drow.lerl by be rise of the seepage water in the well. Actually, a numeer of motors are said to have been ruineJ in the United Provinces in this manner." "The di nculty has been overcome by using centrifugal pumps with vertical spindles and driven through vertical shafts from vertical spindle motors installed 8 to 10 feet aJove the pump. The only drawback with this type of pump as o:£ered by the tendering firms was that its discharge varied more rapidly with a variation in the total pumping head,than in the case of other types of pumps, otherwise it is the most suitable type and has been proposed to l:::e used on the Karol TuDe-Well SchcT.e." "The propeller type of pumps gives a fairly comtant discharge against all heads, but its efficiency is comparatively lower than that of the centrifugal pump. The bore-hole type of pump was also examined, but on account of its lower efficiency it has not been adop cd for the Karol Scheme. The use of a bore-hole pump is obligatory when the suction head exceed 22-24 feet and sump wells cannot be constructed to place pumps of other types at a lower level due to large changes in water table. . ' The vertical spindli)' certrifugal pump which have been used were specially manufactured by the Harland Engineering Co. Ltd., and are known as the "Spiroglide pumps." The following special features of the Spiroglide pump set are noteworthy:Pllmp and Motl)r. The pump is provided with cutless rubber bearing instead of the standard ball and rollar bearings. This arrangement renders the bearings immune against the effects of dampness or flooding of the well. It also means that the pumps require no periodical lubrication, one gland being the only part requiring occasional attention. The headgear is extended downwards and provided at its lower extremity with a steady bearing. The unsupported length of vertical shafting is thereby considerably reduced, giving additional rigidity and freedom from vibration. This feature avoids the necessity of the pruvision of an intermediate steady bearing for the vertical shafting carried on a girder spanning the pump chamber, such bearing being prone to get out of alignment in course of time due to the settlement of masonary walls of the chamber, which alter the position of the girdtlf supporting the cearing, thereby causing vibration in the vertical s'1afting. The weight of the vertical shaft and pump motor is carried on a thrust ~earing located in an accessib~e position in the headgear, where also is the means of adjusting the position of the shaft and the impeller in ttc pump casing. The vertical shaft between pump arid motor is of an abnormal strength, teing of 3l" diameter. The reason for using vertical shafting of such a large diameter is to ensure that the first critical speed of the shafting is beyond the full load speed of the pump sets, so that when the pump is bJing started when running and when being shut down, the shaft does not pass through a critical speed which would cause vibrations. The motor-supporting headgear is of massive construction and has a large area base, machined on the under-side for supporting on chamber. After erection, dowe pins area filleted

28 through the headgear base into the girders SQ that should the neccessity arise for the headgear to be renewed there is no difficuity in re-erecting the pump set in correct alignment, the gjrders being levelled when first installed, so that no .packing strips or shins are used between, the headgear and the girders." 13. Selection of Strainers. A few types of straines usually used in Northern India are described below :-:-(a) Cook Strainer. This is manufactered in America and consists of a solid drawn brass tube slottered with wedge shaped horizontal slots. The slots are cut with a circular cutting tool from inside the tube, to variouse gauges to suit the coarseness of the sand, the usual gauges in the ~e!ltral Punjab varying between 6/1000" and 16/1000". The strainer lengths are generally )Olnted together by means of screwed collars of brass . (b) Tej Strainer. This is manufactured 1 y tr.e Rtr<. ble Water Supply Service of India and consists of a brass tube consh ucted of a 1 rass shtet bent round to form the tube, the vertical joint being brazed. The slots are wedge shaped and cut cefore the sheet is tent to various gauges to suit the coarseness of the sand. The strainer is made in 8' lengths generally and from 3" dia: upwards, the lengths being joined together by means of screwed collars of brass, ' . This strainer is similar to the Cook strainer, except that it is not made from a solid drawn tube. It is niether so robust as the Cook, nor are the slots cut so accurately. It possesses the advantage of ceing considerably cheaper and is easily obtainable, ceing locally manufactured. .

(c) Layne and Bowler Strainers. They are iron slottered strainers. The strainers are made in America and, consist of wedge shaped st.-el wire wound to a suitajle pitch round a slotted or perforated steel or wrought iron pipe the lengths teing jointed together by scr !wed collars. These ar,~ heavy and ronust and can stand rough usage, but having to be importe 1 from from America, it take.>, a considera~)le time to get delivery. (d) AsUcrd Strainer . • The strainer is generally made in 8 feet lengths, the lengths teing·jointed by half rings bound with wire and soldered over. This strainer has to be very carefully handled lest the (wires are broken or displaced. (e) Brownlie COllvolutei Strainer. The strainer consists of a polygonal convoluted steel plate round which a copper mes~l · itrainer consisting of heavy parallel copper wires woven with copper ri::>bon is placed.' (f) ltggett Strainer. " · This is new strainer provided with cleaning devices in the shape of cutters which can •be turned in the slits and it is claimed, by this means, that the clogging of the strainer by the , deposition of solid matter on the outside of the strainer and in the slits, can be prevented. 'The cutters are operated from the surface. The strainer is said to be somewhat expensive.-• t (g) Phoenix strainer. It is calcium plated and is supposed to be free from the danger of choking and corrosion caused by the chemical action. All brass Tej strainers appear to be the best because br(,lss is not readily acted upon by water and is easily procurable locally Coir and Munj rope strainers have been used in the Punjab with success for .small supply tube wells meant usually, for domestic purposes. Hard wood slottei strainers are at pre3eat in ;:.a eX.?i!rimenhlstag,~ hr ilie on tube wells in the Irrigation Scheme in the Punjab. 14. Choking of strainers. The strainers get choked up usually in two w~ys; (a) che:midal1y (b) mechanically.

29 (a) Chemical action.

The chemical action may deteriorate a strainer in two ways, firstly by choking and . ~condly by corrosion . . If calcium 'b"icarbonate be present in water to the extent IS parts per 105 the reduction of. pressure'. due to pumping releases carbon dioxide and causes calcium carbonate to be precipitated .on the strainer. The .effect is th . c~mulative. In c~ur:,e of time yield begins to fall on account of choking. The corrOSlOn of the stramer metal results In the complete collapse and the sub ;eq uent choking of tl1e portions below it. The mil(,i steel and cast iron are attacked by the sodium salt. Zinc is particularly susceptible to s)diu:n carb.mate and aluminium is even more so. Copper is attacked by sodium carb)nate and sodium chloride. Brass is not readily attacked by solts present in the soil while calcium in the form of plating is non-corrodlb~e. The sub-soil water in the western Punjab is usually saline and unfit for drinking purposes when salinity is more than 15 parts in 105 , and not suitable for agricultural puposes when salinity is more than 60 parts in 105 . The chemical choking by deposition of carb)nates is very much reduced by providing a large slit area or low velocity of inflow -which means less cepression head and the redu~ed liberation of CO 2 , •

0

,

(b) Mechlnical Cho',ing-. It is simply blocking of slits with the mlterial such as fine sand. This can be guarded against by providing suitable slits expanding inwards. The surest remedy to remove this trouble is tbat the vebcity of inflow should b; lower than, the, optimum velocity which can. te expermently found capLi'?le disturbing the material. Theprqper screening or shrouding of the strainer with coarse material will remove this trouble to a large extent. The pulsating action of the centrifugal punps tends to break the adherence of the sand, particles in the slits by arching action and is also. useful to retard the deposition 01 the carbonates. IS. Size of Tube well Pipe and Strainer Length.

The minimum diameter of the suction pipe is fixed after the considration of the maximum permissible velocity through the pipe. The frictional losses vary as the square of the velocity and directly as the wetted area, A 10" diameter is considered suitable for suction pipes for a discharge of 1'5 cuseC5; this gives a velocity of 2 76 feet per second. which is less than 3'0 feet per second, the st;ll1dard permissible velocity in water supply schemes. The factors a"fecting the design of a tube well strainer are: (a) Transmission constant of the soil, (0) Depression head, (e) Length and dianeter of the strainer and (i) Shrouding. The transmission constant of the soil varies considerably fro!n stratum to stratum. In wa.ter bearing sand, consisting of particles" say: 16/1000" mean diameter, a mean velocity of 0 005 foot per se'cond ha3 ~ee_l fOU::l it) n w,~ 0.11y tIi') fi.lf~3t PiLrticles of a ncgltgible daimeter. This would limit the disclarge to 'OOS cusec per sq. fo::>t the strainer surface. Large diameter strainers are, however, very expensive and, therefore. to keep down the cost shrouding is resorted to. From practical experience a 10" dia"lleter strainer of 123 feet . total length is found suncient to give a disc'large of 1'5 cmecs with a maximum depression head of 120 feet. The dialleter of the strainer sl.ould, ho Never, be n::>t less than that required for the optimum velocity., . The in draw into the strainer is not uniform throughout the length of the strainer and the gross discharge does not yary directly with the length, of the ,stI;':Liner and, therefore, it would be uneconomical to have a uniform diameter of the strainer throughout its length. It is desirable to vary the,dia'1letet of the strainer retaining the optimu;n velocity of three fe€t per second in the pipe as far as possiole. .. Suitable lengths of strainer of varying diameters from 4 inches to 10.inches may be used. A}ypicallocation chart is shown in fig. 1. The saving in cost <:onsequent on using the smaller diameter strainer is considerable for instance:The cost of strainer and plain pipe for one tulle well of uniform diameter of 10 inches t.hroughout i~s length. is Rs. 4 575/- compared to .Rs. 3,48~/: when stl'ain~rs and pipes of varying SIzes from -4 lll, to 10 lll. are used for the same tUje well glvmg a net savmg of about 25 per cent in the cost of strainers and plain pipes. '

,or

30 There is, however, one objecti~n to the use of the small diameter str
LOCATION CHART OF STRAINER .bO PIPE. TYPE DESIGN SeA.L • • 1401t: ':.''..

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31

Water Jevels.-During the process of boring, observations of water levels in the bore are . recorded regularly twice a day.eefore starting the work and after finishing it for the day. ~he difference in the water levels observeo on the close of the day's work and tte nex.t mornmg before starting the work gives an indication of the recuperation of water levels m the core and the nature of the strata at the bottom of the casing pipes. Location of strainer and shrouding. After the completion of a bore, a location. chart of strainers and rising pipes is designed, guided by (a) the transmission constants d the SOlI strata, (b) the analysis of samples of water, and (c) the water levels in the bore. After the strainer has been lowered in the bore according to the location chart, !hc process of shrouding and extraction of the casing pipes is started simultaneously. Shroudmg consists of i in. Pathankot bajri retained on 1'/10 in. mesh. An accurate record of the material used in shrouding is maintained showing its calculated quantity as also. that .a~tually used. In certain cases, specially at the junction of sandy and clayey strata. bIg cavItIes ~re formed which require considerable quantities of tr.e shrouding material to fill t.h~m. . Dunng the location of the strainer, great care has to be taken so that the strainer and nsmg pIpes are always suspended and are not allowed to rest on the bottom of the bore as otherwise the strainer at the bottom is subjected to unsafe loads, and is liable to te crushed. To ensure that the strainer has been located and the shrouding has been done without any da'uage to the strainer, it is necessary to take soundings inside the tube well ~t frequ~nt intervals. A history sheet for each tube well is maintained at site, giving complete mformatlOn regarding each bore. '

17. Eccentricity in the bore. In all cases where borehole pumps are installed, whether the wells are compound wells or otherwise, it is of great importance that the finished well and the bore itself should be as nearly vertical (i.e. in plumb), as possible. Borehole pumps ge~erally revolve with a speed ]::etween 1,500 and 3,000 revolutions per minute, and it can easIly be imagined how damaging the effects of eccentricity can be in such cases on all the moving parts of the pump and motor. The setress and strain on all bearings, shafts, bushings, etc., are. so greatly increased due to the eccentricity that all the care and patience exercised in securmg a truly vertical bore is amply rewarded' by the ease and smoothness attained in the installation and working of the pump later on. In spite of exercising reasonable care in boring the finished well is likely to ge~ s~ight~y out of plumb partly due to some eccentricity in the bore itself and partl) due to van.abon. III the verticality of the top pipe when earth is filled round it after extraction of the bonng tute, e.g., when bell-sockets are used for a compound well. 1he ins~de diameter of the top casing pipe is always kept slightly larger than the outside diameter of the pump bowls, so that there is a certain gap letween the outer face of the pump- bowls and the inner surface of the casing pipe. So long as the eccentricity does not exceed the clearance allowed in this gap, advantage can be taken of this in reducing the eccentricity. The eccentricity will be neutralised if the pump is installed not centrally in the casing pipe, but in such a way that one edge of the lowest pump bowl is almost touching the ca5ing pipe on the side to which it is inclined. But if the eccentricity exceeds the clearance allowed Py th;s annular gap (i e., the difference between the inside diameter of the casing pipe and the outside diameter of the pump bowls) it cannot be eliminated without setting right the eccentric casing pipe. Me3.surement of eccentri~ity-A simple method for measuring eccentricity in a bore is by the use of a reel-like instrument which can easily be made by joining together two circular discs of the same diam~ter by means of a central hollow tube. The tu,;e should have threaded ends with nuts to fit on to these so that discs of diEerent diameters, according to the size of the bore. may be fitted on to the ends of this tube as required. The discs should have holes punched in them so that they may be immersed in water without any obstruction. The discs and tubes should be sufficiently heavy to enable them to be lowered in bores full of water without difficulty.

32 ,.'
The tube with discs can te suspended by means of a thin strong steel wire or copper wire so that it can be moved vertically up or down in the bore. A tripod having a pulley' rigidly fixed to its apex is placed over the tube-well and the disc instrument, fitte.j with discs about 1/8th inch smaller in size than the inside diameter of the tuhe-well, is sus?cnded frOill it with t1;e wire passing over the pulley. TLe instrumcnt can now be lowered or raised as desired. The tripod is so adjusted that the ,disc instrument will ·come centrally over the top of the tu' e-well when freely suspended. Let us assum~ that the ~isc instrument is so hung that its top disc is centrally situated and flush Wit'l the top of the b)re tube. Let the distanc~ tetween the pcint of sus;:;ension (i e. the pulley of tripod) and the top of the disc instrument, when its top is flush with the top of the tube-well, be 10 fect. The instrument is then lowered in the bore, say, by 10 feet. This distance can be found out y taking measurements of the, length of the suspension wire, Let us assume that the wire deviates from its central position and the deviation as me\lsured at the top of tte tube-well is l/lOth of an inch. Therefore at the top of the upper disc (whic'l is 10 fcet inside the tubl~-well) the deviation will be' twice this much i.e. 2/lOth (l/Sth) of an inch from the vertical line throug~l the pulley. Hence in going down 10 feet it has become eccentric by 1/5th of an inch or thc eccentricity is 1/5th of an inch in 10 fcet. (It will be noted that the eccentricity is not l(lOth of an inch in 10 feet, but 1/5th of an inch). The e,:centricity at 20 feet, 30 feet etc., can similarly be observed. Setting right eccentric wells-If the eccentricity of the larger diameter casing pipe (in which the borehole pump is to \-e lowercd) of a co:npound well is found to exceed the :: clearance allowed by the annular gap 1 etwecn the inside dia'neter of t'1e casing pipe and the " outside diameter of the pump bowls, the casing pipe will' have to be Drought into plumb before the borehole pump is installed. A simple method of setting right an e~centric casing pipe is to loosen the earth on the sice t6 which the casing pipe is inclined and te;cn to force t;10 casing pipe b:lck by applying jacks on the other side (opposite to that to whic'l it is inclined). Wacl1 t~e casing pipes have· been forced into plumb, eCLrth and gravel are filled on the side opposite that in which the pipe was inclined, thu'> p 'eventing Le casing pipe fro.n resu ning its cccentric position. To set right an eccentric casing pipe, a new bore, say acout.t\\O thirds the diameter of the casing pipe, is sunk close to the casing pipe on the side toward5 which the pipe is inclined. Tlm bore is carried down to about 10 feet a,-;ove the b)ttom end ,of the .. casing pipe (which as explained earlier is generally at a'~out 80 feet to 100 feet b.~low ground level in the case of compound wells). The point where this new bJrc-is made is kept su!'ficiently away from the eccentric casin~ pife so that on completing the bYre its b)ttom end does not come into clash with the bJttom end of the ca';ing pipe. Theboring:tube is then withdrawn with tte borehole left intact. Powerful jasks are next appli!2d on the side'opposite to that in which the casing lJipe is inclined and at a point a out 8 feet ! clow tre surface of tlc.c ground. This enables the jacks to be fixen pro~eJy and theY,get a g()od :se;:}t bClind for applying force. As the b:lttom end of the casing Dil=C is fixc r !. and the~e is hollow space made by t1e boring on the siee opposite to that fro:n ,,'h~re j;Jck" arc applled. i\e ca5ing' pipe can easily te pushed till it is ab301utely vertical. Whia this has be';n accomplished the:e will be a boUow space left J-etween the neN and th.e old position of the ca5ing pipe Earth and gravel are then filled in. this open space and also in al1Y orcn space Idt on the opposite si,'e where the new boring was made. The ca.sing pipe is thus fixe 1 in a vertical position and all e:centricity is rerriQVe.v rC:l.ly for installation of a 1:)) [e'1,ole, pump.

to

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'

18.

Back washiag and back-blowing of strai!lcr wells.

In thc case of strainer wells 'it sometimes happens that the strainers get choked with fine particles of sandancl clay or due to bridging (descri' ecl before) and thus have to be cleaned; or it is found neccessary to draw ollUargcr quantities of sand from thc surrounding strata through the. strainers, to inlprove the yield of the well.' This is done by resorting to "back-blowing". Tl:e process of fo'rcing out water or air under pressure from inside the tube-welt through the strainer slots, into the surrounding strata is' called "back washing" or

'back blowing" respectively. In some cases satisfactory results are obtained by these methods md it is advisable to try these for improving the yield from a tube-well whenever it is found l~cessary.

If su T:cient quantity of water is available from a high level storage tank or from a pump which can pump water under pressure into a tube-well, "back-washing" can easily be done with water. This water entering the tube-well under pressure passes out through th strainer slots into the surrounding strata and thus pushes out and carries along with it all the fine particles of sand, clay or dirt and cleanses the strainers substantially. But if the strainers are only partly clogged, the water may pass out of the strainers through the unclogged -rcrtions and tLe whole of tte strainer may not get cleansed properly. In such ca~es a. water jet is carried (lown to a point directly opposite each portion of the clogged strainers by using a small pipe, which can be lowered freely inside it. At the cottom end of this water-pire, tLere is a foot piece alJout 4 feet long with rerforations on the sides and with it5 lower end sealed with a can. The top end of this water-pipe is connected to a high level storage tank or the pump. The water from the storage ,tank or the pump emerging under pressure hom t1 ese perfora tioll5 in t1.e foot-piece passes through the strainer slots thus washing tLem thoroughly and cleansing them. If any of the was~ed material falls inside the tube-well it can be pumped out from the tube-well along with the water from it. The other rr:ethod is to use air unc!er pressure, from an air compressor. The plant consists (if an air compressor and air line, foot-piece, eduction tube, etc. The air line is a G.!. (galvanized iron) tu1)e from 1 inch to 2 inches in dameter, through which air uncer pressure is passed from the air compressor to the foot-piece. A foot-piece is a perforated tube ab0ut 4 feet long and of the ,same diameter as the line with its lower end sealed or plugged with a cap. An eduction pipe is used for discharging water along with any sand, etc" which may have come into the tube-well due to i_lack-blowing. The well pipe itself can te used as an education pipe, but as the washed material from the strainers, etc., has also to be pumped out along with the yratl)r it is preferaole to have a separate eduction pipe about 4 inches in diameter, so that tue ~lelocity of water pumped out may be sufficiently gleat to carry with it all the clogged matrtrial, etc" from the well. The tube-well is sealed with a sealing cap at the top and the eduction pipe and line pass through it There is a sluice valve on the delivery side of the eduction pipe which can, c closed when air is to be passed out through the strainers and can be opened when it is dsiord to pump out watr and sand, etc. from the well.

The eduction pipe is lowered into the tU2e-well till its t:OttO'll is al~out 2 feet ahove the top of the strainer pipe The air line IS then lowered inside the eduction pipe till its footpiece comes dirctly opposite the strainer pipe, The sealing cap cetween the tu')e-well and eduction pipe is then closed as also the sluice valve on the eduction pipe. The air c )ming from the air compressor and passing out of the foot-piece has now no passage for escape except through the slots of the strainer pipes, and through etese slots it pa~ses out into the surrounding strata. But in doing so, as it passes under pressure throug'l the slots, it cleanses them and removes the material which was clogging them. When one portion of the strainers has teen cleanerl, the eduction pipe and air line can i)e lowered to the strainers lower down and graduallY all the strainers are cleansed. After cleaning each length of the strainer the sluice valve on the delivery side of the eduction pipe is opened and the water containing the washed cloggings, etc" is Ipumped out. Thus gradually all the clogge,j strainers are cleansed and there is a proportiom.te increase in the discharge from the well. In the case of compound wells an eduction pipe of a suitable size, which can easily be lowered inside the main strainer tube, should generally be used for back-washing and back- 'Dlowing purposes. But if the diameter of such an eduction pipe is found to be too small for satisfactory operation the main strainer pipe itself can i:e utilized as an eduction P!pe, In such cases a loose joint is prepared for extending the length of the main strainer pIpe h ground level For this purpose plain pipes of t'1e same diameter as the strainer tube have to be lowered from ground level inside the compound well. A rubber ri.ng fGrming the loose joint is screwed on to the bottom end of these plain pIpes and when lowered inside the well rests on top of the main strainer pipe, The bottom

34

por~ion of this. loose.joint is tappered so that the main strainer pipe slide3 into it and abuts agamst the ru?ber rIng, thus forming a water and airtight joint due to the weight of the pipe on top of It. This pipe is then used as an eduction pipe and the air line can be lowered inside it and worked as described a bove. When the straners have cl~aned, the upper plain p~pes with the loose joint can easily be lifted out of the compound welll~aving the well clear for Installation of a deep well pump as usuaL 19. Te3ting the T'ube ..Well.

After the ex.traction of the casing pipes is finished, the tube well is tested for discharge. If th.e Yield of the tube well is satisfactory i.e .• it yields a discharge of abottt cusecs 101'.2 lmiXlmw~ aepresslo!7 heCla ot l2'') teet, the C0!75tmctf<:1ll of the ma,Smzary p~rt the work is taken in hand. The arrange~ent of the stilling c'1amb er and IT.eter flUme measure the tube well discharge is shown in Fig. 3. The most int~rcst~ng feature of the. constructIOn of a tube well IS the put ting in of a water-tight joint between the top of the nsing pipe and the suction sluicevalve. This joint is 7 fef~t below spring level and it is not possible to fit the suction valve when water is rushing out of the rising pip~ under this much head. T() over· come this difficulty a mechanical rubber stoPPer has Montagu, in Fig. 4. A.M.R. been devised by Mr.

its 1'3 of

to

PlAN" MlASIIIIIJII; DlYI&E FDR 1.6 &USEe D/SUIAR(;£ Sc A J. E. •

Sl'cr/ON

1/ /'00

ON

A.II.

...:frr--=;::::::o'i--":=:""

""i'~'d'~~~111~~~~~!!~~j:;;tijr-;;;;;;;>i3~

Th~ stopper COIlJ.pletely staunches the flow at water in the risin.g pipe. It is then Fig. 3. 9uite .e~sy to put in the rump founea tion after ttc suction sluice-valve m positlon.

has be(!n put

20. ExtraetioJ. of strafilers an 1 pipes in the case of umuccessfu} wells. If, on testing, a tube-well it is found to be u::lsatisfaciory and it becames necessary to extract t~e strainers and pi~(lS it can be done i)y lowering a wire rop~ with a ho 'k . inside the strainer pIpe so as to catch tnc "eye" on the bail plug and then pullmg the stralller tube up. As d~LriOed. 'oelor<;. .this can casily be acco 71 plished provided tne strainers a.nd plain pipes ha ve not been m poslho~ for a long time and have thus not been jammed b;: the surroundlUg soil. If these have been Jammed in position the wire rope method of. pullIng .them ~)Ut may not be successful. In SU(~h a case a simple device is to use a tapenng, comcal, pIece of wood like a fr.ustruJ?- of a cone, loosely fitting inside the strainer tube, whic:1 c~n be lowe~ed. inside the stramer ;t)lp~ bY.Jneans of steel rods. This conical piece of w?od IS l~wer~d I.ISlde the tube-well. wlth .ItS wlder edge at the lower end. to some point OppOSIte a plam plp~. It it is lowered to a pomt OPposite a strainer tube the latter may get damaged when pullmg l( out. Gravel or stone chip, are thea poured inside the tU;Je-well and these collect round the conical piece ?f wood and form a sort of a wedge between the wood and the pipe. .When th· wooden piece .IS now pulled up by means of the rods it gets jammed to tte ~:)lpe [;ecause ()f the ",:edgmg effect of ~he gravel between the pipe and the wooden cone an~ It tends t~ P1l11 the pIpe also along WIth it. A clamp is tightly fastened to the steel rods lust ~DOV~ tne 1:op of the ~ube-well. an~ re.sts on it. Another clamp is fasteped .on the tu :e-~el~ pIpe Itself on t~e outs1de: holdmg It tightly, and jacks are place:l below th1s clamp .to hit It up .. The pull IS transmItted from the jacks, through the clamp~ to the tube-well pIpe, and th~ pIP~S trcmsmit it to the cla!llp. on the steel rods resting on top of the pipes. Thus the ro? .Itsel~ IS pulled up and transmIts the pull to the canical wooden piece inside. The tu ;e well IS m thiS way pulled

35

-

up by the jacks directly from outside and by ~he. wooden piece and the wedge of gravel from InsIde and is gradually extracted out. This is a v~ry convenient method of extracting strainer pIpes and can be used where the strainers have ~:een lowered for a long time and have got _ _ _ _ _ _ _ _ _ _ _ ~_ Jammed. The advantage of this method over ~1'IItr.,."K,,"'_ the hook method is that instead of the tensile 'OUJzt..~~b~OI7:r--~ force teing applied to the hook on the bail plug only, which may get Lent or sheared, it is ~1Ij\':1'l a:)plie 1 to a large surface of the tube-well pipe 1===iFl .3' .~ 9 itself and is therefore more effective.

IIrtNAIIIQJ. SrfJl'l'ER'DR ID INC_ _ ~ , ScAl£4~: '''I

,./.

l

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.

special collapsible

steel tool is also

(, btal.nable which, can ~e low.ered inside the tub~-

:well mstead of We LOmcal pIece of wood. ThIS tool can be expanned out after being lowered insi ,e the s~rainer pipe.s thus forming a so'rt of wedge to gnp tte pIpe Just as the gravel wedge holds the pipe in the method described above. 9. Miscellaneous We rks. After the tube well is installed, the following works are carried out :(a) Construction and lining of water course. The earthen water-courses should at least be run for one crop for consolidation before the lining is done. '

(b) Pump Sumps. A suitcble design is shown in Fig. 5. (c) Measuring devices. It should be in the form of long crested weir to require low working head of the type of meter on canals, Part II Chapter IX. A stilling cevice in the fornl of grids will generally be required after the water leaves the delivery pipe. (d) Operator's Quarters. Two rooms with a verandah. kitchen ana court yard will give enough accommodation. 22. Assessment and Water Rates. The esta~lishment required for each well consists of· one operator and a beldar. The operator's duties are as follows; while beldar acts as his assistant : (a) to start "and stop the pump, F:ig. ~. (b) to record the time and the meter reading at the beginning and end of each cultivator's turn, (c) to record tIle area irr:gated and the crops sown. (d) to issue cultivators' recei?t~. (c) to prepare tie daily routine return. (f) to look after the Government channels, A ziiladar is required for about 20 wells to check the revenue work of an operator ann to prepare the demand statement. Besides a supervisor is needed for about 20 wtllls' who is supposed to we rk as a mechanic and an electrician to carry out the necessary repairs.

fa

36

"

.,

-~i;-fj~~I~~~~~~~:£J~~

The Operator maintains a printed and b}und log book containing tfle following information : (a)~Datc. (b) Time of starting and stopping the motor. (c) Meter reading at starting -and stopping (d) lCnits used by ca h cuI ivator. (e) Value of electricity used. (f) Field numbers irrigdted. (g) Name of crop. (h) Area irrigated.' (i) Gauge in measuring tank. (j) Total volume pumped in cubic feet. In addition to the log took the operator maintains a cultivators' receipt i:ook. This is in triplicate. When a cultivator has finished irrigation, he signs the receipt which shows ttc time of starting and stopping the pump, the number of units consumed and the amount assessed. The oFerator keeps the counterfoil with himself, sends the duplicate to the zilladar and hands over the triplicate to the cultivator to enable him to check his water dB at the end of the crop. On receipt of the cultivator's receipt, the zilladar posts the units used in a ledger in which he leaves a page tOf each cultivator, This forms the b)s's of the demand statement. The ledger is also kept in dupl'cate. The cup'icate copies arc di3tributed to tte cultivators at the end of each crop and take the place of the pare '~a (demand notice) v~macular form No.8 A used in canal irrigated areas. 'Water charges have ceen fixed per 1,000 eft. of water. Actually, however, the rate is converted in to electrical units by actual measuremert ts.

At the beginning of each crop, a complete te3t of each tube well is carried out with re ;pect to its discharge, electrical consumrtion delivery and suction head, pump efficienc:e5 etc. Electrical consumption per 1,000 eft. of water and the cost of an electrical uuit for each, tube well is work(~d out and intimated to the nmindar concerned by posting notices. The rates per thousand eft. of water are uniform for aU the tube ~'ells, iJut the rate .Fer unit of electricity varies from "ell to "eU, depending on the number of units required to raise the standard volume. The advantage of this system is that the cultivator can read the Fig 5. and kn ws exactly how much is to be deb:ted to meter before and after his turn starts hi, account. Water rates r er 1,000 eft. of water are the same as charge~ in the United Provinc~s. These are three annas s~x pies per thousand eft. of water for khan! and tW? annas fo~r pIes per thousand eft. of water for f,rabi, These correspond t.o Rs. 2.12 per watenng of four lllches .in rabi and Rs. 3.18 per watering of four inches in khan.f.

37 Assuming deltas of 1'8 and 1'1 for kharif and Rabi (vide paragraph 5 [ the cost 01 maturing one acre of khan] crops works out at Rs. 16.7 and of rabi crops at Rs. 6.81. 23.

Discharge from a tube well.

The mathe,natles to determine the discharge from a tub~ well has not yet been fully deVl'loped. The approximate methods to judge the discharge of a tube weU can be applied in two ways. Firstly, very nearly correct estimate of discharge can be made from the actual performance of the existing tU'le wells. In the Punjab Engineering Congress paper No. 129 ot 1929, M.1:. Ho Net Sll?erinten(ling Engin(~er has given actual performance of a. large num'Jer of tube wells varying in discharge from 8 to 36 gallons jJ~r squar~ foot of the strainer surface per fcot depression head. The safe figure for an estimate of a tu')e-Ncll disc'large may be taken as ten gallons per hour per square IFATUIW. foot of the strainer area per foot depression head. Secondly an estimate of the discharge in a tube-well can 're fanned by experimentally determining the safe optimum velocity of say, 005 ft./sec. as ment~oned before in this chapter which will disturb the soil particles irrespective of the depression head, The soil samples used in such experiments should be representative samples of the soil crust in which the strainer is to be put, which is not generally practica'0le. The formula of discharge was first developed by Dupuit {I863) and then developed by Kozeny (1927). Reference is invited to pages 255 to 260 of book 'Public Water Supplies' by Turueaure and Russel, New York (1924). Fig. 6. Fig. 6. Let Q=total discharge of the tube. H=Deoression head =D-d D=Depth of water table above the impermeable boundary. d=Depth of water in the tube above impermeable boundary. r=Radius of the tube. R=Radius of the influence of the streams radially entering the strainer. k= Tra.nsmissi.on consta.nt of the soil. ' The formula of discharge in cusecs

_1fk

(D l_d 2)

:.

"'

Q--Rlog. - r

In this formula k depends on the porosity P and a soil constant S'By X' so th3.t k=k'P The a'3su'llption in the derivation of this formula are:(i) Water table is at rest and is horizontal. (ii) Bottom of the strainer rests on a horizontal impervio'ls layer. (iii) The flow is radial and total diseharge Q remains constant acctoss the surfaetof a series of concentric cylinders. The formula is not correct because the assumptions are not justified. There are ne concentric cylinders Gf equal discharge entering the strainer. There is nG theore tical limit to the value of R, radius of influence. The assumption of the impervious lower boundary h absolutelv unjustifierl. However tables are given in the a'Jove quoted reference to predict. the value 01 R and the likely values of k in different soils based on the observations of the authors. :

24. C niitions in the Punjab and the Unitej Provinces compared. The conditions of tube-well irrigation in the adjoining provinces of the Punjab and tht United Provinces, in India are CQ apared below:(a) In the tube-well areas of the United Provinces, the geological. conditions an such that an immense sub-soil stream flows parallel to the crustal warpings. In the Punjab the flow is transerve to the warpings Consequently in the United Provinces there is (f uniformity of conditions in respect of depth to water table belcnv natural surface. whic~.

38

does not exist in the Punjab. Such uniform conditions lend themselves to standardisation of plant and n:ethods which make for maximum econO:T y in sinking and equiping of tube-wells. In the funja b, the variety of geological condifions necessitates every single site being carefully examined and tested before the tube-well is completed and equipI=ed. Apart from eXI=ense, delay in construction is certain to occur. . (b) The nature of tte sub-soil, in the tube-well areas of tb.e United Provinces is l:enticles of clay in sand. In the Punjai), sheets of Leds of clay occur irregularly in addition to numerous lenticles both Jarge and small. There are no geological maps which would enable the engineers to avoid such deposits when siting t;~e new wells. Conser;uently in the United Provinces the entire water table is interconnected and the whole of the stream cantiL utes to tI-.e discharge of the tubc-well system. In the Pun: ab, the irregular 'geology of the sub-soil results in pockets of water cut off from the main stream. If a pump should accidentally be sited in one of these pockets, the discharge may cease abruptly after a few months' working or may te greatly reduced. (() In the hbe-v,ell area" of ttc Unitec Prcvircc,_ He soil is l'gJ t in texture, uniform in quality, free from salt with a pH value aproximating to the neutral. Conditions could hardly be more favoura')le. In the Punja b, t 1,e widest variations of soil occur. Many areas are impregnated with various salts the pH value varies from 8 to 9'2 and over. Unquestionably ther,: ar,~ areas suitable for well irrigation. Such areas must be sought for, and carefully tested. Otherwise Government may fined itself saddled with tube-well irrigation ;ystem in areas, which may deteriorate in course c.f time. (d) In the Punjab the water of the su~)-soil reservoir is not sweet every where as in the United Provinces. The salinity and the Salt Index of water for every strata where thestrainer is laid, must be tested, otherwise the tute-well iu:gation: will fail in the Punjab by deteriorating the yield of the crops, matured with saline water. (e) In the Punjab. the areas which are available for tube-well irrigation are very much scattered unlike the areas available for the United Provinces Tube-Well Irrigation. because the major portions of the Punjab plains are under canal irrigation. It is only the patches, uncommanded by flow irrigation or those adjoining the Dhayas along th' rivers, which needs artificial irrigation. (j) In the plains of the Punjab, average rainfall is 5 to 20 inches per annum, while the rainfall of the areas irrigated from tube-wells in the United Provinces i~ more than 30 inches per annum every where. The number of waterings from tube-wells to supplirr:ent the effect of rainfall in the Punjab will be at least double of those requ:red in the United Provinces. The Punjab cultivator shall have to pay abJut double the price of water. The average cost of irrigation per acre from tube-II-ell wells is Rs. 2-4-0 per watering in rabi and Rs. 3-4-0 in ,~hanf. If the number of waterlngs is 4 in raM and 6 in khari/, the cultivator will pay double the amount as compared to the canal irrigation. 25. Financial aspects of the tube well schemes In t1:e Pun;ab. The financial aSI=ect of the tube well irrigation schemes is not at all bright in the province of the Punjab. The type of expensive irrigatian cannot be popular because large areas in the Pnnjab are already being irrigated by flow irrigation from the canal at very cheap rates. The electric energy has been prepared in the United Provinees at a cost of less than three pice per unit, while the cost of energy per unite from the Mandi Scheme in the Punjab is more than two ann as. The cost of sinking tube-wells must be more in the Punjab than that in the United Provinces, because the water bearing strata are irregular. The lifts are also relatively nigh. The life of the tube-wells in the saline waters of the Punjab can hardly te taken as 12 years, while the depreciation charges in the United Provinces are worked on the basis of 17 years life. In spite of these difficulties, the tube-well irrigation is likely to pay a very important part in the future irrigation schemes of the Punjab Province, because there are lots of areas

39 where water can only be supplied by tube-wells, and because it is likely that cheap energy may be available from canal falls by small hydroelectric sehemes or from crude oil engines using country fuel. Moreover, the tube-well irrigation may have to be extended as an anti-waterlogging measure in the waterlogged tracts or as a famine relief measure in certain arid tracts. 26. Clnal Versus Tube-TNell Irrigatim. A few of the disadvantages of the tube-well irrigation are stated below:(i) Working expenses are extremely high, as wells depend on mechanical means oi raising the water. (ii) The wells are dependent upon a source of energy. Apart from the question of cost referred to in (i) above, a failure of the energy supply is accompanied by a stoppage of all pumps dependent thereon. (iii) A tube-well is liable to progressive deterioration. The strainer is l'able to choke and is difficult to clean. Replacement of the well may be necessary after comparatively short period of operation. (iv) Maintenance of a delicate mechanical installation will always present its OWfJ difficulties. \v} The tU"be "ell water is clear i.e., free from silt. Cousequentlv weed growth an at th.e time of sowing and maturing of crops which havt already been used up in the Punja'). Flow irrigation from the canals is essencially accompanied by a great loss of water in the distri lUting channels and the wasteful use in tht fields. This wastage brings in turn the curse of water-loO"ging. The disadvantages of canal irriga. tion are dealt with in detail in part III Chapter II. 0

27. Exa.mination Questiom. (i) Discuss the merits of irrigation by means of tube w~Jls against irrigation by grav:ty canals is

the western dis:ricts of the United Provinces. (ii) Describe with sketches an electrically worked tube-well installation used for irrigation. ExplaiL &!l air lift pump for a well lift 20 fcot. (T.C.E. 1935;

2,

(a) Name the different types of wells.

(6) Why woull you prefer wells over other sources of supply of drinking water? (c) Describe the various me hods of boring deep wells,

3.

P.U.l9~

(If) Yo?r are required,to place all order for pumping machinery. Please lay down specification, which you, as a CIVil Engineer, will communicate to a firm of suppliers, P.U.194:2 (li) Describe the various type.; of pumps suitable for use in the tube well irrigation. Which tyl1' do you consider best and Why?

40 (a) Why is t.he cost of the tube well irrigation more in the Punjab than in the United Provin~es ? (b) Why is delta in the tube wen irrigation lower as compared to the flow irrigation from canals? (a} What is the life of a tube well machinery in the Punjab and how will it compare with its life in the United Provinces conditions? Describe the various types of tube well strainers used in the Punjab. Which type in your opinion is the best and why? (a) Describe the various factors which con tribute to the reduction of yield from tube wells in the Punjab in course of time. (b) What precautions and remedies would yeu suggest to minimise choking of strainers?

4.

5. 6.

7.

8.

(a) What is the suitable discharge of a tube well meant for irrigation?

(b) "'hat points will you keep in view in designing the water-course sy,tem for irrigation from a tube well?

28.

BihliJgraphy.

1. "The Construction of Wells and Boreholes for water Supply," by J. E. Dumhleton. The Technical Press Ltd, L')ndon. 2. "\Vater Works Handbook" by Flinn, \Veston and Bogert. Megraw-Hill Book Company, Inc., New York anb London. ' 3. "Oil-Well Drilling Methods," by Victor Ziegler. John Wiley & Sons, Inc. New York, 4.

"Hydrology and Ground \Vater" by J.M. Lacey. The Technical Press Ltd., L')ndon. "Tube-wells," by T.A. Miller Browrr\ie. Thacker Spink & Co, Calcutta. 6, "Oil Gas and Water \Vells," by Luecy Manufacturing Corporation, New York. 7. "Casing Troubles and Fishing Methods in Oil Wells," by Thomas Curtin. Bulletin No. 182, of the Department of the Interior. Government Printing Office, Washington.

5.

8.

"Johnson National Driller's Journal," St, Paul. Minn.

" A Study of the Yield of Water Wells.

Bulletin No. 1238:'

" Testing Water Wells for Yield and Drawdown No.638." .. The Chemistry of water.

9. 10. London.

Bulletin No

1237."

Brochure issued by the American Well-Works, Galveston, Texas, U. S. A. "Water Analysis," by J, Alfred Wanklyn and E.T. Cnapml.n.

Trubner &. Co., Llldgate Hill,

11. "Baroda Blue Book of Water Analysis for Agricultural purposes," by Dr. C. C. Shah, Agricultural Chemist, Baroda. Printed 1938. 12. "Hydraulics and its Applications:' by A. H. Gibson. C:>nstable amI C:)ill,nny Ltd., London. 13. "Minutes of the Tllbe-wf'lls Conference, United Provinces, July 1934." prjnted at the Advertiser Press, Saharanpur, United Provinces.

. 14. Notes by Mr. F. H. Hutchim;on, LS.E., Superintending Engineer, Development Circle, United ProvIl:ces, on Pipe Lines, Shajra Sheets etc. and instructions for the gUidance of Tube- well Operators, Section MlstrzS and Supervisors.

. . 15 "The Ganges Canal Hydro-electric Scheme with its associated State Tube-well Project," by Sir Wilham Stampe, Superintendent, Printing and Stationery, United P,·ovinces, Allahabad. 16. onwards.

Irrigation Administration Reports of the United Provinces and their supplements from 1929-30

17. "Report of the Royal Commission on Agriculture in India." Printe:.l at the Government Central Press, Bombay, 1928 .

. 18. "Report of the Indian Irrigation Commission, 1901-03, Part I, General." Supenntendent of Government Printing. India, Calcutta. 19. .. Compressed Air Plant," by Robert Peels. Ltd., London. Season Edition.

John \Vilay &. Sons, New York.

Office of the

Chapman &. Hall

20. "Brochure issned by Messrs. Ingeroll Rand," Co. of U. S. A. reganiing Air Compressors. 21. "The Physics of the Divining Rod." by Naby and Frank is. Publi~hed by Bell and Sons Ltd.,

London, W.C. 2.

22. "Notes on Tube Well" by John Ashford Paper No. 40, Lahore 1918.

Punjab Engineering Congress,

23. Article on Unreinforced Cement Ccncrete pipes and pipe-lines by Mr. KG. Smith,I.S.E., Indian Concrete Journal, November, 1942.

41 24. Report OD the State tube-well project estim~te, 1934-35 to 1942-43 by Mr. F.H. Hutchinson LS.E. 25. Note by Mr.R. S. Chaturvedi, C.E., A.M.I.E. (INDIA), Assistaut Irrigation Research Officer, United Provinces, on "The investigation of groundwater resources in the western districts of United Provinces." 26. Report on "Well construction and pumping from wells for drainage and irrigation in California and Aizona, U.S.A." by Mr. A.R.B. Edgecombe, I S;E., United Provinces, Public Works Department, Irrigation Branch. " 27. "Water supply from tube wells by T .A. Miller Brownlie paper No.39, Punjab Engineering Congress, Lahore, 1918. 28. "Hand Book on tube wells" by: K:D. Sanwal GovemmenJ::,Prjtiting Press U. P. Allahabad 1944. 29. "Tube well in Borstal Central Jail by W.S.Dorman The Punjab Engineering Congress, Lahore 1920·

30. "Tube well practices of the Public Healt Circle P.W.D. Punjab by D. A. Howelh The Punjab Engineering Congress, Lahore, 1 9 2 9 . : !. \ 31.

"Tube wells on N.W.Railway by J. Varden The Punjab Engineering.Congress 1930 papers No. 13t

and 152. 32. The Karol Tube-well scheme by H;L. Vadehm and A.R. Talwar, ;Fhe'Punjah Engineering CongfetJs Lahore ISH. 33.

Bulletin 182 of the Department of Interior published by the Washington Government PreiS .. 11.S,A.

--: 0 :---'

PART II

CANAL IRRIGATION Chapter I

CLASSIFICATION OF CANALS Irrigation and Navigation Canals. Canals are divisible into two main classes viz .• irrigation canals and navigation canals. Examples of irrigation canals of appreciable magnitude are available in India starting with the Ganges canal which was designed and built by Sir Proby Cautley in 1845 and the Madras -canals by Sir. A. Cotton at about the same time. The finest ex:amples of th.e irrigation canals are now available in the Punjab as shGwn in Plate No. l. Navigation cannot be expected to be successful on irrigation canals. because they have to follow the main water $lleds or ridges so as to provide a sufficient head of water to flow over the adjoining land. for irrigation. Moreover. they have to be designed with velocities sufficient to guard against their silting up. consistent with the limitation imposed by the permissible scouring velocity for materials forming the bed and the sides. An ideal navigation canal on the contrary. should have a very nearly still water channel, so that navigation may be possible in both directions. rt should generally follow low country for economical construction. Moreover, a navigation canal should approach conveniently large centres of traffic. Examples of large navigation canals exist in the western countries such as Suez, Panama and Kiel canals. An attempt was made in the beginning to combine both the functions in the case of Ganges, Western Jumna and Sirhind Canals. In these canals, small country boats were used. The bridges had to be designed high enough to pass the boats underneath and at faUs, lock gate arrangement was provided. The velocities in these canals are 3 to 4 ft. per second, and loaded .. boats cannot be pulled for the up traffic by men or animals. The income from traffic by boats has been too low to justify the cost of the additional works for this purpose. It is mostly the first class of canals i.e. Irrigation Canals. which will be dealt with in this volume. 2. Classes of Irrigation Canals. The irrigation canals are divided into two classes. (a) Permanent Canali. A canal is said to le pel manent when its source of supply is SUfficiently well aSSUred to warrant the construction of a regular graded channel supplied with masonry works for regulation and distribution. The canals which are provided with permanent canal head works fall in this category. The permanant canals may be perennial which receive assured supplies from the rivers througout the year, or may te seasonal such as kharij channels in which regular supply is available only in the kharij season. (b) Inundation canals. Inundation canals are those which depend for their supply on the periodical rises in water level of the ri.ver .from whi~h they are taken 0'1. They are not provided with permanent headworks. Water IS Simply let mto thea. when the river rises through the marginal flood embankments and the~ are pr?vided with a regulator 3 or 4 miles away from the river. The proolems connected WIth theIr working are complex and peculiar and are dealt with in Olapter XVIII Part II. I.

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43 3.

Financial classificatIon of canals. The financial classification of Irrigation Canals is two-fold(a) Productivc works. When the forecast of the income usually prepared at the time of the preparation of the project of an irrigation scheme shows that the income from the proposed canal will exceed the yearly charges of maintenance by a sum equal to at least 4 per cent of the capital invested, the work will rank as a productive work. The precentage of the net return is fixed by the Government from time to time according to the prevalent rate of interest in the market. A certain number of years is allowed for the development of irrigation after construction of the canal, during which the interest charges accumulate as a simple debt to be paid off as the revenue gradually increase3. On the expiry of the term usually ten years, H.e net revenue receij: ts ~Lculd have cleal ed off all the interest accumulated during the construction and developement, after paying for the running charges. (b) Protective works. Protective pu~lic works are defined to be those, which although not directly remunerative to an extent .which would justify their retention in the class of productive works are calculated to guard against a probable future expenditure for relief of the population. They usually take the form of famine relief works. The construction of an otherwise expensive irrigation scheme may be started tJ employ the population during famine3. The lining of the canals though not directly a. remunerative work is a very useful protective work to reduce the future expenditure on the antiwaterlogging measure and to save the deterioration of lands by water-logging. 4. Receipt from Irriga.tion Canals. The receipt which make up the income of a canal fall in two categories (II) Direct receipts and (b) Indirect receipts. Direct receipts comprise, firstly, the income of the water rates fixed for the different crops irrigated; secondly, the receipts from plantations; thirdly, the income from water-power such as mills or hydroelectric power; and fourthly. the mi'>cellane:>l1s receipts fro:n water used in bulk for filling tanks, for building houses, for watering road-side trees or for consolidation of roads. Indirect receipts are the receipts creditable to the canal department due to the increase in land revenue by canal irrigation to barani or chahi lands. The difference cetween the usual barani or chahi land revenue rate and the revenue rate of the irrigated lan
(e) Minors.

Sometimes when the country is such that the water-courses will have to be longer than two miles to reach the fields. it is usual to take off small Government channels from the distributaries, which are called minors. (f) Water-courses. This is not a Government channel and constructed and maintained by the cur tivators according to the' alignment sanctioned by the canal engineers from an outlet down to the fields of the cultivators. Their design is dealt with in detail in Chapter No. XVrr Part II. ' 6. Punjab canals. A list cif the Punjab Canals is given in Appendix 1 at the end of, this chapter. The earliest canal constructed was Western Jumna Canal about the year 1817 from the Jumna river. then came Upper Bari Doab Canal in 1850- \859 from the Ravi river and then Sirhind Canal (1872) from Sutlej river. The Lower Chenab Canal was completed in 1902 from Chenab river and the Lower Jhelurr Canal in 1905 from the Jhelum River. The Triple Canal Project for the construction of the Upper Chenab Canal. the Upfer Jhelum Canal and the Lower Bari Doab Canal was commenced in 1915., In .this project. the Upper Jhehlum and the Upper Chenab canals are mostly feeder canals connecting the Jhelum river with the Chenab river upstream of Khanki, and the Chenab river with the Ravi river up stream of Balloki respectively. The last· named 5 canals (serial Nos. 4 .to 8 in Appendix 1) are called the five linked canal because the waters of the three rivers mentioned above can be jointly utilised in these five canals according to the seasons requirements. , , ' .

The canals at serial Nos. 9 to 19. take off the Sutlej-Beas system and were constructed from 1922 to 1928. and are called the Sutlej Valley Project canals. Most of them are khari/. channels The Haveli canal was completed in 1939. This is also a feeder canal from Trimmu (Chenab river) to Sidhnai (Ravi river) and its water has been utilised to 'give perennial irrigation to the old Sidhnai Inundation canal. . , The old Inundation canals in Muzaffargarh and Dera Ghazi Khan districts taking off. the Indus river were taken over by the irrigationDepartment,P.W.D. from the civil administration in 1880 and the Shahpur canals taking off the Jhehnn river in 1894. The· lower Sohag Canal and the Para Inundation Canals were built in 1882 from the Sutlej river and have subsequently been absorbed in the Sulej Valley Canals .. The Sidhnai inundation· canal was opened in 1886 taking off that the Ravi river at Sidhnai and has subsequently teen aosorved in Haveli.Canal Project. They took water from the rivers in floods, without any permanent head-works. . The p~ )ject to irrigate the Sind Sagar Doab is under construction' by taking off that canal with a. disc~arge of about 6.000 cusecs from the Indus river at Kalabagh. Lots of areas of Hissar and Gurgaon districts in the Punjab and in Bikaner state need protection by canal irrigation and tank irrigation. Projects for constructing dams in the hiUs are under contemplation for this purpose. 7. Distribution ()f river supplies to d.I:IIerent canals in the Punjab. Some canal systems are inter-linked and tt.e supply available in the rivers is not always sufficient to meet the indents of all the canals. Consequently. the supplies of. various' ... rivers are distributed among canals according to orders framed from time to time by the Punjab Gevernment. The following may te taken to te the usual procedure:(a.) Western Jumna CanaI.-The Supply at the river Jumna at Tajewala is distributed. between the Western Jumna Canal in the Punjab and the Eastern Jarnna canal of the United Provinces according to regulation rules for the canals. . (b) Sirhilld Clnal.--Th~ Sirh~d cana~ is entitl~d to take up to its m?-xim,um capacity, all the supply avaIlable m the flver SutleJ at Rupar. . . (c) Upper Bari Doab Cloal.-The Upper Bari Doab Canal is entitled to take up to its authorized capacity, all the supply that reaches Madhopur with the sole exception that duriJl~ kharif from 1st April to 31st !:eptemcer the Kashmrj

,(5

(Basantpur) Canal on the right bank has a prior claim up to a maximum of 120 cusccs. (d) The Northern (Linked) Canals.-The Upper Jhelum and Lower Jhelum Canals taking off the river Jhelum, the Upper Chenab and Lower Chenab Canals taking off the river Chenab and the Lower Bari Doa)) taking off the river Ravi are inter-linked and they are entitled to all the water in the river Chenal:> and Jhelum which they can take up to theirauthorized capacities. When the supplies of the Chenab and the .1helum rivers drop helow the combined capacity of the linked canals, a destribution programme CO'illes into force. (e) The Sutlej Valley Clnals.-The Sutbj Valley Canals are entitled to all the water that '.. COUles down the river Beas and a'1y surplus from the riv.;r Sutl~j ov:r and above the requirements of the Sirhind Canal. The actual distribution of supplies among . the' three partners. (The Pu:<jab Government, the Bikaner Sta~e. and the Bahawalpur State) of the Sutlej Valley Canals is carried out in accordaTlce with the orders issued by the Government of India, based OIl the Anderson Report of 1935. (1) T.!e Montgomery Pakpatan li1.k.·~rs entitled up to its authorised capacity to all the water availa:)le in the river Ravi at Balloki. (g) The Haveli Canal.-The Rangpur canal, the ThaI canal and the Panjnand canal are regulated according to the orders issued by the Government of India, based upon the recommendations of the Anderson Committee. (h) The Inundation Cluls.-Draw up to their authoriz~d capacities all the water that they can tap from the rivers both in rabi and kharif. i. Fnuctions of Canals and other Irfigatim Works. (a) Proteeti::m.--The most important function of the irrigation works iq to protect the area dealt with against serious loss during seasons naturally unfavourable for agricultural operationS.. They provide protection against famines. There cannot be any famine in canal irrigated areas. The surest remedy against the recurring famines in the Hissar district of the Punjab is the introduction of the canal irrigation. (b) Improvemen\s o{ erops.-Another function is the substitution of superior for inferior classes of crops. The natural result of the introduction of a permanent supply of water to a tract formerly dependent on a fluctuating rainfall. Thus. in some Indian districts, we find wheat replacing barley; sugarcane and indigo replacing light millet crops and, as a general rule, the cultivation of mixed crops practically ceasing. _. (c) Manurial value of canal water,·~The rivers of the Punjab are all alluvial. The water of the Punjab canals contains a sunciently large percentage of fin~ clay and silt in suspension. The silt in the canal water has a great manurial value. The yield of crops raised from the canal irrigated fields is more than that of the crops irrigated from wells without other manuring. (d) Addition to the wealth of t.he country and the Government Revenue.-The irrigation works add to the wealth of the country both directly by the enhanced value and quantity of products, and indirectly by an increase in the valve of the land. The increase in wealth of the Punjab province can well be imagined from the figures of the irrigated areas as given in the following table ;-Irriga~ed area In Year. Source: acres. 1,025,156 1867-68 Wells and river spills. ;! 2,341.103 1877-78 U.B.D. & WJ. Canals added. , ,.'4; 6,039,944 1907-08 L.C.C. & Sirhind Canal ap.ded. fit I " 9,063,901 1917-18 Jhelum Canals, U.C.C. & L.B.D.C. addeQ.. 12.800,()OO Sutlej Valley Canals added. 1937-38 14,000,000 1942-43 Haveli and Rangpur Canals added. t

.~,

~

The government revenue in the Punjab, as credited to the canal department, from ,the realisation of the owners and water-rates, was about 8 crares of rupees tefore the World War II out of the provincial revenue of about 1I crores of rupees. The expenditure on the maintenance of the canals in the Punjab was only about 1! crares of rupees annually, The profits of, some of canals r efore 1920 after paying for the interest charges on the capital outlay are shown in the following tables : . Profits expressed as Canal percentage of Province. expenditure, Pwljab.

Western Jurnna Canal Upper Bari-Doab Canal Lower Chenab Canal Sidhnai Canal Sirhind Canal

12·3% 1.6'5% 43'6% 31'S to 51'8% ,., 21'7%

Lower Jhelum Canal 24'0% (now 35%) Upper Ganges Canal 10'4% Bijnor Canal 11'0 % Bombay. Bombay Canals 10·0% (e} Population,-The absence of famines by the introduction of irrigation results in an increase of manpower. Good and sufficient feeding results in good health of the population. There is also an increase in popUlation. This increase in popUlation is absorbed in additional labour required for agricultural operations and for the maintenance of the irrigation works. The robust manhood of the Punjab has always been the pride of the Indian Army, (f) Effect on climate and health.-The Irrigation Works such as canals and storage reservoirs are feeders of the sub-soil supply. With the rise of water table, the climate becomes damp. Irrigation on large scale affects the climate by making it cooler and damper particularly at night. The average temperatures in the Sargodha and Lyallpur districts of the Punjab have dropped by about 10 degrees by the development of irrigation, on account of the increase in the cropped area and the other vegetation in the form of gardens. The dust storms have been reduced by 75 per cent. Damp climate and vegetation naturally increase some diseases such as malaria; but this is more than counterbalanced by the increased vitality due to better standard of livmg_ (g) Phntation.-The banks of large canals are generally planted with trees, This is a great advantage to the tracts through which they pass on account of the shade, timber, fuel, and fruit that they provide. Trees and shade are a real necessity in very hot climatES, and as constant extensions of irrigation tend to break village plantations up into tillage, the niaintenance of permanent and well-cared-for plantations on the irrigation works themselves become desirable. Moreover, these plantations, if well managed, become large sources of revenue. (h) Navigation,--Another important function of a large canal is the facility it offers for navigation. This function is often neglected probably because the engineer is Irore attractEd by· the manifest advantag.;s of the result of the attention he pays to extensions and improvements in irrigati n. It would be bett(r, however, to take a broader vi6wof the situation and endeavour to develop all possible sources of advantage to the people and State, and the utilisation of the fine waterways formed by great canals should not be neglected as it has so far been, (i) Bathing.-The domestic advantages of irrigation works should not te overlooked. The facilities given for bathing and watering cattle must be greatly appreciated by the inhabit<J.nts of the towns and villages situated near the banks, In the colony areas of the Punjab, can~l wafer is USed for drinking purposes as the ground water is brackish. ' ! (l 1 (j) water-Power.-Water-power is frequently made available for Use by the constntclion of canals and tanks, In India up to the present time this source of revenue, has to a large, extent been neglected, owing mainly to the fact that the sites suitable for power generation (falls) are United Provinces.

frequently far removed from the manufacturing 'centres. Electrical generation and its transmission o~fers such a simp~e solution of this difficulty. tha~ ~e may look forward ~o seeing a great advance m a few years hme and probably many great CIties may soon owe thelr lighting. ventilation. and commercial prosperity to the same beneficient work that supplies them with food. The Ganges grid system in the United Provinces in India has proved a great success in the electrification of a large tract of that province. Considering the above-mentioned advantages of canals. the irrigation is the best cottage industry for the predominently industrial Province of the Punjab. 7. Examination Questions. (i) Explain the follOWing terms : -

(a) Water-courses, (b) Branch Canal, (t) Minors, (d) Indirect r~eipt8, (ii) What are productive and prot'llCti\>e canal works P (iii) What are the difficulties in having combined channels for irrigation a.nd navigation t (iv) What do you understand by permanent and Inundati'On canals? (v) Explain briefly the Triple Canal Project and the five linked canals of the Punjab. (vi) Elucidate: - "Irrigati'OD is the best cottage indus try for a predominently agricultural Province of the Punjab." (P. U. 1942 )

Chapter I AJeP-,,-",DI,{ 1

CANAL IRRIGATION IN THE PUNJAB PUNJAB CANALS

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Canal (S .. C.) 9040K Area 5257 ~ {Rupar) I1 UppC'r Bari Doab Canal 6900K I [U.B.D.C.] Madhopur. ~5770R Lower Bari Doab Canal 7000K [Balloki] L.B.D.C. tis;>\).\. Vpper Chenab Canal 13084F [Marala] U C.C. Used in Irrigation 5180 Lower Chenab canal 11 032K [KhankiJ L.C.C. 995SR Upper Jhelum Canal l\1argla Head (D.] C.) 87 83 F I 8 47K Used in Irrigation 1242R Lower JheJum Canal 4099 [Pasul] L.J .C. Pakpattan Canal 6094+ 735 [Sulemanki] [M. P. Link] Dipalpur Canal [Ferozepur] 6950K E8stern Canal [FerozepurJ 3320K ! Gang [Bikaner Canal] 2720 4917 1 Eastern Sadiqia Canal [Sulemanke] Fordwah Canal 3366 [Sulemanke] Mailsi Canal [Islam] 4883K Bahawal Canal [Islam] 3000 Qaimpur Canal [Islam] Abasia Canal 230 [Islam] Panjnad Canal [PanjnadJ 7770 Haveli Canal [1939] 5249K [Trimmu] 2750R Ran~pur Canal (Trimmu) 2710K Shahpur Inundation 12010 Max: Canals (5 Nos.) ,----1295 ord: \' (]helnm river) 1

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I. ·

PART IT

CANAL IRRI GAl ION Chapter II

PRINCIPAL CROPS AND:ASSESSMENl' 1,

Introductory.

The primary object of all types of irrigation whether lift irrigation, cand irrigation or tank irrigation is to supply water to mature agricultural crops. It is, therefore, considered desirahle to acquaint the students with the principal crops sown and matured in the Punjab. The procedure of their assessment is also described briefly. The major portion of the revenue of the Punjab is derived from the assessment of the irrigated crops. The economical design. construction and the maintenance of an irrigation project is a means to an end which can be jurlg'2d in its efficiency from the quality and the quantity of the agricultural crops produced and the revenue which they bring to the state. The subject matter of this chapter is no doubt the domain of an agricultural engineer, but as the efhciency of an irrigation engineer can best be jurlged from the revenue return from an irrigation scheme, it is, therefore, essential that he is incharge of the assessment of the revenues accrucing from irrigation enterprize anti is also equipt:ed with the requisite knowledge about the agricultural crops.

2.

Soil conditions in the Punjab.

(a) The quality of crops grown depends upon the texture of the soil. The texture of soil is determined by its clay contents. An average soil in the Punjab contains clay from 12 to 15 percent. The soil containing less than 2 per cent clay is useless for crops other thn Barani grams.

Classillcatlon of solIs. Suitable crops, '.; Sugarcane, rice cotton and wheat (Produce of the last two below normal). Normal soil 10-20 Cotton, wheat: maize, vegetable, oil seeds, fodder crops. All give the best product. Light soil ~ -8 Wheat, Gram, fodder crops etc. Yield of wheat celow normal. (b) The ~hemic~l charac.teristic of the s
-I

Clay content% 40

50

researches in the Irrigation Research Institute at Lahore that soil with pH value from 7 to 8'5 gives normal yield of all the principal crops sown in the Punjab. The yield declines with pH value from 8'5 to 9 and with pH value equal to 11 the soil is infertile. The soil of Gangetic plain in U. P. is very nearly neutral and there is no trace of sodium salts. The pH value is no where higher than 7. 3. Rainfall. The crops require fairly well defined quantities of water at definite stages of their growth. Mr. Wilson, the Scientific Research Officer, Lahore, estimated the following total requirements of water for some of the principal crops:-Crops. Irrigation in field. 44" Rice 40" Sugarcane 20" Cotton Wheat Maize

. 12"','

18"

9" Fodder The rainfall will reduc~ the depth of irrigation required by artificial methods. (b) In the Punjab, the rainfall is very variable. The contours of equal rainfall called Isohy'ets are shown in the map of the Punjab appended as plate 1. It is evident from this map that in a very narrow strip near the foot of the hills b::>rdering north-east, the rainfall is 35" to 40" on the average in a year. In the plains the rainfall is , ; . everywhere less than the normal requirements of the depth of waterings required for the princi1;. ,pal crops sown in the Punjab. The rainfall cannot be turned on and off as required by the crops at the time of sowing and maturity. Moreover in the Punjab, the rainfall is concentrated up to 7S percent in the rainy months of July and A.ugust and for the remaining part of the year, the rainfall is very scanty and is very precarious. It is therefore, that the Punjab needs very badly the help of artincial irrigation which has lead to the development of canal irrigation system and which surpasses in its efficiency all sueh works in the world. 4. Prin(ipal crops in the P'lnjao. . The principal crops sown in the Punjab are given in the Appendix. No. I appen~ed. to thIS chapter. The English and the Hindustani names of the crops are gIven. The tune of sowing and harvesting the crops is given in columns Nos. 4 and 5. The column No.6 gives value of depth of the canal irrigation required in feet known as Delta. Column No.7 gives the average produce of the crop in maunds. Column No.8 gives the approximate water rate charged for the irrigation water. The value of delta varies from canal to canal according to rainfall and the efficiency of the cultivators. Similarly water rate changes from canal to canal according to the soil condition and the anticipated produce. The average produce is very variable according to the nature of the soil from one district to another. The average produce is fixed in the settlement reports of a district according to the nature of the soil. The figures of the columns Nos. 6 to .~ __ should be taken merely as a guide to acquaint the student with approximate usual valueS.-·-"

5.

Fertilizers and Manures used for agricultural crops. Introduction. Of the principal food materials required for growth of plants by far the most important one in which the Punjab soils are dencient, is nitrogen. The deficiency of nitrogen is the main problem of manuring. Much of the farm-yard ma::mre is burnt as fu'.)!, while a larg~ quantity of combined nitrogen is exported in the form of oil seeds, food and other grains, and animal products such as hides and bones. The only way of stopping the wasteful practice of making manure into cakes and burning it, is to provide an alternative supply of fuel hy planting quick growing trees 'near the villages. .

51 Farm-yard Manure.

Farm-yard manure increases the retenhve power of the soil for dissolved substance~: It causes the soil to be puffed up and increases the pore space which improves the tilth and general conJition of the soil. It increases the water holding capacity of the soil and helps the biological activity going on in the soil. Farm-yard manure contains about 75-80% water,' 0'6-0'7% nitrogen, 0'1-0'3% phosphorus (as P 2 0 S) and 04-0'5 :/0 potash (as K 20). The urine is much richer in nitrogen and potash but contains only traces of phosphorus. A to~ ?f man~re c<;mtains about 15 lbs ..nitrogen. 5 los. phosphorus and [0 hs. of potash. The composItion vanes wlth the type of the ammal, the quality an~ the quantity of food, proportion and nature of litter and the stage of decomposition that has taken place in the manure itself. 5illce the liquid part of the manure is much more valuable as compared with the dung, far more car~ should pe taken to preserve this than is usually the case. The 'Lest method of collecting urine is the use of litter. Any waste material·wheat straw. w'z'Jat b'ZU:>l, tJ/ia or SZ'SO,'1, p.tlllr," sug ~rcane trash, grain bhussa and any other vegetable waste can be successfully used as an absorbant of urine. The litter should be spread under the catth in the evening and may be carried next morning along with the dung into pits, which may be of any suitable length and breadth and only two feet deep. When the pit has been filled, water may be occasionally sprinkled over the stuff so that it remains moist but no free water stands. A turning is given to the material after every two sprinklings of water. 'Ihe ~tuti becomes ready tor carting in. a;}out g mont'ns' time. As stated in the introduction, quantity. of f~Hm-:yard manure available for use for crops is inadequate. Something can be done in thls dlrec hon by the manufacture of composite from any rwbbish material on the lines suggested a )ove. Compositing of waste material is now a recognise? part of the activity both of the ag!i.cultural exrerim~nt stations and village improvement assoclations and we may expect some addltIon to the manunal resources of the country as a result. Green Manuring. Another method by which the deficiecy of farm-yard manure can be made good is by green manuring. It provides all plant food ingredients in the soil and supplies a large amount of humus which improves the texture and water holding capacity of the soil. Experiments show thatGowara is the best crop for burying in as a green manure under condition in the canal colonies while (san) hemp appears to be the most suitable crop in the submountainous tracts. Green manuring with D'~ainch(l has proved exceedingly advantageous under waterlogged and alkaline conditions prevailing in the l(allar tracts of the Punjab where rice is mostly grown. Artificial fertilizers. Of all the essential elements required hy the plants only three viz: nitrogen, phosphorus and potassium are important froal manurial point of view, because they are found generally in small quantities in the soil. (a) Nitrogenous fcrtiliZers. They tend primarily to encourage above ground vegetative grGwth and impart a green colour to the leaves. They delay maturity of the crops. In cereals plumy condition of the grain is increased while straw gets weakened with exce3sive applications. Examples are ammonium sulphate, sodium nitrate. (b) Phosp.llatie fertilizers. They are a? .essential part in t~e formation of grain, hasten the maturity of crops, counteract the condItIOns produced by mtrogen, encourage root development especially of the lateral and ~brous rootlets, ~trengthen the s.traw cer~als and increase the weight of grain comI;>ared WIth ~hat of straw, mcrease the quahty of gram of cereals and of grass in pastures and mcrease reSIstance of plants to dieases. Superphosphate is the common material used as a phosphatic manure. (c) Potassi3 fertilizer. The presence of available potash h;;\s much to do with the general tone and vigour of the plant. By increasing resistance to certain dieases it counteracts \he ill effect of too mucR

52 nitrogen, while delaying maturity it works against the early ripening effect of phosphorus. It is essential in formation plumb and heavy grains. Putassium sulphate is the material used as a manure. The results of manurial experiments in the various parts of the province with regard t. th~ use of manures have shown ;. (i) Farm- yard manure has almost always given the best results. It is the cheapest means of adding organic matter and nitrogen to the soil. Average quantity required per Ol"Op is about one to two cart loads pC! kanal (tacre). (ii) The application of nitrogenous fertilizers such as sodium nitrate and ammonium sulphate has given good results. The quantity of manure required per acre per crop is al;out one maund. These manures increase the yield of wheat, but the increase hardly covers the cost of manuring. In the case of cotton and sugarcane, these manures have given profitable returns. (iii) The application of phosphatic and potassic fertilizers has almost always resulted in a financial loss. This is due to the fact that the market prices of such fertilizers being high, it is not economical to use them for agriculture. •. Plant Diseases of thc Principal Crops. (i) Cotton. Cotton is mostly damaged by ;(a) Boll worms. (b) Jassids. (c) Root rot. (a) Boll worms. In the beginning of the cotton season the cater-pillar bores into the top tender portion of the shoots. When fiowers, buds and bolls appear, the larvee turn their attention t) them and flowers add buds of bolls of the plant are attacked; observations have shown that up to 75 percent of the flower buds and 60 percent of tne bolls may be damaged by this pest. . Remedies. There are parasites which feed on the boll worms. This parasite should be encouraged. . In the beginning of the cotton season alld burnt.

the attacked shoots should be collected

.

The plants should be shaken thoroughly by dragging a rope over them. The boll worms The ground should be immediataly watered to drown the boll worms. After cotton crop is over, cotton sticks should be removed from the fields, cutting them 2" below U e ground. (b) Jassids. The adults are reddish in winter and greenish-yellow in summer. The pest attackS €6tton in Juneand remains on the plant up to Novembtr. It sucks the sap from under side of the leaves with the result that the fruit capacity of the cotton plant is very seriously affected. No effective control against this pest is known. Rough hairy leaved types are slightly resistant tt) the attacks of the jassids. . w(U drvp on the ground.

(c) Root Rot. H appears in patches. No effective remedy is known. It is suggested that cotton should Bot be sown for a year or so in the field in which root rot has appeared. (ii) Sugarcane. There are two main diseases; red rot and stem borer. Red rot is an insect disease. The insect bores into tht stem. Resistent varieties should be -sown. The caterpillar in the case of the stem-borer attacks the central shoot and kills it. This is called the 'dead heart'. These dead hearts should be collected and burnt. The insect also hybernates in stubbles which may also be removed and burnt

53 Interculture and irrigation recommended. Crude oil emulsion placed in irrigation channel is also useful. (iii) Rice. The caterdillar is the most destructive pest of rice. This kills fhe central growins leaves which dry up. but when plant is attacked at t\e fhwering stage. the ear-h~ad stands beeD and is devoid of grains. To control this pest the best remedy is not to provide facilities for the borer to breed. This can be prevented by the a')sence of the early crop of the rice. Rice stu"jbles should be ploughed up. collected anj burnt. . (iv) Gram. Gram suffers from wilt in the month of February. After flowering, the plants dry uP' Recent work indicates that salt in the soil accelerates the intensity of the disea'ie. In reclaimeo land the attack is less. The gram cut-worms. The caterpillars get into the pods and des(roy the seed. The damage never is very seriollS, (v) Weelt. The most common diseases are:(a) Ear-cockles or Mttmni.-This is caused by worms which produce black bolls in place of grain. Seeds free from disease should be sown. (b) Rust or Kttngi.-This is a fungus disease which is serious only in cloudy wintel's. The leaves show yellow or black spots. Rust nHistent varieties of the seed should be sown. (e) SUint or Kangiari.-When this fungus attacks the wheat plant black powdery suBstance is produced in place of grain. Th'} seed before sowing should. be treated with hot water. (d) Bunt.-This larglyoccurs in hills.·~ 'Kanctls of grains are destroyed and replaced b~ ill-smelling blackish powder. Seed from healthy crop should be sown. 7. Economy of Water. Water is the fiinished product of the Irrigation Department and has been broug~t to tht . fields by incurring a great expenditure in the construction of head works and the canal system. It is very essential that it should be used very ~cono nically. It is both in the inter~st of the Government and the cultivator to use it carefully and economically and thus o')tain more and better crops. (a) The cultivators should be encouraged to line the water courses. They can savt about 20 percent water and thereby increase th~ area irrigated by 20 percent. (b) Wastage should be avoided by adopting khat kia'fl system of irrigation. In this system a field is divided into AU kiaris of one kanal and su1)sidiary watercourses are construted so that water does not flow through the already irrigate 1 por" tions of the field. When one ki((ri is full. wateris closed and ,! led into another one. The arrangement shown in Fig. 1.

There used to be legal binding to enforce this very economical system under the rules of the canal Act No. VlII 01 :51, 1873 but this has been stopped since 1928. The enfring~­ ment of these rules used to be punished by levying additional water-rates. (c) The wastage should be avoided by proper alignment of the water courses so that there is no heading up in thf Fig. 1 water course to command any field. (d) The water cours=s should De properly maintained to avoid wastage from breaches in them

54 (e) Excessive depth of watering should b~ 'l.voided. It is no u.se flooding a field with one foot depth of water when death of 3 inches will do. (f) Economical use of canal water is an effective anti-water-logging measure in the water-logged areas to reduce the menace water-logging. Excessive watering is also injurious to the plants.

8.

Sub Irrigation.

ll,

,Ir-

There should not be any bend up or down as the pipe line is not closed, that is, water tight. If the ground is very uneven the arrangement should be as shown in Fig. 3 (iii IS" deep trench slightly wider than the external diameter of the pipe be dug a little water to flow after laying 8 to 10

and pi pe laid feet length. (iii) The lateral spacing of pipe line differs for different crops. Lawn 8 ft. intervat Lucerine 6 ft. interval. and vegetables 3 to 4 it. apart. • (iv) There should te a vent at the end of each pipe line for inspection and to prevent air lock. (v) The crops need irrigation as below in dry weather. Grass and cereals 3 to 4 days. Vegetables and Lucrines 2 to 3 days. (l) This system of irrigation is only possible when water is available every two or three days but in smaller qnantity. The initial expenses for laying pipe lines are very heavy. This system can only suit small gardens under' strict supervision. Water saving is no dOUGt large.

9.

Internal distribution of water.

Water is supplied from a permanent masonry structure called outlet or moga, the capacity of which is fixed according to a water allowance for a definite area as explained in detail, in Chapter No. (iv) Part II. The chaks are designed in such a way that ehe discharge of the outlet is not less than one cUSeC and more than 2'75 cusecs. Water is conveyed to the fields through channels which are called water courses or "khals". Mainwater courses are de~igned by the Irrigation Department and the work is carried out, the cost being recoverable from the cultivator with the land revenne in small installments called acreage rate. . All water courses are essentially zamindari channels. The cultivators are responsible for their maintenance under provisions of the Canal Act No. VIII of 1873. Usually only one

55 naka is given from the main sanctioned water course to every square or holding of a cultivator. The water courses as shown in Fig, 9 are constructed alJd maintained by the individual owner of the square or a holding, (/;) The distribution of the water by the cultivators amongst themselves is essentially the concern of the zamindars. [hey can take the help of the Canal Departrr:ent under provisions of Section 68 ot the Canal Act No. VIn of 1873 to get share or wari of individual sharetlOlder Only Divisional Canal Officers are fixed acccrding to the area owned Ly him in a chak. authorised to investigate and pass orders on warabandi cases. The turn is usually tix d in 'hours' and sometimes in 'pehars' in villages whue the cultivators are illiterate. l~sually the cultivators maintain a common clock and a gong. (c) The cultivators then follow the turn and the time allotted to each shareholder of a water course. Lots :of disputes arise in the internal distri'oution of the canal water but a canal Officer does not interfere except as provided under the Canal Act Section 68. The revenue staff, the zilladar and the p:ltwari, are supposed to give the necessary advice when required by the zamindars. In the cases of warashikai (taking water out of turn) only r"medy available to the canal department is that the person who disregards an authorised warabandi promulgated by the Divisional Ca:1al O.hcer u'l.ier Section 68 of the Ca:J.al Act, can be charged special rates under Section 31 and 33 for using water in an unauLlor sed manner. Such cases are instituted by the canal officer on the written application from an agrieved person. It is generally possible to set right irregular working of the wari by rendering sympatfJetic advice to the cultivators. (d) Nikal is often the cause of great trouJle. The last man receiving wa.ti on a water course ben~fits by the amount of the water contained in the water course when the turn changes to the lands in the begining of a water course. Sometimes the cultivators who get water at night have a great grievance. The night wari can be changed to day wui in alternate year. (e) The changes in chak bandi, ndas and supply of water through the intervening water courses are made under Section 20 of the Canal Act No. VIII of 1873 by the Superintending Engineer and the Divisional Officer. The Divisonal Officers posses final power in the case of water courses and the Superintending Engineers in the case of chak bandi changes. 10. Un~Zs of measurements of arelS. The land measures are of two kinds, in the Punjab the bigha measure and the kanal or ghumao measure. They are shown in the following table:1. -Description. 1 sq. karam 20 Biswansis 20 Biswahs

(a) Ordinary Bigha Measure,

Indian equivalent. 1 B swansi 1 Biswah 1 Bigha

I.

Area in sft" 22'6875 543'75 9075'0

(b) Shahjahani Bigha Measure.

Descriptl~·o:=n.:_._ _ _ _ Iu-cdian

~'Gatha

20 Biswansis 20 Biswah

Description. 1 sq. karam 9 Sarsahis (kan.) 20 marlas 8 kanals

Area in sft 6806 1361'25 27225'0

equlUalent. 1 Biswansi 1 Biswah 1 Bigha

II. (a) Indian equivalent. 1 sarsahi

Area in acres. '00156 '03125 '624=5/8

Remarks, Note-This IS used in southern Punjab and in States.

Ghumao measure; Karam 5.0.

1 marla 1 kanal 1 ghum ao

II.

Rpmarks.

Area in acres. '000521 '010416 '2083=5/24

Area in sft. 250

Area in En.((lish acres.

225'0 4500·() 36000·0

'UUU574

'00516 '1033 '8264

(a)

Central Punjab. 1·21 ghumao equal to 1 acre. {c} One karam is two paces of a man or 3 trots. (b)

(b) Acre measure; Karam=5f (colony areal

""D""-es-c-ri"'p-t-iO-u_-._-::::: ----iI"'n"""dian eq u i valent. 1 Square karam 1 sarsahi 9 Sarsahi 1 marla 20 Marias 1 kanal 1 acre 8 kanals

Sq uare feet. 30'25 272'25 54'45. 43560.

Remarks.

Th'iSTsliSed in

Acre. -000694 '00625 '125 1'0

(ii) (iii) (iv) (v)

rutting a Government Irrigaion Channel. Enlarging or damaging the outlets. To oj::en the outlets when closed under proper authority in tatils. Warashikni (taking water out of turn), the powers have now generally teeJl transferred to panchayat. (iv) Waste of water" Abzai."

(b) Water lost from breaches from water courses is. charged at special rates as it is the duty of the cultivator to maintain the water courses in good condition. The special charge levied in each case can be upto six times occupier's rate at the diieretion of the Divisional Officer.

14. M.iscellaneous receipts. Miscellaneous revenue falls under the main heads and is charged and collected by the Slib-Di visional Offic-er according to the rates sanctioned hv the Gover!1ment w hen the authority to 'IlSe water has previonsly been o'Jtained from the Divisional O'flcer. 1. Mill rents. 2. Fixed contracts for water supplies to Municipalities and other local todics. 3. Minor items. Water for construction of hou'>es, burning bricks etc. The usual rates for miscellaneous use of canal water are as below : (a) Brick making and pise we

(b) Concrete & masonry (c1 Metalling of roads (d) Consolidation of kacka roads (e) Water "upplied in bulk

(j) Local bodies (not commercial purposes) (g) Watering avenues (kharif) (rabi) 15.

Rs. 0 3 0 2 10 0 30 0 1 0 1 0

0 0 0 0 0 0

2 8 0 5 0 0

Unit 100 eft or 100 No. 100 eft per mile D~r mile 2500 eft 6000 eft per mile per mile

Duty of canal water.

Duty is the measure of the working of a channel. It is defined to be area irrigated a crop, per cusec of the mean discharge. It is got by dividing the irrigated area by the mean discharge utilized in the period in question. The mean discharge in any month is the aggregate of daily discharges during the month divided by the number of days in a month.· The mean discharge of a channel durin~ a orop is the aggregate of the daily discharges throughout the crop divided by the mtmber 9f days in the crop. Kkarif crop=April to September=183 days. Rabi crop==October to March= 182 days.

Delta is the average depth poured on land in feet in a crop or per annu"!Wl.

DeltaL.=2-~-N

(1)

Where L. =Depth of water in feet Q=Mean daily discharge in a crop A=Area irrigated in acres N =Numcer of days in a crop Delta in feekoAcre foot. Acre foot is the term llse:! in America. representing one foot depth acre, i, ,. 43560 eft of water.

of

water ever 6ll1t

Full supply duty of achal'lRel is th area irrigated divided by the full supply capacify of tke channeL

It Full supply factor is the authorised or the stipulated area per crop or per annum for (:)ne cusoc discharge at the outbt head. This is used to work out the proposed discharge @f the outlets. Kharif rabi ratio is the ratio of the proposed areas to be irrigated in kharif crop and in rabi crop. The mual ratio is 1:2. i.e. kharif area is one half of rabi area.

Intensity of irrigation is the percentage ,)f the cultura'Jle commanded area which is proposed to ?c irrig~te~l. .Son:e land should. be allowed to have rest ?uring 0l:le year.. The usual intensIty cf IrngatIOn In colony area IS SO to 100 percent and In propnetory vllla~es about 40 to 60 percent depending on the existing wells in the area. 16.

Eillcien~y

of ca!1al L"rlgation.

In consequence of the. devehpment of th_e c~nal irrigation throughout the Punjab province, the wa~er of all the ~Ivers have to be dIstnbuted .mo~e ~arefully than i!1 the pa'it. I t is very essentIal that the engmeer sho~ld watch that the dIstnbutIOn of supply IS eqvitab1e to the individual watercoursos. The efficIency of the actual performance of the water used from individual outlets and the channels is watched by an engineer by adoptihg the following methods:(a) Actual discharge observations of the water course by the use of a\lthor's pJrtable tin flumes or ciwllete wires.

(b) By watching monthly delta nlculations for every channel in a delta statemont and then final delta for the crop. (c) By ploting the outlet efficiency dia.grams. The form and the outlet efficiency diagram is given in Appendix II appended to :thiS chapter. No outlets .are reduced simply on account of excess in the area irrigated by a water course because It may to due to good husbandary or timely rainfall at the sowing period.

17

Examination Questions.

1. A distributary is designed foralternate runnin~ to irrigate 4800 acres in ,.abi with discharge of 44.cusecs. In a certain year it runs for 60 dayti in rabi with an average discharge of 30 cusecs and irrigates 3000 acreS. Work out the channel's (il Full Supply Factor, (ii) Duty [iii) Depth of water (Delta) and explain what you understand by each. 2. What do you undentand by fluctuating assessment ? How doell it diff~r frora permanent asseSiiment ? 3. What measures can an engineer take to ensure economy in the Uile of canal water? 4.

Exp:ain the follwing

term~:-

(a) Nikal, (b) Khata Khasm (c) B::mdo1ast, (d) De:ta., (e) Efficiency diagram, (fl WJrashikni, (g) Tatiiing, (h) Shajra, (i) Shudkar, (j) Khatauni. 5. Describe briefly a few of the common diseases of the following crops and their remediei. (a) Rice, ,b) Sugarcane, (c) Wheat, (d) Cotton. 6. Give the times of sowing and maturing and the likely produce in maundi per acre f!lC ttl, following in the &anal irrigated tracts :(a) 7. S.

Wheat, (b) Rice, (c) Cotton, (d) Maile, (e) Tobacco, (f) Barley. What factors govern the suitability of the soil for various crops? How doe .. all. Engine6r watch the efficiency of the distributing channel. P

60 Chapter II Appendix No. t. Principal crops grown on the canals in the Punjab.

<5 Z OJ

·c Q)

3

2

1

4 Sowing time.

Name of Grop.

From

Hindustani

English

5

6

'"M8oof:!.

Harvestiag time.

To

From

To

Ifl

8

7

...cd a;

...

",;::Q)

~

"'::I'd "

._ Pol • ~ • ~

~ 'S:;s ~ .;; o...S 8. ~~~~ aj

0

---------,-.---"~----

Kharif Crops. Jhona, Dhan Chawal Munji Makki Jowar Bajra Charri

Rice 2 3

...

5 6 7 8 9 10 II

12 13 14 15 16

,/ ""'l~'

~.

--

'is' 19 20 21 22 23 24 25 26 27

Maize Great Millet Spiked Millet Millets Pulses Vetch field Cotton False Hemp Hemp Italian Milet Indigo Henna Gingell)' or sesame Sugarcane Minor Millet Chillies Melons Water nuts Turmeric Vegetables Lucerne Grass Cowpea water melon Raghior Mandhwa or'

~oth

;t

Mung, Mash Guara Rui,. Bari, KaJ?~ SaUl San Kangni ~ ~ ·ti ,_-._'~! Neel Mehndi Til Ganna,ponda Naishkar., kamad Madal Mircl:l Kachra (phut) Singhara Haldi Tarkari Lusan Ghas Rawan Tarbuz

-.

.',"'.

'''{ ,I" 1 2 3

4

Indian Repe Turnips Potatoes Vegetable

Toria Shalgam1," Alu Tarkari

June

July

Sep.

Oct.

2·5

8

June June July May June June April April I July July March March June June

Sep. July Aug. july July

Sep. Sep. Oct. Aug. Oct. Oct. June Sep. Oct. Oct. July Aug. Oct.

Nov. Oct. Nov. Oct. Nov. Nov. Aug. Jan.

1'5 1'0

14

July

June July April June Aug. July

Aug. Dec. Nov. Feb.

June March ;';1' '\

)if)

July April May Aug. July

32

}",)

8 8 32

10 1'0

15 125 1'0 1'0 1'5 1'5

.

3·0.':!·

if,

-75

Sep. Nov.

3/4 3J4.

',1;)

,(11

uP l'

·,d

51 4 4/12

8

. 4/12 2[8

32 8 ~l 8 :ri 8 }

8

\ :~

,?t

8 .to t--· 8 8 $

,;

;:D

3

Sep. fr"J

Nov. Oct.

.

Jan. Nov. Jan. Nov.

'0'"

' Feb. Feb.

6f'

4/4

2/8

6/4 4/12 7/8

6/4

5/8 2f8 2/ 8

2/8 4/12 2/8

Nov. L

6/4

ll!~

30'

8 June

3/8

8

8-

Nov Dec.

41·

218

2/8 2/8

1."1

2'0

J';~e

,,-,'

61

Nov.

Sep. Oct Oct. Nov. May Dec. May Oct.

~dD1arif

~l:·f

8

1'0

,.;

March May Feb. July June March Feb. Oct. May June July May

10

6/1

(,f;:,

1'75 21l 1-75

S 8

i

8,

8

"

414 5/8 5/8 SjS

Rabi Crops. 1 2 3

4 5 6 7 8 9

10

11 12 13 14

15 16 17 18

Wheat Barley :Mixed grain Oats Gram

Gehun, Gandam Jao Berra Jawi €hana, Chhola Nakhud Masur Matar Post SauDf Dhania Kasumba Sarson Alsi Alsi Taramira Gajar Tarkari Lusan Ghas

Oct. Oct. Sep.

Dec. Nov.

April March

Sep.

Dec. Oct.

Feb. April

Oct.

Nov.

O~t.

..

Lentil peas Poppy ,~U Nov.--::) Kiseen S~p_ Coriander Oct. Safflower Rape Linseed Flax Linseed Rocket S~p. Carrots Aug. Vegetables Oct. Lucerne Grass N.B.-Crops gra7.ed are charged follider rate (F) and crops used

.

Nov. April March April Jan. March

125 April

1-5

1'25 1'25 1'0 1'0

April

1'75 20

April Mav April April

1',5 1-75 1 75 Ie" 1'5 1 '5

NJ~v. Oct. Dec.

14 8 12j 11 11

4/4 6/4 414 414

3/4

8 8

3/4

8 8 8 8 8 8 8 8 8 8

6/4 6/4 614 6/4

S/8

4/4 4/4

4{4 4/4 5/8

Feb. April 1'5 5/8 June 2/SF as green manure are not ckarged at all.

61

S. No.

Sowing time,

Name _of crop. English

. ----~---~-------.

19 20 21

22

23 24 25 26

27 28 I

2

Millet Person Clover / Radish Mustard Fodder Egyptian clover Garlic Cumin Chico.ry.

..

Maize Millet

3

,

Yo,)

9 10 II

Cucumb~r

5 6 7 8

N.B.-Crops

"_

ii.1

lIt g~

f-

...

Tambak~'

\.

Q

0)'

b.OuOOl-oi ~ .S t q) t1l::;"tlU t -g~ ~ ..... "'-' ...<J > ....",-,.~~""'-' ~e~" < (OJ

Nov.

Feb.

Q)

•

F~b. Nov. March Feb. Nov. April April

2/8F 2/8F

April March May FeIJru.ac,

8 3

April May

8 8

May

-8

?,I

April

March

Ti

....

, ~l!ld

,:

I

May May

Jnne July Aug. June

June May June May

June july juae

j~ly

l/.».;: ....

:.J. ' ::' ~JL J

2j8F 5/8

4/4 2/8 .2/8 ;6/4 -6/4 0/4

1'0

'2/SF 2/8F 2/8'F

'2/8F

i"1

;~

nT

r March

Feb.

Kharbuza Tarbuz M~y : I Piaz Jan ,j Alu • Feb. L Tarkari ,e! :J:!J 1 ' Khira I';';

T()

S •

Zaid Rabi Crops.

I

:7

Oct.

Sep.

,',

Makki Chalri Swank China

..

&t

From

td .....

0:;

iU IU

.-----~.----

S::;p. T N~v.~:) Oct. Sep.

Harvesting time.

7

.

Nov.

Oct.

( ,'/-

Common t ~1 Millet Tobacco " ,;" Melons Water MelollS:' Onions ,) Potatoes )'; Vegetables

4

----~-

Maina Senji Shaftal Mllii Rai .0' 1-) f. Methra. /J Berseem Lehsaa Zira Kasni

t,"

'

To

F.rom

Hilldustani

6

5

4

3

2

t

~f !(,t{J! ~

are charge~ f!»4!l~,tI,te {FJ

Feb.

2'0

8

l'G

3 8 8 8 8 8

I'G 2'0

~;<

i

:

'I~

March

Aug. June

0/4 4/12 4/12

ud crops used as green manure are not charged at all.

5/8 5/$

5/$

PART II

CANAL IRRIGATION Chapter III

HYDRAULICS AND CONTROL OF LARGE RIVERS 1.

Introductory.

India posses a high mounain range called the Himalayas forming the north boundry , throughout its vast Sub-coIltinent separating the North Indian plains from Tibet (China" Russia, Caucassia and Afghanistan. Himalayas is a Sanskrit word meaning Home of Snow. In the Himalayas, there is pcrpttual snow which Leds the great rivers of Northern India by melting. The rivers get their peak discharge due to snow melting in the months of April and May, which period synchronizes with the time of maturing of the raM (winten crops and the so~ing of kharif (summer) crops. The rai.ctfall in Northern India is concentrated in its intensity and magnitude in the months of July and Augu st to the extent of about three fourth of the annual average rainfall. The rest of the rainfall occurs in the months of Deceml:er and January when the river supplieS fall down due to decrease of the Snow melting in the low temperatures during these cold winter month. On account d the heavy rainfall in the month of July and August, the rivers of Northern India rise in high floods which are many times more than the normal supplies in them throughout the year. The ratio of flood discharge is about SO to 100 times the normal winter supplies of the rivers. All the rivers of Northern India emanating from the Himalayas carry in their waters lot of suspended staff in the form of fine silt and clay, when flowing through the vast plains after leaving the hills. All of them form n~w lands and erode some whil.~ passing through the plains. They are, therefcre, called alluvial rivers. The hydraulics of these rivers is very complex and peculiar due to the flood discharges being very high as compared with the normal discharges requiring flood scctiom vastly out of proportion to the sections req uired for winter supplies. I

2.

Major divisions of river channel.

The river channels of the large rivers of U~f! Indo-Gangetic plainf are divided inhl four major divisions ;(a) Mountain stage.

The river flows through the hilly gorges with _rocky bed. Water is clear. The bed slopes are very sttep from 1 in 100 to 1 in 500 wi:h occasional rapids and adrupt falls. In hills it is mostly snow water.

(b) Bo.tlder stage. When the river leaves th~ mountains it flows through the sub-mountainous tracts withboulders beds having steed gradient of the order of 1 in SOO to 1 in 1000. Water is generally clear except in the rainy season. [he section is usually well defined. The boulders of the round splunial shape vary in size from adout 1 foot diameter in the' hills to about t to I" siz€ shingle or pajri as the river entcr:> the plains. H

(e) Trough stage or rlYers in plians.

Th~ r~ver sectio-'_ls are well de~n~d chan~els with high banks. Water ()arries large amount of sIlt III suspenslO~. The ~elocltles are hIgh enough to erode the bed causing d€cp ~cours an.d to damage the SIdes ca~sl-'_lg serious erosions. The proportion of suspended mathn III water m the form. of clay and sIlt It usually as high as 1/300 to 1/1000. The bed slope is pretty steep from 1 III 1000 to 1 in 2000.

(d\ Dcltaic Stage. . . The ri:,er in .this stag~. is near its .out!all into the ;;ea. The river fans out in many tnburanes and IS su bJect to spIlls. VelocIty IS low. Slope IS generally very flat from 1 in 5,000 to 1 in 10,000. On account of the low velocitv the river red is generally silting and rising. The water surface is also rising, eventually spilling over and forming new channels. The process of land formations is shown in Fig. 1 The cross section of tht' country would show tte river running at the highest point and the land falling on each siee of it at a very gentle S~O;1f. Fig. 1. In course of time the river would break t~rou:(l one of its banks and assume a new course, when the sarr:6 process of the gradual rise in its banks would take place. A valley would thus be for'lled retween the Fig. 1. two courses, and this itself would ev.!ntually be obliterated by the river breaking into it :md similarly silting up the area. Thi" action of gradual rise in the country by successive d !posits of silt along different courses of the ri vcr occurs chiefly in its deltaic portions. but if may also continue higher u') when the river breaks through one of its banks and take, an entirely ne ,v course, The silts is of a very fine. unsta')le oharacter, and thus the river flows in a c:lannel. the bed anr\ sides of whic'l are quite una'lie to resist any violent attack by t1.e r:ver. Where the river discharge is fairly constant, a rrore or less permanant regime might eventually be establis"ed, l'ut this is far fro'll being the case, for during the flood season it may 1::e fifty to one hundred times the minimum winter capacity. lnL7A'r'C ""'''fAYtDN

In a Maximum flood the width may be 10 to 20 times and the velocity and silt in sl1spension several times what they are during minimum low water. The great fluctuati( n; in discharge are thus continually changing the conditions, and it 18 the fioods which chiefly affect the regime of a river. . 3.

Torrents and Streams.

: ,;

(a) The presence of a delta close to its mountain source may I::e held as a feature distinguishing a torrent from a river or stream. The course of a torrent may, like that of a river, be separated into four main divisions, viz., the hill portion dehouching in a ravine width, for a short distance below, a deeply cut head: this rapidly merges into a delta. or broad spreading fan of sand and hill de:)ris, tailing as a rule into a swamp or broarl marsh formed at the finer clay particles brought down by the torrent. From this marsh small drainage~ break out in places to unite further down into a defined channel or stream, Fig. 2. ,,', These physical features are marked by on~ peculiarity, \.; . the complete a')sence of . visible water in all the divisions except for a short tim6 during heavy rains. Even the final nallah rarely contains any wate} unless it derives it from S')mf spring unconnected on the surface with the torrent. The floods which pass down these torrents are short lived, though extremely violent, and the slope on the fan generally varies from 25 to 15 feet per mile. Two seccessive floods rarely or neveJ occupy exactly tte same posi· tion on the fan. for coming down loaded with silt the~~ spread out in dif'erent direc· tions, reing constantly forced asife by their own deposites. 11 will l:e easily understood tlea' Fig. 2.

.. ......

64 the surface of the water in a torrent is not smooth like a river flowing with an established section, but a series of waves one following the other at short intervals. It is now generally admitted that down to a certain limit, the bed in the fan moves with the torrent. and that the snrface of tte fan after a flood does not by any means represent the actual bed during the flood. Ib) Streams.

Streams derive their supplies from hill springs, sometimes from lakes which are simply reservoirs filled by rainfall~-in the last case the supply must be considered as extremely precarious. In the passage from the foot of the hill to the low lands, a considerable proportion of the supply is absor;:ed in the soil and many of the smaller streams entirely disappear a short distance below their sources. In the larger streams the water thus lost by percolaticn probably reappears to a certain extent lower down a channel, but the water from the small streams simply goes to feed the great su':J-soil reservior. Canal can be marle most profitable from small hill streams and springs with their headworks in the gorges, but the channels have either to ce lined with masonry to pr2vent excessive loss from percolation and erosion of the bed from the great velocity engendered by the high slop2s or to be given comparatively .flat slopes and numerous falls, including depJ1>its which help to minimise the loss from percolatlOn. !.Of spring streams there are two distinct varieties viz. the small river with distinctly marked channels emanating from hills, dry or nearly so near the hills, but gaining steady increments : ,to its supply, as it passes through the heavy clay lands below; and the local stream rising from a swamp or nest of dry channels, which gradually accumulates more and more water in its -down-ward course. A river of the first variety has generally a tortuous course, a sandy bed, and is subject to severe floods. Its channel sometimes occupies a local watershed, and may indeed be said to be slightly deltaic in its nature, and it differs from the large rivers in not possessing-a valley-this renders tce floods more violent in their results and causes them frequently to spread over the surface of the country_ and to eventually find their way into the adjoining rivers on either side, thereby often cutting up the doabs by cross drainages.

4. -

Molley's River Regime Theory.

Fig. 3 on plan and longitUdinal section illustrates the theory of R.A. Molloy, late Exp.ctive Engineer, Punjab Irrigation Department, published in Technical Paper No: 1 t8 of Government of India, Central Printing' Office. Simla. - (a) Taking the plain first it will be seen that the river bends alternately from one bank to another. At the crest of each bend is deep water and in the lengths where river changes over from one side to the other, shallow 'crossings' or 'bars' are fonned by deposition of silt in the bed.

(b) The bars are produced by the action of the side channels. The side channel has the "off-take" and the outfall as shown in the plan. The su btraction of discharge into side channel at the off-takes results in the reduction of velocity in the main stream which results in the deposit of silt forming 'bars.' (c) Eetween the side channel and the main river are "islands." These islands are formed when fl)Od subsides and the river divides itself into main and side channels.

(d) Levels of the river. The longitudinal section shows the conditions of surface levels. Mean gradients are shown by dotted lines and actual ones are shown by firm lilles. (1) Taking low water L. Section, it will te seen that owing to obstruction offered by, 'bars' actual gradient compared to the mean raised above the bars by an amount indicated -by "e" and is depressed by "d" to gain sufficient velocity to pass the bars.

(ii) In floods, the conditions shown in the top L. Section are brought about when flood is rising, the bars are silting up and the discharge of the side channel at the off-takes tends to inc~se. This tendency is resisted in two ways as the floods continue rising.

65 (a) Rise of

+ k and drop of -h at the off-takes resulting in reduced gradient of

the side

channel. (b) Back flow at the outfall.

This process will continue till 'he flood covering the full section " e onditions sketched in tte L. Section Fig. 3 are bronght arJout. . I

IS

reached and the

~

MOLLOY~ RIVER REGIME THEORY

~

Q

t:

"

lot

III

CI:;

~ ...

..;, "'If ~

...

fie

i!

':!

..,

0

I ~

~

::a _, Q

C"l ';(

b.O

1L:

~

ts ;r:

"" ~ ~ ). t-

(e) Defilnations. - h=the lowering of surface d the main strea"u due to discharge having been drawn oft by a side chan!1el.

66

+k=the corresponding rise in surface level at the outfall of a side channel where' it rejoins main stream. +e=the heading up above the off-take (and the adjoining bar below it) of a side channel the discharge of which is reduced or stopped altogether. -d=the lowering of water surface at the outfall of a side channel which becomes dry or is closed. -l=the general lowering in levels of the surface and ted caused by a cut-off. zero=the condition between a general lowering and a general raising. +l=the general raising of level of the surface and the bed due to an increase of the tortuosity of the river. General remarl,s on Molloy's Theory. Molloy in his theory explained all variations in the behaviour of rivers by change in discharge, but there may be other factors such as change of curvature and change in gradients also contributing to changes in river regime. He states in para 7 Paper 118, Governmen of India "Such inequalities in the range of rise and faU are only to be accounted for by grea t variation and disturbance of momentum" Usually the implied postulate of all river formulae is absolutely uniform in condition, section, gradient and.velocity. But the actual characteristic of a reach of such a river "(an alluvial one)" is irregular alterations of all the conditions and consequent changes of momentum. The term channel does not apply to such a river; it is rather a series of pools, or compartments, of which the sides are the high-level islands, and the bar crossings are moveable, transverse panels very difficult to move". This description of river by an Engineer who studied the rivers as life time problems clearly shows that rivers are not channels like the irrigation channels as Mr. Lacey considers them in his theory of channels ~n alluvium as described in 'Chapter VI of this part. ;).

Other River Regime Theories. (a) Oldham's River Regime Theory.

Mr. Oldharq following the theory of':M. Dausse. French Engineer, enunciates his theory hy four principles. . 1. Every stream tends to a condition of equilibf.illm in which the velocity developed s just sufficient to enable the stream to transport its s0lid butden. It the velocity is in excess, the stream will cut down its bed thus reducing its gradient, the veloCity and the silt transporting power. If the velocity is in deficit, the silt will be deposited, thus reducing the section, and ;llcreasing the velocity required to transport silt. 2. Every stream is alternately collected into a single well defined channel called a . 'reach" or spread forming a "fan." Fig 4. These fans are seen in river bed when it dries (I p in winter. 3. The gradient of a stream is not a uniform one. The bed will be flatter in the "reaches" and will be steeper in "fans" relative to the mean gradient. Fans are shallow and th us with reducing velocity. 4. Both "reach" and "fan" work gradually upstream. "Reach" encroaches the upper 'fan" by erosion and is encroached upon by the lower one by silting. Fig. 4 (b) Mr. 'Ellis' Tributary

Theory (Vol.CXII The Engineer December 15,1911, uvtlines that a rivers bends to the infalls 01 the tributaries owi~g t~ its b.ank being there blank, and thus weak, and the tributary forming a channel on that slde. fo bnng tae flver under control he says some points should be firmly fixed, and no tributary stream should be allowed to enter nor irrigation canals to take oft from the river except at fixed points, He observes that the conditions usually oI)tained are:-

.(i) No stream coming in on either si'ae-a straight, well defined channel. (ii) Streams coming in on one side-a well defined channel on the other side only.

(iii) Streams coming in on both sides an ill-defined channel and a disposition to form a shoal in midstream, (c) Another theory is that rivers running north or south attack their west bank owing to the rotation of the earth Dringi:lg those banks against the current. This assumes that the water of the' rivers does not acquire the same rotatory motion as does the lands, which assumption does not appear te:la·)le. The destruction of Dera Ghazi Khan on the west bank of the Indus was said by some to be due to this cause; Mr. Molloy held with much greater reason that the westerly trend of that river there was owing to its deHectioL by small reclamation banks on the eastern side which were maintained year after year in the interests of cultivation. 6. Meandering and Avulslons of Rivers. (a) An extract from River Training and Control by Sir Francis ]. E. Spring C. 1. E. Technical Paper No. 153 of 1923 of the Governmeut of India is given 'relow which descrites aptly the process of meandering of large rivers of the Indo-Gangetic plains. "The manner in which rivers of Northern India fined it necessary to meander more and more nearer they get towards the sea-in other words the lighter and less coherent becomes the sand composing their beds, may be illustrated by a rough measurement of the Indus between Kalabagh, where it first becomes alluvial. and the sea. In the following table, column (A) gives rough measurements along'the centre line of the river, while column B gives more accurate measurements round the 'cends, Both columns have been scaled off a 32.miles to an inch map and doubtless if column B had been scaled off a one mile to an inch map,the proportionate increase of length due to the river's windings would have been considerably greater than shown here :A Lenath measured fairly direct.

Successive 100 mile lengths. 1st 100 miles, beginning at the sea 2nd do 3rd do 4th do 5th do 6th do 7th do 8th do 9th 100 miles to near Kalabagh

[

72

100

75

100 100 100 100 100 100 100 100

72 69 82 82 93 98 97

!

B Length measured round bends.

Percentage of

meandering. 39 33 39

45 22 22 7 2 3

--------~----------------------------------------------------------

The meandering of the Ganges are less regular, as may be seen from the following statement, which, however, as showing irregular distances, is perhaps not very convincing : -

A Length measured fairly direct,

Successive Sections,

From the sea to " ~'Sara " . . Benares " ,. Allahabad " .. Cawnpore " .JRajgbat " ., Garhmuktesar ..

Sara Ben ares Allahabad Cawnpore Rajghat Garhmuktesar BaJawali

B Length measured round bends.

Percentage of

meandering.

185

200

8

425 85

540

110

135 195 42 73

27 51 23

175

37 65

130

11 14 12

If lines be drawn conneting tt.e limits of the bends of such rivers, it will be seen that while the meanderings of some of them do not extend outside the breath of one mile, those of others, e, g. the Indus at 700 and the Ganges at 200 miles from the sea, extend to a breadth of 10 or 12 miies. outside these limits are slightly higher lands, but still for t1:le most parts alluvial, into which the river has not as a fact cut. But the fact of the river not having cut further to right and left may generally be ascrie:ed less to the mat3rial of th~ untoched land being of a more holding nature than that in the river valley, than to the fact that for each part of each river ther2 exists some relationship between Clhesive properties of soil and velocity as qualified by cross sectional area, such that no more than a certain extra percentage of length of channel is needed by the river to prevent its cutting still further into the up lands. But even when such rivers are being described have meander cd as for they ever will within the limits of the shallow vallevs which they have scored out for themselves in the alluvium, they are no nearer than ever to the attainment of a stata of permanency or equilibrium within those limits. Indeed in the course of years, there is scarcely an acre whithin the valley limits which will not sooner or later be eroded quite away and in turn reformed. Action of this sort goes on for the most part during the flood tim%, and much of it beneath the .surface of the silt-laden water. What happens is somewhat as follows:-When the flood ~eg.ms to rise with the melting of the Himalayan snows in June, it finds (a) ready pr2pared for ~t smce the previous year. a more or less deep channel. As it rises higher tb) it spreads' Itself over the low sandy s[Jits and fills short-cut channels. At its half fioods stage (c) it finds itself topping extensive areas covered with he3.vy reeds, grass and brushwood. Later again' (d) if it shou~d happen to rise somew:1at hig'1er t'1a:t that f.":e'1t years, it t:ns cultivd.ted area, and drive3 the mhabitants of the more or less temporary villages, to whom the cultivation is due, to take shelter on trees, boats or house tops. This last state of things (d) is seldom of mlre than a few days, duration, but the canditions descri'oed at (b) may te of six months and the intermediat stage. (e) of perhaps three or four weeks' duration. Now, owing to the comparatively brief time during which the flood tops the higher levels where cultivation is being carried on, it seldom has time to do any surface erosion at such places on the contrary, the tendency is to raise such places by the deposition of silt, owing to the great reduction of velocity due to the lessened depth of water and the restrining influence of the vegetation. Moreover, a skin of vegetation. though of no avail against the edge, caving Jr erosion, is a very effective preventive of surfac," erosion. Therefore so far as mere superficial a~tion is concerned, the tendency i:.-, for the higher plac3s, below highest flood !ev21 to grow hlgher still to the great profit of the cultivators, to whom a f2w day of exposure and semistarvation are of slight iinportance in comparison with the incre" sed fertility of their latelv flooded fields. ' But, flowing as it does over a great breath of the valley, swiftly in the deeper parts where ~ast season's chal!gel is, and more slowly in the shalbwer parts, the river finds itself taking shallow short-cuts across gre3.t be;11s, at a C) n)1rativ0iy l).v velo:!ty a Nm~ t) the shallowne:iS, and then cataract~ng down into the m3.in stream at a very high local velocity at the down'stream end of <each short-cut. It ofte:1 happ::ns, that if the bend is a very big one, the s\ort-cut channel has not time enough to erode its bed and banks to any gre3.t ext:nt; ani 1:1 this case 01 the fall of the river, the results of the action will be exhioited in the form of an a')ortive chan l"ls, which, had the flood only lasted a few days or hours longer, might have esta )lished itself right across the bend. But should the fiood stand up bng enongh fJr the short-cut channel to erod~ itself adequately, we find the folbwing stat~ of things, viz (a) the main river mnning round a great, say 10 miles long, with velocity due to a fall, say, one f,)ot per mile measured reund the bend, and with a favouraDle stream cross section; and (D) a comparatively small side shoot with the same fall, say 10 feet, in perhaps 3 miles inst::ad of ten, but handicaDped by its comparatively unfavouraDle cross section, If the net result of the favourable fall and unfavoura'olE! section should be that the velocity in the narrow she>rt-cut is e fective in cutting its way so as to rapidly widen a!1d eeerer. tte small siee channel or chute, with the conseqUEnce that, in a few days or hours-the author has seen such a change occuring on a very large scale in 2.1, hoursthe small side channel will itself have constituted the main river, widening itself by caving, and the 1'ng bend will have got silted up. A summary of Mr. R. A. Molloy's aCCOU.1t of the causes of cut-offs, in rivers of the Indus class, has already been given in this chapter.

69 Now this short-cutting actio::! is constantly going on at one or the other part of the river. Sometimes it fails and sometil1es it succeeds; but whenever it succeeds; its effect on the river for many miles up and dowlJ-stream may easily be imagined. For miles above and below the recently established short-cut, there follows a period of utter lawlessness; banks caving, channel silting and new channels forming. u,ltil at length. proba',)ly with the advent of the cold weather 10"1 warer conditi.ons. tb.<>re IS a truc~ for a few mO.:ltbs. The next rise of flood finds things still a bit chaotic, a:1d velocity in places quite in excess of what the soil can stand upto; and the result is perhaps two or three more months of lawlessness, untill at length, by increasing its tortuosi.ty, the stretch of 20 to 30 mil2s of river eiiected by the one short-cut settles d:Jwn into a st;; te are armed neutrillity, ready to exite itself afresh. as badly as ever, when the next short-cut happens to succeed in estaolishing itself. The action which the auther has attempted to describe is that which Northern Indian river Engineers have Leen in the habit of calling avulsion; but the author prefers to use the term CUT-OFF, as expressing better than avulsion the action in question." 7.

Extent of meanu.t>ring 01 Rivers.

An idea of the extent of meandering or the alluvial rivers can be had from tables in the last paragraph An attempt has been made in Publication No.4 (1939-40) of the Central Irrigation and Hydro-dynamic Res?arch Station Poona, India, to work out the formulae connecting the dimensions in a meander belt of a river as sketched below in Fig. 5. W =width of river.

·.n~_ .~":
Q=Actual discharge of the river. r~~~f1"" ~1i~_: ,q~~Jz:):' pi

oj;

~~1Jj.

,',\!i

'''.1 ..... " .

q

~~l"tr,.~

..... t; ...

.'.'':~' '~·rY'. ,~,j'J, v,}tli ['

S

:; '~J

;.

Mb =Meander belt. MI =Distance between successive meadtR~ on the axis of the river. R=Radius of the meandering land.

The incised river data gave W=2'48

;JC

Q!

Compared with the Lacey relationship .\ .1

-.lj/'"

d:lfn~;

it'" (,

l'-.U.I,,',l

~

:,!

Lt~i':~~:r~;-i-r1 :}d~ 1<) ~fIHJr.H :td; ~ : ! : ' ",lil; ;.;vtllJ:J ~t1J hril; :~'JU;d :,iJj .. !, 'C"

;:~,'",·r

!J;',(:,,",'

.

P=2'67 Q2 for regIme channels. EXTENT fJF .ANIJER1Nti

f---- --

The data appear to comfirm that Mb MI and W (i.e P. wetted

0' /lIVER

--/If, -.-.--.----j

perimeter) all vary roughly as Qt (in other words, are scalar) and tLat the meander length is of the order of lOP or ronghly 25 1. 1. Q2 t030 Q2 Radius of curvature was worked . 'out from the ~ame data as shown below~-

Fig 'N'o. 5.

.j

(1)

For incised rivers: overflOWS)

I

~

(High flood section cut below N.S.

and not

liable

to

MI =25-4 14 Q~

v

(2)

Mb =56-4 vQ; and W =2'48

For rivers in flood in plains: high floods).

Mb =29'6

20v'g. 8.

V Q;

vQ

Mb =84'7

V Q from which R= 14·23 viT,'

say

(River likely to flood the country on both sides in .

vQ; and W=4'88 vQ~

from which R=20'64

vQ.

say

River Erosion.

Erosion is defined to be the destructive eFfect caused by the river's lateral action on riparian lands and works, while scour is that due to the river's vertical action on its bed. Erosion may be said to be of three kinds :(i) Normal.

This is caused by straight, unobstructed currents parallel to the river's bank. Such erosion proceeds gently and regularly, and may deepen the river channel next the bank from 30 to 40 feet below low water level.

(ii) Abnormal.-It is caused by straight-flowing currents impinging at an angle against the River bank. Such erosion produces caving, or embayment, of the bank, and may I:;e rapid; it may deepen the river channel next the bank from 60 to 100 feet below low water level. (iii) Extraordinary.-This is caused by rotatory swirls set up where the onflowing currents are bounded i:1y dead or non-flowing water. Such erosion is extremely destructive locally, and may deepen the river channel where it occurs from 80 to 120 feet I:;elow low water.

The principal factors on which erosion depends are; the velocity of the river, the duration of its flow, the nature of the material of the bed and banks, the angle which the current makes with the bank and the curvature and general alignment of the bank, Erosion is due to the local lowering of the surface and the bed. A rise of surface level often reduces erosion, and, when this is combined with the reduction of velocity, erosion must stop. 9.

River Scour.

Scour is defined to be the destructive effect due to the river's vertical action deepening its bed. Scour depends diefly upon velocity but also greatly on the amount of silt carried by the river, if that is in excess, there will be silting; if that is in deic'cit, there will be scour; and if there i~ only just the amount of matter suspended in the water which its velocity will enable it to carry, there will be neither raising nor lowering of the l::ed. Thus scour is worst during a falling river, because the water then contains a small amount of silt; during a rising river the water is charged with silt, and this tends to fill up the hollow in the bed. DEep channels are likely to become deeper owing to the concentration of flow down them, especially when the water is not fully charged with silt. When a flood is at its maximum it has already deposit~d som~ of its silt 'upstream and will therefore tend to scour; thus a river may be deepened, although both the flood level and the velocity have decreased. An unerodable covering protets the bed from scour, thus a rl!ined masonry structure dumped stones and refuse, or matted vegetation, will tend to prevent scour under them. 10. River Swirls. A swirl in a channel is formed by a formed moving current by the side of still water which thus gives the flow a circular motion. An obstruction to the flow in river, such as an artifical spur, will produce dead water and a fast river stream passing near it shall cause formation of swirls both near the upstream and the downstream ends. The

71 obstruction may be in the form of an ol~mas(mry bar in the bed, or stem of a tree sticking in bed and causing dead water and the c~nsequent swirls : (i) The reason why swirls cause deep scour is that they throw off to their outer circumference the silt that was suspended in the water or scoured from the bed and fresh silt can enter the swirl area from caving banks.

Ui) Swirls have dead water at their centres which may cause silt to deposite there when they occur near a caving bank. silt falls in on the land side, thus raising the bed there; the deepest water is always en the outside of a swirl. (iii)

Tne destructiveness of a s~irl depends upon the velocity of the current, the area of the still warer, the size and nature of the sand of the river bed, and the duration of the flow.

(iv) Swirls are the most destructive form of erosion, and protective works should therefore be designed so as to avoid them and certainly not to produce them.

11.

Silt in River Water.

-

'There is a vast different cetween the sands of various rivers and even between the sanci, of various localities on the same river. People speak of the sand of the river bed as if all river sands were alike, whereas as a fact, there is as much different tetween sand and sand. as there is between, say, pumpkin and a potato, or between road metal and powdered wmdow glass. The shape of the grains of sand bas a good deal more to do with their transportability than their size or even their specific gravity. - In the boulder stage of river, the rolling mat,rial near the bed may te size 6" to 12" diameter, and the suspended sUJstance from 1" diameter to the road metal size. The suspended SU9stance called bajri or grit does actually travel always above the bed like the silt of the canals, or the suspended sand in the trough stage of the river, but it strikes against the ted at some angle and is again shot up for some distance. Further down along the great rivers of Northern India the rolling substance is grit or bajri and the suspended substance is the coarsest sand. In the plain in the· trough stage th rolling substance is coarse sand while the suspended substance it silt and clay.

It is only in the deltaic stage of a river that the ted materiel and the suspended substance are of the same nature and consist of silt and clay, It is only in this stage that a river could be said to re flowing in self-silted aluvium but in this stage it has no definite channel. It is always discarding an old course, forming new channels. It is usual to classify both the bed silt and the suspended silt by mechanical analysis using standard sieves. The classification goes according to the mean diameter in millimeters of the particles. The C~ntral Board of Irrigation, India (C. B. 1.) and the American practice is given below:Classification 01 Mean diameter in M. M.. Class of Silt. Colloids Clay Very fine silt Fine silt Medium silt Coarse Verv fine sand Fin~ sand Medium fine sand Madium sand Coarse sand Verv coarse sand Gravel

Central Board of Irrigation India. () to 11256 1/256 to 11128 1/128 to 1/64 1;64 to 1132 1/32 to 1/16 1116 to Ij8 118 to 1;6 1/6 to 1/4 1/4 to 1/2 1/2 to 1 'I to 2 2 to 4

American, Below '001 0'001 to 'OOS (),(lOS to 05 (silt.!

0"05 to '1 '1 to '25 ·25 to '5 (sandl '5 to 1 '0 1 .to 2

72 The specific gravity of sand ar;d grit in a river varies .very little. from 2'63 to 2'74, but it seems to have no bearing on the subject of sand transportatlOn III the nver waters. The angle of repose of the bed sand of the Northern India rivers does not vary much. It is about 31 0 to 37 0 , and it does not appEar to have any law connecting it with the fineness and the coarseness of the sand. There is also very little variation in the pore space of the silt and sand available in rivers. It is about 40 to 45% of the volume irrespective of the diameter of the sucstance However the coarser and heavier the sand, the smaller the amount of scour and the comequent erosion.

12.

Vellocities in the Punjab Kvres. Velocity of a river varies with the gradient, the nature of the cross sectional area (H.M.D.) and the character of the ced and banks (N, the coelficient of rugosity). Thp velocity depends more on the depth than on the gradient. The prevailing velocities of the winter supplies in rivers may be from 0'1 to 5 feet/second and in floods from 15 to 30 feet per second. As greater scour follows inc~eased velocity:. th~ tenden~y is for th: deeper parts of the section. to tecome deeper still. A nver has to adjust ItS' velocIty to what ItS bed and banks can stand by changing its section. The velocity of a falling river is greater than that of a rising river. In the former case the channel is draining away, while in the latter case the flood as it rises has to fill the channel pools and its res~rvi?r area. When t.he v~loci~y is retarded, ~ilt ~s drope?, and :vhen the velocity is increased, silt IS pIcked up. A fallmg nver IS most destructive m scounng actwn. A deep channels scoured out during the flood season may silt up ·in the succeeding lowwater season, as its section will be ..too great for the reduced velocity then. In the following flood season, the silting will at first reduce the velocity below what it was in the previous one; but if the floods continue sufficiently long and are sufficiently instance, they will scour away the deposite and re-establish the former deep channel. If, however, for any reason the floods are small and last only for a short time, they may not have sufficient power to scour, and the silting up may remain permanently and thus affect the flood regime of the river.. "iv.c' I:.' 'J Hi ,

13.

~

Permanent ReClamation or Protection Works.

"t,

(a) Reclamation Works. The object of reclamation and protection works is three fold:

: .OrH 10 ']1 fl ~)L_'hj l.i (i) To remove sinuosity of a river to ensure a well defined cha_·!(;,i"i

(ii) To.reclaim land subject to floods for cultivation.

~ r ;r.;:

(iii) 1'0 protect valuable land property on the side of a river which is subject to erosive action.

The river main stream wand~rs from side to side, and therefore the most important principles for reclamations are:,

"Never throttle; always close and work with a full head" (Molloy's). In other words, the river should not have its main channel narrowed. The closing of scour side channel and the prevention of spill over fore shore should be affected by what has been usually called a "reclamation bund." Reclamation bund unlike the Guide Bunds are temporary works for local use. They also require more repairs. ,b) Design and construction of a Reclamation Bund.

The highest point. of a mi~stream island and one protected by vegetation shonld te selected for an. abutment lilt? whIch the bund should "te well keyed. The bank of a bund should be contmued some dIstance beyond the length to be protected. Where ridges and cross channels are met, cross spurs 300' to 500' long should be constructed on the ridges both upstream and downstream as shown in Fig 6.

, ...

~..

,."".

."".

The cross spurs serve t. produce still water especially upstream to induce silting and to protect the main bund. The best material to construct the bund is pure sand and failing that the soil of the locality. The material should te obtained some distance away from the bund on the upstream side. The axis of the bund should be preferably at right angles to the riveLand not less than 60 in any case. A good key trench should he dug 6' to 8' wide down to spring level. The bank should te raised 4 ft. above the flood level allowing about 2 ft. free board and H' to 2' afflux head. The section should 1::e raised according to the required strength. If necessary, an escape channel should be constructed .

'RECLANAT.1DN .UNO .~N£1t4L PLAIf

C. CNAIINIL

1'1 ...."". 1"" It. 1110.£ S ••- .....

0

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f.,' .of

;" L) ~:JrlO! .1<"

AT •.

(' :(L'.:!

.,~ ...~.~~~," ~

1"" ,•.1>,;<:.._ .ii"----~.,

Fig. 6 (a).

"'

.

To protect the bund from wave wash pilchi mattress or grass fascine should be provided. A roll of 6' diameter will do.

The reclamation should be recorded every month and 'contours plotted to watch effect of Reclamation Bund.' I

:.~

(c) Spurs.

The earliest form of river control was the construction of spurs projecting from the Lank into the current so as to deflect it from the places threatened by the attack. Where the soil of the bed is firm, this form of protection answers very well. loose soil there is danger of outflanking.

I.

A spur is essentially a fixed obstruction. It is bound to cause swirls both upstream and downstream near the ends. The swirls will cause deep scour and are very destructive. The spurs on account of the formation of swirls near their nose are sometimes used to induce a deep river channel on the side provided with spurs at regular intervals. The protection of banks 'by spurs is only successful when the extreme upsteam spur is well-founded in unerodable soil. The spurs yield only temporary relief and it is preferable to resort to the construction of guide banks.

(d) Form of Spurs. (i) An ordinary type of spur consists of branches of trees Or jungle and stone ia alternate layers so that the spur is previous as well as capable of sinking unevenly without breaking up. The stone being the permanent part, the more the better. '

74 (ii) If ston~ is not available at the site selected, and abutt:nent is rormed by digging a trench which is staked and lined with brush wood mats all round. This is fille i with bags of earth. The bags are well trodden or founded. The stakes are hraced. The construction is extended into the current. The materials are perishable and the life is not long , (i:i) Planks are some times driven to form a continuous sheeting, instead of stakes or brush wood. (iv) In Egypt and the Punja'J spurs are so:ne times made entirely of stone. Permeable spurs are considered to induce silting up by the slow flow through them. The stone spurs are permeable.

The spnrs are usually constructed sloping downstream at an angle of 120·. A spur of le~gth L normal to the bank protects a length of 3L upstream and 4L downstream•.'. ~e) Gro~nes.

Spur8 of permanent nature are called Groynes: weir is a type of permanent spur,

Denehy Groyne as used at Norora

The led of the spurs is in the form of T, Fig. 7 a ,out 400 feet long and is connected to a guide bank, the main ft.ood embankment (Guide • Bank) by means of an earthen bund. The Groyne is heavily faced wi th stone and is proOE.N£H Y GROYNE tected by reserve stone piled on the spur at the T end. The Groyne most upstream should be well protected or finished with an impregna'Dle head, 14. Temporary Reclamation Works (a) Brownlow's Weeds. M .... ""'''.11 III,. ... ..;1 These consist of !! ;" r series of lines, each c. $'CTI(JN DN 6.F. fastened to an anchor i;'r--$'...-t&l~1--'-' ,--.,,--,--,-.-;-..:.t-+.6+~ t lock upstream in the river 1 ed. and supproi~de¥b : ,~w ~"1' ted downstream by a bum'. Trees and brush Fig 7. wood are attached to the lines, which by deadening the curre,',lt couse silt to be deposited. A spur of any d~sired ,length can be formed by increasing the num~er of the lines. The success of the weeds depends upon the holding of the anchorages, but when once silting commences, they hold better. 'uQ(iJ;

'I

(b) The Bengal "B.m:1'tal". This is a primitive ccmtrivance for causing minor and side channels insilt carrying riv~rs to be silt~d up, so that the main channels may get a concentrated 'flow down them which will kee? the:n clear and cause them to scour This results in the :,reclamation .f their foreshotes for cultivation. A bandhfll comists of a line Qf bam000s upto 50 or 60 feet in length and from 1 to 3 inches in diameter, worked during low water into and across the bed of the channel to be closed and fastened together with a string at the top to form a temporary fence. which is rendered sufficiently impermeabl~ by fixing mat screens to it.

75 (c) Hurd\e

.'

D~kes. \

Description of Hurdle Dykes. is available III ~ on Missis~ippi l}aw!!O~,. 1900. The arrangement is shown in Fig. 8. . t. ::/;. . .

river )'-"Y'i':t';. F._ ,:

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11

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, To p :event e~osi'an of the river ted from undermining the dyke, a flxibl~.· mattress is formed on sloping ways, brought on to platform carried on special barges. and is lowered on· to the bed, weighted with stone. It is manufactured fre m wattling brush uron poles, spaced about 5 feet apart, and these are lapped together and fastened by spikes and wire to give the required ",idth. The l:ursh wood matteress is spiked to the po!es at the -edge and elsewhere at intervals to every third pole. The width of the mattress vades from 60 to 120 feet. according to the depth of the water and the liability to scour. The hurdle consists of. a row or parallel rows of pil1:e!rdriven thtogh the mattress at about trd of its width from its upstream edge, either singly or in clumps, each consisting of three or four piles, the tops of which are drawn together

76 i>y wire rope to form. a 50rt of pyramidal structure, the piles at river bed level being from I to 10 feet apart. In the im[>roved from, the'curtain, or wattling row, is braced at an angle of aOOllt 45" by vertical diagonal braces. which are heeled against a row of clumps and securely

--~7~;

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- ---------------

--~---------------

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•

'Fig,9. GlIIDt.

BAIIIt pRo.T£eTION

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To

/ME,.." Ie...... seoll..

THItlIf"••• 0' .,,,,.• • T.,.I.. A/U,f V

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2·... T(If+fl').

.I".. A 0' A,..""" STOIf! AS LAIl'."~ D To

MUll T/f/C.,,,.,, 0' .""0If A. ""/0. "'.T. /JIIl1I1I TIIICIo,.." ., ",."." _ .",..H.,.:

77 fastened at top and bottom to the pil~s against which they abut. The piles vary in length from 25 to 60 feet, and they are driven into the bed for about 15 feet, witt the largor end down, by means of a hydraulic jet and weight of a:)out one ton. They are spaced so as to come to about one pile to the lineal fo;)t of the dyke. The tops of the pil.os are kept about 20 feet above low water, except that of one in e 1ch clump of wattling row, which is 25 feet above th at level, in order to catch drift and prevent it from' passing the hurdle. The piles of that row are connected along its upstream fdce by wattling of fine brush or by curtains mude of brush: this hrms a permeable barrier, through which the silt-laden current passes, at a velocity so much reduced that silt is deposited on the river bed upstream and downstream of it. The great arlvantage is that they can reclaim a fore shore on .vhich permanent reclamation 'L unds .. can ce designed, (d) Cross Fixed Spurs.

They consist of double lines of stakes 3 to 5 feet apart with ropes passing r mnd. Brush wood and twigs are filled between the stakes and are usualy loaded with .sand bags. They are quite successful in the case of ~mall streams and torren :s.

15.

Extent of narrowing by constracthn of Guide Banks.

The great rivers of Northern India, have' very high maximum flood discharges. It often happens that in the course of a great river in the plains with surface width in maximum floods from one to 10 miles an Engineer is confronted with the problem of constructing a bridge fot a road or a weir for a canal. It is. not generally possi~;}e to fined near about the site a rockey gorge section or aq increased section in plains, It will not only te exp<:nsive to span the whole width, but also nnengineering on account of the uncertaip.ty of the deep scour in .a very wide section. The section can safely be curtailed by, constructing artificial gorge \Yalls known as guide banks. when t le river is sandy-cedded and capable of enlarging its section by scouring its bed without any appreciable afflux. \

In the case of bridges such as railway bridges founded on well foundations, the factorS governing the extent of narrowing have been summarised by (late Sir) Spring in 35 Technical Paper No. 153 on River Training and control as gi ren bel>w :-, ..,.. "The experienced engineer will without any dout x:ecognise the wisdom of selecting the place on the riv,er's cross section where the bridge shall be located, so that the area of scouring out of bed section that must be done in the first rise of flood shall be minimum-other things, of course, being equal. Also he will not fail to observe that, within lirr its, the greater the narrowing, the deeder may be the scour, and therefore the mere expensive will Le tJte stone protection of his guide banks. Thl:ls a practical limit for narrowing is soon reached. The author is inclined to the opinion that in an ordinary sandy bedded river of the class under notice with fall of 18" per mile and less, narrowing may in practice l:e limited to what will cause an aU:over mean scour of from 8 to 16 feet 1 et~ ecn a:.;utments. The comparison between the area before and the area improved by scour after contraction should be made with regard not to area alone, but to discharge throug,h the old and the new areas, as gOVerned 1y the velocit~, got at the varying depths of the successive com?artments of their CfQSS s2ctions." The construction of the river ~ection is also done in the case of canal we'f3 bV the of guide ban~s, but the problem is much .m?re co.mplicate~ tha~ that in the case of. bridges' with open foundatIOns on account _of the p,erm,lsslble dlscnarge Intensity, the allowable ajiux and the required crest level of the weIr to mallltalll a fixed pond level to feed the canals. The mathematics and calculations are given in Chapter XIII of this part to arrive at the permissible contra~­ tion at canal weirs.

16.

Design of the Guide Banks (Bell') Bands).

A type plan and cross section of a guide I::aak respectively.

IS

shown m F'ig, 9, and 10

.J~L ~~to~t and alignment of Guide Banks. (i)

Guide Banks are constructed in pairs symmetrical in plal'l.

78 '(ii) It is essential that the design should be such t:lat no swirls are prodhted; The" pair of the guide banks should be ac; smooth as possible. 'There should te no spurs projecting from the guide bank as the s~mrs produce swirls. In order to exercise a gentle entrance for the river between the guid~' b(l_nks, the embankments s~ould be curved inland near the ends. The widening shou,ld not be excessive, otherwise it will lead to the formation of islands. (iv) ,

.~

.

(v)

Care should be taken not to select a site for the bund where the rivH has a tributaryor a sirfe channel flowing paralbl to the bund. These four factors ensure proper alignment of the Lund. Sufficient still water area should be provided as in reclamation bund. This" can be exercised by providing separate and additional bunds 'of reclarnation type . upstream.

as

The essentials for a -guide bank are :-A proper alignment as symmetrical possible, a sufEcient still water area, an ample apron, impregnable head, and -a large reserve of stones for r;epairs during its early years., '_ FiK. 9." is a typical plan and Fig 10. is a typical section of a guide bank. fhe ~ uide banks are permane'nt works unlike the reclamation bunds. (b) Section of guide bank.

Top of the bank should not be less - than 10', and in the Railway practice 20 to 30 Side slopts should le 2 to 1 and free' board . to 5 ft. In calculating the height, allowance should _be made for heading up, and also for ~e~tlement of the banks which may be 10,% of the height, The inside slope should Le protect;}d with stone pitching. and the outside one by good pacca earth; and floating ropes with jungle ~~
~eet to allow the working of the material trains,

(c) Slope of a guide bank. (1) It is essential that the slope shold neither be undermined nor slipped. If it fails, " b \ teach would occur as the earthen bank behind cannot resist the river action. Ample stone ~ \)ttld be provided in pitching on the slopes and reserve stone should be stacked on the back : 0 replenish the weak points. '-,

(2)

Pitching should be atleast 3' higher than High Flood Level.

",.'

(3) The pitching stone should be selected having a high Specific Gravity and weighing 100 to·l60 ths. In water it loosE'S its weight equal to the wight of the volume of water '; l~Placed. The effective weight is, therefJre, reduced.,

t?ln. th

(4) The stone should l::e laid on 6" deep spawls to pr-otect the bank from wave wash rOugh the intrestices in the stones, I

vet,. (5) As, regards thic~ness of the stone req~ired, it w mId ~aturaIly incr, ase with the inclcity of the flver. Mr. Sprtng used the followmg ta')le of thlckn~sses which apparently ttdes the layer of spawls :-

---...... p'lI.I] "'Pe-r-m-il-e-o-f-r-iv-e-r-in-in-c-h-es-'' - - - - - - : - 3-

9

12

18_

24

~ -----------,--------------------------~--~--------:o>aQ'i...classification, Thickness of stone pitching in inches. VeI'}"

coarse -----------------<\""e -

Co

-F:Vleq i tun m~

Very fine

16

19

22

25

22

25

28

28 34

31

:14

31, ." 37 •.

40

37 43

40

,;uO

46

43 49:,;:J

28 34 40 46 52

79 (d) Apron of the Guide Bank. Apron is the name given to the p:ut Df the pitc'1cl slo?~ onth~ river side of the Guide Bank which is laid horizontal at the bN water levd. In ord ~r b ma,l{e the apron safe and to arrange it efficiently, it i" n~ccess~ry to asc~rtain th~ d~pth of the d~epe.>t scour negl~ct~d .swirls. The breadth is not to 'oe less than It/time.:; the deepest scourin Fig 10. The av~rag~ depth .should be 11 times in gentle arid It tim~s in turDulwt river of the sbpe pitching thickness when launched. The apron is laid at low wa ter ltwd and it launches by it; own wdgh: when the scour starts in floods as shown in Fig. 10. The average slope which a properly laid apron a5sume when launched, is 2 to 1.

Impregnable he!ld of the Guide Banks.

(e) J.

Mr. Spring's design of Impregnable head,

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'tt)

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':..... j;:'?~l J ~~

1.

The entry should be gentle.

2.

It slould be curved hto reduce embayment.

The proper radlus to be alloweG. depends on the velocity ofthe river, Mr. Spring gives Ul.! following ta:,le to design the radii:- ' . ' Fall p'·r mile of river in inches, Sand classification.

Probable ill'l.ximUill, abnormal scour,

... Very coa::se

" Ccarse Med;~m

. ..

Fine

Very line

3

"6

"

9

J~~~12

--'---'j-_._._-,---------_.__._. :

200 ' ,2,50',! \300 II 350 1 250 310'1,375, 440·; 300 '. 360' i 425 f 490 ' 350 430 I 510 i 590 400 425 I 550 I 625 I 450 550 I 650 '\ ',' 750 ! 500 590 675 760 1 6 0 0 , 725 825 I ,,925 sOO :,',,' 700 8i)0: 900 \ 800 900 1000 1100

I

I

':1-

l. The upstream curv~ should be carried 120 0 to 14 0. foun,d hI': protection of the inl~nd side.

17.

"b~Gk

2.

Pitched apron should be carried throughout the curve.

3.

The curved portions should De of full height of the bank.

4.

The pitching at the impregnable head s1.J.ou 1.d be 25% extra.

5.

The width of the apron should be double fw deepest scour instead of

Constru~tlon

1 I

l .L_~ __ _ RadIUS of u.pstream Curved End in feet

".._..... .L......:

--~---~-~~-

, l)nder 20,feet, ,Over . . . . 'eiider 30 feet " Over .. Under 40 feet Over .. Under 50 feet Over .. Under 60 feet Over

I

to

40<} 500 550 670 700 850 8S0 1020 1000

1200 "CCUI<'

II times.

of the guide banks (B~ll's Bunds)

The construction of the guide bank should De commenced from the a'}utment, that is tht weir, and should proceed regularly upstre'lIn~ If its conpletion cannot be achieved il1 one: season, the reduced length c0mmenced should be fbished off and should have a tenporary imorcgna'Jlt head formed at its upstream end, so that it may hold the river, and n0t De O,lt l1an~~ed oy aI, e nbayment. In the su'.)sequent s 3aso.1. this head should be removed and the guide hank similarl~ continued or completed, To ensure rapid progr3s, proper aDd early supplies of stones should bt al'ranged for, and it will facilitate w;)rk if these can be broug;1t to sit~ by trains. The slope and the apron should be built between tc nplac~s 100 feet apart. In par'" 16(d: the construction of the apron in the dry condition has been descriued, but this may not alway Ot 'possi'Jle, and part of it may unavoidably have to be formed in deep water. When thi~ is tht

80

or

ca,e, the quantity of stone required for the sU'Jaqueous part ,the apron should be' calculated; this amount should be carefully and regularly dropped iI?-to the water from, boats and pr:ecautions sho~ld be taken ,at fir,st not to extend the apron too far lest it be ,undermined and the material wasted. In the most difficult case, a length of the' entire guide bank, including the em',ankment, may have to be formed across a deep-water area. If possible, that area should be temporarily reclaimed by silting it up, 'DUt if this is not feasi'<,le, the apron should bt: formed in advance and gradually built up auove the ,water level" after which .the superstructure can be constructed in still water but this involves avery large expenditure of stone, ~he cost of guide banks for a Railway Bridge has varied from Rs. 7S to Rs. 184 per foot run. Those for the Sara bridge across the lower Ganges, wher.e the deRth ,was ;excessive and the sand of the river very fine, were estimated to cost Rs. 475 (£32) per foot run. The cost depends greatly on the price of the stone, and that i" due principally to the l'~ngth of its lead and nature of its haulage. The extent of the sectional area of the protection also affects tne cost.

18.

(a) Retired Embanklllents.

, The conditions of :unembanked rivers are unsuited to the cultivltion of the adjoining culturable lands on account of the fact that the areas remain under water throughout the flond season i.e., July to Septem>er. The river Jhelum floods the lands on the left bank from Rasul to Shahpur upto a distance of 30 miles in high floods exceeding 6 lac' cHsecs,' tlie maximum being about 9 Tacs. [his is a typical case wh ~re protective embankments would go a great length to save the residential property and the destruction of crops in floods. But it canalised river with closely constructed embankmenrs is prejudicial to the certain repatian' tights of the popUlation who derive relatively greater benefits; as compared with the loss in floods, from the bumper crops in the spilled areas for a couple of years following the floods. A system of' retired embankments provide5 a solution of the problem. The embankment should enclose the area which has no other means of irrigation except the river spills and cut off the area which is ensured of irrigation from canals or wells. ' (b) Advantages of the retirement of embankments. (i) The minimum interference with the natural operation of the river in raising the country by slit deposit. , (ii) Tt e maintenance of a large river reservoir capacity.

."

.... ,

(iii) The filling of this reservoir reduces the' peak' of the high flood. (iv) The emptying of this reservoir will maintain the river at good irrigating level for a longer time. (v) It may be practicable to utilize such a reservoir so as to give temporary storage of water for canals when the, river: level falls. • (vi) The, redw::tion of the high-flood level will preserve -the regime of the river, an i thus it will diminish the erosion of good land and the throwing up of sterile sand bal}ks. ' (vii) The longer life of the embankments will permit of their being constructed carefully and slowly, well in advance )f the period when the river will approach them, and thus will give time for their self-consolidation by settlement. (c) Disadvantages of the retirement. (i) In'.lreased cost.--Against this lUust be set the saving of replacement of embankments 'oy retired 106ps and the loss cif crops on eroded and inundated areas. (ii) Increasei of open canal head.·_·As the embankment is retired from the river, so will , th~ length of the open canal head between the two be iIJ.crea:;ed. Not being protected from floods, it is particularly exposed to silting.

81

(iii) Reduction of the spi1lcd area. Ge'1erally it will he pos~ible to grow on the riverine area post- irtunriation crops, such as wheat, instead of rice, and where this is not practicable, 'iorests might be planted. (iv) They interfere with the river's natural operations in raising the cou'1try generally. ~v)

They deprive tllt' protected land of much fertilising silt.

RIVER TRIJNINC WORKS AT KHANKI HEAD-WORK.5

Fig. 11. (vi) By shutting Dff inundation water they cause the protected land to deteriorate by the rise of 5U )50i1 salts, (vii) They raise the river high Bood bvd. (viii) They cause the river, by changing its course, to erocIe its cultiva Ie banks and to throw up sterile sand banks. Of these disadvantages

~os:

(iv) , (v) and (vi) refer to damage to surface conditions

Le" cultivation etc., and:\' os: (vii) and (viii) affect the natural regime of the river. (d) The aclvantages of the retirement outweigh the disadvantages, and indicate the desirability of constructing embankments well away frem the ec"ge of the river. By adcting reclamation bunds to the retired em'uankments, the latte' can I:e made safer by the silting thu~ induced, which will tend to produce along them foreshores tree from scour channels and more suitable for post~inundation cultivation or forest plantations, If work is carried out on a proper system of reclamation, the emhankments can be provided with spurs projecting to, the points OJ the river main channel where it is likely to attack the cultura ,h; land. If necessary, the spunshould 'ce ended with Deneny's Groynes.

19

Marginal Bunds and Spurs,

(a) The marginal (unds are aligned and deSIgned iike the retired enba'lktnent upstream of a canal weir on both sides of the river. Their chief o')ject is to protect

'82

the' countryside' from the river spi.lls which will be caused by the afflux head of 3' to 5'. usually provided in case of canal \\elTS and to guard against the outianking of the weirs. These works are required in addition to the usual guice banks or Bell's Bunds in case of the canal ~'eirs, unlike the road and railway bridges where river bed is capable of teing eroded to enlarge the section witl:out any afBux head. The marginal l-unds are usually provided with earthen spurs protected at their ends like the Denehy's Groyne out to the main stream of the river to protect the land enclosed by ~he marginal bunds and to have a defined and straight flood discharge section upstream of the welTS. Arrange'T'ent cf the marginal bunds and spurs as provided at Khanki Head works of the Lower Chanab Canal are shown in Fig. 11. The marginal bunds have a free board of at least 3'0 feet in addition to the afflux he~d provided in the weir design above the highest flood level. They are projected upstream of we1rs upto lengths wh~re the top levels thus calculated coincides with the ground level. (b) Spurs. In India. and especially in the Punjab, besides guide ~a~ks several o~her guide works have teen constructed in the rivres above barrages. The trammg works chlefly 0nsist of armoured spurs at suitable points from the river banks or marginal bunds. fhe types cif armoured spurs adopted in the past are:---

1.

Hockey spurs.

2.

Inverted Hockey spurs.

3.

Point spurs.

A.

"T" Head spurs.

The type found to be most satisfactory is the "T" Head spur. The spurs are constructed in stone with heavy aprons. Various arrangements of/-these spur~;' h~ve bee:n adopted in the past.

Spurs constructed along one bank of ~h~ river. .In so~ cases, s~)lirs have ;o~ly been constructed along one bank. Arlexample of th1S lS the nver Chanab aDove KhankI Headworks. :\t this place more than a dozen spurs exist along the right ,pank. Spurs (onstructe~ on both banks of the River. In '~ther cases, spurs on both banks of the river have been constructed. On the river Ravi above Balloki, armoured spurs exist on both the banks thus tightening the river. " ,

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On the old weirs of the Punjab, large natural betas exist in, frpnt of the central bays of the weir. These' betas extend sometim~s for a length of two ta three mileS, as at Khanki, Rasul, etc. In these cases, the central bays of the weir are masked and' their capacity to escape the flood disch;trge is reduced. From a persual of the a'oove, it will be seen that methods adopted lti the past for traIning the river were not ver)' satisfactory.' ' ; .'. ' ' :, . . , '

\;

(c) The Pitllhed Islands. The e (fect of the pitched island on river training was examined by means of models by Uppal and Mushtaq Ahmad in 1936. In addition to, this . oth~r method, of river training i e., armoured spurs coustructed at different places on both the, riv~r banks anJ on one bank, extension of the guide banks and the sandy bela, along the guide banks wen.! eX<,lmined Results obtained.showed that the conditions obtain~d with the pitche'l(:island were the most satisfactory. In 1943, A.M.R. Montagu again revived the idea of the pitched islands, The construction of.a pitched island in the river-~ed effects a change in the velocity fluctuation and the tractive force. The tractive force near the island considerably increases and causes scour. It draws sIt wly the main river channel on to itself and holds the river thew. The working of the island is satisfactory, especially in the vicinity of control pJints i.e., weirs and railway bridges. It has proved very useful in actual practice upstream of the Islam weir. :," ~

The use of the pitched islands helps in : -( Paper No, 276. Congress, Lahore.) (i) Training the river ~e~t.ralal--ove the 'r'eir.

Th~ Punjab 'Engineerihk

Relieving the the intensity of flow on the marginal 'b~nds, 'the guide bank~ and, outside of river curves.

(ii)

(iii) Training the river in the reach away from control points. (iv)

Protecting ,the valley land agaist devastation as well as rec~aiming i~.

(v)

Improving channels for navigation.

20. Layout of river embankments. (i) When any new line of flood embankment is under consi('eration the inhabitants shouk\ always be consulted. An embankment may shut off the floods from' land whi;ch has hitherto benefitted from them and the people may prefer the old ,Hrangements to the new one. A single ra.bi crop in the year (HIe ra.bi is generally the more valuable crop) with freedom from canal assessment, may suit them the best. Their villages or homesteads are usually placed on high ground or protected by local ring exem0ankments. Thue ma y thus be a temptation' for the people to cut embankment, an extremely easy operation because the men who watch it can be evaced. For the above reasons the location of a flood embankment should be very carefully, considered, and there should be no delay in providing means of irrigation. If no alternative means of irrigation are provided, there is a great temptation in floods to the population to cut them to spill their lands for ra.bi irrigatioa.. (ii) A flood embankment should not be so near the river as to be in much danger from erosion, but the ground, as already stated, generally falls, in going away from the river, so that when an embankment is set well back it is in lower grould, mare eX[lensiye and mQre liable tv breach. The most suitable alignment is a matter of judgement and depends largely on where the main stream of the river is, at the moment" and' on wheather it seems' likly to shift. If the main,stream of the river has lately made aij. inroad and cU,taw:ay ~n em'iJankment, but has'not shifted its course, great caution is ne~ded in fixing the line of the n,ewembank)nent. In 1882 there was an erosion on the Indus a fe,,, miles north Of Dera Ghazi Khan, and a flood embankment was cut away. A new embankment was constructed a mile inland. ThA erosion recurred and the new embankmeht was cmt away within a fAw months of its completion. Embankments are, where po'Osible, made in -,straight or properly curved rtaches. A flood embankment, at Wast at its upstream ~d, termin
(iii) The ,top of an ecn:Ib~nkment is generally 2 or'~';r~et",al>ove the -High Flood Level of the rWet, It should, -of course, ,c' be gntded c pa'f'a-lle~ to- ilie~Iteral'-'f4... F. Level. but neither the gradient nor the height of the fbod is known with accuarcy, There is generally a record dr-'mark' of some high flood, anri this is taken provisonaUy as the flood levd or the level is calculated approximately from the flood readings on the, nearest, river gauge. If experience shows that the- embankmen1:'is tooilow; it IS tai~ed. " t' ; ,; I

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(iv) NaturallY,a flood, embankment shall ce e~onol}lka~ if the, alignment follows the cobt0urs of high land bu.t this will usually set the bUJ;ld V~J,y mij,ch., retired from· the" river .and shall also increase the length. Often the embankme,nt .shaU lJ.qve to 'be lopped inw<;1.rd to protect r;,,, ' ;'. '1' I ' , some village or <;lther, valua'ole property,

" , ('1) In the neigb'bourhood of Deta Ghazl Khan it' n~s IO:'1g been" the, ctisto'lIl ,to ha,ve a double line of flood emhaDkments in places wh.;te the fir'sf line is in any!sort bf danger, eith ,r from river erosion or from ordinary breaching owing to lo~ ground or bad soil. Tlli§,shoul,d be I accepted as a principal for all localities in which the breaching or destruction of an embankment will cause widespread damage. Even if erosion' i.s foreseen: it may be very rapid '~nd there t? ly not, be,time.to mako a second line. It should ,be there before hand. 'Sometlme3 the lInes tit" connected by cross embankments whose function is to'localise damage in the event of a breach' occuring in the main embankment; Sometimes there is local embankment the func!ion of which is to proteoLa local- area itt casetlle maitl'embankinent is bteached htgl1e,r ~?; 'for mstance.. the' j

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84 cantonment emtankment. The flood em'ja',kments at Dera .Ghazi Khan are .shown in Fig. 12 ';';hich gives the g .nerallay"ut of such works. .

21.

Cross seetim or margin, I bun;!

Of

retirei embankments.

(a) G( neral re~uireme'lts. A river emban·kment should te high enough to prevent itts o::ing overtopped by a:l extreme flood, shouL! have a thoroughly consoliclated section sulici~nt to prevent percolatio!, watel from causing it to slip, should have a width of hase a1)le to suppor the SUptTstructurc:, and to l'revent creep of wat r under it with a key trench where necessary' to ass~st in resisting this. It s':lOuhl have its slopes protected {rom guttering by rain and from erosion by wind and wan-lap. To retluee. tte cost and to increase safl ty the highest land ptacticab1.; should 1e selected, l ut care shoul,[ i e take 1 not to trav, rse, if possible, ground which is sandy, fr.a le, ntUc:\ cracke,i. or i'npregnate,l wit'1 S3.{ts, or intersected hy numerous channels, or irregular in longitw;inal or CTOSS se,ction, as his wiH lead to di, erenccs in s(-'ttle~ ment. The ne;g,],_ol1rlJood of villat;es sIwuhl be aV<)iJed, as their preSe;1C<3 Lacreas,"s trespass Ly traffic. When an embankmp':lt is likely to be breachedby ero";on of the rh'er, and a retired alignment is decided ori, which it may, e nee 'ssa "V '0 exte.:ld her oa.fter, it will be necessary to U!/Rq 6MIl(J"""'''''r !I. join the end of t .e n'2W i ank AB to .tie Ql:d line CD by.~ /~-------- cl·ossLank. Ca' e sL,ouhl i.e taken IV ,"e hg.13) that. thIS Si.-// ~ . cross-I. ank I as a do\\ nstr am f'ireCi ;(Ill, BD, and not an --~~ "j,b~l ---:-::"1:1. ul,q;eam one, ): C for tl:e latter .will form "vIrat is known .. -lIftvt!tt/" e as a 'pocket'. WI' n the 01(1 j ank s Lreached and flood i " 'wat r is aUIlitted to tile new )'2nk it will in the latter case Fig. 13 . ':," ~;: pond up at B to tLe level of the river opposite the cut C, but in the former one the water will rise at B only to the level of the river oppo5ite it.

tb) Section. The proper section depends on the height of the bank, the nature of its material and foundation and the way in which it is to be formed. A typical cross section is given in

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Fig. 14 Fig. 14, If the river water is likelv to be on b'Jth sides, the bank slopes should re 1 in 3 ell I-oth siees, The earth work without clods should be laid in lavers of not more than 6" thickness and ccpsolidated before the next layer is laid. '-"'here tile g;ound is l'ke to give way unc'er the bank: the base should Ie widened so as to gain the necesEary amount of "upport. Where wave wash may be expectEd, the riVc'T side slope should be flattened and wl~ ~: thl.~ material is uUielia\ Ie hoth the slores ~bould be 111creased. The top of the bank shDuld be given a slight slore for drainage to the land side, so as to diminish t~'ndency of the river s'ope to gutter during rainfall, as rain scoreS will aid wave wash in damaging that slope. (e)

Key Trench.

Inspection of river banks will show tl- at owing to the absence of pressure and the eff2cN of U:e w(ather, a surface soil is gemraUy more porcus and fissured than a subsoil of similar' matErial. Foreover when· watn meets two disshnilar materials, ·such as mate earth and natnral soiJ, it has a tf'w"ency to collect a.t their junction and to endeavour to P1SS tetwfen them. The key trfnch which is a small rrjddle trench provides the junction which unites the' body of the emtankment to the Stl :soil, destroys the continuity of the base plan ani secures the thorough examination of the part of the base it occupies, and the removal from it of

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Insptction of river banks will show tl- at owing to the abser1c~ 01 l-'l<:;""Uc'~ --of tte weather, a surface soil is gem rally more poreus and fissured than a subsoil of similar; material. Fore over when, watn meets two dissimilar materials, -such as mace earth and natnral soil, it has a tE'n(~ency to collect at their junction and to .endeavour to pass tetwEert them. The key trench which is a sman rrjddle trench provides the junction which unites the' body of the embankment to the su :soi1, destroys the continuity of the base plan an:i secures the thorough examination of the part of the base it occupies, and the removal from it 01

85 vecretation, roots and ru',1,ish. A key trench ls most imnorhnt where thegrounrI is porous sandy, or b is cracke~ a'1d tran,svcrscd by fissl~r::s or bv wate~-C0U~S"S etc. Its section will depend upon the 11lgh-f1o"d (epth.agaqst tile el~b\,'kl1'llt, till~ nature ?f the sub-soil and the importance of tile em ank IF'nt. OiUiH:J,,,ly It, Lottom wHlth may vary from 4to 6 it. its de lth ~FHn 3 h 5 fe"t an,l i~, s i!e slo')f's J} to 1 or 1 to 1. A water-tight foundation is essentially necessary for aa orcl1uary hYllrau~lc work. ~b)

&lip Trench.

Wherever there is a~ ahrupt c1:lange in the level of tJ...e ground, or of the top of the em l)ankme.lt un,:er CO,lstructIOD, one or m');-e ~:,:) t ,;.ac.;,es Fig. 15 s\ould be marie so as to form SLIP TU./If£H£$ jU,JC~:U;l (;0\\ ~:i tp f''' \-enc ti,e cr.,(:;p of water al(wg the junClillNNfM. ell"S$'~ BANi( JUNCTION ct:0_1 (J :e of (t:e ('aHh work, They mily have a bottom "ie; tt of :3 or 4 [eet, a depth of 1 ~ to Z f; :t, an,t s~'l." slopes 1 to 1. .1, e'r SI([,S and t1Jose of tlle iryegu:,u:ly bl'ing dea.t with s ;oull j>e sIo:)ed so that He eminnk:nent during sc:tLl ,nellt may seL:e 1 !,(ltly a~,,'il,t Lem. TjH~ l~ss the ca!)aC~LY of be so t to \\it:istand p"Tc::;lation, tl,e more numerous and the larg.cr s;lOuld te Le the slip of trenches.

(e) Banquette (Bel m) or Pushta. Fig. 15.

The advantages of berms as shown that they :-

Fig. 16. are

III

Fig. 16.

(i) Cover the hydraulic gradient of the internal percolation line and thus render the embankment less liable to slip. (ii) Provide space for a roadway which is b2tter located there than on the top of the embankment. (iii) Provide space for stacking material, or an area from which soil may readily be olltained for the emergent raising of the emLankment when necessary during·floods. (iv) Furnish a better cross section for subsequent enlargement or raising of the embankment.

22.

E:){amination Qnestions. 1.

Explain with slreches the (1) Dimehy's groyne (2) Bell's Bund. the tength~ 0\ both I

2.

(a) Sketch the most suitable type of a pacca Oroyne.

3,

Describe various typeB of river training and pro\.ection 'Narks,

4.

(a)

What are the main featufes distinguishing a torf€'nts from a fivet or a stream?

(b)

What ate the main divisions in the course of a river and a torrent I

(b) What points will you consider in designing groyne training wo

What considerations deterlJ1ine (T C.li, 1933)

'ks ?

(p,D. 1942)

(P,U.1942)

(P.D.1941)

5,

Sketch a suitable cro58 section of a guide b,lllk as used in river training works. Explain the process of launching of aprons in such works? (P. U. 1943.)

G.

(a) \Vhy don't the Railway bridges need a system of protection w rks embankment in addition

to guide b3.nks like the canal head works?

86 (b) What points will you keep in view in determining a suitable layout of a system of marginal ,bunds with spurs ?

7.; (a) What is the function of retired embankment and what are their advantages and advantages?

dis-

{b) Sketch a suitable cross section of a:r\ earthen embankment and explain the f0110wing : -(i) Key.

"

Trench (ii) Slip Trench (iii) Berm or Pushta. 8.

Describe with sketches 'a suitable layout for thc design of guide banks and the function of th curved ends up and downstream.

iI.

(a) Explain the following terms in the case of rivers:(i) Erosion (ii) Scour (iii) Swirls.

('D) Why are swirls most destructive in their action?

PART II

CA-NAL

IRRIGATION' Chapter IV' ,) ,.

HEAD WORKS Introductory.

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j

Permanent canals are prcvided with permanent works at the site from where they take off. These works known as head-works comprise the construction of a perm<}nent W~f or a dam across the river along with other subsidiary works which will be dealt with in thi$ chapter. The aims and objects of the canal head-works are summarised below : (a) To prevent water required for canals passing the. head-works at a level below that at which it can be utilized an,d when total supply is wanted in the canal to prevent any flow downstream.

(b) To raise the level of -the supply so that it can commaJld by flow the area to _ be irrigated.

(c) To gain command economically when the canal hasto pass in expensive cuttin~. (d) To reduce the fluctuations of the level of the river. (e) To cont~ol the silt entry into the canal. )

" (f) To render the headworks permanent thus ensuring the require.d supply C'anal and to prevent them from being affected by the vagaries onhe river. ' "

2.

~nt~,i f~~

Selection of site.

(a) The decision whether the headworks of any canal should be situated in the hil boulder tract, or in the sandy trough. must be determined by the{ position and level of the country which require's irrigation.· There have been warm controversies at various times between experienced canal engineers. regarding the relative advantages of both positions, but the pr~cticability of both classes of site having been demonstrated by actual co'nstruction, it is quite eVIdent that at the present time the area to be commanded must determine the selection, unless the excess of cost renders one of the sites a financial impossibility.. f

(b) There are, however on general grounds, four strong arguments in favour of the trough site. Firstly, the well known fact, that a dam in the boulder tract, even when it is to all appearances perfectly water tight, does not hold up all the water in the river, for there is alw~ys a strong sub-soil flow which appears lower down, and which combined with the percolatIon fro~ the country side along a river, and possibly with the supply from some affiuents, will give an Increased discharge at the trough site secondly, a canal from boulder head-work,s is certain ~o lose a lafgp proportion of its supply from percolation, and this loss may be greatly increased l~ the channel passes through iights and also, which is mostly probaiJle, before it reaches the firm solI of the dob. Thirdly, the tracts lying at a short distance from the hills rarely require wat~r with the same urgency as those lower down, and the quantity they need can generally be gIven by petty works from minor hill or spring streams. Fourthly, the certainty of getting all supply in the river at any moment when required, is ensured by a masonry·· weir fitted with proper regulating arrangements better than by the boulder weirs in b0\11der reaches which are not absolutely water- tight. ' . (c) The trough weirs are more expen~iv~, tflan the boulder weir as the stone has to be Imported from long distances. Trough weirs require very expensive training works and marginal

88 bunds. A heavy annual expenditure on the training works must be considered a necessity for all big trough weirs. (d) The points to be kept in view, whib selecting the site of a weir in the boulder reach of a river are as follows:-

(i) A side channel should be so12ct('d which is not dir2ctly SU')j 'ct to Hood action and into which the cold weather supply can easily be diverted froTI t'.le \lui 1 challel. (ii) The side or supply channel should lr.ad dir'Cctly to the fixed o'f-taking site for thr. excavated canal. If the canal was to take-off from the main channel, it shall n2ed very massive and expensive works. . (iii) The control over the suoply channel is mJ.intained by m:lkin'S its be i slope after the first thousand feet or so something less tban that of the main river. Tho site shoq.ld be such that a rise of 5 to 8 feet is attained at the canal head. (iv) The sitesbould be such that sUlht':lle Sit2S wit'1 firn_'}cd a'1j "'ld~s are availaJle for, 'constructing a bund at A~ a weir at B and a waste weir at C shown in Fig. 1.

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(e) The rLain requi,sites of a suita:~le site for fJ~t: " '. _ h' ad-work in the trouge ._____-::;::,..?J__ ":J'--~~' stage of rivers, may De ~ /-~ ~--:t-1"-~"r~-:;-~ <' t / ; / / \, briefly stated a's--;-firstly, :,_______...--, "'-.e"", 1j'~ ~' ~;> ~ ./:,., .6- C· I / a. na:row, straig~t, well: _:;: ----... --.:.._-~.5:.")/ _. ' d .fined ~hannel WIth banks -,', ;'-.Il')(;'I." ni ;-? .------~ __::__,,~_CM~ .!..".!!!~J::__ not sUi)merged by the H".Uo. highest Hood; secondly Fig. 1 a canal line capa1lle of attaining command of the irrigable area, with,necessary slope by moderate dig;:sing; an~ thirdly, the presence of_suffiClent material for construction near the site. The a]:)senceof mat~n~l~ such ~i; clay for bricks,' sio~e fo~' building and lime, timber, etc., can be got over by the provlslOn ot c.

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89 railwaY line-the (xpence of long transport is. t:owever, a serious item. Inferior sites for the weir can be improv, d and rendered safe by training works. but no expedient will thoroughly corr~ct a radically bad canal channel line if carried far along the Kha.dir; it will alwa~ s be open to attacks from th fiver, rendering "a solution of continuity" possible, and most expensive and training works over lrng distances a necessity: moreover, th~ evils of over-saturation and deterioration of soil will 1e severP.ly ttlt and found difficult to cure. If aligned again in deep digging for a grEat 1 ngt1-J.. the initial cost 0' (0 lstruction will be enOrmous and repairs h<;avy. as the alignment must b: merely 1 S5 straight the expend ture in the adjustment of drainage, waich it cannot cure tv ayoid. will be no light item. Of the two causes the channel in digging is pro ably the better in the long run. :~.

Layout of HeadwJrks.

A typical lay )-It of tl:e canal hcadw,",rks is showning Fig. 2 and in aerial view of Ylerala F esd works in Fig. 3. It consists of th' fo1l0.ving works:(i) Weir proper,

di\'i(~e'l

into bays 1)\' divide pier5.

(ii) Under-sluices. (iii) Canal head regulator. (iv) Fish ladder. (v) Divide wall. (vi) RiVET control works. . Thp weir should be situated at right angle s to the main stream of He ri\'er as far as possible. Fig. 2 shows U:e layout cf the teadworks at Rasul for tte Lower Jtelum Canal. 1 hf' Rasul weir is 4090 feet long. It is divided into 8 bays of 500 feet width each ty the divide pins to avoid cross fiow in floods. The fish ladc1er is situated at the left end of the weir. The divice wall Ee~ erates the weir from the undersluices. The undersluicfs arc constructed on the side of t1;e river where the canal takes off through the stl ucture known as He tead regulator of the canal. If there are canals taking oft from both sic'es of the river upstream. Hen ttere shall be two unc'ersluices, one of each sides. There shall sirr.ilarly te two divic:e walls. The river control works consist of guic'e tanks in contiJuation d tte a utrrents supplemented by the marginal bunds and spurs to control tht' river spilling the country-~ic'e upstnam of the weir on account of the a-FEux calJser! by tl;e weir". T11e headworks site is verv suita Iv situated betwen high ground on both sic:es and tI-.erefore no extensive embankments ar' sh )\~'n in Fig, 2. The extensive river control works at Khanki are shown in Fig. II i 1 l'r,;vi 'Ui C'l'l?t!r ano th')se at Sule:nnki in Fig. IS of this Chapter. 4

T) p~~ of Weirs. (a) Weirs are classified into t .\'0 classes according to the design of their

1~()Or3:-

(i) Gravi.ty weirs.

(ii) Non-gravity weirs. When the we:ght of the masonry and tl~e concrete of tLe floor of tl:e weir oV.rcotl1e~ t1:e upward pressures under the floor caused ly the head of water against the weir. it is called a gravity w;ir. In tte caSf of the modern weirs. SUC'1 as, the Emerson Barrage at Haveli the HOt)r consists of t1::e reinforced concrete slaD and its weight is less than the upward pr.:sstrre. The R. C. floor sla') is conti'luou:; under the divide weirs, the weight of which keeps the structure safe as a whole against tht~ uplift pressures. Such weirs are call d n()r:$,~ravity weirs.

r

(b) Weirs are clas,ified into two classes acc.crding to the conJrol ,.f tr.e snrface flow OVer

en. (i) Op'n weirs or simple weirs.

.1

91

(ii) Barrage.

In the first case, the crest levd of the weir will J e determined by the permissi~,lt afflux during the maximum floods, the discharge per foot run and the pond level. The plmrj level can be maintained by a permanent masonry crest with its top at pond level as at Rasu! or one at a lower level supplemented oy the fallinf shutters as at Khanki or Marala or counterbalanced gates as at Sulemanki and Islam. Permanent raised crest is unsuitable, 'r;ecause i: shall cause excessive afflux head in maximum flood and there will re no control of the river in low flooes. The choice cetwi en a, weir with shutters <Jnri one witL counter-balanced gates is largely a matter of cost and convenience in working. A shuttereri weir will be relatively cheaper, hut witI lack the speed and the effective control possihle in the case of a gated weir\

A barrage is a gate-controlled weir right across the r:ver with crest at one uniforn; level. The Sukkur weir in Sind and the Ferozepore Panjnad and Haveli weirs in the Punjab are examples of this type. A barrage provides a perfect control of tht river channel upstream in low floods and affords better facilities of inspection and repairs. A barraged weir should provide efficient control as the channel leading to the under-sluices and there'D), help in the control of the silt entering the canal. . (c) Th· weirs are classified as below according to_ the function. th<-y perform" (i) Storage weirs, (ii) Intake or Diversion weirs, (iii) Wastf ~eirs. The storatge weirs will [l .fealt with in Chapter HI. Part III along, with the storage reservoirs. It is the second ~lass of weirs which form tke subject matter of this chapter as med for diverting the supplies mto the canals. Waste weirs are escape channels for floods which cannot be stored in the reservoirs. These are constructed to ensure the safety of dams and their design is dealt with in Chapter III Part IIr. . \tl) Part of a weir.

A typical qoss s~ction of a weir (Bligh type) is given in Fig. 4.

....

-

..

t-"-L,--I------.--

I..

Fig. 4

A ~'elr consists of the

following:-~

(i) Upstream curtain waU,

{iiJ Fore apron. (iii) Crest. (iv) Downstream Apron or floor. (v) Downstream curtain wall

(vi) Riprap or Talus

01'

pervio11s protection

(vii) Wells under the crest.

(i) The upstream curtain wall used to h~ of shallow depth 6 to 8 feet feep. unlike -

the modem sheet piles which can be sunk to any depth,

'(ii) The length of the lore apron is determined a~cording t~ the empirical formula evolved by Bligh on page 169 of Design of Irrigation Worb.

92 W 0:=4/ '-"ri where W ~ leng th in fed of fO:'e apron (=creep coefficient H=head against the weir The floor lev·J upstream of the weir is determined from considerations of the penni,;sible scour depth below the maximum flood discharge level at tre site of weir plus the afflux head allowed, The scour depth can be worked according to Kenr.edy's or Lacey's Theory of design of Trrigation Channels as shown in calculations i.l chapter VI. The thickness of the fore apron is determined from considerations of water tightness because the uplift pressure below is balanced by the weight of water above it. About 1 ft. mlsonry over 1'0 to 1'5 ft. of concrete will do, (iii) The masonry Cfest is designed as a wall retaining the water pressure as shown in L. Fig, 5. The worst couditions for the weir floor are _"_ when the water is headed up to the top of the shutters upstream and is at the Talus level downstream. , The rfsultant pressure P is equal to the shaded area of the p: e sure diagram acting horizontally at the ce~tre of gravity of the shaLed trapezoid. Similarly wel~ht, W of the crest acts v~rtically at the centre of gravl1Y Fig, 5 of the crest section. The resultant of P and W must pass within the micdle third of the base. This determines the width at th .. base of the crest wall and the top width is fixed from the practical considerations to allow enough spaces for the anchoring and the working of the shutters. The height of the weir crest is determined from considerations of the permissible afflux to pass the maximum flood discharge as shown in t~e calculations in Chapter V. The required depth on crest for tte maximum flood discharge WIll fix the crest level. (iv) The length of the downstream apron the total length of the impervious floor a~ determined by the allowable creep coefficient for the particular soil of the river as given in para 2 Chapt-er V .of this part. The method to draw the creep gradient line shown in dotted is explained therein, The thickness of the downstream apr.)n depends upon the adual pressure acting below it according to tr.e creep gradient line. It is calc hted according to the formula.

:::r;

H~h

_.- ..---~~-

p-l

Where t=thickness of the floof in feet. H=Total head as shown in Fig. 5, h=head lost in creep up to the point where thickness is to ~ determined, p=Specific gravity of th" floor material 4 -represents the factor 3

0'1

",afetv .

/~~--'-

P is 2 25 for stone masonfY and COllcrete in stone ballast and 2'0 for brick work and concrete with brick ballast, The level downstream of the weir crest used to be kept the same as the upstream floor level (top of the fore apron). It should be kept the lowest as worked from the following three considerations :_-(a) Depth reqUired for the flood discharge with the actual surface slope of the river before the weir construction for the intensity O'f discharge per foot run over the river. (b} From consideration of the depth required to form a hydraulic jump downstream of the weir on the impervious protection.

93 (b) The floor level downstream should be ;tepressed su"ficiently below the upstrealh floor level to allow hr the retrogression of the ri' ar bed levels which follows the construction of the weirs across alluvial riveT as explained later.

(v) The downstrp.am curtain walls too used to be very shallow, usually 8 to 10 feet deep, because it was not p::>ssiblc to c()nst~u~t them as the spr~ng level in tne river-be~ could not be lowered very consIderably by pumpmg. In the modern weirs the sheet pIles are drIven to form a very deep cut off at ttle end of the impervious protection. {vi) The total length of the pervious protection is calculated according to the tormuia

for free over-falls, L 1 =10C

vi

r~-qlOx75

and for sloping downstreem aprons, Ll =

.

lie I Hh ~ q; vi

lOx

j

jPage 16401 Dams and weirs by W.G Bligh of 1918).

Where L) =length of the talus c=Creep co-efhcient for the river-bed soil q=dischaJ~e per foot run Hb = Higb. of the crest wall above bed The wells under the crest simply serve as nails in the river bed. Their usefulness as ilfstroyers of creep head had neVEr teen attahed \\ith SUCC€Ss bHauEfI the sraces in bet\\een them could not be made water-tight. The usual attempt to drive wooden piles betweea the wells has not bef'n much successful. It will be usual to consider these shallow wells as an ac:lditiona} factor of safety and the creep length required was provided, without taking them into consideration. 5. AtIlux;

Afflux is the rise in the maimum flcod level of tIle river upstream of the weir caused as a result of its construction across the channel. In the beginning, the effect of 1he afflux in raising the river levAls is only felt up to a short distance upstream according to the length of the back water curve but in course of time the river bed rises due to the silting up caused By the additional waterway added to the section upstream of the weir by the afflux height and the effAct travels upstream till the river slope upstream of the weir is the same as before its construction, In the design of weirs founded on allu vial sands, the afflux is limited to 3 to 5 feet. The amount of a fflux will detemine the top levels of guide banks and their If'nghs and top levels and sections of flood protections. It will govern the dynamic action as the greater the afflux of fall ot levels from upstream to dowDstream, the greater \\ill be the action. It will also control the depth and location of the s tanding wave. By providing a high afflux the width of weir can be narrowed but the cost of the training works will ~o up and the risk of failure by outflanking will increase. The discharge per foot run, tbe depth of the scour with the action on the loose protections upstream and downstream, as well as the depth of piles at either end will increase with the afflux. 6. pond level The pond level is the water level required in the undersluicfs pocket upstream of the head reg~lator of the canal to feed the canal with full supply The full supply level in the canal at Its heads nepends on the levels of the country which it has to irrigate, and the peqpissible ~lope in the canal. The working head at the canal head regulator should be allowed to be about 3 to 4 feet. while the waterway for the head regulator may be designed with less than ha~f ~he available head. Enough margin should be left in fixing the pond level for the f U1 ?re sIltmg up of the canal bed and the silting up pf the river bed downstream of the well WhICh will cause sluicing difficulties for occasional washing down of the silt in the pocket.

94 , , Pond level dete.r.mi~ the hmght ()f the undersloice 'gates and the height of the shutters above the permanent mwM'Y ,crest of the' wQir.'· ,; , ,

7. Waterway for weirs, The waterway for the weirs has in the D::J.st been kept arbitarily limited by the permissible scour depth wkkh, would fix,the floor level upstream of the weirs, Tt the water":ay is restricted very much., the float' level., will be relatively low necessitating heavy and expenswe pumping to lay the upstream and downstr,eam impervious aprons. The scour depth for a discharge per foot run be worked from Kennedy's silt formula Va ='84 D'64 which applies to the Punjab conditions. It can be'modified to suit othe" i?ra.des df silt by introducing another factor known as C. V, R, and denoting it by x. ", ' :" Va ='8.\. x, D-M .

.

.

\

Let the discharge per foot run be q cusecs Tlten q = Va 1>: ='84 x

: :'0= (it .(~.) , .• ' X

.

I

:

1)1-« ,

,61

..

!.:

',"

•

,and wheri~ x is HIiity D=l:il q.&l ''

,~) Anotaer method to determine the sconr depth is that given by lacey in his papel . N~

on .,Stable Channels in Alluvium" "

'

4736, (19:JO} Institute €If Civil En~ineer6; London.

,'·('QiL.~I):1;6' ","

"7'

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,

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"h~(di~~harge. per, f~ ,...,

.

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Substitui!lg i.n terms of q

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~=j305 (3~fL)1 ".\b~t P .. 2'67 Ql,

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1.

:.,

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, •

run or :(i==~= ~~=yQ' , P 2'67 vQ ?;ftJ7 w

)1

q2 R=.9 ( -f~' , ,; ., (c)' In t.he table given below, the, actual waterway provided' between the abutttJent§ is compared with t)Jat worked out according to La~ey's formula F -:-2'67 Qi .in the case of , some of the Punjab weirs, Waterway for weirs, for the avp.rage conAitions in thp Punjab shoulrl be 1'5 times Pw worked out according to tb,e ALacey's formula. The eXperif'nce has shown that' even the restricted weirs like ~hose' at Ferozepur. and Islam sliMer from the satne tendencY' of forming islands upstream of the weirs as in the case of the reJatively WIder weirs. The

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96 restricted waterway increase the scour depth and consequently lower the, upon levels. entails relatively higher expenses of the pumping to lay th~m. 8.

This

Effect of weirs on the Regime of a river.

(a) The river regime is affected by the construction of a weir across its channels in tlw following ways. (i) The slope of the river upstream of the weir flattens due to the pondhg up of sup pEes (ii) An increase in tortuosity, as a result of ponding up, as the bulk of silt charge of th" river water deposits in the pond, leading to the formation of irregular shoals. (iii) A progressive degradation or retrogression of bed levels downstream, due to the picking up of bed silt by the relatively silt free water escaping over the weir. (iv) These ef:ecb continue lor the first few years. but l~ter due to ~ontinom siltlng up of oond and increasing tortuoslty, th:! bed levels of the stream wIll t2nd to fIse as the b~d levels at the weir are fixed. This can be explained by t:1e fact that the water will need great~r head, to overcome tte increased distance which it ha., to travel. An increase in tortusity will necessarih' enhance the rise will be felt higher U? the river than would otherwise be the case As a result of this progressive rise of bed level, there will be tendency on the part of the river to regain it,.; original slope, (v) A stage will come when u;Jstream pond ab30r~s no further silt burden. Owing to the off taking canals drawing cOTnparatively silt free water, the exeess of silt will g) downstream of the weir wl i~e the amount of water passing over the weir will be below the normal due to canal withdrawls. The river celow the weir, will, thus, have to carry an excessive silt charg ~ with a lower discharge, This will result in progressive silting up downstream, an increase in tortuosity and, therefore, a recovery of bed levels downstream. (b) The changes in the regime of a river caused by the coustruction of a weir have an important bearing on the design of ihe weirs as outlined bdow;(i) Retrogression of Levels. In the nrst f~w years following the construction of a weir. the retrogression of bed levels downstream is rapid and progressibe. In the case of the Punjab weirs this has ranged cetween 4- to 7 feet. This lowering of the bed levels in the early stages if not duly allo Ned for in design may result in a failure like that of the Islam weir in 1929. The retorgre5sion may. undermine the stability of a work by an increase in the exit gradient beyond the safe limits. It will increase the destructive action of the standing wave as with the increas:d fall and decrC'ased depth of downstream water due to the lowering of the water lewIs at that eLd, the wave will tend to travel down to the Dlock and loose pr ,tection area. As a result of the retrogression in bed levels, while the low water levels have been found to drop from 4 10 7 fe~t, tIle maximu-n fio:)d levels have not bee \ knoNn to have dropped by more than 1 to 1'5 ft. The dow lstrea n rlood level should I)e depressed below the upstream river bed by about 4 feet. (ii) Restoration of the original slopa upstream of the weir. In the course of time the river upstream will regain its original slope wh:ch implies that the effect of afflux due to the construction of the weir will not be confintd in magnitu 11.: anll length to the usually accepted distance as determined by the back water curn (apPfJximatel:v :l.Ha IS It will travel very far up and will be felt in full all that distance. In other words, the entire bed of the river will ultimately rise uniformally throughout the zone of protection and training works. As, however, the full affect will not be felt until after lapse of many years, the free toard, may, in the first insta 1C::-, De reckoned a JOve t'le H. F. L. a, determined by the back water curves (iii) Recovery of downstream bed levels. The process'ofrecovery of downstream bed levels after the initial retrogression, is SlON but steady. It may take 20 to 30 :vears but the bed levels may rise higher than those before

f17

the constlUction of the weir, At Khanki the rise above the original bed level has blen of the costruction of the weir. At Khanki the rise atove tl~e original 1 ed level has i een of the order of 2 feet. A rise in the downstream [-ed levels may lead to the loss of control of the river in respect of silt regulation, making it necessary to raise the weir crest, Khanki and Marala are instances of ,>uch raising. The Khanki weir crest was rassed hy two fe3t in 1910-11 in days numbered 4 5 ann 6, and in 12[7 in th1 rella i ning bays It was again raised hy a further two feet in , 1920-22, Marala was raised by two feet in .1925-26 in order to o:Jtain control of the river and to improve silt conditions in the main line. Tht'se facts point out the nec .. ssaty of cesign for a pond level suffici -ntly ahove the full supply level in I the canal so as to lea\'e ample margin even after He rise in the downstream ced has i taken place .

+ ••

•

.#

9.

t

(a) Object of the underslulces. The nndersluices ara required to keep the river U:l.Cer control aiming at the following 1'oi[;ts :--

.~

:

Undersluices

(il To scour the silt deposited on the river ted in the pocket upstream of the canal head regulator. (ii) To preserve a clear and defined river channel approaching the regulator. (iii) To facilitate the working of the weir crest when movable in the form of shutters or counterbalanced gates. (iv) To lower the highest flood level.

(v) To pass the low floods without dropping the shutters, th~ raising of which entails good deal 'f latour and time.

I

+i

.

i 't

!

1

<.

'I

i I

. ___l_

Fig. 6

(iv) To control the silt entry into the ca'1al (\'ii) fn the case of sudden fkods, the undersluices can te opened to fill the river l eds downstream to protect the downstream Talus from the H.rdraulic jump action.

Fig. 7

(1 ) Tte capacity of the undersluices. The capacity of tte undersluices is fixed on tte following consi(~eratins :-

(i) To fUsure scouring capacity, it should 1 e at least dou'ole the canal discharge. (ii) The undersluices shouid be capable of passing the low flood diseharge excepting the three month of the monsoons without over-topping the shutters. (iii) The uncersluices should l-e capable d ra~ing the winter fresl:ets under thi): gates with canal in flow.

98 (iv) At high floods,. tllc undersluices should he capaule of passing about 10 to 15 Yo of the maximuHl flood disCharge. Jhis aims at rerIucing the length, of the .weirs became long weirs will cause idand formation' upstream and will also serve to maintain deep water chann~l towards the canal regulator.

If there are two off-takes, one on dther sil~e of the river, there shoul(j be' two undersluices of such capacities in each case as ddermillerl from tl!es~ consicerations. (c) Design of the undersLi:es.

The following points should be kept in, view in dtsig1ling the llndersluices : (i) The crest and the floor level in tte pocht :upstn am should 1 e at the . lowest It is usually kept at, tte Je!l;el of the apron upstream 'of the weIr crest. pr~ctica'Jle l~vel of the rivtr.

(ii) Large spans are preferable. In t);6 case of old '~eirs the lllH'ersluices span~ used to Le not longer than 20 feet tecause wic:er gates were not availa' Ie and were diificult to work. Now the gate design has teen very much improved by the use of counter r alanced weight as in the ca,e of stonyc's gate arqmgement cescri: cd later in this chapter. .Kow spans of :30' or more are used. (iii) The floor thickness and its legth are (;etermined according to the weir design as outlined ir. the next chapter. (i\,) The discharge intensity leing maximum in the undersluices. the foundations, floor and the Talus should te maue extra strong.

the

(v) '1 he floor downstream of the crest should not I:e keDt level with the crest level because the formation of a proper hydraulic jump as destroyer of energy is very uncertain on a level floor. ~breover from the considerations of retrogression, it we, uld I e advisable to dpress the downstream floor up to the likely retrogression b~d l:v,'i downstream which may te at least four, fec·t.· , (vi) A' bridge downstream of the unrlersluice s)lOuld always I'e ployided to lift the hy cranes if Stoney's arrln.g~m~nt fniL., on a:ty account.' Typ~cal sections of the u:ldersluices are shown Fig. 6 and 7.

gate

The length of 11npet~-ions apron \lpstream~of the sluice gat!; is got from the empirical iormula.

C=crer,p'ccefficien{

H = Height of the shuttered water Lv< 1 allove The length of the Talus below the undersluices is got • Design of Irrigation works" by W. G. Bligh. , I ,--- 1-" ;, \

j'

Hb ,) 75 q 10 .Xv

Huot

level.

from the formula on png~ 216

',\" nere [' ~',~ 1:ngtlll1 l ' fee t ;

C= creap coe:11cient Hb

c,~height

of tht p,:rdtallcn t welr cresC

'. and q = Discharge intensity per fC run,

The thickness of the floor IS calculat..,d fr<Jm the creep gradient the~ty iik'~ the welf:;, The depth of the Talus is 4 to 6 Jed, usudlly one and half times the depth of floor downstream of the; weir. . .

99 10.

DivIde Wall.

The divide wall is s.imply a long divide groyne built betwecd the weir and the ilndersluices. It separates the turbulent river in maximu"m floods from the pocket in front of the canal head regulator. The wall extend, upstrean to a little distance Jeyond the 'oeginning This NaIl of the head regnlator and dowustr'am to the eur: of the Talm of the undersluices. plays a very im~ortant part in controlling t~e entry of silt into the c mal Jy enclosing a pocket of very nearly stIll wat ~r awl. by se::n.ratmg It fro n the tur ml ~nc~ and vagaries of the alluvial rivers in floods. OIVIDE

WALL

In the case of old headworks such as at Rasnl. the divide wall is simply in earthen bund protected with stone pitching on both sides and provided with stone apron as in the case of guide banks. The upstream end is provided with extra strong protectio'l in the form of aprons. An earthen ctivi('e groyne requires a lot of space for its section and shuts 1ff a c'lllsidera' Ie efective water-way of the weir and it is, therefor!:', now usual to buiI:i the divi,'e '.vall in ~olid masonry as Shown in Fig 8. Normally thE Ie will be water on both side,.;. _,,"CH';;": ~.~ I• ........-·.--j but di erence of pressure on 'loth siclEs of the wall is Lk ly, due to still water I,eing in the pocket Fig. 8. and a strong river current (~estroying its velocity head by striking against it. Similarly, if flood is being pa?sed thr~)Ugh the undersluices, there will i:e rdatively less de?th on the weir side. It is usual to deSign tht wall for a pressure difference of 3'0 f et depth of water <)n either side. In the case of masonry divide wall, it is necessary to provide Nell foundations for as least 100 ft. lE'ngth fro:n the extreme end taking them well below the deepest possible scour. 11.

Fish ladder.

Irr the large rivers, the ftsh are always moving from one part to another. In the beginning of winter they leave the cold water in tbe hills and move down to tl e relatively wann water in the plains. Before the monsoon in the months of m.'tY and June they move up again in search of clear water. In the mOllths of July and August in Northern India, the female fish lays eggs in the water which meeting the juice created by the I'1ale fish in clear water fertilizes th~ eggs. The meat of the fe-nab fiish is usually piosonous in the months of July and on ac(ount of the presence of eggs in the 'Dody, The fish t!terefore travel up and down hundreds of miles along the large rivers and it is, th~rd')re, essential that as )ace should DE' prov:(:eJ in tLe construction of the modern weir for the unintt:rrupted movements of fish. Fish Ganeasily travel against current of water with velocities up to 100r 12 fect rer second. The design of the fish ladc:er should 1 e such that'the velocity of the current against which the fish haw to nlove s~lall not I e higher tha!l this limit. There is usually a head of a'~out 16 to 20 feet from the upstream of a we'ir to the downstream water level 011 the river in the winter m.mt!lS In an op:n gap in the weir just like the O:le in the Ganges at Hardwar. the velocity of th" current will l e very high, and therefore even the strong flS'l will not Le a;.Je to travel upstream. It was nothing short of <.:ruelty to these poor animals to see swarms of large fish 2 to 4 feet long collecting downstream of fish gap in the we'ir at Hardwar an i dying of sheer exhaustio_1 in attl!;npts to move upstn:am. A prop:,r fish ladd'cr ha~ no",' Leen provJ(:led there. In the modern weirs the fall of water is broke:l ill small strips. Typical \;e3igns of fish ladders are shown in and Fig. 10. Tiie suita ,Ie site for tlH! fish ladder is near th'~ divide 'vvall because there is wat'!l throughout the year in river bed downstream uf the undersluicts (lUly. It ¥; usually localed Letwe.:; the wtirand the c:ivide wall'and in SOme cases it ha been !uilt vithiil 1h, divide lAal.. The walls are huilt oblique and holes are also staggered as shov"n on tLe plan so that the fish can

100 take rest after passing O:lC hole before they move on to the other. break the fall in small steps as shown by water line in the section. 12. Read Regulator.

The;e walls also serve to

The object of a canal head regulator is three fold:(i) To regulate the supply entering the canal. (ii) To control the amount of silt entry into the canal. (iii) To shut out river floods entering the canal.

(2)

----1Tt&k]

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------

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i

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:~~§~

~

S'_f.JFf':O tJ£Nfl. DESN:N , " " Wlot. flANGE IN /IPS'f11EAM

Fig. 9.

wmR!nn

JOI

r t

I

Fish ladder long Trimmu Weir Wall under construction Fig. lOla). I

j

A view of the fish ladder long t he right divi,:e wall Trimmu Weir Fig. lO(b).

10'2

Upper Chanab Canal Head Regulator as remodelled in 1937

Canal Head Regulator Downstream view.

The water-way 'Of the head regulator is fixed so that the full snpIJly dio>charg-e 01 th~ 2anal couIc! easily pas3 over the crest of th~ heitd regulator with th'~ d_;signed pond levd, with lmple· factor of safety, to allow for any silting up of the canal. The regulation is arranged Inprovicing gates son-:e times in two set~, O:1e r·sing on the other dropping. as shown in Fig n is in the case of the Sirhind Canal '-egulator and Upper ChaCla-) ('anal hC:ld regulator ifI rig. 12 a) and 12 (b).

5JlfHINO CANAL RECiUl.ATOFt.

In tllf~ cas;; of old Head regub. )rs, th~ spans were small usually 5 to 7 feet, by providing dummy piers dividing U e sp"n of the downstream bridge. tecause the gate liWng arrange· ments ~ere crude in the form of travelli" win'h mounted or, rails. 1 h(> original Sir hind. canal head rfgulator har! 39 spans 01 5 f '( t each. In the modern canal head regulators, the modern arrangement of radial arm gate, [ift<,d by the rack ane{ pinion .ATfS CLOSED GATlJ 0l'£1f methJd has reduced the numeeT Fig. 11 of the head regulator bays the spans of 20 to 2S f. et are now quite common. A s :;ction of the canal head regulatO! aking off at Haveli is given b:~low in Fig. 13. t

~fCTJON THROUGH HAVlLI CANAL HEAD RE.:

1-'-. - •• --~.-- •• -.,.."

. ...

"1 (

.........

". ,

.

i- ,·4-4 4 ,;..L..:...I Fi~.

la

The silt control in the head regulator l(esign is provided by ha.ving a suitable raiSe(1 :rest. In the Sirhind Canal a crest wall of 7'0 feet height was put in dU3 to a serious troulile in he Canal. A rennanent high crest shall need a high pond level to feed it in winter with higtJ osses from th\) pond and it is, therefore, lIsual to provide a rising cill g ,te as shown in Fig. 11. The head regulators at Khanki and Panjnad have teen provided with silt excluders in ront of them in the pocket. A separate Chapt~r.No. XI of this part. has been devated to the iesign of silt excluders and silt ejectors. As tIle riwr conditions in the pccket are usually ver~' nuch di'>turbed, the silt excluders in front of t~le head regulators in the pocket have not proved ;0 efficient as a silt ejector ruilt in the canal WIth steady flow af-Jout a thousand Ieet downstream )f tht head regUlator as in the case of the Haveti Canat: III the case of the maximnm floods, tbe head regulator of a canal is to be completely :losed lest heavily silt-laden water of the river silts up the canal. There are now daily silt )~servations being carried nearly at all head'tlorks measuring the sil.t content of water passing nto the canal and that of water escaped under the sluice-gate. 'VVhen the percentage of silt ;harge in water entering the canal exceeds a C6rtain figure fixed in ea(:h case, the canal is closed

l04 WATER fJlt£$SlIRl OfAeRAM5.

IIfllOtlt:

.;;

Fig. 14

This function of the canal head regulator has a very important effect • on its des;gn. In maximum floods, the worst hydraulic conditions are created. Hydraulic head causing flow under the regulator is of the order of 25 to 30 feet with the canal closed which may be about dou.Jle the head for which the weir floor is Such a high head shall designed. require a very IOil~ impervious floor with the modern introduction of sheet pil's, and excessive floor thickness. The gravity sections will ce impossible and even the invertetl arch or reinforced concrete sections will te wry expensive. Tbe economica solution of this trou'Jle in the cas:o of large rivers would be to make the whole floor of the pocket impervious by providing a water-tight concrete of say a'...:out 1'5 to 2'0- feet depth ensuring that the joint of this floor \\ ith the crest of the Canal head regulator is abso~utely \vater tight. Such a floor is required when it is desired to provide a silt excluder and shall also lessen the cost of the undersluice aprons,

The stability of the head regulator piers should be tested to withstand the overturning momenis caused by the high pressure head in floods, The designs of the crest wall of head regulator, the gates and the dreast wall will he worked out for the water pressure diagrams shown in Fig. 14.

It is now usual to provide a solid masonary crest wall and a brellst wall in reinforced concrete The horizental arched breast walts ar,; now o:)solete. The reinforced, concrete breast wall can also te reinforced at its bottom to act as a beam to support its own weignt of the gate lifting arrangements instead of providing additional as'in the case of old hearl regulators. Tce layout of the head regulator is usually at right angles to the tndersluices, parallel to the divide groyne wall. Sometimes oblique entry i.nto the can II is considered desire able and the head regulator is splayed out 1 in 4 from the uncle rsluice, taking OJ the canal at right angl;}s to the splay. This has hen tried at Sulemanki, This will provide additional still-pond \\ etC'r-way in the pocket and sllall also insure relatively ~mooth ently into tl:e canal. There is no mpirical formula to determine the length of the Talus dONnstr2a'11 of the head regulator. It wouH ce ample to provide a Talu~ equal to 4 to 5 times the de?th of cam.! ani 2 to 3 feet thick in concrete blocks of stones of 110re than one foot diameter.

i3. Silt control at Head Works. There are three n ethods of reguLttioll ll'iually acloptc(', at the canal hcadworb to control the silt entry into He canal. (a) Still Pond System.

In this system the river water in excess of the cd!lal requirements is not allowod to escap; under the sluice gates. Only the supply required for the canal enters the pocket. Thl~ . velocity of water in the pocket is very much redUCer{ on account of its excessiv'J \\'ater-way. The

105

silt deposits in the pocket and clear water enters tho canal. This syste'1l presupposes that , the canal regulator is provided with a hi.gh crest wall as shown in Fig. 7. Wilen the silt in the pocket has accu:nulated to say beioN 24 hours a_1d the stui~e gates are o;->ele1 to sc)ur out the silt deposits in the pocket. This process is rcpeated when egain the silt accumulates in the pocket. (b) To take supply from the curved river ap~roaeh cJ.ennel.

In this system, the undersluices remain closed and the river is allowed to develope a approach channel by e3caping su??ly i.l e:'{ceS3 of c:nal re'i.uir~m,ts over the weir by opemng shuttered portion or by co Istructing an)ther set of Ul ierslu!ce, in the midJI~ of the weir as at Khanki. The wat~r is the:1 taken fro11 the outside of th3 curve wh~n t:le chann~l section is deep as shown in Fig 11 Part l[ C Ul)ter II 1. Then i, cross flO'N of silt in. a channel sectIOn on a curve which re~ults in bw silt charg" on the outside of a curve as co:npared with that on the inside. After thus selecting relatively clear water froen th~ river channel. this system can be cem'Jined with the still pond m~thod for further silt selection in the pocket itself,

curv~d

(c) To usc under SlUice Gates to escape ex~ess river Suppl~.

In this system, the river supply in excess ef the canal requirem:mts is escaped under the sluice gates. In this system reliance i., placed on the fact that the coarse silt shalf conce~­ trate near the po~ket floor and it can safe~y be escaped below the gates. This system though ~t looks sound in theory is very treacherous on account of the uncertain approach chann21 ~ondl­ tions in the river. When this system is used, there mUst be provided a fairly high crest of head regulator with suitable desigh, Even then the daily silt obServations mUst be teken to find out the silt content of water entering the canal. When it exceeds a certain figllre for the particular canal, ;t should be closed and tne pocket cl~ared. The still pond system has ceen very successfull at Rupar and Marala. This is by far the most effie ient form of regulation far canal head works which are not )rovided with silt excluders with the only def"ct that the water has to be wasted in scouring the pocket for aboul a day in a month. 14,

Guide Ba.nks & Marginal Bln1s.

The chief idea intlle design of these works is to concentrate the river into a narrO\" channel by a pair of long guidd banks. It is claimed for this arrangement that is not only iuduces a clear and direct flow to the weir but it also greatly reduces the nUll'Jer of spurs needed along the margmal bunds. Being forced into one restricted c':lann~l, the river...-has no room to swing abont, and there is no possioility ·of cross flow just upstream of the weir:' 1£ the river does swing a"Jout, it must be a )OV2 the entrance to the guid~ ba 1ks w:1ic~1 is SO far from the weir that little or no harm can occur do the protective works behind the guide banks at the weir itself, The fullowing points should be kept in view in the design and layout of the guide t anks:-

(i) The choice bet\veen parallelism convergence and diverg3nce must be dictatd bv the concition of the ted of the river,_tor constrction purposes, during the working jieason, For it is better, if possible, not to be oJliged to lay the apron in deep water. (ii) But, if practicable, it is Letter that the guide banks should approach each other r.ear their udpEf'cnds, tefore their uppe: curves begin. The urnount of construction may be say, anything up to dou·)le the CO:1l )inej thic~me,s of the bridge piers helow low water. (iii) The length of the upstream part of the guide banks may be made equal to, et say upto to a tenth longer than, the bridge. But attenti))1 should be paid to the possi0ility of the river tending round above one guide bank into the still water area at the back of it, and eroding the main approach bank. In specially wide Khadirs this may involve the me of very long guice banks.

_--

--

_ --'. ...

;;. i

"

Fig. 15,

107

(iv) The lenf th of the downstream part of a gUIde may be a tength to a fifth of the length of the bridge, ~ccordin~ to the jugdment that. may be formed as to the ~ctivity of. the swirl or disturbance lIkely to te caused l y tbe splaymg out of the water on leavmg the hndge, for the swirl, if there is one-must be kept sufficiently far away so as not to endanger tnc approach bank .. (v) The radius of the curve of the downstream end of the guide bank may be such as the material trains can run on, say 200 to 600 feet; because it is convenient to take ttc stone service line by this route. (vi) The radius ef the upstre~ 11 CUlVeo part of the guide .bar,k maybe

any thing from

SOO to 101_0 fe3t, according to the estImate of the PrJ >a )le v J )Clty of the current past it. curve should be carried well round to the back fully 1200 to 140°.

fhe

Free board for guide ba.'1k should be 3'0 f3et to allow fuV afflux head above the highest flood leVel. The thickness of the sto_1e in slop~s and aprom should b~ as given in the last chapter paragraph 17. In the case of the Sulemanki head works the guide banks curve inwards forming bottle neck, the width l:etween the noses being 1600 fe:~t compared with 2223 feet between the weir aimtments. The 0 \j~ct was to induce central flow b floods and to prevent the formation of shoals. This 0 )ject has not been attained, because the island formation on this heabworks is as acute as on the others, but on the other hand, this has resulted in a strong flow in floods round the guide wall towards the unriersluices with the likely effect of damaging the ted protectIon upstream in the pocket. The marginal bunds with the protective spurs are required at all heads in addition to the guide banks. A typical layout is shown in Fig 15 as used in the case of Sulemanki weir. The underlying idea in the design of these works is that firstly, a partially controlled and restricted flood by the marginal bunds or retired eml>ankments should approach the river section between the guide banks, and secondly, they should 1?rotect the country upstream of the weir from river spills due to afflux caus~d by the construchc~ of. the weir. The design and layout of such pfJtection works has already reen dealt WIth m Chapter III. The free board is kept on similar considerations as for the guide banks.

]5.

Movable Weir Crests or Shutters : (a) Objeet:·-

The object of placing a movable crest on tht pmnanent crest of a weir is ·to secure the maximum fair weather supply level required for the canal, and the maximum high-ftoodslevel, so as to lessen flooding, the height of flood .embankments and the danger outflanking. When these two level; .:orrespond, the greatest eillclency of movable crest is oDtained. Another advantage of a movable crest is that it lessens the silting up of the backwattr pool, which if it occur, excessively, may interfere with the supply to the canal. Movable FlASIIlIIIA_ crests are~ ho.wevEr, very t:xpensive. ItfVAYIOH nCTIOH and may I e d~ffcul~ to. work; as their . c~st and J?1amp~latlOn mcrease greatly -:WIth theIr heIght. It is generally advisaUe to make nem low, and to depend upon the solid weir to olltain the I alance of the elevation necessary. Movable crests may following categories:-

l.,..... ., •• t.""

(b) Flash Boards.

,... Fig. 16.

te divided .into

lU

They are usually of wo;,d as shown Fig. 16.

lOR

The ordinary flash board is suitahle for all cases where the head held up does not ,5 feet, although, if. the h',ight is more ollan 4 fe~t s1lUtters will prolJa' )ly be more efficic:>:t. This tYfJe is simple in construction anrl can be used in all cases. Even although boulclers may damage the flash, boards and tlJeir spports, th'se are ch~ap and can be easily replaced. Flash' boards are, hO\\ever, di:ficult to repltce until the water has fallen to the leve of their [Jase, and are therefcrc best ada pte 1 to high (;ams or esc-are v,·cirs over which the water flows" but rarely.

excee~

(c) Hinged Shu,tters.

Th shutters are iron gatts hinged :1t tLe rase ?n th~ weir crest. The hing~ ing or otJ-:er guiding arrangerr,ent ~t tl~e base of the shutters IS a .dlsadvantge, i eeause many stoT}es of first siz~, or great~r, c rned b~ ~ost of t'le stream" are ha)b to lodge in the spaces' ., in which the hinges and gUlde or spportmg rods, work. HING£D SHU-rTERS SfCTION

lLlVATION

!;."-'!.•..e'!..!~!..!~'.!:

•

__-

f~!.~_I:~:..L

..,tv

fW ./.'" 'AfIII

,

I,,, '''ON

." wtQ' • ., •• "TO'"

Fig. 17 shows a typical shutter used in lncia, wh:ch is dro ?ped Iy releas:ng the curved honzental lever. Ttc raising of the shutter is erected by a hand crane which hooks on to the smaller (hanging)' loop on' the upstream face of the shutter Trained men can raise and set these shutter wite ease,S, 6 or even 7 feet of water, provided that the backwater below the' dams is not so high as to interfere with the workieg of the crane.

The dropping of these shuters is perf, ctly easy, provided that they are not over-topped. If once over-topped, it is almost impossitl~ to get them down> Fig. 17. although this has been effected with some risk When the river did not rise rapidly after over-topping the shutters. If the shutters are over-topped. and tl~e rise of the water continues> the dam will probably re d~stroyt d, not so much by the impact of the water falHpg over the shutters~ as by cross-currents mduced alo;lg the dam from the portion where the shutters are up, towards that wtere they are down. " . (d) Automatically Droppin5 Se~tt,ers.

.

~

OIA I H _

,I.tt

, '" ~; lilA, ","

They are hinged Type Shutters up to 5 or 6 ft, height. As a rule the oesign. consis--" ts of a projecting bevelled arm which is forced by tbe fall of one shutter and pulls out the key and sets the next one free. The arrangement is shown in Fig. 18 They are raised by men with about 2 to 3 ft. depth of water, or raised by using traveling crane on the crest or from boats. The shock produced by thc simultaneous fall of a long line of shutters is a seJvere trial for a \veir. :;

~ig.

l8..

.. , :~

IIJ~

, HINGED HYDRAULIC SHU'TTE.RS

IfUS.~.

(e)

Hinged Hydraulic Shutter'.

An expensive but reliable {OIllJ of hinged shutter (Fig 19) is worked tJy mears of a hyciraul:c ram, of \~hich the plunger has a niller at its top J earing against . tht shutter, and is actuated t.y ~ ater under hydraulic pressure conveyed in a pipe in a water-tight tunnel formed he low, the weir crest. The shutter can thus be raisell or lowerc d when drsired, and is under complete control; it can 'r:e made so as to st0re up to 8 feet in depth. (/) Trestle Weir Crests.

1--.- ,:.-.__, Fig 19. This form is of. I,'rench ongm. a.oJd has l een made to store as much as 20 feet in de pth :mt a)() CIt o:le-lalf of this IS a usual limit. The trestle; (Fig, 20) are made of iran and are built up as lattices; they arc hinged at the base to the we:r crest, to WEIR Clf66T rUST/I.E ~vhich they are normal, and are preferably spaced apart at a distance equal to th depth ; 'of water they store, so thac they no not ovcrlal) each other when lying flat on the cr .st. When 'fl1ey have to be fn:cted they are hauled up by tackle, and then net-dIes are plaCfd ,against them; the lenght and onscquent weight of these determi:C1e the height of the trestle. Long needles .ma\' have to 'be Uted bv machinerv ; their section and thus their w~ight, can· be re,luced uy supporting them by removable walls hung ,on chains between the trestle.s. Some higt, trestles have wooden needLs 2 to 3 feet wide stiffened by steel angle irons; and are worked by machinary. Som ;ti TICS the trestles supports horizontal shutters, a'ld then, on aCCOll11t of the weight of these and th a'1lOnnt of water pr~ssur" on them, tb· trestles l:ave to 1e spaced cbscr. Thi~ form has not i een used in In(lia. 1t is adapted to the case 'Where there is a consice~a ble depth of \yater in the rivN " downstream. "Fif; 20 (g) Mac'1anical Weir ShuttH3. " In America a favuorite type 'vi machanical weir is th 'Bear Trap" of which t) ere are seyeral" varieties. In its simp1 5t "'tA It TItA ,. IfI!EI1f . from this consists (Fig. 21) of two Ieawr" pivoted at t]-,e base and working in a closed cham"er; thes:. when raised for sCClri1g storag", make '1 triangle \\ith the weir crest. To rai.se thG leaves, water is admitted 'under the dovvnstream one which is thus lifted and carries the upstream leaf with it; to lovver 'them a downstream valve in' the chamb~r is o'Jcnecl and as the water level decreases, the leaves fan and lie flat in a recess on Fig,21. "

the ted. As the upstream leaf has no upward pressure on it, it is sometimes made in two parts with a loose' idler" covering the upper one to keep out floating debris; in other forms the upstream leaf is joined. Forllerly the leaves wer~ made of w"od, 'out recently they have l~een built up of iron plates and fram<'s in length up to 70 to 80 feet, and are braced to secure :igidy. One objection to this design is its cost, at the total cross-sectional length of the shutters 1<; about three times the storage depth; another is that there may not enough natural head available to raise the trap-artificial pressure is then supplIed to overcome this deffect. But traps have however teen successfull in use for many years and have not given trou·Jle. _ _ _.....-F5~AT

~ W~C.H

GATE.D WlE..R5

16. Gated Weirs. (a) Gates moving vertically in grooves. These Weir Gates are usually made of wood for small spans say 10 - 12 ft. or these are fa'lricated from steel for large spans, and raised or lowered by means of winch or a 1 ravelling cranes. Tf ese gates usually operate in cast iron grooves embeded in the masonry of the Piers. The general arrangement of this type of gate is shown in fig. 22.

()) Counter-bah need Gate. Th is type of gate consists of a gate hinged at the bottom of the channel and counter-balanced as shown in fig. 23. This typo of arrangement has hen used in the case of Hydro-electric schemes when excess had to be passed over. When the prssU'fe on the upstream side of the gate increases due to increase in the upstream waterlevel, the gate is made to tilt with its fulcrum at the hinge. and it permits excess to pass over when it is automatically back to its normal position by virtue ot the counter-weight. (c) Walton Gate. These are provided with a hinge at the bottom about which the gate revolves as its fulcrum. At the top of the gate a projecting lid about 2 - 3 ft. with a slope usually 1 to 5 is provided. This slope helps in smoothing out the path of the fluid in as much as it prevents presenting a sharp edge. This design has been found to give a high co-efficient of discharge which is about 3'6 as in the Weir formula. These gates are counter-"Jalanced and are operated through a winch fig. 24.

Fig. 2:1.

through the roller

(d) Sluice Gates with Rollers. Fig. 25. In the case of large gates or gates subjected to high fluid pressure, the frictional forces between the gate and the grooves in which it slides. are of sufficiant magnitude to prevent the movement of the gate. In ordeI to facilitate the working of the gates. the rollers are interposed between the groove and the gate in ordeI to avoid sliding friction. The usual method is to mount the roller on the gate by means of a rolle bm. and the roller rotates through a pin which passe~

bO_li.

Ie) Stoney's Arrangement When, however, the pressure is very considerable due to" great head d water or the exceptional dimensions of the opening. anot~er arrangemen~, viz:, thal of free rollers, is made use of. These rollers run on axles, but there IS no pressure mduced 01 the laHar: the axles are only used to keep the rollers at the proper distance apart, and are fiKec

111 n a frame. This roller cradle is suspenied in t'l:l grrJ:)ve un'\ttac"t~d to the gate. As the side of the gate bears a~ainst the rollers, wh~n the former h moved, the r.)ll ~rs r ~vovle and the whole frame of rollers rises and falls with the gate. The friction induc ~d is pur,~ roller frict,on. which" between smooth surfac~~, is so nettling very snlll in be 1. s} m,e'} S1 t ut iti c~-e licient can be entirely ignored, the lifting pON~r b~ing only t'le weig'lt of the gate plus the friction of the lifting apparatus. Again unlier sui~a,)le conditioll3, the gate can 'oe cO~lbrp:)ised by ",eights hanging from overhead pulleys. and in such cases gates of the larg:!st size can be manipulated bp o.ae man. These free rollers are termed "StoneYs Patent Antifnction Rollers".

1.;f~.~..." Fig. 25.

Fig,24.

The dirgram Fig. 26 represents a sluice gate fitbd with. free rollers ill sectional phIt allti elevation. It will 'te seen that the fro me of the gate on plan ju:;t clears the sluice wall. and proj~cts beyond the greove. Thes~ spac;s are cla~ed hy staunching rods. These are simple round rods of about 2 inches diameter, which are fast~ned to the gate, but have l.. teral play. so that when the gate is under pressure thes;: are hrced into the COLler, e:fectually closing the

•

, '~. ItDLLOf ~'"

(.

RADIAL ARM GATt'

.... .... .................

~.aou

. "..

'_.A • • AIIt ...

~7_."

(.«tt

....

en•• , i (

J

Fig. 27. aperture. On the gate being raised they are carried p with it. still bearing agaiFlo:;t the side of the gate ; nd the sluice wall, the friction thus iuduced is, IO'h"Cver, quite trifling. Owing to the susperrding J ulleys the roller frame moves haU as fast as the gate,

1

Fig. 26.

rrz ~;"

~a'

.' ff)

Radiai

Ar~ Gaff s.

This type of gat~ is illustrated m fig. 27, and IS hinged at 3I It is rai.sed Of l.)wered by mBans of a winch, and where the un;tler-shot method of regulation is. desired. This,

Ie pomt as s!town in the drawing.

this arrangemeat is. used

Fig. 2S'r

type. of gat-e', therefore; finds general applintio-;:} in the regulation of Hydro·electric channeh. The usual devices to reduce friction against be end of the g ltes usually fail due to rusting

\1f5CA.,."

W'IiIt:N orr nSf

111'\1'1'(,:"""""

4r:T'ACN4.

or de}}ris eatching im the hll1t rs. The modern practiee is to· provi(e Ranial Arm Gates. In tl:e case oi can'aI regulators, the gate is used behind the opening. It has 110 side grooves or roller bearing Lut . is· pivoted above downstrea.m wa.it r level as shown in fig. 27.

17. ".

"4,

G~te'

Lifting Arrangements,

(a) Screw Gear. A simple arrangement of screw gear is shown in fil!. 28. This arrangements is· used for lifting small gates with small hfts. The gate is sllspended from a rod which is screvved at its U'pper end, and is raised or lowered by means of. a nut to which is attached a: handle or a hand- .vheel. The s~rew is raised or lowered bv rotation of the hand-wneel 01' the handle. " (b) Ec:reW Wh'eh. The usual winch used fm lifTlrii-minor and distri;:,utary gates is sketched in Fig. 29. In this the power is applied to the male screw, which can be. quite short, a little over the lift in length. As sho\\ n in the illustration. the thrust collar and plates are situated at the rod head and consist of three plates. the upper, the distance plate. and the base plate. The screw is threaded through .th ~ base plate, while the u1?per plates are superimposed. ann the who]!'

Fig. 29.

113 jolted Ie of

througb as s'hown on plan (Fig. 51: The upoer a.nil lower plates snoulli brass, the middle distallce plHe, W;llC\ is su jeet to· no strain of friction. lx:ing of iron. ,The solid screw rod paises into a pipe in fhe head d which is be female scre\v. This shoull 1e of htass' and in some ca"es, the whole dpe is ma<'e of ,brass but t:lis seellS a needless e:dravaga'1ce. Th'~ pipe hear! is held rigid ')'Y t" 0 arms running in guide 51 .is cut in the frame of tile stanr!ard. Thus tLe, tor.,iona Is tr, ss is at on, e absoy', lcd and the position of the ends o'f e,e arms ono r.f which can "c ma('e ~o pr0j.~ct . eyo.ld the frame, inr'iraterl Iv I]'cans of a pointer ('n a graduate,l scale, showing t~,e e~ act height at' "vI ic 'j t.e gate stands' a~:ove its sill Tre pile is rigi
...

(c) Travellers. In some canals tho gates are not fitterl with Ii fting arrangemement individually, ',ut t::e regulator is proviLed with a traveller wmen, which Fig. 30. __-----------------------

RACK-::=-~----~-~.< f; PINiOH ,.c"RHANGE.ME.NT '.'---=-=-:e~ ;;;;r

UPSTREAJ'.1

Fig.3J.

114 win~ consist;;; of a win,~h fitted over a trolley, moving on rails ov~r the regulation gates, and this trolley is brought over the gate to be operated upon. The winch consists of a simple reduction gear and a drum carrying a chain or wire rope for raising or lowering the gates.

is use'd for raising or lowering- the gates when necessary. This traveIIing

(d) Gear ~inch. In the case 01 large a.nd heavy regulation gates, it is desireableto provide each gate with its own lifting arrangemer. t. In this case the gate is suspended from rope-drums, winch, in turn, are operated through a series of reductIon gears as showf in fig. 30. •

,e) Rack and PiIlioD Atrangement. This arrangement is illustrated in Fig. 31, and in generally used for DislfJ butary Head R€guJator Gat~s The lifting arrangement coes~!s of a worm and worm wheel reduction gear, to which is attached a pinion which works against a rack attaehed to the gate. The rotation of the handle causes th pinion to rotate. and these raise or IoweI' the gate depending on tho directi()D of rotation of the handle.

PARTU

CANAL IRRIGATION Chapter V

DESIGN, OF: WEIRS ON PERMEABLE FOUNDATIONS 1.. Introluctory.

Practically all the big canals of Northern India take off from rivers after they have left the hills. Rocky foundations are not available for the weirs constructed across them to pond up supplies for the canals. The weirs are usually of small height, 10 to 15 feet (as distinguished from the dams) and are constructed in the permeable river-ced. The irrigation engineering in India occupies a very conspicuous and poineer possition in the experience of the design and construction of such works. The science of the designs of weirs on permeable foundations have developed by leaps and bounds in India as the student will find in the subsequent paragraphs in this chapter. :!.

Development of the Theory of Design.

(a) The law of flow of water through permeable soils was enunciated for the first time in 1856 by H. Darcy who, as a result of experiments, found that the velocity of flow· varied directly as the head and inversely as the length of the path of flow. [his law is expressed hy the equation. . .

H v=kL Where v= Velocity; H=Head L=Length of the path of flow k=A constant called the "transmission constant". :Darcy's law is of the same form as the law for the movement of water in capillaries eIlunciated by Poiseuille in 1841-42. . The validity of this law in relation to weir design was tested by Col: Clibborn in 1896 in c<'Imection with the proposals for repairs to the damage of Khanki weir on the Chenab ri ver in 1895. This weir which feeds the Lower Chenab lanaI, was completed in February 1892, In January 1895, 100 ft. of the weir crest in Bay No; 1 subsided by about 2 it. This was the first major weir to be construc,ed ~n the alluvial ted of a Punjab river, aJ?-d this damages occurring so soon after the constructIOn, gave food for thought to the engmeers respensiule for its construction and maintenance. But this inve,tigation, though affording the fist rational basis for design, embracing as it did the conception of failure by undermining and by uplift " due to the flow of water through the sub-soil (of the weir, did not matenally add to the knowledge for the p~rposes .of pr
(b) Hydraulic gradient tht ory. .

TheIiydraulic Gradient Theory for Weir Design, apparently orginatod between Sir John Ottley and Thomas Higham and was developed as a result of experiments by Col. Glibborn \1895-97). • . .

116

With the pu'Jlication of the results of Col. Glibborn's experiments in 1902, the Hydraulic Gradient Theory came to be generally accept ~rl in India. The following passage from Buckley's Book "Irrigation Works Tn India" (1905) Page 175 will bear te:;timny to this: "rt has been mai1Jtained that, in those cases where th-o chief danger to a weir is from under scour and not from parallel currents, the true measure of security of a weir in a per:ne'able hed is the distance through the soil which a current of wat'or would have to travel before it could rise up below the weir, and that it is of little conse1uence whether masonry is laid horizontallY on the weir be,l or sunk vertically helow it, so long as the curre::J.ts passing thlOUgh the soil below the structllre are exposod to the friction of the same length of passage. This view appears to be sound, but it is ess~ntial to attach to the application of this principle, the condition that the weir must be protected from horizontal scour on the face of the toe, that it : must have sUTIcient weight to resi~t the horizontal pressure of the head it supports, and also 'sufficient weight to oppose the up'Nard pressure in the base of the foundations which that head may produce and, fui-ther, that the surface of it which is exposed tJ erosion should be of material sufficiently hard, and sufficiently heavy to resist that erosion."

(c)

Creap Theory of Bligh.

In 1910, W. G. Bligh enunciated his creep theory in his book "Practical Design of Irrigation Works" and elucidated further in his book "Dams and Weirs" 1918 He did no ~xperimental works, out aTlalysed tIle failure of the Narora and the da'llage to the Khanki weirs. According to this theory, the cr~ap was marc important and destructive to undermine a weir than' th~ percolation through the soil b~low it. The tnginneer:; haVing the experience of closing hreaches must have felt the truth of the statement when they find that it is most difficult Or rather impossible to close a leakage by the side of a log of' wood or . roots in the soil. A oank of a distri~)uting channels, oth~T..vise strong. b~com~s unsafe if out-let walls be constructed right across it and it neej;; a speci3.1 eJort to IT13.kB the joint between soil and masonry effective a.gainst creep. Bligh assu ned t3e percolation wJ.ter to "creep" along the contact of the I)ase profile of the weir with the sub-soil, losing head enroute, proportional to the lentgh of its travel. The length of travel in a weir profile as given in Fig. 1, would be : - I·'

_=_-L_e;;.""u' ./ue,'£Nr ---_

_:

.. ~

,,,,It

"'(a_ULIC "'AD •• 1tIT LI",. --1_

"1I0!t '" .. A ~

L=b1 +d1 +dl +b2+d2+~+b,

m:P' ~.~!

=b1 +2d t +b2 +2d 2 +bs If H=total head over the weir the loss of head per unit length of creep would be :C= __ . _ _ _ _H ____"_~. . b l +2d l +b2+2d2+~ .

'

,ir, "

";

.' 1

Fig. 1.

He called this loss of, head per unit length as Creep Co-e'Iicient· and assigned a safe v~lue of C for different classes of soil. T~us, if in a given weir design, the value of C· were less than the safe value assigned to it for the given class of soil, the design would be conside~ed safe. The following were the values of C recommended Page 155 "Dams & -\Veirs" bY Bligh. Class I: River beds of light silt and sand, of which 60% passes a lOO-mesh sieve, as those of the Nil~ or the Mississippi, percolation factcr C= 18. Class II: Fine micaceous sand of which 80 per cent of the grains pass a 75-mesh sieve, as in the Himalayan rivers and the Colorado; C=15. Class III.

Coarse-grained sands, as in the Central and South India; C= 12.

Class TV : Bonlders or shingle and gravel mixed with sand; C varies 9to5. ,

117

Because of its simplicity this theory found general acceptance Some works desjgned 011 this theory failed whil() othe_rs· stood, dependi!lg nn the extent to. which the then engineers ignored or took note of the Importance of vertIcal cut-offs at the upstream and downstream ends. ld) Electricity Flow Analogy.

Pavlovsky (1920) approached the problem of the flow of water through sub-soils of hydraulic structures from the analogy of flow of ebctricty th[.)u~h a conriuctor, According to. Ohm's law: --Potential difference E A E Current C=--=B --. ReSIstance L' p .L --0·----

- _ . . __ .-

Where E=Potential difference A=Area of section of conductor L=Length of conductor.

",!

and p=Specific Resistance of the material of the conductor. Darcy's equation for flow of water through sand viz:

This

IS

itlentical'-

H

v=k-L The work was pUJEshed in Russian. Pav]ov,;ky ac1lieved success in solving a number of proble:n:>, :'ut as the laJoratory csults could not be shown to agree with the field results, this m ?thod d d not i 1'l?ire C).1 i. I :nce a 'uClng the engineers and remained more or less of academic interest. The remits 0 )tained on the Panjnad mod:l in conjunction with tht' researches of Dr. Vaidhianat:1an onthe electric models have shown ~onclusively in Vol. No.4 Irri~ation R~search Institute, Lahore, for the first time in the history of research on the subject that :--

(i) The distribution of pressures und~r works on sand reproduced on hydraulic or electric models.

foundations caD be exac Uy

Iii) All seasonal and other variations from the normal conditions can be reproduced on Hydraulic models by superimposition of silt, temperature, or hoth, and by simulating the stratification. (iii) The pro~)lem is suscepti )b of ~athematical treatment. The conclusive proof about the reliajility of model and mathematical results in applicatio:l to field ccndition; marks a gre it advance and de:luite lancl-:nark i.'1 the development of this branch of engi:1eering which has led to a final solution of the pro;)bm of design of: weirs' 0:1 permeable foundations.

(e) Khosla's Investigation in the Punjab In 1926-27 trou-)le at the syp!1ons under the Upper Chenab Canal (Fuuja~)) became acute. Cracks app~ar~d at the u?stream and downstream ends due to, the undermining of thj;, sutJ-soil. Repairs wer~ carried out on the acce?ted Bligh theory, but the trou_!le persisted. A set of pressure pipes with. weH points were inserted in the floors of th.:se syphons and th~ observations disclosed that the· pressures indicated by these pipes had a':lsolutely no rela tionship with those calculated from the BI gil Tleory. The3e re3earches were ca.rried out by Khosla and are embodied in the Punjlb E:lgineering Congress Papers Nos. 13~ and 142 of 1930. The simple creep theory of Bligll was repudiated aild some provisional and important conclusions. were arrived at, nataLIe among which were :-.

(i) The outer faces of the end sheet piles were much more effective than the inner ones and the horizontal length of the floor. (ii) The intermediate piles if smaller in length tha,n the· outer ones were int!ffective except for local redistribution of pressures. .

11S

(iii) Undermining of the floors started from the tail-end. If the hydraulic gradient at exit was more than the critical gradient for the particular sub-soil, purticles would move with the flow ot water thus caus'ng progressive degradation of the su'o-soil, resulting in cavities and ultimate failure. (iv) It was absolutely essential to have a downstream end to prevent undermining.

r~asona()le

deep vertical cut-off at

the

(v) There was an urgent nece,sity for research work in the la')oratory with regard to pressures under th.e existing and the new structures. The former could Ice done by ins~rting suitable located pressure pipes in these structures and by maintaining a continuous and comprehensive record of the observations of pressur~s form those pipes. In 1929, it was decided to extend the Panjnad Weir \Punjah). This afforded the opportuJjity of putting in a comprehensive set of pressure pipes and of conducting full sca~e experiments as suggested in the Punjab Engineering Congress Papers 138 and 142 of 1930. ThIS was the first full-size e~p;>riment in the world, and the results o:)tained from it (1932) paved the way the finC'll solution of the pro5lem. The main conclusions of 1921-29 derived from reseaches at the Upper Chenab Syphons were confirmed and the following facts were established ;-(i) The flow of water through the sub-soil is in stream lines and therefore susceptible of mathematical treatment. (ii) The ratio (Q) of uplift prefsure (P), at any point along the base of a particular weir founded 'on premeable soil to the total head (H) is constant and independent of: . (1) Head (H)

(2) Class of sub-soil so long as it is homogeneous. (3) Upstream and downstream water levels. (4). Temperature, provided it is uniform throughout the s,_tb-soil; but it vades (i) Silt deposit or scour upstream or downstream of the impervious floor. (ii) Temperature which varies from point to point in the sub-s'}il and in different seasons of the year. (iii) Law of loss under the floor was nearly a straight line and far the shpet piles something like logarithmic. Sir R. P. Hadow suggested that the field results be tested on a scale modle in the Lahore Research Laboratory. It was not tilllatft in 1934 that a model of the Panjnad weir was set up. This investigation was carried out by Dr. Har:0ans Lal U pp:lI following. Hele Shaw method and the findings were presented at the Punjab Engineering Congress in Fe';)ruary, 1935 (Paper No. ISS). The results clearly vindicated the correctness of the field observations made by Kho~la at Panjnad.

I, '/

The results of the field investigations made by R. B., A. N. Khosla, I. S. E .. Punjab, supplemented by the work of Dr. Vaidanathan by electric methods and the work of tracing stream lines by Hele Shaw method by Dr. H. L. Uppal of the Irrigation Research Institute, were merely qualitative. Professor Warren Weaver, Head of the Department of Mathematics at the UniveIsity of Wisconsin and at the time working with the Rockfeller Foundation, developed his mathematical treatment of the flow of water through the permeable sub-soils under dams. Weaver's work, as will be seen later, provided the inspiration for the complete solution of the problem, which has been summarised in this chapter from Central Board of Irrigation, India Publi.cation No. 12.

(f) Weighted Creep Theory. .

~ In September, 1932: La~e analyse~ over 200 dams, all 0v:er the worl~, and evolved his WeIghted Creep Theory, whtch III effect mlght be called the BlIgh Creep 1heory corrected for

JI9

vertical cut-offs and slopping faces. Lan dropped .I weight of three for vertical r:e p and one!> horizontal creep. While this theory was an improvement of the original Bligh Theory, it W 15 ,~mpirical and lacked the background for a rational blSis for desig1.. His m~morandum on the su~ject app3ared later, as Pap~r No. 1919, in the 193; Transactiol1s of the A'11erican Society of Civil Engineers. This pap~r is valuable for the wealth of information aO:o11t the numerolls weirs it deals with. . (g) Exit Gradient Theory. In 1929 a notable contribution came from Kifl Terzaghi (V. S. A. and Vienna). He stated and proved by laboratory txperiments Hat failurC!s occured by undermining, if the hydraulic gradi~nt at exit was in exc~ss of what he called the "tL> atation gradient". This Nas t~e same as the critical gradient enullciated by Khosla, but it was more explicit: in so far that It implied a state of floatation of the soil mass at the to~ of the work if the exit gradient there eXCl~eded th3 limit 1 : 1 a1 which limit the upward force due to th~ flow of' water was almost exactly counter-balanced by the weight of the soil. In 1935 Haigh (Paper No. 182 Punjab Engineering Congress, L:;.hore) and Harza (PapeJ . ~o. 1920 American Society of civil Engineers) independently pr lduced two very useful papers on almcst similar lines. Fundamentals were once again introduced and a definite attempt was made to break away fro',n empiricis~n and to lay a rational basi" for design. They took .!fote oj ·the exit gradiends as a controlling factor in the stability of weirs and discusse~ the distrihut_ion of pressures which could be considered a" safe. Harza got agreement between th<=or~hcal values of uplift pre:isure'i and those o'btained fro~n the electric models for some of the sImple cases dealt with by Weaver in his mathematical sections. (h) Failure by the uplift pressure due to the formation of the jump of the downstrel.tn apron The worst condition for the sub-soil flow occurs when the downstream. bed of the riveJ is dry and water is he lded up to the pond lev 1. This recieved attention oi'51lmost. all th.e investigatox:s as shown above. The failure due to the uplift ptessure also· occurs m m~xlmum floods in the region of the trough of the hydraulic jump form:!d 0:1 the downstrea;m :apro~: Thf shaded area in Fig. 2 shows the amount of uplift pressure which is of the o~er of 10 to 15 feet in the case of large rivers of the Punjab. This causes da:nage in tW0 way;, ;firsHy by rak-

.

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.

I

,

...

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ing out the joints of the masonry floor and th~n lifting the klvlra'lja a1'ld secOl'!.dly" by \lif.ting th~ floor from b.;low the bOttom profile of the Nelt. The damage due to the first metho4 IS usual, but due the second it has never been experienced, because before the full effect'· ,ofl the uplift pressure is felt, when the flood subsides. This factor as influenc:ng the design 'otmVf;em weirs i!idealt with in detail in the author's Publication No.9 (Indian Engineering Odo'oor 19~). (i) The pressure dllIerences due to the river acting as a sin'{. , Yet th~re is anothe~ v~r~ impo!tant fact,or de~~rmining the stability pi a wei~ which ha~ e~caped the ~lOtIce of the various mvestIgators, rh~ flver and seepage. dr.,ins act· as strong smks coll~ctmg the seepage flo~. .The p,:"essure dIfferences causing the flow produce uplift pressure If the oed be cov~red With Imp~rvlOU~ floor and also cause strong floatation gr
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to the highest water level recor?ed in the pipe. (This level has been defined to ~ the Basic Sub-Soil Pressure level in Cha Jter Irf P ..lrt .;) T 1! pr,nsure diJ ~r !nc~ bus r'~c )rl~lIti above the free wate~ hvd i.1 the riv~r be~ is the pre'>sure det~r:mn.i.lg t'1e minilll~rn ttlic~n'J1S of the gravity floor m the fiver bed, and 15 a measure to dete:mme the floatatIOn grariJe:,ts Ttle author o-_)served 200 feet away from the downstream end of the wLir at h.hanki. ~ pressure difference of the order of 3 to 4 feet. Thes~ forces call ~ into play irres ective of the hydrauli~ pressure by pondin~ up water against the weir . rest causing flow undi,r \\eirs and should, therefore, I-e separately determin~d and allowed for in the wdr cesign in river led and the design of the floors and bridges and the meterflumes on the drains. ' 8.

Practical Weir Designs.

(i) Rock fill Weirs.-In the original rock fill weirs of the type at Okhla in fig. 3. (a) there was no curtain wall proj.~cting i..·elow the 'Led_ The stability d the sand foundations is tntirely dependtl.:1t on its weight and effective base h:ngth These weirs were not wat r-ti~ht II.lld in floods the downstr;;am aprons were very much damaged and had to i_e repaired l.very year. Clay puddle lining of the fore apron very soon fLlllo\\ed as in bg. 3 C.) and the top 'Skin of the downstream apron was abo laid in mortar as in fig. 3 (c) to protect the loost! stone frOl1l Leing ripped up in floods. The neccessity of deep curtain walls under the crest and otter point lower down was soon felt and walls wt:re introduced as in }jg. 3 (c) and 3 (d l . Insr;i.e of these improvements th. early type d weirs could not be called rennanent structures, tccaUSe thQ exce&sive leakage. c{Hl.(inued and enormous am"ual repairs \\cre necessary after the flcod$. (ii) PermaDent masonry weirs.-The first attempt with vertical crest and pacca fio(' . downstream was made in the case of the Narora weir. fig. 3 (c). Tl.e downs ream fiOLf ·and the previous apron were soon damaged which pointed out the necessity of an impervious rear' apron and the insuJiciency of the oase length Vertical drop of 13 fe.:t at the crest. waS ·considered to Le excessive causlll~ river action in the downstream talus. Hydrautc gradieI,t theory was then generally accepted. Bligh, analysing the failure of Narora, brought out his creap theory stating that a ·creep gradient of 1 in 15 was necessary. The wtirs which followed were designed accoroing to Bligh:s conception. Tpe su~sequent weirs had sloping downstream aprons "ieh very small drop 7 feet and 6 feet at Rasul and Marala provided in the sloping aprons 1 in 15 in both cases instead of vertical drop. The weirs were provided with shutters, Lut no raised crest. These weirs shown in Fig. 3 (f) and 3 (g) were provided with deep upstream curtain walls tut Loth of them suffered from tne undermining of floor due to insu:ficient Lase length. The apron at Khuki was only 108 feet long, while It should have teen 195 feet, allowing creep coe:ficient of 15. The Marala weir has 3 well lines which are pretty deep but it is doubtful if they are water-tight in between the wells i~ecause this weir has Deen constantly giving trouJle due to ,tIIldermming. Khanki and Rasul Weirs were re ,uilt in 1934 and 1931 respectively. The failure was nearly complete by undermining due to the well lines not hing water tight and no provision of sound end curtain walls for cOlltrolling the graaient. They were hollowed out in -course of time and the collapse came in flood protally due to the uplift pres~ures caused in the trough of the jump. Marala weirs actually did not give way, but in 1930 floods, the • Kh.ranja of the downstream floor was ripped in the region of the hydraulic jump. The pile lines upstream and downstream have now been provided and the ~ctions rebuilt. A beautiful example of Bligh weir is provided by the Ganges weir at Hardwar shown Fig. 3 (i). There are shallow curtain walls both upstream and dowmtream and the gravity doors arc provided according to Bligh's conception. This weir has stood very effi~jently the te,t of time. The unprecedented floods in the Ganges in 1935 left the weir very nearly IlDscanned. III

(iii) HaveU Project Weirs in the Punjab. Two ?f the Sutlej Valley Project weir sections are given in Fig. :3 (i) and 3 (k). The era of sheet plIes started. At sulemanki, there was a clay layer below the weir and it was considered enough to put only one line in the begining. Panjnad weir Fig. 3 (kl shows thr••

125

ery deep sheet pile lines. They were gravlty weirs and in some eases top KhaTanj(l, Wilt ;:'placed by lightly reinlorce.d concrete ~laJes to withll~and effectively the hydraulic jump action on tnt Hoor. SutleJ VaHey Project weirs. 4 In Dum,;cr, stood extremely WtlU except the one at Islam which collapsed due to the retrogression of river levels downstream. A comparison of the last Bligh's weir in Fig, 3. (iJ and those which followed as in Fig. 3 (k) J (j) and 3 (1). sbows that tte introduction 01 deep shH~t pile line introduced new factors whieh did not exist in Bligh's weirs. Bligh's weir had shallow curtain walls, 6 to 10 feet ceep, upstream ~ ... d downstream and even the inside corners were filled with concrete. Bligh's cCfap theory could ;;ry well apply to shallow curtain walls. He could never imagine that his successors would put in sheet pile lnes 40' to 60' d~ep. It is grave injustice to say that Bligh's theory had reen repudf' a,tefl, or that his conception had reen proved absolutely '\\rong. Naturally with deep cut-ofts c:reep 'Would re v ry nearly impossible, the loss of head shall have to follow some other law. It b.as already re(>n stated that R. B.. A. N. Khosla, I. S. E., Punjab did the nscessary work in this. direction. His theilfY to calculate pressure is explained later in this chapter. Even now the law of loss under straight floor is very nearly a straight line just like Bligh. and it is only in the case of deep cut-ous that the change has come in. (iv) Khosla's weill.

The Panjnad and the Emerson Barrage Fig. 3 (k) and 3 (1) are eeantiiuI examples ot Khosla's weir's. Emerson Barrage is tho cheapest weir which has so far been constructed. in India. Tt is not a gravity weir. Th. floors are of reinforced concrete slabs to resist thp· uplift pressures and are weighed down by the Berrage piers.

Khosla. has brought out clearly the importance of exit gradients which had beeR the great source .f trou ,Ie in the past weirs and hilS supplied the engineering world with a correct ~ethod of calculating the uplift pre&Surilli with d~ep cu.t-olb, and of deslgning weii' floor~ conomlcally.

e 4. Math,metl. te .etermine uplift prMSures.

A very mnch abridged summary of the formule is taken from Chapter VII, Central Board of rrrigation, India, pu~lication No. 12 by R. B., A. N. Khosla, 1. S. E., Dr. N. K Bose. Ph. D. and Dr. E. Mckenzie Taylor, O. B E. B. D. Sc. The student should refer to the original book for the detailed knowlerlge of the sU'Jj'ct and the proof.; of the formulae stated het.in. It is generally known that the stream lines of flow under a floor AB as given in Fig. 4 art' confocal ellip,es with the centre at O. ~b6 middle of the floor AB (=b) the major Fig. 4. axis and with foci at A and B. One of tt:e stream lines will be AB, which is the limiting form of this family of elli~es.

The ellipses are given by the equation X2

-(-~-c-O~Sh~U ..hen

11

r-- + ( ~-

y2

sinh u

r

=1.. .......... (A)

is stream line ftmction.

From this equation any particular stream line Yall1e to u, So that equation (A) will take the form : Xl

yl

A2-+-SI-=1

call

t;e detffcmill~d hy giving _.

II.

iait..b~

126

The stream line along the door AB is given by putting u=O from which cosh u= 1 sinh u=O and equation (A) reduces to y=O, that is the line A B, The line of equal pressure are at nght angles to the lines of flow and are in the above· casE' given by

x2

(~

cos v

r

=1

(B)

where v is the pressure function. From this equation any particular equi-pressure line can be obtained by giving suitable value to v, so that the equation (B) will take the form : .' _!-~ __ AI2

_y2.

=1

Bl2

,\t the upstream end A,

V = 1T,

the total head or pressure,

Substituting this value in (B) we get y=O, or that the full pressure line is AX' which is horizontal and in plane of the floor at the upstream end, The entire head or pressure V=7i' is gndually lost along the direction of flow throug~ the sand medium till it is finally reduced to zero at its exit along BX, The ra:e of loss 19 given by the spacing of the equi-pressure lines shown in Fig. 4, If P is any point in the mediu-n, alld the pressure and stream line functions at this' point are given by u & v, then the relationship (A) and (8) can be expressed as below;

Z= -.!:>_ cosh- 'if)

2 where Z=x+iy and w=u+iv

(C)

The position of a p:>int P in a phle (5ay Z-platl~) is usually denoted by the two i::artesian co-ordinates x and y. It is convenient to denote this numryer pair (x y) by the compound symbol (x+iy) , and this number pair is conveniently called (after Gauss) a complex number. In the fundamental operations of arithmetic the complex number pair (x+i'O) may ')e replaced oy the real numJer x defining i to lnean (O-i'!) we have i2=(0,1) X (0,1)=(-1,0) and so i2 may be replaced by-I. :.

i:l=~l

5u')stitnting these values in te) we get x-Hy= ..~ -cosh (u+iv)

c= ~nquating

~ ~h u

cos

v+i sinh u sin ~

the reals with the reals and the imaginaries with the'imaginaries we get :~ b . hu' cos v. x= z-cos

and

-z-

'h u sm . v y= b sm

(E) (F)

127

or cos v-

x _b2 -cosh ... u

sin v=-,.;--,---,,-Y_-i) • h

-2--sm u

Squaring and adding we get:__X_2_ _~+ ,'f·· y2

cos2v+sin2v=l=

( -}-C9Sh u

r(

+-sinh u

which is the same as (A) Similarly we can get equation (H) as ;-

r

..

'\

x2

cosh 2 u -sinh2 u= 1

( _lJ-cus v )

2

In the case of a si.nple floor the pressure at any point along: it (whete Y'=O) is given by equation (E) by substituting:-

u=o or or orl,

b 2 'cosh 0== 1

x=-cos

".,:";"", . f ' ,_:,~'.,

-,

or as

V

v=eos -1

V='ncP. cP= _I_cos -1 7r

(2x) x

G -

General Form.-If under a floor we introduce a vertical obstruction like a line of sheet

pile or wells, the configuration of stream and pre;sure lines of Fig. (4) will be distorted. it is possible to bring [1ack this distortion to the normal configuration of Fig. (4) a transformation known as Schwarz ChristoHel transformation.

But by means of

The fundamental general equations for pressure distrIbution under th;, foundation profile as sketched in Fig. 5 with the sheet pile at any point under the floor may be summarised as below :.-

Fig. 5,

128

c..... .....,... L

.+. = ty

V

trK

+ O.

,()..coS'Y-l'<~-I_d.. -dl ..."f(ACO'Y~Aa)

d,-.,.

j

Prtl5.r••t E :-

.. =cos

c:09 _ i

(->")1..1_1)

_1

(A~+l)

Preuure at C : -

Pc = ....

L

I,{coo v- A .),-'1 } +;ld,-d,)

F. =H-

m.

'It

fr

,r_are at D :-

PI)

~

=

COl _I

(A~It)

Where J{ =«=05 e i. ghen by taD '-9= .. &

ad )1..,= Lt-Ls 2

. . . . "- 'RIM of ~ aDd L. are given by equatbt.1t~, ~~,~ GE at ,

c= _ip~ (exit) dy

,,-,

L.-~~~"\1 '"

tI

" "

\

, r", '.

•

'-,

y~,

U(_!_), ==_1 d1-d. d,=d.. =d 'I7d

W-: ••all now deal witb particular C'ases 01 this gellttal lorm. , .M ".. _" Iftaift~ ClDDCel'Ded WIth the values of ,the pressures· at the key points, ED and C aa~U,* ,...... .. tIae nt« Ifadients we shall obtain. onJy the values of these quantities. ' . ' CJase 1. Floor with pile line not a:t end Fig. 6. 'this is Wtaver's genetai c~. ' ...... - J , 4' Pt ' _'-(tt L ......" .. __ d

f-.- - - , -----r tI

I

• ••

fi~. 50.

I

/

·129

Pl'essures are;,as below

== _II ~os _1 ('\'C:L) ',. ~ , A

, PE

,r

Pc -

H cos-

(~1_:+-'I)

1

7T

H

_1

P D =- -

({..L)

COS

7t

These values of P E, Pc and Pn.re given in plate II and Table I '. , .

Case 2 ,,' '. . Floor with pile at end ~a'i tn Fl~7. Here dt=d:=d. b 2 =(J il\d Ql-b t

p

E

H=,,,w

cos -

= -.

and PD

( A - -2) "A

',~

c')s

A,

, .

I

I

J., ,0

)

Fig. 7

C·,X) _"_() )(

A=

.,. where

f:-:-

ti

X

W

!\

.

QIL-

(. - -.----

'R _1 '-. cos

,; Pc =

t

.-

A-I,

_1

w,

~.,_,~J, -_,_-.~

...:.-.!!p . ,

•

",

H

A

c

1+v'I+u,2"b - - - - ecause 2

"

'

, > 11 2

=b

2

=0' Values oIr

at

'

~nd PD a:re give~"ln .',

Plate, No. 't'I A. '

Vo~. ~I. .

,i, Exit grapdient at C. H

.)

GEXIT

= ~7\'d .

I

\!.\:

\1alu6s ~f GE are, given in plate No. III Vol. ~

: A=

v' 1+4,2 +1 +v~~~ . -~~-' '2 ---~-- = I,as· !Xl ==a 2 =0

H

I

r":X1T

'::!;:'

lI't<'I

'"

~ ~:~PI: fiOO!,._k~O pile

" . 'h6'pressures along tie ba.Se are glven by _1

P::!!II: ·.Hw---cos

(

2) .

-D~

Exit Gradie1.t ;H _I 8XIT

.:. nI. When the flooris absen:~

--$_f1"wmm&uzwny¥Z1-~"'''.~...:.::;''' ~-' ':,' I '. t.;

l<.'

\.~t ,.

,. r .

J;

-

I I

t

r

Y.

7i'XO x \l A "",x : , Fir. 8 In a simple floor the exit gradient a.t. the immerliate toe is infInity. which as will h

"""

:aplainp-rl in the next paragraph. contians a condition of deiillite inst~bility., 'fhl:! puticles a e toe must mov~. . ..

130

TABLE I' Khosla', Table for Pile at end.

l."

..

d'

'-~---

b

,a

'02 '04 '06 '08

ri't;

'l()

J~-4

')2

21'2

"--/'1140'

22'7 ,24'} 25'3 268

-f& '>1 t+ '2~

,aij'o., 37-0 38'9 40'6 42'2 45'2 47'9 50'4 :;2'7 54'7

27-e

'22 '24

287

-28-

.30~

32-) 336 34-g, 36'0

"&? "&6

-40 -44-

;;';

-4S

37'}

'52

37'!)

56'7 58-5

"liS

:lS'1t 39"tJ

00'1 61'7

40'S

63'2 64:5 65'S ' 66:9

-60

'64' '68-

40'9 .I't; 42'1

"7Z '7r;.

....oo . ~

~

~

'90

:too IJ() 1'2() 1'30 }'4(),

NO<

I-GO<

1'70< 1'8&

19t

Z:OO'

f! .

..__ I'")-r

4-2'0 43'7 446 45'2 45 S 40 0lj 46-7 47'1 47'3 47'7

47'9 4S'): 48"9

6,92 9,56 ..;" 11'34 __ 1'2-S0 ' 14 12 IS'I6 16'12 1697 17'85 18'61 19'27 19'80 20'91 21'S4 "_,-: .. ' 22'63 23'41 24'07 24'71 2S-30 25'81 26-30 26-72 27 1 ,8 27'01 , 28'00 "';" 28'3S.

12'7 17'9 21'S 25-1 28'& 30'S 32'9

8'<]

12'6 Ill:,}

-

"

...

~-....

,.-

6~N

r

70-7 728 74'7 77-1} 79'~

'

'. C'

'

.:

80 .. 81'4 82'S 83'6 84'1

8Ht

30

25 20 18

}6 14 12 11 10 9 8

'5 4

3 ! 1~ I

lilt 1/2 lJ4 \)

,

""'-'

.~~

O'H6 ., .'"

)'000

"

O'31S

.1;,

.1 • • . ,.1..

."

,

;l3'5~

33'90 34'21 ' 34'30

0103 0-109 0116 o 1:!5 0130 , ,.0-136 0'142 O-ISO " " '0'158 0'169 0'182 ~l 0'199 0'225 ---;--0'252 0269 ' 0'289 0800 0309

4 04 3'54 ,305 2'561 2'08 1'62 1'401 1'207 1'125 1'057 1'015

6

,

o {}9~

453

;'

7

"':'

0;063 0'066 0-070 o'07S 0-0807 0-088

2S'545 l3'O06 20'S06 IS-007 15'508 13010 10,S!2 9514 8 SI6 7-518 6-S20 11020 5'S2 503

as

,0'

3000 30'6S 31'21 31'75 32'23 32'70 33')0

7tH

:

2(.r21~

50 45 40

'.

~"

't'",

.. ,-

.'

,-! 4-

,: ;~

.~

..

"

:- -.I

,

','

,', ".4- : .::-1~·; " ~

':

~!.i

13t

TABLE

2

Khosla's Table for pile not at eDel

t/>E

p H

-~xlOO

1 -1 (A A 1)

7t--cos

=100 X u 1-

h,

I

1>1 or base rates b

-b

0

0'1

0'2

0'3

0'4

value of

a 0'1 ()'2 025 1/3 1)5 () 75 1'0 15 2'0 2-5

3'0 4'0 S'O

60 7'0 8'0 9'0 100 11'0 12'0 14'0 160 18-0 20'0 25'0 0

:~O-O

h

b

bl 2 Y : u 2 = 'do- «=--d

3'16

n 22

786 995 14'93 21'90 27 '18 35'80 42'48 47'40 51 22 5698 tH'07 tH' !2 tl6'88 IlS'S4 704S 72'01 73-14 74'37 76'23 7772 ~8'93

8')'00 1'210 :-14'21

282 567 7'10 929 13'74 2000 25'40 33'70 :19'93 4480 48'67 54'37 58'17 61 3( 6365 65'43 1l7'OO 68 12 69-11 69'96 71,38 72'27 73'20 73'84 75'10 757Fl.7

255 5'06 6'31 827 1230 1800 22'81 30'90 36'79 41'50 45'21 5048 54 OS 56'64 5S'&4 ,,000 6!'L; (,ZOO9

2'22 4'45 5'53 7'26 10'8:1 1580 20'08 27'40 3H'29 3760 4' '03 45!86 49'01 51'32 $'292 54'1:1 5541 55'96

1)2'89

56'G()

63'44 6454 65'28 65'86 66'37 (17'()4

57'1(1 58'01 58'64 59'17 59'43 6030 ()()'75

(,7'77

0'5

0'6

1'59 317 398 539 7'82 11'50 1493 20'50 2491 2850 31'32 35'25 37'90 39'77 51 15 42'28 43'04 43'72 44 28 44'76 45'48 46'24 4650 46'83 4746 47 88

1,28 2'.';2 3'17 4'15 6'22 900 11'87 16'H) 20'32 23'50 25'89 2935 31'76 3:HS 34'48 359:l 36'67 37'fl9 37'fI'l 38'3:-1 39'00 :i9'60 39'S4 40'41 4102 41'H

0'7

0'8

0'9

1'0


1'91 3'SI 4'75 6'24 9'37 1370 17'38 24')0

29'18 33'20 36'42 40'74 43'62 45'79 47'11 48'22 49'15 50'13

51H7 :-10'9(' 51'74 52'oS 5300 5:i'14 53'81 iH'2:l

0

0'96 1'87 2-:lS :l II 4'66 6'50 8'92 12'50 1544 1790 19'84 2292 2509 26'76 27'98 28'91, 297ii

:10'::1::1

O'6~l

126 1'58 2'OS :1 11 4'50

5'S7 S'30 10'24 12'20 13'46 158:1 ]7'63 19'06 19'62 21'11 21'88 2257

:H~41

23 '(\l) 2358 24'32 24'92 25';17

33'71 :14'06 :l4'6:l

25'87 26'45 2(1'95

:3{)' 96 :H '43 :12'15 :-1274

0'35 0'63 0'78 0'99 1'56 2'00' 292 4'20 :;'03 6'10

6'85 8'08 9'27 11'09 10'90 1160 12'(10 1Z'74 13'22 13'68 14'37 H'93 15 HI 1588 16-68 17'32

0 I)

() () ()

u 0 0 0 0 ()

0 (I

0 0 0 (I

0 1.\ ()

0 0 tI 0

O. ()

132

TABLE 3 Khoala's Table for pile not at

~nd

Floor with pile not at end

bl

1)

rpD ==

PD ~HX

0

0'1

100=~ ~Ocos-l(~l ) 0'2

0'3

0'5

0'6

0'7

0'8

4998 4992 49'90 49'83 69-62 49'20 4878 47'71 46'83 46-18 45'63 44'93 44'50 44'17 44'11 43'98 4393 43'85 43'79 '3'78 43'72 43'72 43'71 43'66 43'63 43'60

49-97 49'87 49'80 4966 4928 48'38 47'57 45'56 43'89 42'50 41-39 39'98 39'06 38'45 38'07 37'83 37'67 37,61 37'43 37'35 37-21 37'1S 37'11 3707 36'98 36'97

49'96 49'81 49'70 49'50 48'87 47'66 46'39 43-63 41'23 39'30 37'55 35'25 3374 32'93 31'62 31'50 31'14 30'89 3066 30-53 30'23 30'07 2996 29'88 ,2974 29'68

0'9

1'0

value of 90

a 0'1 0'2 0'25 1/3 0'5 0-75 1'0 l'S 2'0 2'5 3'0 4'0 5'0 60 7'0 8'0 9'0 10'0 11'0 120 14'0 10'0 18'0 00,0 25'0 300

0·4

50-08 50'07 50'25 50'32 50'40 5048 50'65 50-83 51-44 51'72 52'94 5370 54'50 55'!l6 58-00 59'20 6099 62'50 63'50 65'18 6546 6729 68-61 71'06 70-87 73'56 72'53 75'47 73'81 77'08 74-68 78'43 75'44 7957 76'01 80'53 76'52 81'33 76'92 82'16 77-25 83'39 7793 84-44 78'22 R5'14 78'40 86'01 78'78 87'43 7902 88'74

50'04 50'19 50'30 50'50 51'13 52'34 53'61 56'37 58'77 60'70 62'44 64'75 66'26 67'07 68'38 6850 6'l86 69'n 69'34 6947 69-77 69'93 70'04 70-12 70'26 70'32

50'03 50'13 50'20 50'34 50'72 51'62 52'43 54'44 56'll 57-50 58'61 6002 60'94 01'55 0193 6217 02,33 62'39 62'57 62'65 62'79 (1!'H;;

62'89 62'93 63'02 6303

50'00 50'02 50'00 50'07 50'00 50'10 50'00 50'17 50'00 50'3S 5000 5080 50'00 5122 50'00 52'29 50'00 53'17 50'00 5382 50'00 54'37 5000 5507 5000 55'50 50'00 5583 50'00 55'89 50'00 5602 50'00 56·07 50'00 56'15 50'00 56'21 50'00 56'22 50'00 56'28 :ill 00 ;;628 50'00 56'29 50'00 56'34 SO'OO 56-37 5)-00 56'40

49'93 49'75 49'60 49'36 48'56 47'06 4550 42'00 39'01 36'50 3454 31'39 29'13 27'47 26'19 25'32 2456 23'99 23'48 23-08 22'15 2207 21'78 21'60 21'22 20'98

49'92 49'68 49'52 49'17 48'28 46'30 44'54 40'80 37-50 34'82 32'71 28-94 26'44 24'53 22'92 21'57 20'43 19'47 1867 17'84 16'61 1556 14'86 13'99 12'57 11'26

133 5. ThllOry of Exit Gradient.

~

. -c' .

A brief summary is.given below. from '~hapter VIII of Central B~af. . d ~f Irrjgation publication No. 12 as mentioned tefore.· "Weir failure from seepage flow can occur by;-oI

(a) Undermining of su'Jsoil.

I ;

(b) Uplift due to pressure under the floor being in excess of the weight . on the/floor. Tte failure due to undermining.is most common, so that a knowledge of it!; causes and of the mtasure:; to prevent it, is of utmost imp()rtance Doth for design of new .works and for ascertaining th~ safety of existing ones. Even in the Second case if the floor be burst due to excessive pressure the fmal failure is due to the reduction of tne e~fective bngth with the consequent increase in the exit gradient. ' The unc'ermining of the sub-soil starts from the tail-end of the :Work. It begins at the surface due to th ~ residual force of seepage water at this end being in exc{ss of the restraining force" of the subs)il which tend to hold ,the latter in position. Once the surface is disturbed tl,e dislocation of sub-soil particles works furtner down;and, if:prog<J;.}ssive,lea.d';; to ,the formation of cavities below the lioor into which the latt~r may collapse, According to the commonly accepted ideas. this undermining is supposed to result from what is knownas "piping" that is, the er.)sion of su i-soil by the high velocities of flow of water tllrough it, when' such velocities exceed a certain limit. But as will be shortly explained, this conception of undermining is incomplete Water has a certain residual force at each- point along its flow throught ,the su')-soil which: aclSj in the direction of flow, and is proportional to the pre:Bure gradieIllt at that point. '. :Au:the tailt end this force is obviously upwards, and will tend to lift up the soil particles, if it is more than the su' merged weight of the lattpT. The frictional resistance, cohesion etc., of the, aoi'!-Cent soil will have to be considered in certain Cases. Once the surface particles are'distutb'id.1he resistance against upward pressure of water will be further reduced, tending to progressive disruption cf the su>-soil. 1 he flow gathers into a series of pipes in the latter ca,e and dislocation of particle~ is acC: lerated. The su·. ,-soil is thus progressively undermined. Soil erosin can also occur thrOUgh natural pipes, or faults in the sub-soil. ' As water flows through the sandy sub-soil, it is welt known that the velocity of flow at JiJ .... p,oint any in them~dium is given ,by Darcy's Law :-

H v=kL <

;

Besides this

, Tris watpr'exerts a, force (F) on the sandy medium along its line of flow. force, the particies of the mediu:n are subject tq two other forces.:;-. " (I) the force·-of grawty, ot weight {W)which acts downwards,

,j: 'anti' (2):.the :i?rce of buoya;ncy (B) which acts opposite to gravity. These two latter forces ;.'!" .. ;ac 1;e comomedillto one and If: : - : ' 'rw ,= Weight

of unit volume

1twater' )

,"

p= Specifk gravity ~f ~and pa~ticJe3 ;

'l;;;

"

: .1

lit

l ; I!;

f

-

in unit volume;thell the )pW ~'" .

':

..

~ight

p~rtieleS'

of sail ' , .. '

, ',' This

: I

• .' . . .

"

'

• "

, ,\.".~.

•

"

per unie. volume ( : " "

'

..

Hence the resultant of ,the forces, that is, the weight '~f tk('> . Ws=w(l- ~ )(p--'- l:) [ i

::o,:_.

"

f"

Theweightofdisplaced~ater~V(17~)=:=B·. (

, ,

LS

-

= Pore space

=W(I- ~

.,'

"

I':

I~Oa" particles

'

"

less

I:

I

buoyaney~ .

,

ma~.be, ~alled, t4~; I)uqmerged, 'Yeight \Y~whlch win obvlol\-Jly\a:lw~ys ~~ qo~nw1l~'1

P IS greater than umty.

(

1 _ •

.....

I' ~

~.

,,

' ..'

'.,.<" ,::

!)

I: .: :': '

134

. .,.

The next step is to determine Hie value of i . Let us assume a cvlinrler of soil along one of the stream lines ,as sho'wn Fig. 9. Let rla=sectional area of cylinder and dl=length of cylinder. . The pressure at face A = p da and ae~ along the' alonge stream line from left to right.

.

I

L ;

~

-~ --!

, ", \

' \, P \.

, ....

The pressure at face B= (p+dp) da and acts along the stream from right to left. Neglecting the curvature of the stream line we get the force acting on the cylinder along the stream line as pda-(p tdp)da= -dp. da

. "'... l

Fig. 9.

..

The force per unit volume .

c£ the cylinder=- dp.da dl. da=_~p . ill

Hence F=-~£""",Ptessure gradient at that point. So that the action of water on any ,dl ' pomt in !he sandy medium through which it percolates can be given by a force F, which, per nnit volume, IS equal to the gradient of pressure at that point and which acts in the direction of flow. Thus the force acting on any particle in the sub-soil consists of as shown in Fig. 10

_ -!~ r--

•,

r-~ ---l~

If'

_1ii:_11 '=iZi::::!l22,::::t:z:::,=::%I, Ii

-.1 ____ _

Z:::Z , :,

I

,

I

/

(a) a force F = -
I

...,

For stability of the particles, the resultant R of F aud W. must have no upward component. Now the vertkel component of R is Jgiven by

Fig. 6.

From Fig, 10 Rv In the region A to C must necessarily be downward as F has no upward vertical component. From C onwards, F has an upward vertical component, which goes on increasing rapidly as the stream line approaches E the exit end. At E, F is vertically upwards; at X' it is infinite, beyond which point it rapidl falls off as shown in Fig. 10, \ Thus for some length beyond X' at The surface, where Facts verticalh upwards and Ws verticallY downward, the resnltant Rv= F-Ws will be vertically upwaros, 'so that, the soil particl,s in this region will be 1if ted up and 'be in a state of unstable equilibrium. This region of unstal,le equilibrium will extend to the limt where R=O or F = Ws. At thi5 point the soil partiCles will be just stable, and F acting upwards will have its critical value whlch will be just· resisted by the submerged weight of the particles acting downwards. The slightest increase in this value of F will lead to instability. The soil particles will start to be lifted UPior "float" so to speak. The gradient of pressure at which this occurs has been aptly. called by Terzghi the "floatation gradient." Haigh calls it the bursting gradiE!nt. Another auther has called it the critical gradient. Thi5 is equal to the critical value of the force Fe and is given by'.

... ualauon gramento:: l'critical =\V. =w(l-E)(p-l) If.the pore space=40 per cent and p=2;65 and:w=J Gf ={I-'4}(2'65-t}= ex 1'65= '99, say umty, , Th?s for th~ class ?f soil me.ntioned above the floatation gra~ient Gf =unity or Th!s floatatIOn gradIent Will vary wlth the pore space of the sub-soil and .the density of th6-. soil particles. The density of the '!joil particles though generally in the neighbourhood of 2'6 £;)' 271 for the Punjab sands may vary in" extreme cases from )'g to 28, Similarly. the p::>re space whir.h for the Punjab sands ranges between 37 and 42%(may he as low as 20 per cent and as high as 45 per cent) Working on these limits. the extreme value of GI may range from 044 to

In..

~

l U '

Table for Gf Densities Pore space

0'20 0'25 0'30

0'35 0'40 0"5

--- --.- --_

",

2.8

2'6

1'4(

1'3;

1'28 1 '20

"26

1 12

1 '17 1'08 0'99

1'04 O'tl6 I}'S8

2,. 1'12 '

1'05 098 O'9( < ;" '0'84 0'77

.,

..

.,'

2'2

. ,2-0,.' . :

0'96 0'90 0'84 078 0-72 0'66

0'80 . 0'75 070

1.8.

,',

o !,.1;

,_

'

1)'65

,

0'60 0'55

061} 0'560','52 0'41'4 0'44

t: "

, The theoretical value of the floatation gudients is given by the formula at this page and the table above, but' in actual weir de.iign there are of her fa'ct.ors which cannot be allowed in theory such as the formation of scour holes and retrogresc:ion etc. All the under mentioned factors increase the value of critical gradi~nt:(i) Scour holes can be caused by the formation of swirls by a tree sticking in the bed har the downstream end 'of the weir. (ii) The exit gradient at the lower end can be increased by the formation of the local surges or waves which resemble the action of the intermittent pump. The rising and the ebbing of the waves produces suction on the soil. (iii) The su.-lden application !1nd reducti
"

the exit gradienf.

"

"

hn<' (iy) The 'pr~sure diff~rence. betwee.n th.e fr~e water level in a drain Qr a Si~K and the ! 1' Basic Sub-Soil Pressure level proouce. flow into, the river bed causing floating ., , gradient and critical flow disturbing the soit praticles.

(v) Retrogression results in th'e lowering of the downstream bed level, with the conse- . quent increase' in the value -of the exit gr'adient. ( , . , ' " • , .:' I

, . ' To allow for such unc~tain river.conditions; a -factor of safe~y is a\10 ~ed' as given-:\~~~ i>elQw'ifi fixing the. value of the exite gradien1:-, ~~, tr.; Nature of soil :<.Ii Fa.ctor of ~afety' Gf Shingle. 4 to 5 -.. "25 to '2 fh " '2 to . 17 ,., Coarse sand .H'T'" ''tf!l'lV-C; 5 to 6 ·,li(1 ,. " .' : ni -17 to '14 Fine sand ..." ' ~i)l.~ 6 to 1 . .. 6 f Sheet .P;)~. .' ",,~, " Sheet Pile Section; .;.>

') ~ , f

,~

.• ~

j , :- .

or

In the modern weir the sheet piles replace the curta.in walls of ma~Qnary well lines )1 B~i.gh's w~ir.,_be~au~e they can· be driven to a~y Qepth ~ith~t ·the; t:edious -pfQcesli of well

.~~iK:;>>mi~t~;>\?,tr{i"'.n ~;~lZ' >":),~;~i,:., ~t~~t®C~',!\,; (';1-,' , ~' ,

lIt. e., 134,

t f " ""

.,.

t'tl~ Tr.:1"" ,:1 ~

'-

"t!

,;::f;

J

.$iilkirig, or the.very'e:lCpen~ive unwatering required in case;o( curtain wall. ,..A typical section of sheet pile is shown iil:.fi~.:t... Th~:fliles are interlocked as <~hown therein.,. ( To aU intents and purposes they are supposed to be water-tight,. M

,. ,._

'''~'.'

............

."

- -""tb} Depth of 'sheet pUes:

. >,

-_ •.,

-.,..

" .. ,

.,_.,_,.... -

.... -

I

.~.:; "~.ilJ.'.,.w,,''\i,.

1 • •

• -

::1 'Tn"'pa:ragf:lph No: j'-ehapter V formulae have been given to d~termine the depth of \ normal s~ur; Thi'l sCour' d~\)ttrus'uafty 'c'a1c'iUated froi\n::-acey-"sToriiiuTi' aTe somewhat higher than those from Kennedy's. It is on the saf~ side to acc~p~ Lacey's figlHes. Accord\ng to Spring scours are classified ~s: '

by the unobst(004ed currents. Abnormal 80 to S:,flt,' ca.u.sed bf 'the defJecte(f~·'·bu.t nevertheless onwards ~oving

(i) Normal.scour, 30 to .40 !ft. caused : ""

(ii}

-

'Currents.""

' .,

i

",' ,

.~.

.

_ "

,

"

(iii) ExjraonHnary. 80 to 100 fLC"tl~!>Cd b¥, swirls set up in forwanhnoving water. Lacey has given a clearer definitjol} of clllsses of scour. ,

.

.

.''1 •

I'

Let R be t!:le depth of scour in a channerIlowing straight with level oed. class A

, .lI

Straighi reach

'

B . , , ' Moderate Bend" <' i: i tClass · '1(' Ii, ~;t .'\fiJ I·.$';~}i ' " "L' ;"w,.;' 1,., ·!lItN~ ,)Class,C ", la~;,r·~:;fil.W Severe ,Senti t· f l _ . , ; Class D ,J;if;llt ;Right-an'gle(l ~~:

1!gRgi

': )

;'..,.,:,.~,'x. _, .'

.

;:2;;- ~ ,'. J:,5, R i

"

;tlif"iw 1'75'R ;.;

- ~JL):0I»2:0 "If t

~ ~ .~ t '), ,.~ ~ "t.', ;:!!~ii,:ijf"" ,~r"f< :1'.!, Class A is likelV to ocC'ur just below or upstream of loose aprons and· Class B along" the aprons of guide banks in a straight reach and C & D at the noses of guide banks, The top level oHhe apt;on!i shoul. be u'fed allowing SC0ur; -depth ,'aceording to', I<enneliy's and the b\,Uom;,of :the sheet, f>iles loollid go. below R as calculated from Lacey's ,' formula Plate III.' .,

•

I

,::'

t

t H ...

•

Ccl F~netton of upstream ahd ~oiriistr9im 'pile li~e.

.. '

" ' .

,.

, . - -~dour hol~~ c~in occur Doth upstream and donwstream so that ~a pile line is: req'uired at the up!'\tream end of the tJoor just as at the downstream end in order to prevent failtlre by slipping of the sub·sQ.i] into the sC!)ur _holes by simple earth pressure. In the case of
': rh~ depth of the upstream pile will be governed by the depth of SCour only and to the rlPWQstteam one by the depth of scour and the exit gradient. l " ' ,~ Under normal conditions the bottom of the scour upstream will be higher than the bott)m olthe scou~ dow!lstea'1l hy the amoun~ of afflux or differefic}i );l~tw~ep. upstream and downstream levels In maxImum flood. The sheet piles at the upstream enG can therefore. be higher t~,an.~hqs\y,a.t\th~d<;>~p~t~~a~;end)?y"tpat,.am~~t: ", , .. ,: .. ' " ,

,

"

•

~

t

~

,.

\ ""The ne't'ef~t)~'forpikstatltM!'~s't1'tlatn'aitd ddWr.!tre'aI'll endgli~1)"bvjoUiJ. '1:hey~are to protect the work against undermif,ing of the foundation soH. The pressures under the dOVv(!strearri door lllcrea~e , as the de?tA of ~he downstream pile ,l'nt1 increa~es. The upstream pile line is relaHvety more effective to destroy rre~sure read and 'reduce~ uplift pres ures under the weir while the pile line at the downstream ell d· is most effective to reduce the exit gradient, '

1:.l1 (d) Function of illtermedlate piles.

The intermediate sheet pile rJ\es are r=quired neitrer to prevent un ierm:ning of ti.t: downstr:am end. not do t:lCY materIally alter he pressure d?~ribution to give l,~ss upl ft pre3sures un er t1e do vnstr 'a n floo. But tf>ey act as i:portant seco!ldary lines of defence SO that eVen if t~e yacCIl (im,?eT ioa?) tJ. o')r, lS damaged at either the up,tream or the d )w"'lstream end iy ,{ulure of t l end ple5 Un er a n r al ure the rest of the fbor a.ld th.~ superstructure will e sav"!d fro n c )ILl.p'a by the 'n r~~dia.te piles, ~he ~Jlift pre,mro.!s, will ~n,crea5e ,mt the, uarIer niilitl~ ~m le arre ;ted as the exit gradie~ts Will s,tlll be ,eto.v ta"! cntlc.ll ,value, . r.1'~' structur: ,will t~u> be sa\'ed fr)'n conplete faIlure whIch on a m,l) lr w?r~ w011: li be dtsastrous, OplllI,ons dlfer ~~ to ~he:' er there should b~ .0:1e or m 1re mter:Oldlate plIes. The best vclue wIll be oAamed wIth om deep pile line diro::ctly under the CLost, . " ",r lj!} ~I . }t 1. KhOS}l's method of Design of ml) lern we'rs ' ,,-: h { J i (; . ,f 'co, i fiT wino to (a) _The two essentials to ~! considered in weitdesign, therefore, are:fl

r at the upstream nor at the

(i) Residual or uplift pres~ure under weir, and

r!

-

(ii) Exit gradients. ,':

't

:.

,~

J je, " ' , " , "

These two essentials are inter-c~nnected_ For any given fcundation profile of a wei! in a given class of soil, there will re a dpunite distriuution of pressure eXit gradient. To safeguard against underrninin!5. the exit grarlhnt mllst not l:e allowe'l to exceed a certam safe limit. generally 1/5 t01/7. The upstream pressu,res must be b:pt as low as possibb. 'consistent with safdy at the exit so as to keep the floor thickness at the minimum. " . (b) In paragraph (4), the mathematical sO,lutiohS, have been given for simple cases to determine tht upltft pressures 'and the eXIt gradIents, A complete methematical solution of a weir section with sloping or level aprons with 3 to 4 she~t pile lines is not vet availa'~Jle_ Khosla evolved a: method of design lrn'Jwn as "rhe Method of fndipe,1dent Varia')ie's the justification of which haS 'Deen methematically given by Dr. J. K. Malhotra of the Irrigation Reserch Institute, Llhore.

In this method, a complex weir section is split up into its elementary standard forms-the mtire length of the fiu;)r wit'1 anyone of the pile line" etc, ma:-dng up on: such form. Each eknentary form is t":~n tre3.te,i a, iurle')~nrIent of th~ others. The pres,>utes at the key points are then rea,d o~ th~ floor of ~late n, These k o ) , points are junetioa points of the floor and the plb lme of ~hat' partIcular e'lementry form, the bottom point of that pile line and the bottom corners 10 the case of a depressed fioor. The exit gradients can be obtained from Pla'te III. The readings at tl)e juction points are, then corrected for:(a) the mutual interference of piles, ,, .. (b) the floor thickness 1;~d (c) the slope of the floor. "1"(I1CB-+~-" ' )-: c~

The method of spliting up a complex

.-<"':'

(c)

Mutual interference of the Piles.

1---- -

"

-_._

,

---t

J

.

! '

1

0

I "

j_

i

. Fig. 12.

1 ).~});ii tll;'~

w!ii section is show~ 'in the catcul~tf~ns' \' ;i

~ ·'''};)oft

'.',

' ;

The lputual interference of piles is w
;

;_-,t:-r.F----Il--:·-·'-~-ir-t"1-

. ' Lj
__

C~ I~JV· ,~D -

'

where (' =the correction to percentage of head .

be applied ,

138

b ' = distant bet ween the two piles. D=the depth of pil:s tb~ influence of which has to be det.,rmined on the neighbouring pile of depeh (d) d=deptb of pile on whlch the effect of pile CD] is sought to be determinep, and b=total floor length. This correction (C) is additi ve for point.; in the rear or hack-water and subtrative for points forward in the direction of flow. This equation gives results within about 2~ per cent of those obtained by experiments and almost exact.y o·)tained from theory uy Dr. Malhotra. But this equation does not apply to the e"Cect of an oliter pile on any intermediate plie if latter is equal to or small~r t\an the hrmer and is at a distance 1 ~ss than twice the lengtn of the out"r pile. Su ject to these li'1litations t~is equ ttian can 'oe a')plied to find the influence of outer pilcs on int~rn c-dia,e ones and vice versa irresp~ ;tive of their depth or spacing. The mutual influene of the piles is locel. It m1.in1~ ex:ends u? to a distance equal to the depth of the pil> beyond which it gradually falls 0.1 till '.he residual effect at twice that distance is n°l!l'gible in most cas's. Where the spaicng IS close and th ~ depth of the piles great, the residual e'1ect may 'Je cO.:1siflera )le. Tee a love el_uatien givts t:11s inluence for all ca~e.s. It takes note of the depth of either pile, of t:le distance between the two and the floor length, thi~kngss.

(d) Correction for the floor

The pressure percentages so o~tained refer to the join of sheet pile line with the surface To o·.)tain the corr '.sponding pressure at E ani C it is necessary to determine the pressure along eac':l faco at L1~ sheet pile line. L1~ pressure dro} alo.lg the face of a sheet

at E, C, Fig. l3.

1-·_·-*·-·_·....-.....11--·_.,- J,. --_.-1 ----.----ll-.~.

"'1

.'i

1

i

. ,.f

- . _ .._J

~ "" i ~/

"Fig. 18. :.)~ •.Jf{).

.

);.1 .

) t:.

If'

pile line, facing ~irection of seepage flow, at any point' disten\,bl fr?Dl ~~~ ~p{'\~tte<1:ll1; e~~e of the floor

=(70-:,~O.,ti-)

per cent

o.~ ,th~ totf}'

.,d,rqp ,;llo_lg

bath the i<we5 of the shft~t pile, the

pressure drop being assnmed to be uniform alog each face. (e)'

CO~Iection

for slop.

The prssure percentages o~Jtained from plate II Vol. II are to be correcte-d in. case -of The pressur~ percentages under a floor s)opir{g down or sloping up in tht' dlrectlOu of flow ~re respectlvly greater or less than those runder a horizontal tIoor for t!:e sa_:ne base raho~. ~s suc~ the per~ent~ge correcticns would !be positive fot the
Sl.Oppl~g floors.

The correction applied iS~ xc whcre I is the hotizontallengfh of the sloP!IlP floor. c is a factor as rad from Fig 14 and h' is the horizontal distance apart of the pile~.

8.

De.ign of wing walls.

(a) In the case of Flank walls and return walls design is complicated by the fact titJfI the soil behind. getssaturated,by the rise of spring leve~ when the river I~ses in floods. W~eIi 'thu 'ver subsides both w:\ter and earth pressures act behmd the w<\Us. It 1S usual to put m filter floints or in verted filters conIlect~d to weep holes to drain away water arid to relieve water ·~ff."sure behind them. The provisionpf.>jwep.p holes should be con5id,er~d as additional factor of safety and thp. wall section shoulri be . designed both for the earth and the water the press8.res' behind the map shlJwn hereafter. 14

:t

U

()

;::

"

IJ

~ IS II:

o

IJ

~

10

~

J-f

;[

'"~

a:

'J

5

t-H-

HT

(l

Q

. 2

"

'n

',1-1ITrl

I"'R

4

I

,

,

,(j

Fig. 14. Slope (honzontal divided by vertical)

lb) The foundation of abutment and fla.nk wall between any pair of pile lines shonld go down to the level of the bottom of those pile lines. [f these latter are at different levels the flanks founda.tion can step down from one .end to the other to suit these levels. This. in fact, meanS of complete boxing in one oithe foundation of the entire weir by means of pile lines of suitable depth upstn:am downstream, and on the two flanks, With such an arrangment of levels for the flank fouflrl::ltions. the uplifts under the weir due to flank flow will not be more than those dlle to direct flow under the weir. The foundation of the upstream and downstream return walls of the Ha.nks should simi.larly go down to the level~ of the bottom of the upstream and downstream pile lines respe _tl vely Ie) A wall for dry and saturated soil. Fig 15 -,- . A,. (il dry earth pressure . 6, ll"., )o,lo I-sin rb ) ~ P1=w1b 1 ( ~-~ .~ U-"":""ATIa .. I+sln't' ,.,~ ~.,_.,......~-n/!. _lwhen Wl =weight of dry soil, hI =beight of dry soil, C ~""''-'';'''~~;!1 y "';-zi ' rf =angle of repose of th'af soil. Fig. No 15 (ii) Pressure due to saturated soil

_.,

.\0"'\ "t_ 1'

.

U

p.=w'! ~

hz(11-S!n :) +sln r. .

where w~=submarged weight of the soil =(p-l) (1- e) xw fils if p=2'65 for sand 2 =40% . ,,' "_ =0251Os. 4> =angle of repose of saturated soil (50 to 10° less than ~ usua.lly) h2= Height of saturated soil (iii) Water pressure height h2 . P a = wh s where w is weight of one eft. of water. ~

- -----------------------,L.

l ___________ ---...-~ ...

. ,

~,~

-,

'.r ~'.

Fig. 17

<

First the calculations will be made according to Crumps's method Fig. 17 (negltctil'lg Ctictlon) Plate No. VI and VII, and then the complete watpr profile will be worked out .ccordin, to auther's method as per Plate VIII to x taking friction into account. K=19'S7 L_4-0 F =Drop in feet to the point where jump takes place it.=upstream depth ar,d )T=Downstream depth

3/ _:U_l~' 13'15 322

C=Ctitical depth==-.:3/ q~~= v g 'V

I

For ' Le' ::::'305 from Plate vr, K+F =2'1. . C .

I

~'35 and J__ =1·3$ c c :.K+F=2 1 x 13 15=21'~ ft. x='565 x 13'15~'7:4 ft. and Y= 1'605 x 13-15=2(,2 ft, , same values of depth 'upstream and downstream '''te VI the Fig. I for level floor. Drop

of the jump are obtained from

fr.~m crest=27'6~ 19''7=1'9

Distance from the begining of the glacis=4x?'9=31' 6 say S2 feet. Actual length is 38 it. which i's O.&. for H,F, cO:Qditions. Downstream floor level=468 Iii) Test for half discharge' ; 211 I K = - ~ X = I~,g it( 2 3-1 '

)2/:1.

Oepth on downstream floor in H,F,

,"

condition=491-46:S=~3

q,=271 =a x 231>/1 . -." " / qa-=1355=kxD5' lJ :.D=·64 X 23=14-12. lt"f:" 135'5 : ,-V.eIoc:ity=- _ - - =9"20 It. per second. 1'4'72 l

- ,"

it.

,. " "," '-,

141 9'21)2 - - = 1'3 feet.

ha=

2x32'Z

The total Energy level downstr ..am =468+14 72+1~3 =481'02 L=(477.S+ 12.6) -484'02=490'1-48.'02 =6'08 feet. C=critical depth=i X 12.6=8'4 feet. L

6'PH

c- =

.

,'. ,

l:T-l =.744 from plate VI.

'fOp from crest level=23-12.6=IOA ft, hich means 41'0 ft: from beginniD~ of crest, x='4137 x 8'4=3.92 feet y= I'S3 X 8'4= 15'4 The Downstream depth is only 14'72 feet and the length of a glacis only 38 and .ere.fore there will he no hydraulic jump on the glacis b.ut it will take place so newhere on t~e vel floor when depth upstream shall crop to the corresponding available depth of 14'72 thIS m not be calcu la ted neglecting friction. ~viiiJ

Author's method:- takingfriction into account.

Upstream flpw >

•

'-'

~

'III,.

It is ~ssl1med that the loose apron shall lunch down in flo;>d§ toa s!ope';of 1 in 3 and he maximum SCOUT depth below floor level is 15 feet. . : . .~ T,.I£.• level upstream=497'2

' h': 40 f eet depth= -271 =6'S feet per second. . Ve IOCI't Y WIt· 40 . .

'. 6'8 2 .~--='617 feet say '6 feet. 64'4 Actual water level=497'2-'6=496'6 Flo N is above critical conJitions against a negative slope . ( 271 271 .) t Average ve!ocIty= 40+ 25- =9'7 feet per seconn, ha ,,;

From Plate X, the corresponding value of £='011 C in Chezy's formula= Yn=neutraldepth= Yc=Critical depth=

~

v'

I 2g ==76'4 f

I q2'.a f 27_!_2--~=3 35 c2s ~ 76'4 2 X i I

q2 '

===

7 271 2-= 13'15 ft,

~ g ~ 32'2 the equation of the water profile

L=

yn_ g

z+Y (.1 +~). s

ftOet.

g

F(/'I

I

.

I

~f f hi' 'N. " C

144

I

j

4Q =ZI = 3 ',:-' = 120

let y L =40' in the begining L yn

For 21 = 12, the value (}f F (Zl) from Plate X =0.91

+~!6~4)2) XO'91

L,=3'3?__ X 12+3'35 (3

t

g

=40x 3+3-35 l3+180) x 0'91 =170+612XO-91=120 +-556=677 ft. ,.

.,

(ii) Let Y2=33,5 feet

z9=L= - yn

,

33'S = 10 & F(Z2l ,91 !

3'35

",, :, L2 =3xS3'S+612xO'9l1=100'S+S57=657'S T 2-Ll=677-657'S= 19'5 f('Pt. [iii] Let Z3=8; Y3 =Sx 3'35=2680 and F (Za) from plateX=0.91~7 ' . , L3=3 x 2S-S+612 xO'9137=80'4+5S9=639'4 L a,-La =657'5-689'4= 18'1 ft .. . Plotting these three points in Fig 18 we get the last point at B from thd plate with y=2.S'O ft.

:_ -._-_F------------------------

~~-~---~~~~--------------~ ~==-t.:: ~ g;_~~ ::_.: _~BAl!_:;_r~~-: ~~J"~4 ._:_~ ---- ---- --- ---~-----

~

\

4{

r--'- 40:. _ _ '"-1

_}

--

II.;

f

l

4'·.

----r~----..::.• <"".~lO~'...!.._·_,_---I'--~'il IJ .

Fig ..I.S '

.:.!.

. . . . . . --...... . . - _,

-

~

.

f.

_- ':: f ...; . . : -_ - __ - -....... ' .,........_. -L l~i ,- Jo:.-.---t--,- --"'- .f'.-"-'---'-1 ......................~ ......... ....~

:l~

~-

lbJ Flow over upstream approacll. Negative slope=i aud cement plastered . Average velocity=t( _22!_ + 25

C in Chezy's formula= vi

Neutral depth=y = n

/ Zf!

.~Z_l__) = 15'6 ft, 13'15

T--= v'

I

l_cr_-~= (

{I c2 X S

per second From Plate X, f=O 0095:22

64'4

0'0095 =83 2712

832 X i

(1

C2) F .(Z)

-_ +-sSg

I

) 1=3'5 feet.';

The equation for negative slope and flow above critical y L=--ll_. Z+Yn

.~

~45

(il Let Y1;= 25 It in the beginning :. ZI = Y -':""" • 2~. =7' 14 Yo 3.:)' & F (Z1)='9148 from plate X

Ll=Y1X4+13.t-( 4+

)

3;2 YO'9148)

<.,

t

=25 X 4+3'5 (4+214) >t 9148= 100+ 763 ~9148= 798'0' f; ' ,

.~

.:

(ii) Let ZI=5'0, Y2=3'5x5~17'5 and F (Z2) ='927

L!=17'5 x4+763 X'927=70+707'3=777'3 L1-L:a=798-777'3=20'7 feet

(iii) Let Z3=4 and Y3= 14'0 :lnd F (Z3)='939 ~3=14x4

"

+763 X '939=716 3+56=771'2

~1- L,= 777'3 -7il'2=6'1 teet. Plotting these points, extend the curve to get the depth at the beginning of the crest, i1 comes to l::e 1:.'. ti feet while the critical depth is 13'15 feet. The flow against a negitive slope wit h depth a1)ove critical cannot drop below critical depth--this indicates that the heading up upstream will he :bigh£r thap 496'6 by aDout a foot and the total energy line cannot be 97'2 but about a foot higher' .

Flow on level crest 6 ft. wice.

(C)

This length IS too small f@r E= 19'7. Double this length shall ensure coptrol section 8:t;lQ parallelism at the middle of crest (Auther's Puhlication No. 10) and crest length equal to EsllaD ensure it to te at the end of the crest. The insufficie>lt length of crest and the energy losses in fric~ion upstream of crest are likl v to drown the weir long before it could be expected r;ecause 4 It. drop on a pnperly deesiglleq wei, should ce su'1icient lfor depth crest of the order of 30 f')et. , The actual position of the control section, cannot be calculated in this case according to th. e'lluation for level floor.

" L= f(Y--{~- ) ,

-:! , i

, " C , '. (d) Fiow on the down stream glacis 1 in 4. ;

f

,

I

'

,

" I Assuming that the levels upstr:)a:n shall adj~'l! themselves as ,ktated ab"ve andJhat th,

, tcritical depth shall be attained at the end of th ~ crest;, Let depth 'in the beginning be 13-12 feet.

'

Value of £='01 from Plate X

c=

,12gf _= ,..,,I~'014

""

=800 nearly

C2~S =(~~!:1 )1

Yo :% {If ;"'36 ,f';" . .i , !',' The equation for water profile with positite stu,.",", dept1itWlowwi~

y L=_o-Z-yo s

(1 ----,_ g

's

2 C )

F (Z)

1M A\

'"'

Y= 13'12 ZI= __!_= _!_3'12 =:J'65 and F (Z..) from Plate X is '943 y" 3'6 .

(_1___

X

L1=.r_-Yn c~ .) 1" (ZI)= 13'1 4-3'6 (4-2001 x 0'948 ssg =52'4S+-3BX J96x '918=52'48+ 706'OxO 948=72]'7 (ii) Let Yz=3 x3'6= to'8. Z2=3'0 and F (Za) ='96~

Lz= lO.Sx 4+ 706 X0'963= 722·j (iii) Let Ya=2'5x:i6=9'0, Z3=25.

f (Z3)='989

Ls=9 X 4+ 706 X '989= 734'3

L z-L.=722'2-721·7=&5

. L,,-La=762'7-734 3=28 4 (a) Water pro11e on the gla,1is d~wnSt~e1,::n of the jump.

,

.

"l

~''1

(l":' .:. -

Water on the·level floor is fi;s;ed as 491

supposing glacie floor =468 Dp.pth =23 0 feet J)cpth above critical, positive slopl'! of 1 Ya =3'6 ft:et as before for the slope

(i)y.=23'O feet Z.=J.2__ = 2?_ :::;6''l Yn 36 . " v;

~S'

L=~

Z-y II

(1- S

Z C--. )

g

.1:) 'j

:. F (Zt\='91S

(:1 ~:, ::f ~ , ,. :"
f.:J

j

.I

"i'·~t~~{(, c·'~'t :f(' Jr~1

Jii1n:"it-:~

l() Ij:i l "<'

~1

F (Z) ')

Ll=23X4+7C6x'918=92+648'l=740 I (ii) ;'::5 & Y.=5x;~ 6= 18'0 & F (zz) ='927 L~lSx4+706X 927=72+654'4=726'4 LJ-!.a=740·!-7264=137 fMC (iii) Let Z3=4, Ya=4x:-t'6=14'4' & F (Zs) ='939 La=14 4X4+706x'939=7Z0 5

I , '1. :L

If, ,

Lz-La=726'4·-720'5=59 feet. Now plot both these prn!lbs a .. sl,o\f'n in Fig, 19 and find out the position of the ju np using ettrves of plate VIII with slo;Je 1 in. 4 a~d Dl on the first curve giVeS Da on ~he otbf>r. Fig. 19 shows that· no hydraulic Jump 15 formed in the highest flood condit)n wit!} floor l~vel 453 jut it c lUll J ~ f Jr ne 1 at thl! p'u,i of the glads if th" downstream floor were lowered to RL. 625, Thp. w ~ir shall work drowned with discharge intensity !7l with upstream lp.vels shooting up frorn ~'(J t~ 4,0 feet. , ple uplift pressure due to Junp w.)uH be of the order of 21.),0 fc!et but KuranJa dl'1lage IS not ltkely asthe flo or is RC. slab doubly reinforced.

(ix) Determination of uplift pressures. (Khosla's method) The worst conrlition will be wh~n the water upstream is ponded up to the pond level Le' RoL. 493 anrl downstream water level is at tioor level 468. Hpad across weir=493-468=25 feet. (a) Exit gradient.

To determine exit gradient, the weir is considered to be of an elementary form, Depth of downstream vel tical cut~:off. d=468-444=24 feet. Total length of impervious floor. b= 140 feet. . 140 H 25 • , « = - =5'83, -_ =--=1'04 24

d:.!4·

~

Acorresponding to

From Plate III

=1'04 and «=5'83

,

Value of GE =0'184 exi~

The critical value of safety=5 which IS ample.

gradient for TrimlllU sandy soil being ",1·,0., tb4t "factor 05

(b) Uplift pressure 1st p:pe line.

Elementary form Fig 20,

Percentage pres'sures •.

Percen_tage corrections. Thkknes~.

Upstream sheet pile line. ' '. :~,

b

"

l,

:

.

_l_=O b

~

:

Total drop along th~ sheet pile;' line";'100-67·f

.=.3.2'5.

.. " "

Drop towards

C=32'5Xl~=9'8.

...

:.q,c"'F.67·S "

Proportionate

L

drop

over

'I

floor ~.• thickness

·0

1'5

}'S feet=-··x9 8=0'8 19

; '.:

Iatprference

'.~

-. ---f

,~. "

D b'

-""-- ""'\ 'I'"

of

the intermediate sheet pile

line ;-

,I

225 72

.

-=-··~=O·312

.'

~+t1 == _E_5.t_lJ'!" ."-),

Fig 20.

cpc

(corrected)=67'S+O'8+3 0.' ~12=70 1

r'"

0'286.L 1:/ 140 ..;.t :. pc=30 (froW plate VI) 1:4 !Jope :, -" 1,11,-. .

~c=3 4 X _!_~::u 1'2

7'1. . PerCl·ntage corrections due to thickness of floor as well as interference of intermediate ~heet pile Ime are additive: the eieet of the intermediate sheet pile line is to ponL! up tho seepage flow so that tl1e pressure at C would rise.

The percerit<}.ge correction dn~ to the upslope in the direction of flow is negative. " . . . (c) Interme~iatp. sheet pile line ;' Section reduces to elementary form Fig. 21.

':i48 Thickness Total drop along the pile line =20 b

(lC=

140

Drop along DC= 1--(0'7--0'53 xO 4) Dropafong-ED=O'70--O'S3 X 0'40

,

d= 468 __-446=636

0'512 =-0'488

~l =.24_ =0'53 b

%

140

:. Drop along D'-:='20 xO'S12= 10'24 along ED=20xO'488=9'76

~-=0'47 b

~'5 =-' -xlO'24=1'6 22 Interference of sheet piles : -

:. CPG =38 0 1>£ = 100-42=58

J.. c 'P

Corrected values :-t"
1135

CPE =19 v -7'l.

/'/.0'5

....

~1'l·"j

J.~,. __ .-I.D'r.--,-

32'0 x-=1'9 14()

,pc=19y'-64- x

39

l4O =3'O

. 1 : 4 slope :-

---t

J..£ 'P

Fig. 21

36 =34x 72 =}'7

The effect of down slope in the direction of flow would be to increase the pressure and a7; such the correction is additive. (dl For the last pile, the elementary form of the weir is sketched in Fig, 22 and the same is used to work out the exit gradient. Thickness correction :Downstream sheet pile line :a= 140

=5S3;~t=O

Total drop=36%

24 b .' 4> = 100-64=36

,',

:, Drop along ED=36xO'3=10'8 ., 3'5 :. cf>£ = - X 10,8=1'6 24 , ; Interference of intermediate sheet pile line:-

!

Correder! value: -

fE=36-1'6-2'8=31'!f!" cf>E =

I9J~64'5-446

X 28'5+(24~3'S)

64

140

1---

=19y'~8~~ X~~ =28

64 Total Head

I Lotaticn.

PCfOSS

weir=2S 0 ft. Head in ft. of water above R. L. 468'0

Percentage Head,

I---~--

140

-----~,---'-""--"

C

E

C

100

70'1

17'5

56-2

426

25 14'1

31'6

o

7-9

J

Upstream pile line Intermediate pile' line Downstream pile line II

,

.

10'7 0

-

I

9;' f')oor

tbiekne~s.

149

'

(aj Floor up to crest.

The downward water pressure is 25 ft. to 15'5 ft. The' maximum uplift pressure h 17'5 ft. The downward water load is more, the thickness may be 2 to 3 ftct from practical considerations. (b) Glacis downstream_of crest.

, Uplift pressure--: 14'1 ft. 4 H-h t=~-­ j

P

(as the pressure calculated bdow the floor. the dividend is p not (p-l) t =thickness for gravity section. H-h=uplift presmre p=Specific gravity of. material = 2',25

'14'1 ' t=--- X --~=8·3 it. 3 2'25 (c) Thicknes5 of the downstream level floor. 4 H-h 4 7'9 ' t=- X - - =_ X _'-- =4'7 it.. a p a 225

(d) The gravity sections are very thick. It is a typical case whf're reinforced coneret!) sections will be not only cheaper but also desirabl~, becaustt ma~onry kharanja has not proved safe for the back pressure in the jump. Reinforced concrete sectinn can t~ designed as a continuou~ slab under ,the piers which are 7 ft, thick and 60 ft. apart. It will serve as the foundation slah for the piers and will also take up the uplift pressur", In the midrile, theoretically, steel at top only will be required but at least half ofthe steel shonld be provided at the bottom So that it is capable of taking up downwards loads due to the formation of probable cavities.

10.

Design of Talus or Pervious FI'lor.

~,tated

"

(a) The length and thickness are now no longer fixed according to Bligh's formula as in Chapter V.

The upstream stone apron should contain enough stone so that whf'n it settles down in floods it should take a slope of 1 in 3 with a minimum thickness of 2'5 ft. The scour bi'low the floor level= 15ft. in thi:; case. 40 ft. length of stone with 4 ft. thick~ess will do. (b) Downstream TalUS.

"'. This has to serve a triple function.

(i) To serve as an inverted ,

.

filti~r.

(ii) To settle d,own to maximum SCout with

Qf 3 0 feet.

a slope' of 1 in 3 with minimum t-hicknp.ss

•

(iii) To withstand very high velocities doWngtream of the !l)'rlraulic jump. the blocks should be heavy.

",C

The

511,C

of

In this case the scout hlow floot level is only 15 It. !llH] thrrrfore R. 1ength 30ft to 50 ft. with 5 ft. depth will do. In addition a If'ngth 30 it to 50 ft. at least Ehonld 1 e provided just downstream of last pile to serve as inverted filter. First a layer of shingle anti gpawls about a foot thick over the river bed sand. then boulders about 20ft. thick of 1 It si;;<;e and then concrete

150 blocks 5' X 5' X 5' size. In the second portion of the T::tlus which is mp.ant to sink, the blocks may be of small sizp. i.e, 2' X 2' x 2' bFc::tl1se the velocities will be relatively low and also for uniform and even sinking, a small .size is desirable.

to.

Examination questions.

1. Sketch a de'li!!"Tl for a weir wit't shutten aeroS'1 a T,~~ai ,treltn to divert W'lter into a small canal. \Vidth of stream SO', sirle ~Jr>n" (/2: I, bel !pvd 1)5,)'0' H'P'L' 1'60'0 Flood discharge 6800 cusecs H. Gradient I in 12. top of banki 665.0. Bed level of canal 655.0 F.S.L. 658.0 (T. C. E. 1933)

2. .

(a) Skctch a design for the head of the canal in question No ; 11) givl'n above. (b) l:'esign ann give a dimensioned

~ketch

of the

cro~s

Bed·width=10.0' (T.C.E. 1933)

section of a weir to be built on fine

r:aiait.cous sand IC= 15) R.L. of F. SupDlv in c'ln1.1 6.J'J.O. R. L. of bei rinr=G20.') Height of dr',?

shutter~

=3 ft. m~ximl1m, discharge per foot of weir=75 cs. \Vinter di~charge of river is just sufficient for canal ·requirements and the weir is just subm'rged: when 4 fe;,t of water is passing over the crest. _.T.C.E . 1935

1

3. vVhat are the functiol"s of upstream and downstream piles line in a weir on saud foundation and What is the objection to a downstream pile line.? (P. I B 1936) (P. 1. B. 1936)

4. 'Describe briefly Bligh's creep theory.

5. (a) You are TPquired to construct a canal Headwork.>. seJectjng the most suitable site?

What points will you consider in

(b) What observations are necessary to makp in connection with such a site?

(c) Why are trough hea1-works preferable to head works in a boulder reach? 6, detail.

State why you cannot do awcty with un1ers[uices in the design of headwork~ ?

(P U. 1942'

7. 'Vould you prefer a hi 11. boulder tract for the heidwork, of a canal or the trough site? Discllss in 'Vhat points would you cou-lider while selecting site at e:;.crl of the three places? (T.C E. 1934)

8. (i) Sketch a typical lav-out fo1' a canal h"ai w()rk~ in the sandy trough stage of a Himalayan .lver showing the position of (a) weir and under,luices (b) Canal Head Regulat'>r, (e) afflux bunds

~

Id) Divide wall (e) River training works and (fl And

other works that are usuallv required.

(ii) What' pOints would you consider in sele;ting a sutiahle

site for hea:! works? (T. C. E.

1935)

9. Explain the siginificance of exit grac!ient in the de,ign of a weir? 'What do you understand by the term unity gradient? What factors of ~afety are allowed in fixing exit gradients and why? (P. U. 1943) 10. De,cribe ·the various methods canal Headworks ?

of control for silt

11. Design a lhnk W3.\l lw,tr~am ()f a w~ir in m1.,::m"V' Ilnd saturated sand for the ne·xt 12 feet to tha bottom of wall. 12. Why is a fi,b, la1 br rqu:re:! ia a wair? In the pond and that downstream of the Weir.

S:ot~h

entering

the

re~aining

dry san1 up to 10 feet from top

a suitl.ble

d~lign

canal usually

for 12 feet

adopt"'d at (P. U. 1943)

differenc~

of level (P. U.1944)

13. D~scribe the effect of constucting a weir acos, an allUVial .river on its regime with spec:<11 reference to retrogression of levels. 14. E:xp1ain th~ w:)rkin~ of St'Jney's gd"l9 a~ U'l"d for the understuicl'ls. lind staunching bar arrangements and explain their working?

Sk3tch the roller bearing, _"ccC

. '.5. E~plain the following terms as used in canal head works, (a) Divide wall, (b) Barrage. (e) Intake or diverSIon weIrs (d) Talus (e) Pond level (f) Breast wall (g) still pond method.

~--

PART II

CANAL IRRIGATION Chapter VI

Design of' Irrigation "Channels' .,

; .

,

• Introduetion. In hydraulics the students have already learnt to work out the sections of open channel!> using Chez)" Bazill or Manning slope formula. Tn"re was no reference to the sf)luhle or th6 suspended material carried in the flowing water. In irrig-ation earthen channels or in natural ttreams in erodable hed, water carries a certain cargo of suspended or soluble stuff known as silt. ~

Silt is defined to be the solid material carried by flowing water whether in suspension or solution. . Sand is defined to be the coarse stuff generally rolled .by flowing water and deplsited in ·the bed of a channel. The problem of silt transport in irrigation channels bafficM the early irrig~tion pngineen and is ~tiil a subject which has not yet rearLed tLe final stage of research. Th.ere are numerou. controversial theuries put forth !,y various authors. T11i" proLkm is very important to a canal engineer who designs irrigation cham els which· oftm silt up and sorr.t t:mes scour. In the Cltse of challnels which are silllDl2'. the water levels change and tte di~triL utlpn of water is disturr cd. Thp.~ is discontent and agltatipn among the cuhivators There is shortage of ::-upply at the tails. The efficiency of the canal liylih:m is lOO much iOlpilir, d that the frt'qUf'Dt :>Jlt c1l:'aranct's ruP. found necfssrry wUch entail a lot d exrenCilure and lablur ~lIld tLe cem, qU(Ilt bc}tbt'ratlon. Similarly the scouring of the cbann'Pls UL se's GistIl)' ution cDO en1:1angul'o Hie sah ty of \\orks I y ulluerllllDlng. This troul-le has led to various inve~tigations in orcer to anive at (.csigns of irr:gation channe:l. which should neither silt up nor scour.

2.

BydJaUlie formulae.

Bffore the developtr.ent of various silt theories is uescriben, it is considered advisable to summarize tl.e formulae fm n:acy rtlennce v.Lich an ly to the design ot sect lOllS jn hydraulit" flow. -~{~

\a) Chezy 1854.

. , . \" . .u·-'r:" ;' .: . . Ch"~v, a yrench En~ineet, produced hts I\mpiricat fonfUila of ~ ~~ channels ....

below by fittmg hIS observatIOns of some channels
V=CyR5

where

'V=mean wlocity

'

.fur,:, . .. .

flowy.t,:;

c,

R=Hydraultc mean deP,th:, S=~tope

C=a co-efficient Subsequeuettt hydtautcians have been ttying tl:) work: out tbt'J math~maHcal basi~ ttl tHs formula as below. in an or-en dianne}, tlia-> pt ~Sure is atmo~pheric ahd may, therefore l::e nez1ect"d. heHd du~ to the slope in the channel is assu J.ed to he lost in friction. H~n:ca th" hydraulic gradIent is equal to the slope of the caanud if t.e laHtr is uniform. d~rive

152

Let S=slope of channel A=Area of the cross section of the channel pw= Wetted perimeter ". T =mean velocity of flow W=weight of one dto! Water in lbs

~

II

Y,!,,'

,~,

"'")

F = Frictional resista.ncp in lbs per second ,> l=absolut(l coefficient of friction between water and sides of the channel pet square foot per foot veloclty. fl = Coefficient of friction in lbs' (per square ft. at one ioot velocity.) Consider a section of water of length l moving along the channel as in Fig. 1.

"I'ig. 1

ASSllme slope of the channel Ulliform and equal to S.

Frictional resistance of the section for length I.

, F =wetted area X frictional resistance pel"1lilit are'a in Ibs~

F=PI.( f.~,

;: ) in lbs.

The value of 11 is taken as 2 as the average, abe surface and the velocita from l.7 tl) 2'3

Actually it varies with tile lu;tllre o(

work done in overcnming friction Ew=friction resistance '=Fxv foot Ibs.

X dj!lt~nce

moved

loss of potential energy per second . ',,' , = wej~htx change of altitude in f~,et ' =wi\lxvS it. I b s . ' Equatin~ ,equations tA) and (B) ,

VZ

,PI fw---=wA 1 v S Zg " 2g A ., ~:'~f~ v-=f--' p ....

ks.

(8'

153

NOMOGRAM FOR KUTTER'S FORMULA KEY Dl.4GRAM·

Fig. 2 "~I .; -,;j ',I itt Shf' ".l

:.:'t'}l

~

.

~ '. '.' -~

,

•~'; ~ >

, :_-;.r ",.J

:':: }~,i ',\ ., '~"::~~ Jlj't lh

~'

~, IJ'Jl< f:w,-~;,. (,',} t.

rd lo ~.uur. ,,.

"!co,:: ',,') .... f

,.'

-~0

Note :..;..In friction experiments to detptmine the value of frictional resistance in 'I't;s ~er

squ.are foot, {' is used to express the unit of frictional resistance. Its value in terms of f is

igiven

by the relation.

i'= fw

2g-

~

1M /-W-

In terms of f'. the value of C=y -f'-

The Chezy's equation of the fundamentRl energv equation of fiow of witter lind is the time-honoured practice. Solution 01 Chezy's equation can l:e got from Nomogram Fig. 2 (b) Bazin, 1897. From He results of his {xpeyirr.ents of flow of water though channels, Bazin decuced tlle foll )wing formula

1575 C=--- where R=H.M.D. & k=a con;tant

1+ k yR··

The value of k de ~ended on the nature of the channel and has the follo\\ing values Clellr smooth sides of wood, bricks, stones etc. k='2 Dirty sides of wood, bricks, stones etc. :Side!r of natura I earth (c) Manning.

1886, Transactions of the Imtitute of Civil Engineers, Ireland.

Manning analyserl SOTJ'1e of the channels in his charge and produced his empirical formula in C.G.S units which when expressed in British units takes the forms .

.,here N is the coefficient of rugosity. This formuh is signifil'd furthff in practice ann is u~ed as :!In {'xpotntional formula

.,f discharge of a channel. Q=kd 6 ! a the solution of which is given in monogram in Fig, 3.

(d) Kutter, 187Q

Kutter, ,a~ American Engin~er, from, hi~ an~lysis of ~he Mlssissipi :River sectionsl produ('e.d an emplflcal formula for C 10 Chez}' s eqllatlOn wherem he made C to depend on fa) nature of bed (b) HydraulIc mean depth and \G) slape.

41·66+~81_!. +_JJgz~

c-

N

S

~~--~~-~~--~--.~-~-

1+'41'66+_~~~28)

t&"

.in <m!tric ml.iCs

2~+_~_+j}~155 C== - - - - - - - .

J+~3+ 'O~15S V'~""

tn ft. ffj, unit!!!:

155 (DISTRIBUTARY DISCHARGE DIAGRAM For Q=kd5 / 3

Clisic, ••

""

"

.J

""PTH ''1

..•

d.

I•

.':1.

Fig. :1 ...,

I"

'

r _C -

.. ~,

.11

t If}}:

"0

,£XPLANA110N:.'t./HE

THROI.ICH r:./'VEH

,~ "'VES VAI.U,. 'II

'LINr.

IUl)IArr,trl

01'

I<

VAL,IJU OF

Q

AIfO

ON "HIII. IUCAI.'.

,-If.OM k rHUS ':OIlNO

'SIV. R';4.¥,R". V" ..... IO 0/1 DIll'TH .. DI.CHAIN.

The gl'nerallv acCpoled values Ot the co-efficient of roughness 'N)are: 'tl'009 Weil planed timber in perfect order and alignment. 0'010 Plaster in pure cement and other glazed stlrfaces. , '0 'OIl Plaster in sand and cement. Iron and other smooth pipes in goad «de:!!'. 0'012 Un planed timber. 0- 013 Ashlar and well laid brickwork. 0"015 Rough Brickwork. Good stone-work ill fair order. 0'017 The same in inferior condition. 0'020 Rubble ma~{)nry. Coarse btir-kwork and regilneD. 0'0225' Canals in earth in tolerably good order and 'regimen. 0'025 Canals and ri-:ers in earth in tolerably good order and regimen. 0'030 Canals and riVETS in bad order and regimen. 0'035 Canals and rivers obstructed by d etri tus and in bad order and regilDeD. ~'050 Torrents encumbered with detritus. 0

156 In actual practire ihe Manning's coefficient of rugosity aDd the Kutter's coefficient of roughness are taken to have the same values as glven above. In fact they ~ the same value ()uly for one meter depth. ' . (e) Barse-s 1916. A.A. Barnes produceo empirical formula in his book. "Hydraulic flow London for earthen channels in average conditions v=58'4 R·694 S496

reviewed"

This wa"',the .first attempt to find out a formula where the variation of the roughness 0 the channel sPCtioll was ign'Jred and '-'. fon:nula covering I3() observations was found without N) ;j,

(a) Rectang ll hr channel for maximum

di~charge.

Using Ch';zY':dormula.

',_

rA~'

Discharge=Av=A.C. ,/J.{-;-=A.C.V, -. S l'w

Let B be the ber!. width aud D as depth. Discharge is Maximum for the sa TItJ slope when PIV B The condition is when D=:C

IS

minimum.

(vide Page 163 of Lewitt Hydrulic.)

{b) frapezoidal channel for economical section. The most economical section for a trapezoida channel will he when discharge is maximum for a given excavaton, This will be the case when P w is minimum. Neces!:ary condition (Lewitts Hydraulices Page 165.) (i) If a semicircle is drawn with centre at 0 (mid point of surface width) and depth 'd' as radiuS three sides of the section shall be tangential to it, Fig. 4. FigA, (ii)The hydraulic mean depth R shall be equal to'Q-where D is the depth of the channal .

2

(c) Circular section f?r 2aximum velocity. . . .. ' . A Depth for maximum vp1pdty is given by the maximum value ofPwas velocity is proportional t.

VH:'_ when S is constant D = 1'62 r; where r is the radius of circular section. (vide Page 167 of Lewitt Hydraulics.) (d) Circular spction for maximum discharge. ,'~,

Depth for

/~

=A x CVR'S =Cyp;: D=I'~O T,

A'J

maximum discharge is got Whenl'w '.'

"

S, the value of S remaining constant,

where D=depth t=radius of the section (vide Page 168 of Lewitt HydrauUes.)

151 4. Ker.:aedy's Silt Theory. The above mentioned formula apply to design of (lpfn ch:'lnneT ~ection') without any refereno'! to the silt which the W;)tPT carries in thp (,::!Tthen irri~ation eh;mnet sections. It was pointed out in the introduction to this chapter that the research work was Vf>TV essential to arrive at the correct section of canals transporting siIt so that they. fe r thl>' snccessful wor~ing of the irrigation system, do neither silt nor srour. The pioneer rese::lrch work on the~e Ime~ was none by Mr. R G. Kennedy, Expcutive Engineer, Punjab Irrigation. Upper B::lrt Doab C:tn::lI. This is one of the oIde[,.t can
Ccl Mean or the critical velocity. The critical velocity i .. defined to be the mean velocity which will just k~p the . channel free from either sitting or scouring. This is denoted by the letter v., • The expression to flnd out critic:o.l velocity was found by Mr. Kennedy t.y pff>ting observations with velocity as axis of X and depth as axis of Y. From this the fQllGwing efluation was deduced : Vo =CDm ='84 D'64

This express;on gave the uen-silting veJrcities for channels ",bieh h2.d silt flF the same. character as in the observr:d channels of Kennedy cn the l'pper Bari Dcab Can'!,l Table 2. ~ut If thl: channels had cilt of different size and gr<:.de, thty Iun nen-silting with a ve10(ity different from Vo {mean velocity).

C. V. R. !critical velocity ratio)-CriticaI velocity ratio is the Iatio of the a~tual velocity in a channel to the critical velocity calculated according to the .Kennedy's Vo fonnufa :-

Vo =x cdm ,

C. V. R represents a facter wl:ich cres not wfl"ct dq)alJ..e frem rq!ime. bttt a factor ~ h ch is a measne of the variation in the silt cenditions on Upper Bari Doab {'anal in the Kcnnecy's ob~(;rv2.ti(ns. It is a1;;0 a factor which takes into account the scale effect o~ t~e diir ers:o;n.s of tIle clanr.eJs. Kennedy consiceTed the question of bank erosion quite dISt r.ct f] rm th fi1t eu! ~hT'., tlngh cf IT.c'cllhtcd irrpcrtance· in fixing the limiting depth and the Eafe lirr.itirg .,;e1ccity of a channel. He HJDsidered tIle safe velocity in fhe· Funj~.h sri} tr Fvard against sice erosicn as :;·S ft. Fer scccnd. This WQuld mean a depth not more tLan 10·0 ft. (d) Slit tr:l.nspnrtive power of a channel. Kennedy found expression for silt transportive power in a channel as below:let it vary as

Vo ..

Total silt canied=A.B.v..

It

A=a factor B=width 'Vg

=not sirting V61ocity.

158 Let p=a percentage of silt by weight in water Q=Discharge

:. A. B.

VO

II

=pd

and Q=B. D. v",

A. B.v!}" =BDv" 1 P

Vo

=(1\ )

I

..-I;;::r

.D

This is of the same form as Kennedy's Vo =cdar equating the values of index of D

'64=~1_

.

n-l

Therefore n=2'S6 or Say 2'5 .:. the silt transportive power 5. Kennedy's Diagrams.

.

v~ ~ v",lf' '. 'ftT>

'"

;:.

j'

Kennedy carried out no investiga.tions to find out the cor~ect slope {orm'u1a, which applied correctly to the design of irrigatlOn channels. He simply took the Kutter's formula. and gaw the value of N (coefficient of roughness) equal to '0225 as the average value for all irrigatiOn channels. He designed the hydraulic d agrams printed at the Thompson College press at Roorkee, India. He gave diagrams for differo:nt slopes showing discharge, depth, v~Iocity a.nd C. V. R. Kennedy's diagram applicable to varying slopes is given in Plate ~o.

XI.

(b) It WaS soon found out that the value of N in Kutter's fomuIa Was not constant. Kennedy 'himself suggested the value of '02 for large canals. Similarly in the case of small irrigation channels, the value of N has been found to be '025. Evidently arbitrary selection of the Kutter's formula and the value of N = 0225 was not satisfactory.

(e) The author had the occasion to work out the value of N in the Manning's formula for the irrigation channels and found N to vary from .018 to .028 as published in author's paper on "Design of lrrigatian Channels" in the proceedings of the Institut:on of Engineers India 1936 The variation of N in Manning's formula for irrigation channels in regime was much more than that in the case of Kutter's. Evidently exhaustive and sound research work u'Ocessary to find out the correct slope fom.ula. applicable to the irrigation channels in r~gim:;. This deficiency was made good by Gerald Lacey as explained later.

6. Woods'normal data of design of Kennedy's channels. From the Kt'nnedy's diagrams for the same value of C. V. R. lot of designs can be got out for the given discharge as shown in an example below. A channel of 60 cusecs may be designed as below with unity C. V. R.

Bed

,f;

Depth

215

2'0

11 4-0

29 4'3

Slape 1 in 5000 1 in 4000 1 in 2000

Evidently all thpse designs are not suitable., }004 admitted the necessity of fixing proportion of Engineer, analysed a lot of data of channels of L. width to depth in a not'~ of 1917. Table No.3 shuws cbannels as given by -Mr. Woods.

Bed with ratio to depth JO'n~

3'8 '93

Kennedy 1:t1 his note dated 25th August; ced to depth. Mr. F. W. Woods, Chief C. C. and issued a table of bed ratio of the normal.data of design for Kennedy's

159 The Woods permissible bed wid~n depth ratio is plotted in Plate No. XI in chain dotted line. The suita'ole channel design will be near about this line •. If the ~ilt c'JUditi >ll5 sIlt gradE' and silt charge). are such that ::\ channel would r?n non-srItlOg wIth a C. V. R ~wer than unity say '9, relatlvely narrower sections will be rtquued and vtce versa, f)r chanD",b requiring C. V. K mor" than unity. Mr. E. S. Lindley. Executivp. EI\gineer, punjab Irrigation, took so~e o~servation~ in ]h::lng Division ann some III Lyallpu: D,vision and wrote ~ap.;r N'J. 4'd. m 1919. P,ll1jJ.') EnJine:;riug c'ongres3, Lah:)rc:, on "R~gime Channels." He ;,.orkc;d OClt th)re"n the fol1ow'!l5 empirical relations. B=3'8DloSl

( A)

V ci = .95 D·57

(B)

Vb=·59B·355

(c )

;1

wnere B=bed width in feet D=depth in feet

(: ,'r(l If,;)

t

Lq = velocity in terms of D in ft; , per second.

i

".~

Lq=velocity in terms ofB ft. pot:

'.

,.

second

cUrt

DM rmklimr l~lf \' rf " I.xflnfiiIMf L'ihe dellC( (ira. ( reL e[a of 6c(( wrut'ir ane( a.3pCir p{a5 an important part in determinirg regim~ seCtions. The diJfect in h,s obscvaLons was thai: tht:;y did not relate to channels known to be m regime. The author was in charg,; of these ct'ianneb soon after and found that none of them was stable Howev0r, it was a valuable mass of data and has been used by Lacey in his analysis I

7. Lacey's Silt Theory. (a) Gerald Lacey, B. Sc., M: I. C. E., T. S. E., p. W. D. Irrigation, United Provincc~, India, considerably advanced the subject Qf silt transportation in channels and their dcsigll worked out in his publications given below :._ '-' (i) Proceedings inst: C. E. London Volume 223

1928.2~

(J)

do

'volume 229

193\.}-31

(iii)

do

Volume 237

1934

(iv) Technical Paper No.1. P.W.!), United Provinces India 1932 (v) CentnI Board Irrigation Publi<;ation No. 20 Simla, India 1939: He has be·~n developing the subjeCt in all these publications by stages. The~stu4'ent h advised to refer to h's htc~t publicat~on No, (V) mentioncrl above as the} a\ltho~itati:c v~r:.son of his th<}ory eVen though It g.ves . V.EWS abd formulae very much at var ance with. hIS ongmal conception of the problem as publIshed eadier. A brief summary is given here to mtrodnce thE stuient to the subject. (h) Lacey's conception of Regime.

According to lacey, the regime COnditions shall fundamental requirements are fulftlled. (i) Dl~charge should be constant.

be estabUshed when the folloWin~

Iii) Channel flowing uniformly in unlimited incoherent allUVium of the same charade! as that transported. Incoherent alluvium h supposed to be . the loose granular material 'which can be sco,l!~.:d O,ll: as readily a~ it can b.: d'!posited (111) SIlt grade (and StU charge\ C(mstant. Ev:dently all the~e nquirements 'lre difficult or rather impossible to be fulfilled it, nature. Lacey, U,erefore, quallfied the regime conditions as b~!ow ;_.

True Regime.--The channel should flow in

a.

unlimited alluvium

piain of the samt

t60 TABLE NO. t Exponential formula of ftow of water in open channels in use

_,

.!~ . ~o,.Q~

'0

,

Q=kd5 / 3; Table

ofS/3

-2

'3 .

'1

power : _D5f3, i.e. (deptb)/O/l

'4

'5

. '6

'7

0'427 2'189 4'916 8'456 12273 17'660 23'222 29'378 36-099 43363 51']51 50'443

0'552 2'42'1 5'235 S'S51 13'IS3 18188 23812 30'025 36'801 44 J18 51-957 60'300

.-9

Z 0 I

2 8

• 5 6 7 8 9

. 10

11

la

0'000 1000 3'175 6,240 10'079 14-620 19'812 25'615 32'000 3~-941

46'416 54'407 62'898

0'023 ] '172 3'444 6'591 10'503 15'111 20365 26'228 32'669 39'664 47'[92 55'234

0'069 1'355 3'721 6'949 10'933 15'608 20'924 26'846 33'344 40394 47'973 56'064

0135 1'548 4'008 7'315 1I '371 16'Ill 21'490 27'471 34025 41'128 48'760 56'905

0'217 1'756 4'302 1'688 11 815 16'621 22061 28'101 34-711 41'868 49'552 57'745

0'315 1'966 4'605 8'06S 12-266 17'137 22'639 28'737 35'402 42'613 50'349 58591

0'690 2'663 5.562 < 9'254 13659 18-723 24'407 30'678 37'509 44'879 52'768 61'161

0'839 2'915 5'897 9'663 14'1::6 19'264 25'008 31'336 38'222 45'645 53'585 . 62'027

TABLE No.2 Table giving values of vo=O'S! D·64 (Kennedy's vol for all values of D (the depth) from 1 to II·9. 0

'0

0

a·oo!}

I

0'840 1'310 }'696 2'040 2352 2'645 2'920 3'178 3'4'l8' 3,667 3,897

2' I

"

5 6' 7 8 9 I() If

'1 0'192 0'693 1'352 1-732 2'073 2382 2673 2'947 3'203 :N53 3.690 3.920

'2

'3

'4

'5

. 0'300 0'954 1'392 1'767 2'105 ,,2'412 . 2'70[ 2'973 3228 3478' 3.713 .. .3,943

0'389 0'994 1433 }'803 2'137 2441 2'729 3000 3'254 3'502 3,736 3,9'66

0'467 ]'042 l'472 1837 2'168 2'470 2'756 3'026 3'279 3'526 3.759 3.988

0'539 1'088 1'511 1'873 2'200 2'500 2'785 3'050 3305 3'55 ) 3,783 4,010

1.' ,~

·6

.,-

0605 Jo132 1'549 1'9'17 2'231 2'529 2'813 3076 3'330 3'574 3,806 4,033 ~ ~-\

'7 0'668 1 179 1587 ·1'941 2261 !?'S58 2840 3'10t 3'355 3598 3.829 4,055

'8 0'728 }'223 1'624 1'975 2'~92

2'586 2866 3'127 3380 3622 3.852 4077

'9 0'735 }'266 }'661 2-007 2'323 2'615 2893 3'153 3404 3645 3.875 4099

TABLE NO. 3. NORMAL DATA OF DESIGN FqR"'KENNEDY" CHANNELS • ._.

1\

•

,Di5charge, \

\

2

, 4

"0

1

6 8 10 12 14 16 IS 20 25

SO 35" 40> 45' 50

6() "

70> ~o.

90., 10~

125 l51) 175-

ZOO 225 250 300

3S!) 40() 450 500

GOO 700

800,,900 ·1000

noo

1200 130() 140() 1500 1600. 1700 180.0 2000. 220() .2-400 !2600 '2800 3000

3300

. ~

3600 3900 4300 4500. 5000 6000. 7000 '8000 -9000 10000 10000 15000 20000

2 Ratio bed, . ,B depth = D

3 Bed width (HI

20 2.7 ·,·3.5 40 4.75 5{25 5'5 6'0 6'25 6'6 7'25 8'0. 8'75 9'25 9'75 10'25 ' 11'0 {2'G 13-0

2'() ,2.3 2.6 2.75 ,2.9 30 3'1 3'15 3'20 3-3 34 3'5 3'55 3'6 3'65 37 ,3'S 3'9 4'0. 41 4-2, 4'3 4'4 4'5 4'6

13'5

4~7

4'8 5'0. 5'15 S'3 5'5 5'7 6-0 6'4 6'S 7'2 7'6 80. 8'33 8'67 9'0' 9'4 9'8 10·t 1.0'5 H'3 12'0' 12'8 i3'5' 142 15-0- . ·16'1' 17'2 1S'3 19'5 205 22'5· 260. 29-8 ~. '33'5· 37-2 41'0 ,H'O 60'0 7S.0

.

14-5 16-0. 17-0. 18'5 19-5 22'0. 22-0 2~'O 26~5

,285 3 1)'5 32'0 355 :39-0 42-0 460 50'0 54'0' 58' , 61:0. 640 675 71'0. 740 . :77'0 83'5 l;l0'0 970() 103'0 ll2-5 120'0 130'0 139'0 {4S-0· .158'0 168'0 185'0 2150() ,250'() 281'0 315'0 345'0 360'0 530,() 696'0.

4

pepth

(D) 10. 1.2 1.4 1.5 1.6 1'75 1'80 l'93 1-95 2-0 2-15 2'25 2'45 'Z'~5

2'65 275

2'9 3'0. 3'20

335 340 3'65 3,69 405 4-30 4'60 4'70 4:8 5'15 5'3 5'5 5'65 6,() 6'1 6'3 . 6-4 6'5 6'S 6'9 7'0 7-1 7'15 ,72 7'3 7-35 7'4 '7'5 7'55 7'65 7-9 S'O 8'0

S-l S'l S'I5 S'2 8;2 8'4 8'4 8'4 8'4 8'5 ,S& 8'S5 89

#

. -

6

5 Gradient I in-

2500. 250.0. 2857 2857 3333 3333 3333 3636 3636 3636 3636 3636 4000 4000 4000' 4000 4000 40.00 4000 4000 4444 4444 4444 4444 4444 4444 4444 4H4 5000 5000 5000 5000 5000 5000 5000' 5000 5000 5714 5714 , 5714 5714 5714 5714 5714 5714 5714 5714 - 5714 ·571-4 6666 . 666S 6666 6666 6666 6666 6666 6666 ,·6666 6666 6666 .16666 6666 8000 8000

BOOO

7 Critieal VeJocity . Ratio

Kuttelf'sN

Velocit~

O-.sG

1'00

'(}225 .0.225

1.0.3 1.00 I.OJ 0'99 1-00 1'01 "00 1'00 1'00. 1-01 1'02 (j'9S 0'99 1'00 1'00 I-OG 'l-Ol 0.'91 «>-98

.O2~5

.

' ,i0225 '0225 -0225 "()225 "()225 -Ot55 'O2~5

'0225 '0225 "()'!2ii «)225 "()225 "()225 -0225 il2'25 0() 225 ·0.225 -0225 '0225 -0225 -0225 '0225

S

Mean

~

1-()Q l'W 11 00

I'Gl 1'01 ,l-G1

~225

to..

-0!25 -()2Z5 •

, t-Oa

-(l225 o()225 -0225 O()225 • ",()225

. .()-9.7 l'O~

I'Gft

!I-OO 1-00 . f·Ql

-()Z2S

,"()225 -0225 -0225 '0225 '0.225 -0225 .0225'

1'0l 'l,()2 'lOS C398 <)-99 1'00 -{,OO

()-9S

-()225

1'00

o()225

~25

-0225 -0225 il225 '0225' "()225

.

-()Z25

.

-0225 -(}225 -0225 -0225 -()225 '0225 '0225 '''0225 '0225 0225 '0225 '0225 '0225 -0225 ~~225

100 1 "()l

101 1'04 i'03 1,02 o()'96 ()'9S .0 97 0() 97 '(}'9i) O():9S

'()'98 0() '98

o()-99

1'00 '1'01 1'01 IO()Z .(r93 0()

94

'()-94,

.'

1.00 :U12 il.07

1.13 l'IS 1'22 :1'25 128 11.'32 1'39 il''46

1'48 a'50 1'53 J·.:;6 1'6'1 .1']3

1'16 1~79

.1'82 ,1-91 :21)0 2'07 ;2' Hi 2'23

:.2'30 ,:2-33 :2'33 ;2-44 :2'49 '.2'54

26Q 2-70 :2'81 2'85 :2'89 ~82

2'85 :2'88 2-89 -2'90 2'98 .3'00 ..3'04 :3'10

3-13.' 3-15 .3ilS 3-~6.'t-

::3'()2, 3'08 • ~'3'h!

3-17 ,S'I8 '3'19 :3'20

,3'25 ..3'27 ..3·3S ,3'35 3'38 :3'13 .319 .3:20

162 grade ::IS the IT a 'erial transported. ThHe should in thc()ry he complete freeilom for latera} movement. Sandy rivprs in alluvium plains achieve to some extent this fleedom and by meandering adjust their length and slope. A constant rli:::charge transporting silt of a given gr::lde and flowing in a. self trans~ p()rted alluvium pl::llll of the same grade, tends even tuaU)' to assume a gradlen t solely determined by thp riis :hargp and silt grade, the mp
[nitlal Re'!ime: -Channels excavated in the first instancq with defectiv;l sl{)p~s and to somewhat Ilct:-r"w dimensinDs an~ free fly immecliatPly throwing down the incoherent silt on !he bed to increase thpir slopes anel by ~Aneration of the in~reaspd velocitv to aChieve a non-s\lt!ng 'Initial Regime. Such channpls if ber,lls are gras<;pd.\\hich is usually the rase of irrigatlOn ('hannel;;. \lill be sUllject to a '·()nsif.eraUe lateral restraint. The channels of this type in the Tniti
(c) Lacey's mean velocity relation. I_af'ey like Kennl~dv recngnizes that the silt l!'l suspenoefi by the vertical component of rddies, awl anvocates that thev are generated in a channel spction at all points by forces normal to the welterl perimeter. For this reason he arlopts the hydraulic m~an depth as a variable rather than the vertical oepth. He rliscarded his original re'lsoning in his latest publications that R being the bed rock of hydraulicians must replace D (the ~epth).

(D In wiele channels. there is hardly any differpnce hetweeri R&D. In elliptic or scmi-ciTcubr chann r;1 s::ction th ;r, is no side in th" tru,] s;']se and therefore R is the correct ba,is, but Kr;nncdy c::ms'dered that the :rrigafon channel se:tions weTO trap"~z::Jirlal in shape in which case th,'_! eddi':;s prod l.c;d fro:n the sides do not appreciably hdo the silt transportation. Kennedy rightly neglected the side in trap ,zoidal channei sections and thcrefo"'e. he evolved the critical velocity formula in terms of d and took the total silt transported proportional to, bed-width. . (ii) There is a greet d:vergence of opinion ;>,bout the shape of the irrigation channel,. Th0 author conside~'s the irrigaton elY.nnels are generally trapezoidal in shape wh'~n thw tra:l,port silt or sand; but when they carry fine silt or clay, they tend to be elipLcal 0,' sem-ci~cular in shape near th'3 tail. reachp.s of the c1istributar:es and in the CaQ0 of Kh",rif cha':ln',ls. Rivers in alluvium in plains are not ch,mnels like the irr'gation Gnes and the sha::n of their section in floods may be el ptical even though form:ng many tributaries <"nd encroached by uJ!yie'd:ng islands and vegetation. The term cha:,mel can hardly b1 applied to large riv.'rs of the Punj<"b subject to 2,vulsions and me:mdp,r;ngs as cxplainc:d in Chaptl;r If of tll (,)1rt. AutJ.o:, oes not consider that one s')t of f07'mulae eouid be evolv,]d which could be app ic~.ble to large rivers of the Punjab and th" small LTigation channels kno\vn as m:nJrs. La~c)y elaims that his formulae are applicable to channels of all sizes. ('ii) Lacey ev'):vcd the forowing formu~a for the mean velocity (non silting velocity to regime conditionsl for the Pllniab data of Kennedy and Lindley:-

L=Ky'

P-Lk =

1.1547

,/FI,K

v = mea 1 regime velocity K

=:l

ror. ... tant

(

A)

162"

fL=silt factor R=Hydraulic mean depth It will he not~cced that Lacey has taken his silt factor "fL" under the root sign. lr. lis own words 'it is pref.~ra,)le, to denote slIt gfJ.de hy a llll':~ar ratio rath~r than by a velocity atio and for this purpDS~ th~ silt fastor "f ,. has b~en introduced by the writer. In t~e Punj:,b c.ondi:ions, taking the value of f . . equal to urlity, he evolved the formula ,y logarithnuc plottmgs III the form v=1'138 R·1995=1.138 R5 nearly. (B) Critical velocity ratio as us ~d by Kennedy is equal to the squ,~re root of the sil factor fL. Lacey's equation for silt fac :or fL =X2='75-;_:

(C)

where fL=Lac;y's silt factor. X=,c. V.R. (Kennedy) v=mean velocitv. R=Hydraulic mean depth The silt factor is nearly three quarters of

;2

which is the turbulent acceleration and 1 4

'J

the silt fast~r when .unity is al"o ~onsistent wIth the rugosity coffici3'nt N.=O·02 ~5 f t / • ThIs equatlOn can b~ utlLz~d to calculate the depth of mJ.xim'ln1 s:::our:; for the bridge foundation in large rivers 2

Q

1/3

R=O'75 ~_~ ='4725 (__ ) (D) . fL fL (d) Lacey's wetted perimeter Discharge relationship. From the logaithm!c plottings of large amount of data, . L3.cey derived the e~piri9!~l relation in the form (E)

and-P ",: =7'11l R

(F)

\ 1." (G) v = O'141~w~ where R Pw=wett"d perimeter Q=discharge in cusecs. R=H.M D. v=me;:1li velocity. The constant 2.67 i~; not a true constant as it varies with different localities. In the Punjab, the Rese?.rch InstitJte. Lahore, found its value to vary from ,2.2 to 3.12 fro 11 24 rebcrime sites keDt under observations for a Ion"b time • Lacev' rematkecl in the India:1 ..., Engineering. Calcutta, AUg(l"t, 1937 as helow : " It must hI} rem<;m bered that the expression P w =2.67 Q 112 gives the valne of th ~ m;nimum stabL; pc;rimeter in channe1s in incoherent alluvium with considerable accuracy. At' the dat-a so fa,' ava'lable with considerable as curacy tends to confirm the expression. Th: value of the comtant in individual chann;l-: vari~s with:n limits ronghly from 2'20; to 3-::W. If the banks are tenac:ous. the w:dth may be less, if the b~d tenacious, the wid::'l may be greatel", the~eforl~, there is no. absDlute rigidity in the constant 2'61 when applied ':) small channels with even a sm'lll admixture of clay in the bel or banks. In lal"Yc ch;l.llnels it is to our inLrest to make then ?s d'~~p and n'l.rrow 'BS i, consistent witt] ~t'it iHy In sma.ll channels ap )roaching the limiting velocity there is Il' ohjection to m lking them wid~r if the clay present provide.> a snall additional measure stability."

\

j_

164

The upper limit of the wetted perimeter constant is about 3'\6 and the lower one 2'2 (or the Punjab Canals. (e) Lacey's general r ~gime equation. (i) It has been said that 1he Kennerly's acceptance of Kutter's formula with value, of N='0225 was noc HI)' safsfa' tOly j acey'~ a'tcn pt tu evolve Regime flow equatinn i<: a great :ldvance to our knowledge. Ignoring the attemp1 s of Mr Lacf'Y to giw' mathematical proof of his general. regime eq~ation using the dimensionless numrer ,he analysed a ~arl2e amo';!nt of data and his regnne equatIOn fits the data very well. Lacey s general reglme equ:ltton entirely fitted with the author's observations puhlished in paptr rear! in the Institute of Engineers, India, 1936, giving variation of N in Manning's formula. La~ey rightlv claims on page 12 Central Board of Irrigation Publication No, 20 "it is very improba )le th'l.t any improvement can be made in this rel
~

~=pw =X Pwl

in the vertical,

. •.

x

p

~ = R}

E==--=~ y P wl

But ,from equation (F)

P w =7'111 v R

~

is

tf'rmed the "exaggeration" E (Le., the ratio betwepn the vertical and horizontal scales). Then, in the horizontal.

Fig. 5

Rl

and the vertical scale be+-then the ratio

y

16EA~ain let HL and HL1 • be the rliffer nees in levels oetween corre~p,:mrling points on

and model, at the end of lengths Land Ll respectively then

Hu--s 1 =5 at).d Ll

1 L, _ =-H...--- . --Y.-·-·1 =y L Hu X

. _____ S .. SI . S

..

~L

prototype

_ 1

_

(J)

VI

-E---v-

-s~-

..

j

This relationship is of vital imporbmce in model experiments. Returning now to the Chezv's fomuia v C Rl1251 12 -V;-'-=~' -R,11 2 S1112

C v R 1. S/12 or--c;- =-v~-' R:I~ . -SI,J Substitut~-f"r S from equation I, C v312 R/12

C.. =

v1 312

(J)

. RIll

But Lacey postulates t.hat streams flowing ill envelopes of the saml'! silt (Le., whose fL value is the s:lme) must havtJ the sarne co-efficient of absolute rugosity N a , hence for such channels, from equation (A) v R1fZ -V-;-=R I 12 I

~ubstitute value of v_

v,

r.

Rl/4

~-= R8 4.......... ··(K)

.

therefore C in the Chezy's formula when applieJ to fegj'ue channels various as Hpnct the Chezy's formula may be written

R1I4

v=KR31451/ 2

or

V=_~I

.

R 3 14

SlJ2 ...... 'L)

i i

a

where N. is a true co-pfficient (a m"asure of the absolute rugosity of the silt envelope.} Datermination 01 the va.lue of Kl Now the values of Kutter's Nand Manning's N coincide at a. depth. of one motre, Lacey <11!cided to retain this coincidence, familiar to all hydraulici
. (Manmng)

N

= l'485R (3-208,2/3 N

== [Lacey)

S112

E: (3'208)314 S172 N. .

whence Rl= 1'3458 and v== 13458 RSJ4 S112 Na.

(M)

166 the above formula is strictly applicahle to regime channels, but may be llserJ. fretly as a, substit1lte for ei~her Kutter'~ or Manning's in non-regime alluvial channeh or channels with rigid boundaries etc. with improved accuracy and greater facility, by adju"ting the valup. of Na . (iv) Regime Slope. Laceyevoh"ed his regime sl()re fOTll,ula in 1932 in Technical Paper No.1, Vnitei Proviuces as S=_1__ f L5 i 3,/Ql/6 but in 1932 in Central Board Irrigation Publication No. 20, it '1788 , has been modified by him to

S= __1_ fL 5 /3/Qli6= 000542 fL 5 / 3/Ql/6 18443

(v) La ;ey's Shock theory. 1 he use of all such equations presents great difficulty in assigning values to the

rugosity co-efficient. The"'e is no Ii 11it to K utte['s "over-all" co-efficient N in obstructed non-regimp. channels, ami for such chanoels no rati-onal equation can be fra111ed. One source of error is in measuring the slop3. This if measClr,:d locally over the discharge run, may be too small to be accura~ely ass?ssed, If mea,und a, gC03l sbp~ OVJr a large slope base, the hydraulic Iw;an d :pth at the di~charge site, owiug b th ~ natural tend'~ncy to select narrow reach% for measurements, wIll often be in exces,; of th:J averag ~ hydraulic niean d';pth throughout th~ slDpe bas~ Th; slope a;; mr;3.sured wir, thus b~ in excess of th0 slope applicab13 to the hydraulic meal d'~pth a; mea,uf.Jd. The sbpJ may also include "sheck" du;~ to bend, 0' irregulari :ie; in th ~ channeL an 1 al30 "shock due to channel condition" as opposed to c'lann~l mal;rial In SUC:1 cir-.:umstances it is prderablc to assign to Na a value \\ hich the bed material warrant3, and to account s')pd.ratr:ly for the energy destroyed in sheck by making an a-;:>pr.:>priat,; d·~duction from the gross slope as measurel. The equatioo can then b,_; wntte 1 i l th·} fmm

V = I"~i-"~ R3J! (5-S)1/2

(N)

J.'II.

The following tahle of thp rugosity co-efficient N recommendeil for different channel conditions demonstrates the futIlity of ~eeking otller than an approximate empirical solution and the arivantage of employing a simple exponenti.al equation of the Manning type. Value of "3" the fraction of the slope "S·, lust in shock due to channel conditions Channel cundition

4'S"

N

Dcs~rlptlon

--------

~-~-~-~

Perfect Good Fair . Bad Very Good Indifferent

goad·

l::l<.d

'0250

'0275 'O~~OO

0330 -_---

----~-

of channel

----_------~----

'000

S '174 S '323 S '426 S ---_----

-

Natural stream channels. Straight hank. full stase, no ri'ft:; or deep pook "EnQ;ineprin'! N pws" V ,I

'u~"5

'0 Iv

;:,

Ea-theril--(_llaH~~~iS

'02fO

'190

'0275

'::31 '437

S S

under urdinary [ondit,ons. BuCkley's In - a ion l"ocket Book

·\;~l.V

S

an
7~

---

1916 Pac:e 371

-a-n~tS----

--------?

The t ,bl,~ ,h ws that mor : than iJrty per cent of th~ energy dest 'oJed in the channel may be d s.sipated by ~hannel i.regulariti;s.. It is- important. to ~ote that if a ~ain canal is excavaLd m the first mst; nc~ to an eX,-" SSiVO slup.; 1t will adjust ll.elf by the cr~atlon of canal irregul2;r.ties. Such a canal would eventually achiev0 some kind of balan~e and remain stablt! the slope, how.:vc:, would be m exc,-,ss 01 that wkch the grade of SIlt Lanspo[ted would demand in a r,,;!Sime channc;1.

S. In'lia.

'i

La:cy's Dhgrams.

I accy pl l li;hed his elia.grams in TechnIcal Paper No.1 P. hes-~ d azra:ns WJre ba ,r;d 0,1 his- original quatious.

W. D.

United Provinces;

167 1/8

V = (JfL2 ) o

P w =2.67 S=··

Qll2

fL 513 .-

R= '7305 .....V2 ~

C)

( D)

fL

~; "

17l'8 Q

D=

(

( B)

3'8

6

(E)

-

~R~ - [ (~R~Y

A B= ----sD

o

K=2(r52+1)112_~

.':;; "W p::' r'lilt _(H) , , , ,The channel sectIOn was assumea'to be t~pez01dal wIth sl(:;es ! to 1 though he believed that it would become cup-shaped aft~r,il.Jii'f· year~,r:unning. Side ~lopcs ",,'. S :!I!~ K Vertical 0 2'0 One half to one . . , 0'5 1'736 60 b slope . i ' 0'5774 I", 1'7321 One to one 1,0 18284 l·~to L

1'5

2'105

The diagn',ms are given in Plate XV bJt they need to be revised tor the equations finally arrived at by him as summ3.rised in paragrdph (7) above. Th'.l origillal diagrams can b~. ,used till new ones are produced. 9.

Examples.

(a) Des:gn a regime channel section discharge 500 CUSilCS and

V 0= (

A=

QfL 2 113=( 500x l'212)l.!G . --~_ .. -=2,4 feet per secilud 3'S 38 ._ _ )

~~O

=208 sit.

R ='~~~Vo2_=~73~S?<~_42 F'brside s'ope

t

iL 1'21 to 1, K=l'736

D=,A :GRK

=3'47 ft.

_/(~ )2_A\t =17'26 '-(298-120)lj2=3'93 ft. l

lRK

KJ

'

B=DA-sD=~08 - ~

x3'93==SI'04 it. '" The channel section should have bed width=51'O ft. and depth=3'9~ J'93

.

.

fr}j3

S=Reglme slope= J788QI/6 =

1'21 5 / 3

•

I788X500 j6='00027 '

say= '27 ft, rer thousand.

168

It is

t~

(b)

Design a channel section for 200 cusecs and'V =·3 vo

save these calculations that the diagrams are usen.

Lacey's silt factor= fL =

(~) 2=

92 = '81

o From diagram XV (h' f0r fL -'SI and Q=200 cusecs,

H=:10 ft. awl D 3'-45 feet From diagram XV(c) for fL= 81 and Q=-=200 cusp.cs. Regime slope S='16 ft. rer thousand feet, (c)

Sectio'1 for SO ('usecs

with~ =

'S

o

2

Lacey's si:t factor fL=(}) ='8 2 ='64 o

From diagram XII (A) f'r fL='64 and Q=80 cusecs. n'lpth D=3 5 ft.ann bed width =B= 16'5 feet. From Diagram X[[ (c) for fL='64 and Q=SO cmecs. Regime slope S='l ft. % (d)

Design Kennedy's section for ,:ischarge 200 cusecs and

'V_= 1'0 and giveh slope

vo

of

ft. per thousand. From Plate XII for slope 2 ft. per thousand and Q=200 B=26ft. and D=3'S ft. From the same rliagram, according to Wood's normal data of d~i&1) for~-~;J; cU~t'!cs B=21 ft. aoo D=A'3 feet. ;. '""" ''',(iu lI, . The ~lope rpquired='216 ft. ~er thomand. 'i':t :-r .(~ 10" A surrmlUY of Lacey's CcnclwfcllS. "In all regime ch:mnpl" in incohprent alluvium the primary funda'1lental variahles are the mean velocity. the hYdraul'c mean depth, the water ~urfac~ slope and the bp,d siH grade Of the four variab~es V, R S, and fL, two only are necess:uy in order to obtain the

.~

third anrl fourth. The first equ1 tion is V = (4/3) t VfL R In this equation when thl) valu3 of the silt Lcto~ is u,.dy th~ grade of sand hal a ruso,ity co-efficient Na of '0225 and standard sand is thm defimd, When the hvdraul'c m ~an deoth b equ8.l to one mf'tre (3'2808') th(' value of .'Ja is identical numerically with the value of N as;igne 1 by the Kutter, Manning or Forchheimer equations for flow, The second equation is v=16'05 R213 S1}3 In this general regime equation the rugosity is implicit, and the equation is a?pEca.~l ~ to every type of regimr; alluvial channel from very fine silt to boulders. FL-J'l1 th3se tW) tundamental equations a variety of other equations can be derived. If a flow equation of the \Ofanning or Forchheimer typ~ is sought it must take the from v=~458R! Sf Na The valup. of Na is given by the equation Na=·0225 fI}14 ! [f it is desirerl to apply the flow equation to non-regim) channels in which shock and athar

'1 . ta1{es t h e f rom v=-N 1·34&::SR.a S ~ ch anne I can d 'ttlOns p ay a part. t h e flow equatIOn ~,
in which s represents the fraction of the gross slope dastroyed by shock. . In regime channels, free from shock, aDd of which the silt is of standard incoherence, thp silt factor ~.nd mean bed s]t grade are correlated by the equation fL = 1'76m 1/11 the diameter mr being me~.sured in millim0tres.

169 If shock is prec:ent in a regime channel as a variable. the silt fa 'tor becomes an 'nversfl t11I1ction of the silt grade and m.,l/2 f.. = rr. I / 2 fL=m-'(2 fL etc. In the moulQed E03e relation, where q =R v='375 Ql,2: Srxm5f6JqU l the slope i~ a functi n 01 ? d silt g> ade and ~he d~scharl2'e intensity 'q' the shock bj 1~ implicit, In the EqUIvalent expressIOn of Lacey Soc fr»3 (fr/iL) 5,3/ q l;3 ; the s~lOck is e"plcit. When there is no shock the expres3io;' s are id,;ntical. The modified Bose equation applies to silt of a stal1dard coherence. The equation of ( asey Sxf 5,3/ql j 3 when shock is absent is applicabb irle3pective of the precise coherence, cohenmce being impl'cit. The s'I?plest dime~s oned ~xpression for. thp. general regime equa i n is the Lacey _Malhotra equat~on v/vo'X p·~)/m 1I2; m wh;ch the kmematic vi~cosily is implcit. Under Ideal CJndltlons when all the varIables ar~ equally fre~ to vary, the wetted perimeter ~nd dis:harg,~ are correlated by the ~acey. expression Poc IQ12; from-this equation coupl6!d wIth the t"'o hrst furdamental equatlOns lU terms of V,R,S and fL, all other regim
(~)

2

of Kennedy.

Kennedy simply stated C. V. R.

(~)

varied according to the silt conditions (silt charge and silt grace) Lacev did not Ip:1ve fL as II guess work but COfrplafed it with mean diameter of ~he hed silt in his formuJa fL= 1'76m 1 / 2 fOJ regime channels and in nl n-regime channels N a =022S fL 1/4. This is a very distinct improveme n1 made by Lacey. This omission in Kennerly's work h:1s, however, ceen made good in author's paper read in the Institution of Engineers. India, 1936, the summary of which is given in Paragrapb No. 13 of this Chapter, (c) The selection of Kutter's formula and giving N an arhitrary value of '0225 by Kennedy in his work was not correct, Lacey has produced a general regime flow equation iD formula V = 16 R2/a 51 / 3 after analysing a very large IT'ass of data of regime channels, R. K. Khanna, Assistant Engineer, Punjab Irrigation also worked on similar lines and evolved a regime flow equation in the form V=13'07 R58 S,3 which is of the same form as Lacey'~. Lacey's work in workng out Slope equation and in investigations of shock ill irrigation channeh stands out conspicuously in th~ domain cf resfarch. (d) Kennedy's wcrk sufiered from the defect that he did not notice the importance 01 bed width depth ratio Thi, dP.ficiency was made gcod by the work of Woods and Lindley a5 mentioned before. Lacey produced his formula to this effec~ in terms of wetted perimeter i.e .. PooQ'f2 and the value of K in the formula P=K Q!lJ, is got out by Lacey as K=2'67 for averag~ regime conditiclDs. He admits that there is no absolute rigidity of the constant value and accepts its valiati( n from 2'2 to 3'2 for regime irr:gation channels. Similarly in. the case oj Wood's bed width rat'os there is no absoh;L~ r:gidity because they are for unity C. iI.R. and tht ratio must change for channels ca,rying silt requiring C.V.R. other than unity. It is, theref~rt'

170

appare.".t that the regime chan ',el <.;p.ctirm ran have wettecl perimet.;rs 20% more or le)s than the L',~ey's fo 'mIla P w='· 37 Q112 and s' 'llilarly 'r11o ving \VO lds' normal data of de3'gn of Kennedy's channel a var:at'on of 20% is q.lite likely. We do need a guide to limit our selection of bed width and rlepth rc~tios whether it i~ in the fOem of Lacey's wetted perimeter formula or in the form of Woods' ned width and dtpth raEos. (e) Kennedy did not fix regime slopes for hi" cha lnel'), However, his diagrams clearly show that steeper stapf's are re1uired f,Jr small channel> and the flatter ones for large channel;,. f

5/3

In h's original wary. Lacey produced a regime slope formula in the form S= 178ffQl/6 and in his final work, Central Board of Publication No. 20, he put this in the form Sex:

where fL is the q3 silt factor and q disch;jrge inten<;itv per foot width of the channel. The final formula shows that there is no rigidity ahout the c< nst tnt::;. Tre or ginal tormula of Lacey allows very excessive slopes. There is not a single channel An the Lower ]helum Canal, Lauer Chenab Canal and Lower Ba~ i Doab Canal where La( ey's regime slopes are available. These canals would have nl'ver been constructed, jf the f!esigr.e s han cared for the Lacey's regime slopes The author worked out in Paper No. 154, Punjab Engiw:ering Congress 193! in reply to Lacey's criticisms that if Lacey's regime slopes were allowed in the Mithalak distri h ut2.ry, the head supply shall have to be raised by 4'5 ft. and if the same pro:ess were extended tc head of Lower ]helum Canal, it would hav._; to b,: raised ahout 15 feet ~ven after consuming all existing falls. The author cons'ders that a further l;mitation in thC! form of r,:;gime slop'~s is not required. It is enough to design the regimfl channel sections with the availa')le slope b'lsed on the general regime equation and cr:tical ve1cc:ty fvrrnula limited by the wetted perimeter or bed width depth ratio consider&tiJns. If a Tegime slope formula is to he used ::IS a guide, then the Pnnjah Trrlgation Research fnstitute formula (1937) S='00209 md 85/Q.2 1 is bett:r ap?l cabl; to the Pclnj ~1 c0nditions (1937.) Annual Renort) where md=mean diameter in millimetri s. Tn designing irrigation channels according to Kemwdy's theory. the author's regime slope formula (paragraph 13 below;

S=~(I+.!_'_?~) 7500

p+'5

2

is the be,t guide as it is di

n~niom.ll\T

marl}

corn~Gt

fL5i/3

than

Lacey's regime

0

slope formulae mentioned above, for all the quantities in this are dimensionless.

12. Defects in Kennedy's and Lacey's Theories. (a) Both of them aimeil to find out the average regime conditions. None of them considered the effec t of the varied silt conductive powers of the outlets and the off-takes on the regime of chann€! Mr. lacey stated that the silt f<,.dor was constant for a canal system which is not a bct, while Kennedy said that C,V.R. decreased towards the tail of a channel, (b) They also took no account of silt left in the channel by wattr that is lost in absorption which is as much as 12 to 15% of the total discharge of a channel, (c) The effect of silt attrition was also ignored in both these theories. The silt size does actually go on decreasing by the process of attrition among the rolling silt particles dragged along the bcd. (d) They also took no notice of the scale effect. The Ravi river at Sidhnai, Indus at Sllkkur and a small irrigation minor may have Lacey's silt factor unity or Kennedy's C.Vft. unity, but actuall)" th~y carry silt charg'_: and silt grad; very many tim;:; different. (e) N(;ither la:ey I:or Kennedy ha5 been able to define the silt grade and silt charge and the size of the chann,;l for unity silt factor or unity C. V.R. 13. Author's design of Irrigation Channels. . (a) The author puhlished his paper on "D,osign of frrigation Channels" in the proceedIngs of the Institution of Engineers, India, 1966. The first 4 factors as p.numerated in Paragraph 12 above were dealt therein as influCllcing tue change of C.Y. R. h Kenn" y's theory. The selection of C.V.R is no longer a guess work which was the major defect in Kennedy's theory. A brid ummary is given here and the student should refer to the original publication for a detail, d study and for the proofs of the formulae.

171 (b) Notations. a1 = Silt charge in water at the beginning of a reach and reptesent~ the ratio of the amount of the silt carried to the volume of water containing it.; a 2 =Silt chargp. in water at the end of a reach; f1 =Grade of silt charge in the beginning of a reach and represents the average diameter of all the silt particles ahove 0·04 milimeter; f 2 =Grade of silt charge at the end of a reach; Pl' P2 etc., = The silt conducting power of outlets in the reach expres~d as a fraction with resjJp.ct to unitv in the reach bv weight; ql' q2 etc .• =The corresponding discharge in cusecs of outlets having silt conducting power as PI' pz etc.; A=Absorption in cusecs in a reach; Q1 =Discharge in cusecs at the beginning of a reach; Q2=Discharge at the end of a reach. rl=~2_=Ratio of silt charge at the end of a reach to that at its beginning. a1

rl=~ =Ratio of silt grade at the end of a rea~h to that its at begining. il

01

fS=·

Q2

=Ratio of discharge at the beginning of a reach to that at its end.

A = Dl = Ratio of depth at the beginnin~ of a reach to that at its end. Dz

R c =..3 2

.

..

Ratio of C.V.R. at the end Of a reach to thlt at its beginning.

Xl

B=Bed width in feet in trapezoidal seC'tion· with side slope '1/2 to 1. D""":Depth in feet trapezoidal section witli sidt(ll2 to 1.

P=-~-=Ratio of bed to depth. X=C.V.R. (Kennedy) in formula. v=x.vo=x.c Dm=:icS2D·68 (cl Formulae. Change in silt charge by varied silt conduction by off-takes and absorption losses. D C ={_g1-(1'lql±i'2q2±PSq3+ ...... ) }, <;\-(Plql+P2Q2: aQ3+···) " {A) 1 Qt-(A+ql+q2+qa+······ .. ) Qa Change in silt grade by varied silt condllction by off-takes and absorptioB losses.

r~= { Ql-(P13ql+P2~~2+P33Q3+ Ch~e . .......

. . ,.)} i

. .

x! in , C. V. R for r1 and r 2 ; R C=-=r 1033 . r.· 3• r.· 1=r1·S3 . r.· 3."- 11' Xl

S "= ~~7500

(1 +__!_Z!_) p+"5

~) (C)

t

3't

...

__Q._.__ tfl&.r:-I.',;m.:oltI £~()ll ,8\t ;.r,:'1 .)'[7' (E) ·t',,,·,,,.,, " " ! , , , .." ., . . ,\ { .6:.!x'1>+.5\ } i '., ,. ' "" :-. ~ f ~~ ,,' 'the ratio of C. V. R at the end of a Mlaeh to that at Its beginning can be calculated from equation (C) or takPn from rlate )otI. (A) Actual non·silting velocity- of a channel section is a mUltiple of Vo by some factor which dt'.peEds upon the silt-charge and it's grade. ·Kennedy called it Crftical Velocity Ratio (C.V.R.) and jn Lacey' 5 theory it appel:lrs as !liilt factor. From the formula given above for the change in cy.R. it is clear that it not anI):' depend.;; on the Change of silt grade but al~o on the chl,lnge of sIlt-charge and the channel sectlOn mverseJy as DI/8. It can only be a factor, as uspd by ltennedy and may conveniently be called Critical Velocity Ratio ,C.V.R.) and not a silt falZtor. A unity D=

i'

\.

'

_....

172 C.V.R. or unity silt factor (Lacey) have not the same significance for a river, canal distributary and a minor. If a canal was running non-silting with C. V. R.=·85(for example Lower Chenab Canal at head) it docs not follow that its distributaries, drawing the same silt charge and grade, would run non-silting with C.V.R=·Sf\ They would require C.V.R. as influenced by the fa.ctor A in eqllation( C) above. It is therlliore, that the off-taking channels from the Lower Chenab Canal are actually running with C.V. R. morc than unity, even after considerable side exclusion at their head regulators. It is nothing bi.it misnomer to call C.V.R. or any power Elf it as silt factor. (d) The design diagrams XIII (B) and (C) for equations (D) and (E) are based on Kennedy's critical vp.locity formula and Lacey's gfmeral regime equation V = 16 RaJ3 SI/3. With the worked out value of C. V R. ir m X[II (A) as eXIllainp.d above, and the available slope, p (the ratio of bed ",idth to dtpth) is got from plate XIII \B). It is just watched that the value of p is not off by more than 20% from Wood's bed width· depth ratio or Lacey's

relation~;

=7·2V.

If p is out by more than permissil>le, the

tentative longitudinal section of the channel should te changed. If it is a case of excess slope giving relatively low value of 1'. it should be flattened by designing suitahle falls. If the slope is fiat giving value of p more than the permissible and also if it could not be steepened, then maximum permissible valup. of p should he selected and design completed from equation (0) and (El. In the latter case, the non-silting design is not possible and the section designed should be aedaTed to need annual silt clearance just before the period of keen demand for equitable distribution of supplies to the outlets. With this known value of p, depth is got from Plate XIII {C) and bed width i~ then equal to pD. [e] It will be interesting to mention here that the regime slope formula as worked out in the said publication is in the form of eql1ation (D). Slope is a function of X ano p only. Both are ratios and have no oirnensions. The slope, which is rlimensionless is uniquely determined by these two oimensionless numOOrs. The part played by X is much mora predominent than that by p, as explained in the discussion of the pape(. Slope is eS8entially independent of discharge. The channels could certainly be run non· silting even with flat slopes, if permitt~d by dimentionless numbers X and p, The bed width-depth ratio is deteTminf'd independent of discharge for a given slope and silt conditions. 14. Examples illustrating the use of Author's 'Nomogra.ms. (1); Head reach from Head to R. D. 16000. Mithalak Disty. Parent channel section U. S of the head, discnarge= 171'0 cusecs, Bed=74 ft .• Depth=7'6 and side slopes ! to 1• . Area=7'6(74+ 7;6 )=591'3 sq. ft. _.

710 Velocit v=s19 1 a =2'892 ft. per second and C.V.R.=2·892=-94

.

~~

. Silt conductive power of the head regulator by weight as deteritimM 'by experiments =90% • 0 9 '\ - .rl == . ;1'.

Depth in parent channel _7'(; -2 '05 d I t -'9 Depth in oft take -3'7 an e r 2 -

actual'

)e

Using formula, Rc=rllp. r· 23.A 1/", from Nomogram Plate XIII [A]; R c =1'05 ·,'C.v.R. required in the head reach of distributary='94 X 1'05='985. Discharge of Mithalak Distributary at head= 14;J'5 cusecs Slope=l in 4444- C.V.R =091:15, from Plate No. XII{ (C) using the n~ocram. Similarly from Nomogram No. X111 (B) when Q= 143' 5 cusec;, p=5'O anj C. V.R.=·985, deptn=3'68 feet Now Bed width=pxD=3'68x5=18'4 feet Use D=S'7 and Bed width= 18'25 feet.

, ...5'0\

(2) Reach from 16000 to 24500 Discharge = 1::J3 CUsecs Slope= 1 in 4'lOO Discharge of outlets in Uppf!f reach=7's cusecs Absorption in outlets in upper reach=~'8 CU'iecs Silt conductive power of outlets in uPPer reaeh= 122 9/()= 1'22 _ Ql- (Plql+P. 2qZ+·········) f]- -

, :

=

----------

Ql"-(A 1 +ql+qZ+ .... ·····)

143':::-7'5x 1'22 co7'-;'5;-:)- =1'010 143"·5;;-----;0;\2;--;0,8cc+

{ 01-(PI3 q c l--Plq,-l- .......... }

". 1~~~~;;:~~~:'. }"!"'~~~) ,L \

fa=

':,

}i

133.7

,Q,

12,

=

143'5= {tlW 13;;5'7

,

:. Rc = Ratio of C.V.R. at 160tlO to that at its hea.d.

Ro

=fl1/3.ra·3.rlllO

'

From Nomogram No, XI1I (A) Rc =1'011, :.X=·985x l'U11=I'O Let p be the ratio of hl"d width to dept:h. From Nomogram XIII (Bj. p=4 66 From Nomogram XIII (CI, !)=3'57 :. B=pxD=3'57x4'6=166 Keep D=3'6 and B= 16 5 feet (3) Section Down Stream R.D. 39275 Discharge = 107 cusecs Slope= I in 4000 Absorption up to 39275='2'8 + 1"{ + l'S +O'8=tl6 cu,ecs. . __ Discharge of A.P.M. outlts set a.t bed level with silt conductive power 12210=60 Cusecs, Discharge of A.P.M. outlets set at S/lOth with silt conductive power 11()~'.=6'36t9·JS +6'31 =2'l'03 cusecs. _ 143 5-(1'22x7'5+1'l x 22) =1'027 107

f 1-

L

( 143·5-(1·2211 x7·5+I·l'X22) 107 .

\-1 _. .• J - 97,

143'5

•

.

--.07 == 1 34 , From Nomogram No. XIII (A) for the 'value of rl.r. and r.. Rc "",1'035;

f2=

r -

X='935x 1'035=1'02 From Nomo~ram XIII (B) p=4'5 From Nomogram xrn (C) D=3·37. ft. B=pxD=3 37 x4 5=15'17 Kedp D=3'~ ; B= ]5'25 feet f \4) Section at R.D. 58,000 Ii Discharge=S8 cusecs =1 in 4000 ;~,'\ "- :, Slope Ahsorption=S'6x 1'3+1'0+1-1=10'0 cusecs , Di~charge of A P.M. olJtlets at bed level with silt conductive power 122%=7'5 cusecs. , Discharge of A.P.M. outlets at 8/lOth :'vith silt conductive powet 110%=22 Cll$6C.q, Discharge of A.P.M, outlets at 9/10 Wl\h silt conductive power 115%=16 clUOIOJ.

174

r 1 ==

r.=

143·S-(I'22X7·5+1·10X22+1·15X16·0+ ... l =1'030 88

Jt= (~~_Q) i

='9~;

143'5-(1'223 X7'5+1']3 x25+1'15 3 X 16'0+ ...... ) "') 88

{

88

..._. J -' ~ .1::;'

143'5 . ra= ---=163

88

For these values of r l , r 2 and ra from Nomogram XIII (A) Rc =1'025 :. X= 1'025 X '985=101 C.V.R. 12'0es on decreasing up to the tail of the channel. the maximum being at

R.D.39275. From Nomogram XIII (B) p is found; 1 When S=--- X=l'Ol 4000'

"' ....

,;,.

I ............

,

f

: ,t

I

:

r

1':

'('p . .

\

I ,

','

I'

'

._

i

i

t"}--'JV

"

4

~. •

,

e'h", ) t··", J":", c. ,\1--·,:, t,~ ~ =', i

:. p:=:j4'6

\','.(:1

From Nomogram XIII (CI D=3'lS .... • r! :, B=3'15x4'6=14'3, Say 14'5 5;)1. :; r,.t.{. ~? 'f~ , 88 , \"U ." V=3'15 =1'75£eetperseconiM~'I" "".,.,)- ,'+'C/_ <:r:, 3'15 (14'5+ ___) . , . ' .. :-l! -or_~\" . " j,fl. ,;J. V ',tf' ItIJ£l'v.o-:- "n. " 2 ".' .0'" 11 "'-: ,.!t ,~ IH ,.. ? lid H p I '(l;';', -{~1!) ~ UW'l I "-.:: Velocity and sUt distribution in a channel section. t ??",,- ?:

.

y

10.

...

1,"

(a) Variation of velocity over cross section of a channel.

l ,

The velocity of flow vari"g at ditferent p()ints of the cross section of a, chanQet The frictional resistance of the sides cause" the water to 5low down towards the sides of the channel; I"

I"

19

I

I

"

~

Fig"

and the frictiol1al resistance between the water and the atmosphere causes a slight reriuction of velocity at thA free surface. The maximum 'velocity will be on the vertical centre lihe of the channel at a point a little below the free. !lurfacc. . The variation of velocity over the cros!'! !'ection •. of a rectangular channel is shown in Fig., (j labove. The cUrves shown are lines of equal velocitYi they have the greatest value at the centre, just lelow the water surface, and dEcrease towards the !'ides and base, In Fig. '1 are shown the variatiJns .of, velocity on horitontal section

lines taken at different depth!'1. The velocities at different points of the section hnes a, b, c, & d are platted on a base representing 'the width of the channel. Fig, 8 ghaw~ the -variation of velocity on the vertical seetion lines, 0, 1, and 2. The horizontal ordinate repnsents the velocity and the vertical ordinate the depth. The mean -velocity on any ~ettica.l section occurs- . at approximatelY"6 of the depth; it .varies with the type of channel and with. the nature 01 the &ides~., The discharge '. of the", whole channel

ci

Fig. 7 .

175

•

may be obtaineo by oividing the section into vertical rectan 1 ano finding the mean velocity of pach rectangle. Using this rn~:: velocity, the nischarge through each rectanglA may Ie obtained. The SlJm of all these discharges will te the total discharge of the channel. The mean velocity of each rectangular strip m::!y be taken approximatlev, as the velocity at a depth of 0'6 or the total deptb. In a branch canal of over 50 ft. bed width trle mean velocity in fr~e nntral !'cgnwnt he.s teEn found to be jnst douDle the mean velocity of tl.e ~k're Stgrnent. 1'1:-.e ratio reduces to 1 ~ on small channels.

sm distrIbution

Fig. 8

in vertical pla.ne.

(b) The author carried out observations to nnd out silt distrihution in vertical plane. The observations we;'e taken in the middle of tlle Bhek distributary, Lower Jhel ll m canal, Pllnj:tb from a platform by means of silt sampling eottles and compared witti He total silt charge by weight passing over th'~ cre~t of a fall Tbe result wtre published tn Fig. II, PJ.ge 4, Author's paper on Design of Irrigation Channels in the Institutlcn cf Engineers India, 1986. They ~re reproduceo in Fig, 9. If rhe silt clnrge intensity over the "ectil)n be 10;), 6f) to 70 p~r cent intensity of silt by weight will be near tbe surface and about 130 per cent near the bed. The cent per c.~nt silt charge iiltensity will be at about '6 D from the surface. The portion 01 DE represented the silt dragged along the hed. It was observed that coarse ~ilt was also available near the il surface as near the bed though in a very small amount. g. Tbis showed that the vertical eddies do work from bed ~ 0.$0 right up to the surfa.Ge in flll depth5. If some disturiJance In the form of ohstruction I e placed causing vertical eddiel", the silt charge intensity at the surface may be cent pF;r cent anti even more.

(c) Silt lifting eddIes In vertical plane.

100

Kennelly stated that the silt was carried by vertical Percentage of silt charge hy weight produced by the roughness of the bed The Fig. 9 eddies ~re defiuitf'iy produced on this account as proved in Reynold experiment.. , and they com,ert the st;eam line motion into turbulent motion. Lacey also states that silt is suspended by tile verticl-ll compon~nt of eddies, but urges that they are gcn~rated at ::lll pnjnts by forces normal to th~ wp.tted p::rimeter. Can such eddies be strong enrmgh to work up ~gainst depth ot 10 to 12 teet in large canals? The silt cany:ng capacity would thus be more in channels with shallOW depths alld less in case of those w.th large depths. Ihe author cC:Ds;cets that very much stronger silt lifting eddies Ate produced hy oti1er factors than by ftJ"ccioCl against the perimeter. One factor is velocity distribution as explained in para 1St::!} above. The velocity distribution in thA vertical phme gives::t rollmg motion Top water moving with rel3.tively higher velocity topples over and becomes the bed water, and the bed wattr lagging behind rises up to take the place vacated by top water. This explains the EtIong boilmg up to the surface which is usuaLy ~et,n-in the ca,e of large canals. In addition . to the forward motion, there is also the rolling motion. Suc~ silt lifting eddies are many times stronger tban those caused by the roughness of the perimeter. it is therefore that the large canals are carah!.:: of ~arrying rplatively higher silt charge by we;ght ane grade. K.B.KhLs'llani in hi_<; article in Indian Engineering. Calcutta, September, 1937 explains the rolling the:'ty {"If waler c('nsidering th'lt the forces acting are in the f,lrm of a couple prodllcpd by the fr.cii.Qnal rt sistance and the forward motion of the mass of water and works out the lever eddi~s

aIm 'of the couple Z=

f

and his regime velocity formula in terms of Z.

176 nii would be the case if the moving mass was a solid. but the ::Iuthor considers that the explanation of the rolling water due to vplocity variation is relatively more sound. The simUar lateral effect has already been found in his observations by A.S. Gi~b ai explained on page 177 in (d) (d) Lateral silt distribution in a channel section. A. S. Gibb, Executive Enginerr Punjab Irrigation, carried out observati')ns on Gugera Branch, Lower Chenab Canal published in hi., paper No, 28, 1916, punjab Engineering Congress, SeCTION

PLAN

-~-I--~-;;-}_....

/_J __ .... _ _•.!.o__

(' -

-

~

---'-X:=-':R;A;

-.,;.nCi t .!uz.--__ ----...

l

__ I

f-"

~'-.! .~l)~_ ----

--,-;;;~AC'_K:-_ ~ ~t"'";

-,

_~

Lahore. He made observations by floats, "The /' path of surface· Hoats gave surface lines dire~tly. and rod floats were aS3Umed to follow, lines givmg a meln between snrface and bottom stream. The line of bottom flow were dp.duced from thtJ observed surface and mean lines. Fig. 10 (opposite) merely I illustrates what is wen known. namelv that in an f·n ordinary straight canal the bottom water flows from the middle towarrls the margin, the surface water flows b::.ck towards the middle, and there is an . t he margma . I strIp. . upwar d current III

".'" <," ~

Gravitation is the only other known force acting on the silt particlts. Consequently from these cross I. circulating currents, allowing for gravity, it is possible Fig. 10 to get an idea of the a:tiv!tie5 of the silt particle~ in a channel. Sand suspended near the bottnm of the canal, as it is carried downstream, will re gradua Uy pushed along on or near the bottom (travelling by· saltation as an American experimenter terms it) into the strip of water near the margin, there it will come uncler the influence of the rising current, and a'l gravity is acting- against the current, the ascent will he considerably retarded with th~ res:llt that water there will be more rlensely charged with silt than elsewhere. At last on arriving near the surface the sand is carried away towards the middle of the stream, fallin~ throJgh the wa'er :IS it goes, its fall being ass:sted by the ultimate downward tendency of the current. Eventually the sand grains again come under the influence of th,~ bottom current and start off on their rounds again. Heavy particles of silt, it may be assnmed always remain near the hottom rather than [ght one:;, anr{ they are thus more under the intlup.nce of the bottom current towards the bank. The d'~nsity of tte silt charge in the marginal strips of water will be still further increased, oHing to the fact that the fo[warri velocity L; le5s there than it is in the middle, and a given quaQtitv of silt, whilp going the round above describpd, must be contained in a smaller volume of water when it is near the margin than when it is near the middle of the steam. It app·..:ars, then th ..t the marginal strip of the parent canal. which is to be drawn off into a distributary, normally contains the most hi!!hly silt charged water in the whole crOl;S section, and tend., contin . lally to be fed with. a specially selected snpply of the heaviest saur{ availabb. The c.ross currents in q11estion result from the presence of th~ boundaries of the channel or in other w,)~·d., due to the relatively reduced velo~ity ncar the sides and higher mean velocity in the mid stream. If the vp.locitv near the side could be increased by providing pitching the difference of vebcity rdative to the mid mean velocity shall be reduced and the amplitude of the cross waves shall increase." (e) Effe~t or convergence. The effect of convergence has been studied at length by C.C. Inglis, Director Research Institute. Pl)ona, India. If a bell mouth approach is construct"d as is US1B.l;y done upstream of contr::.cterl meter flumes, the silt tenli to concentrate in the mid-stream. If water be abstracted from tht! bell mouth approach, the silt charge on the off-tak~ is rela,ively less. (f) SOt distribution at bends. The cross section of a c.hannel at bends is as shown in Fig. 1 t There is shallow depth on the inside of the curve and greater dept'" toward3 the outside of a curve at a b~nr) in a channel. The inside tends to grow berm, while the outside is eroded. There is flow of silt along the bed as shown by arrows in the Fig. 11. --.Iti' _ _ ~,

~__

-----,------

__J

177

Fig. 11

This results in ~he. conCtntration of silt charge on the InsIde of a curve and there is reduced silt charge towarfls the outside of a curve .\\ hert the channel is deeper. An off-take taking off water from the out~ide of a curve cont~ins relative Iv low silt charge by weight and grade .

16.

Diurnal and seasonal variations in the silt charge in a Channel. (a) There is considerable variation in the silt charge and silt gr ade of the silt c:lrried daily in an irrigation channel. A few observations from the author's paper on lJ"sign of irrigation channels are given below showing variation of the silt charge card·d at R. D. 1351)0 of the Bhek distributary, Lower Jhelum Canal. These observations were taken by the author while engaged in experiments for determining the silt conducting power of different outlets. Si;t charge in Disty: expressed as ptrcentage by we.ght of W3.tr

Date 16-5-1931 55-1931 20-6-1931 9-7-1931

--

,'102 ,171 .132 .275

27-8-193-1 3-9-1931 13-9-1931

,331 ,350 .165 .14 .182

18·9·1931 1-10-1931 2-10-HI31 5-10-1931 7-10-1931 8-10-1931

.150 .:203 .120 .I!-O .150 .160

13-8-1931 21-8·19~1

-There -is a free fall R.D. laSOO.

The longitudinal section of the reach upstream ot at this fall was observed nc~asionany to see if it was silting or scouring during the course experiments. The observation'l showed that the bed of the channel did neither silt UJ) nor scour during the period in '1uestion, in spite of the fact that therl'l was a ,~onsidf'r'lble variatiop in the silt ch~rge carried in water from time to time. The Bhek distributary is II. rt'gime channel. n has not changed its levels during 43 years of its running. The variation in the silt charge by weight was from '12 to '35, about i. e .• 3 times. Two points are explicitly c{lnr from these observations. (i) In the formula for the change in C V.R .• (Rc=T 11 / 3 r2'3. A 11&) if the depth dops not change, and if r1 the silt charge changes. there must be corresI onding reduction in ri silt grade in order that Rc does not change causing neither silting nor scouring. (ii) Silting or scouring does not take place immEdiately as the stlt charge or silt grad. is changed. TheTe is some natural resistance offered by bed bdore it is ero "led (b) The seasonal variatio'l of silt charge is well known. In my observations on the Lower Jhelum Canal I found it to vary from·5 per cent by weight in summer to a little ~elow 1 per cpnt in winter. 1he silt charge by wFight is maximum in the rainy s.-·ason when the pa.ren' river is in floods. The summer silt is muddy and winter silt is fine a.nd coarSe sand. The irrigation channels pa-;" tile high silt charge in the months of Jl1ne, J11ly and August "ithrmt silting up. The channels berm up most in the months of July and August. when the fertilizing' fine s'lt charge is very high. Deterioration of channels in the rr.onsoons is mostly due to .berming up. The irrigation distributing ch:mnels silt up most in the months of October and November mostly due to the falling p~rent river picking up coarc:e silt in digging the winte)! channel and partly due to the water picking up of the coarse silt in the canal itself due to th~ large reduction in the silt charge by weight.

0'

178 t 7. Silt

attrition.

(a) The subject of silt attrition in canals has received little recognition so far and it is generally argued that on account of the low velocities in the canal, there is no possibility of silt attrition. MoreoVfr. it is sometimes argued that the progressive reduction in the silt grade is not Clue to the silt being worn down by attrition, but due to thp. silt selective behaviour of flow in dropping- coaT~e stuff and picking fine sh,ff. This wculd be the case if the velocity were reducing but in Ion,; lengths of canals with fl.) change in velocity, as the lined Bikaner canal, the redllctinn in silt grade mmt mean nothing but silt attfi tion. In rivers the part played by attrition is evident. The pebbles (grit) are ground flown fiIst to coarse sand and then to Lne sand by the process of rolling and impact against the bed and among themselves, as they are transported from the hills to the plains. The silt attrition is therefore an establIshed phenomenon, but the limits of its operation remain to be determinea. rhe velocity at which tu!"bulence start;; is known to be al-,out '80 foot per second, Thoore mmt be a sfc::md critic::ll velocity beyond which the silt wou'd drag along the bed and the condit:om n .. cesoary for silt attrition would come into play. D, Owen determined such a vdoc:ty to be equ:l1 to about 2'5 feet per second. Observ:ltions and experiments could alone determine sllr.h a velocity in actual canal practice. The author saw from below plate glass bed in the C'lll!"se of some other experiments that the silt was rolling and dragging arong the hed of the Mith1.lak Di3tributary, Lowpr .Thelum Canal, when the velocity was onl:? 2'0 feet per secon n. It is pro'Jable that the second critiGal velocity necessary frlr silt attrition might be va.ria:ll0 with the q,untity of the silt to be d:-agged along the befl. There can he n') denying th'~ fact that the drag~ing of the silt along the bed always ta'<0s IJlare at least in the case of main and bra1l6 canals. The effect 0 f the silt ~ttritioD mu"t :It least come in th+'! design of the1'~ channels, The author in his paper on "Design of lrrigation channels,' worker! out the effect on the value of C,Y R. if the silt grade changed from fl to fa by attrition There was then no authoritative record of experiments to determine the actual change in silt grace. . (b) Experimerits have been carried out by C.C. Inglis C.I.E, Director, Central1rrigation and Hydrodynamic Research Station. Poona. "The object of this exp'~riment with silt abrader is to see whether abrasion can be an explanation of the feature of large rivers th::lt the bed sand becomes progressively finer from the hills to the ~ea As described in the annuall'eport for 1937-33, the Silt abrader c()nsists of a circular tank of 2 ft. radius. 4 feet high, with a central shaft to which three tiers of hlades are fixed, each tier being set at 40 degree to the other two, The shaft was revolved 30 times per minute. so the velocity of the blades at the outer edg~ was 6'9 feet per second. Sukkur silt was placer! in the tank to a depth ot 6" and water maintained at a constant level, 3'-6" over the bottom of the tank. The abrader was work"d for 1637 hours (68 days) since last year's report, the total working hours up-to-date being 8787 hours (366 days). At the end 01 this time, the silt on the bottom was thoroughlv mixed and analvsed by the Puri siltometE'r. It will be spen, that hetween 7150 and 8787 hours abrasion of silt particles of 0'25 to 035 mm grade took place, resulting in the increase of percent silt between 0'11 to 0'25 mm, diameter. Thtlre wa~ verv little perrentage increase <0'08 mm., which shows tbe limit of abrasion becau<e helow that limit, the silt goec; in suspension, "Table II shows the progres~ive reduction in the graile of silt at various periods during the experiment." Table II. Total hours of working

dmm. ....

Original sample 3775 hours (t57 days) 5S8l hours (224 days) 6220 hours (259 days) 7150 hours (298 days) 8787 heues (366 days)

0229 ,_ 0216 0196 0'193 0'181 0'169

fd=J.76y'dmm ba3ed on particles 0.075 mm. diameter 0'84

0'82 0'78 0'77 0'75 0'72

[c] The Poona experiments dearly show the cff!C!ct of sJlt attritirn. or abration, _ nut aClual obst:fvations in canals are m:eded where the discharges and the velCcitiCs do not

change

179 in long lengths as main line Upper Bari Doab Canat Bikaner lhed canal or Haveli lined canal to determine the act.ual reduction in silt grade.

18. Silt movements. The phenomenon of silt movements is peculiar to the large distributing channels in the tail divisions of a large canal. The channels of the Jhang Division Lower Chenah (anal in the Punjab (]hang Brancrl lower in its tail reach), Bhango Branch Dhaular Distributary and C.ultan Pakha distributary are especially notorious in this respect rbe water leveL; suddenly rjs~ fr,)m'5 ft to 1'0 ft. depending on the size of the channel in ilS middle reaches even though no excess supply has r fen admittrd at the hf'ad, This results in suious leakage and brraches The authnr had a personal experience of this trouhle in the channe1~ menticnf>d above . . It was at first argued that there was actual increase in the di:;chargc of the channel at he'l.d due to relatively muddy water coming in the canal. This is quite likely when the regulation is done with referoo.r:e to a gauge fixed downstream of a bead in an earthen channel. There is about 10 to 12 % increase in discharge, if muddy water follows a clear water flow turn in earthen ch;mncls without any change in the section due to reduction in the co-efficient of friction. J. P. Gunn Executive Engineer, Puniab frrigation carried out detailed observations on meter flumes and found that an mcrease in discharge dlle to muddy water was 3 to 4 percent. The remedy would therefore be to construct meter flumes near the head of snch. channels for precise reguhtion. The Dhauler oistributary was provided with one at R. D. 500 in 1925. This has not. however, cured the silt movement troub~e which is now (1943) the worst ever experienced. There is one peculiar point about these silt movements that they are the worst in the beginning of November and about th", end of Fehruary every year, synchronising with the change of 5easons. TbA Authe, considers that tbe silt movements are primarily due to temperature ~hanges and the r.omequent viscosity changes in the channel baving fine b~d silt. The bed silt is lifted up in water and the piling up of water is due to the unerona')le bars in bed or the drownrd bridges and the increased fiction on acconnt of relatively coarse silt in suspension. The silt movemtnts are no doubt intensified in the lower reaches of a canal. if there are a lot of rais~d crested falls in the upper reaches suhject to long periods of low supply an·t also if 11)t of silt exclusion has been resorted to in the case of distributary h~ad regulators in the upper reaches of the canal by constructing skimming platforms. 19 Berming and Siltillg-up of Channels. The distributary channels silt up most in the head The mindle reaches are generally free from sUt trou)le.

rea~he_;

and b:mn in the tail reaches.

Tile rea:IO:1S for sihirrg up in the heli relches Y'

I

I~ .f-. 1""'; ., t"t "t 1l:1 r.,,_r • [iJ Non-regime section. I rf the spction given is not suit;l.ble, tte cbannel water would drop its cargo of silt which it cannot carry in the head reach and the lower reaches will thu; d0al with silt in water, out of which objectionable silt had already been dropped in the head reach _5. .-•

[iii Defee tive Bead Regulator.

If the head regulator design is such tha t excessive silt charge enters the distributary, the coarse silt would raturally drop in the head reach. [iii~

Insufficient slope.

If the channel~as been given insufficient slope, it would naturally tend to incrPil.',e the slope by silting up in the beginning of every reach in the channel downstream of the control points.

[ivJ Defective outlets. If the outlets do not draw their due share of silt, the channel would silt up in. the head relch mostly a.nd iu other reaches to a less extent.

180 [v] Fluctuations in the supply. If the channel runs long pf>riods of low supply it would silt up most in head reach to adjust its cargo of silt from thp. reduced depth and velocity. After the adjustmflnts of the silt C::lrgo in the head reach of a channel,· the middle reaches pass off the supply safely without silt trouble. The lower or the tail reaches of a channel are again the source of great trouble dUll to berming up. The reasons are enunciated below :-

[i]

LOW

velocity.

On account of small depth and small velocity water is capable of carrying a reduced cargo and low gratie of silt. The side velocity being very low, fine silt deposits there to being with [ii] Growth of grass on the berms.

The growth of berms flourishes most in the tail reaches due to low velocity and the fertilising fine silt deposited on 1he sides. The deterioration of the channel section start!; from the sides. Water is headed up on account of the rflduced section, and spreads over the berms with the consequent rise of the bed. The berm rises up by grass growth and silting in turn in bed encourages further rise in levels. It is, therefore, that berm cutting in the tail reaches is "ery necessary to feed the tails in the months of July and August. ~O.

Silt Sampling an:l Analysis.

[AJ Silt is transported by a stream either in suspension or by rolling on its bed. Silt sampels are,analysed as below:[iJ Coarse sar.d, i e. particlfls above .2 m. m diameter. [iii Medium sand, i.e. particles between '2 and '08 m. m. diameter. [iii] Fine silt, i.e. partfc1es h( tWeen 'OS and ·02 m. m. diameter. [iv] Dissolved material and clay below '02 m. m. diameter. Item (v) i'l ignored and the summation curves are got for the first three items to work out the mean diameter. Silt intensity can be calculated from the mean value of coarse sand, medium sand and fine silt observations taken at a prticular site by the formllla:Silt intensity in eft. per% eft. =grams per litre X 5/8 and silt intensity in eft. per cusec-day=grams per litre X 54. [B] sampling, of suspended silt. [a] Bottle -:SQ)pler. It consists 01 a brass frame bolding a one-litre bottle fitted with a rubber stopper. The stopper is operated by a lever at the top of the suspension pipe. When the lever is pres5eo down, the bottle is openc(l. The length of the suspen!'ion pipe of the sampler is varied to suit the depth of water in the chanr.el at the sampling site. Tte two essentials regardinl'!' the working of the sampler are:[a] The roouth of the bottle slJOuld be opened only when it reaches the >requiren depth. [b] Th~ mouth of the boWe should be kept open for the minimum time required to fill the bottle . If the bottle is kept cpen for a longpr time than that requirpd for actually filling the bottle, coarse silt particles keep on falling into the bottle f>vpn after it is full. The time required to fill the bottle should be ascertained experimentally by the observer. The iliap
The Tait Binckley S::lmpler ccnsists of a ((ntral pipe with rubher extensions on both sides. The f'xtensions are twisted by an arrangement fitted at the top of the suspension pipe to enciose a sample of water. [c] Uppal Samplc:

The. Uppal Sampler, as developed by Dr. 1I. t. Uppal of the lrrigatiotl Research Institutt>, Lahore, consists of a brass barrel with guides fitted at each end. Brass diaphragms

181

move in the guides, vertically, like the shutters of a photographic camera. Both the dia.phragms and guides are ginn a slight taper to secure a leak tight contact. The top end of the diaphraa-ms are conn~cted together bV an iron rod which is worked by.a lever at the end of the 5 uspen;on pipe. Detailed descripto) with photograph" is g;ven in the Report hr the year ending April. 1940, of the Punjab Irrigation Research Institute. Lahore. {r.) B:lr} Silt Sa;npling. The old method of filling cigarette tins from the oed of a canal in a closure is !'lOW discontinued as silt thus sa'npled out is not considef(~d to be a repre~entative sample of bed silt carried in w14ter. cecause wh~n the canal supply is dropping before a closure, some fine silt in suspension also drops down which i, again picked up in full supply conditions. The samples of bed silt are taken by m~ans of an app1.ratus which is described in detail, in the Punjab Irrigation Research Institute publication Volume 11 No IS. This consists essentially of an eccentrically mounted scoop which dig5 into the bed when revo~veri and a cowl which protects the sample from being washed away when the apparatus is brou ght to the surface. To take a sample, the apparatus is lowererl to the bed and the top rotated which in turn rotates the scoop by m ~ans of wire. It should be noted that the pip~ forming the handl!1 is kept clenr of the cowl so as to avoid the water in the pipe interfering with tho sample. The sample is air dried and approximately one lb. kept for examination. The following hydraulic oatas are obtained at th~ time of sampEng:Q (Discharge), A (Area of cross Rection,) S (slope of water surface X I02).R (Hydraulic mean raclius) , D(Mean dcpth).Pw (Wetted perimeter). B(Becl width), N(Kutter's co-efficient for rJughne;; and G (mean ga1Jge of the ch'lllnel during discharge observations). The temperatu:-e of water is alsl") recorded at the sarr.e time. (DI Total Silt Charge Sampling ill a Canal. The me!hods describ~d in paragraph (B\ above omit the silt rolling nlong the bed and the method described in (C) above omits the silt in suspension. Th~ author used a scoop in a trough intercepting the jet at the downstream end of a free fall long crested weir to collect II total silt charge sample Thi" method is described in detail in the author's paper No. 168, punjab Irrigation Congre:is, Lahore, 1933. (E) Silt Analysis. (a) Ke:medy's Siltometer. De ailed description is a availahle in pap~r No.9 Technical Publica' ion cl:tss A. P. W. D .. Irrigation Branch, Punjab. It is now obsolete as thi" method gave qualitative results on l ". Thtt dropping silt in a tu~)e was collected in a gradu'Ited bottle and the times of filling the variolB divisions were noted. (b) PUri's Siltometer. Th's is an improvement over the former. A detailed description is availa}lle in the Punjab Irrigation Research Publication Volume II Nos. 7 l\ud 9. nlC bottom of the sijtomp.ter tube opens into a circular trough proviaed along its circumference with detachable cups which are just large enough to b~ covered by the bottom of the tube, e.g., after 2 !,26.::iO seconds, so that each cup comes in turn unner the tube and receives the particles which reach the bottom in the interval between two movements of the trough. When all the silt has passed down, the, cups are taken out and the silt in each is washed into a separate glass tube with a narroN long bottom graduated in cubic cp.ntimeters. The valume of the silt which settles down io; rea.d assuming that the density of particles of all sizes is the same. we gd a proportion to the weight of the particles received in each cup. The sizes are read from a table prppared and the volumes for the cup,;; are Stlccp.ssive totalled up to give the total volume below each size. This is then plotted against the siz': to give a summation curve similar to the pressure size curve obt4lined from the optical siltometer described below. (c) Vaidianathan's Optical Lever Siltometer.

1t is described bv Dr. This is the most correct method of silt. aMlysis. Va:dianathan in paper No. 167, Punjab Engineering Congress, 1933. A prief description is given below;-

182 .Optical Lever Siltometer

(i) When a given sample of silt is released from the top of the siltometer tube the arriv,Ll of various partiCles at the bottom of the water column is indicated by a change in the pressure as shown by the fall of th~ mercury meniscus (M\ in the m~nometer Fig. 12. This is magnifi~d by the optical lever arrangement and the movements recorded on photogr lphic paper. The light is intercepted at known intf>rvals {usually one second} so that a spiral curve broken at the corresponding intervals is obtained A base lin'; from which measurements have to ce taken, is obtained when the slIt has completely M passed down. The onJiTlatesof the spiral curve are measured from the base line at the varicus breaks in the curve. They give numbers proportional to the pressures of various in"tants, The theory connecting the time of fall of the particles at a given temperature of the water column with their average size is described at some length in paper No. 167 Punjab Engineering Congress. , 1933 Here it may only be stated that from a knowledge of the time and tbe temperature i~ is pos3ible to read the average ~ize of the corresponding Fig. 12 partcles from a previously prepared table. This t::tble can, however, serve only for a given length of water column and has to be sl'parately prepared for each silto meter of a differf'nt If>ngth, The rate of change of pressure at any given instant on the other hand has been sh()wn to he diredtly proportional to the rate ot change of the weight of particles deposited at the bottom of the siltometer tube and consequently the rate of change of weights is directly known fr Jm the pressure readings. '

.

Thus we get the corresponding valnes at any instant of a number rroportional to the .... total weight of particles deposited up to that " instant and of the aver"ge diameter of the partides arriverl. at the bottom since the previous measuremt'nt of time, These values are entered on a sheet and are plotted on a graph. A free hand curve pas3ing very closely through the plotted p~int is now drawn and the curve and the values are passed on to the statistical section. Form of curve is shown in Fig. 13. Iii) The percentages. The plotting anrl. the curve are checked first and then the values of the presslJres read from the curve for integral values of the diameter of the particles. If the value of the pressure Particll' size in mm. for the datum line is not zero it is then subtracted Fig. 13 from each value We consequently get a series of numbers proprtinnal to the weights of all the, particles . whose mem diameter. is less than the correc;ponding intgeral value cnterer! in the prevlou5 column, The las~ number 10 the column (savL! is proportiunal to the total weight of the silt !"ample. . , . 'Eash number is then divided bV the number Land multlpltpd by 100 to give the percentages by weight of the particles below. pach size, The last are w:lat are known at .tht "summation" pncentages, ie, they re Jrl'spnt 1h~ mms, of the ~epar;Jle per,centages by weIght of all tIll' particles whose sizes are less than the glv0n sIze. If the snmmat.lOn percentages are plotted against the values of the mean diameter we get the so called SUillmatton curve. Pressure-Summa tion -Curve

(iii) The si'le distribution curve. Each value in the summation percentag" cohmn is next suhtracted from the value just su('cee(:ing it. Th~ difference.s form a new ~olumn giv~ng the "dish.i mton ~ercpntages:' lhese give the proprrtlOns by wClght of the fractIons of particles whose dIameter hps bf>tween

183 the value .of the diameter .entered in the p~evious column in the same row and its next lower vallIe. It 1S thought suffiCIent, for all practIcal purposes to take the mean of these two values as the mean diameter of the fractions. The distribution percentages a"e next plotted as ordin'ltes against the diameters of the fractions as abscissa. A free hand curve passing closely through the individual points is next drawn. It shows how the particles are distributed acording to the m~an sizes and is known as the size di,tribution curve. A typic'!.l siltogram or the paotographic record of the analysis of the silt sampl\! is shown in Fig. 14, and a typical sllmmati)ll curve in Fig. 15.

SILTO::;'RAM OF BED SILT

.--".

£--"tii~ 'L ~}J;L&' . r

-----8

AS..£.

J

Eig. 14

SIzE DISTRIBUTION CURVE

Fig. 15 (d) Uppal's Air Sntom,ter.

~

Siltometer for quick and accurate analysis oj: silt samples has btltlD developed by Dr. 'H L. U ppat A jet of air bas been utihzed to separate the par tid-es ,belonging to diffenmt grades. The apparatus consists of the following parts ;N A blower. (iij A stiHmg cbamJer. (iiJ) An air tank. (iv) A collection chambet. A standard blower supplied by Messrs A. Gallenkemp has been 'Used. The speed of the motor is aojusted by means of a tachometer. In the stilling chamber, which consists of a woorlen box 2' x 2', the air is stilled befote it begins to flow in the air tank. the air tank is m~de of glass plates 4'x3 i and oW apart. fhe top two feet pJrtion of the tank is used for th'" passage of a stream of air, whiie the bottom one toot i" occupied hy th0 coilection chamber. A sample of the silt is introduced at the top left hand comer of the air tank. The air blast separates it into different grades which collect in the collection chamber bel<Jw the air tank The collection chamber is divided into one hundred compartments by mt'ans of celluloid

184

strips. At the top-ends of the s t 6p" fin" needles are fi Ued so as to a void any turb~lence which might be caused by the jumping of thp particles. Each compartment of the collectlOn Chamber has been calibrated for a known speed of this bhwer. A direct distribution curve is obtained by the use of this siltometer. The bottom of the collection chamber is removable so that after analysis the sample can be readily tal,cen out. A large number of samples have been examinei in thii apparatm and it has bl'l3n shown that duplic:ltes :lgree well and that the method is rapid since it Saves a considera">le a.mOUI:lt of labor:ous calculations. 21. C.>rrelation between Silt and hydrauli'.3 Data Size Distri:mtion Curves tflongh characteristic of variou" silh are not con venient for defining them for purposes of correlation with the other hydraulic data of the channel. ~or tUs purpose it is neCeSS!'lTy to define the silt by m~ans of" smgle values" capabb of be~ng derived from the summation of distribution curve. The single values now being used are:(i) Weighted Mean Size "m". The summation curve of a silt sample gives the percentage of paricles belo'" any gi'len size. Bv taking the reaclings for two ginn siz's and subtracfing we can a~certain the pe:centage of particles who~ e diameters lie between the two sizes and w~ic 1 m ly very nearly be assumed as having a diameter lying mldway hetween the two siz~s. If this last value is multipLed by the corresoonding percentage, and the sum of all sur.h products is divided by the S,lm of p~rcelltages (usually 100) we get a value for the mean diameter of all the particles contained in the s tmplc. This is the wp.ighted mean size or"m" and furnish83 a useful measure of the degree of coarseness of the sample. (ii) Standard Dcvia1ion "a". Every sample does not consist of particles distributed in exactly the same way, and it is quite possible that two samples with the same mean size may differ, one hiving a preponderance of parti.~l~s with diam~ters near the mean size. and the other with diameter va.rying much more widely. Hence it is necessary to know how the variolls sizes are distribuh'd a:7out th~ mean size, and consequently the "standard D.:;viation" is calculated as a measure of their" dispersion." To o~)tain this the deviation of each size from the weighted mean size is squared and multiplieci by the correspondiug percentage and then the sum of such products is rlivided by th\) sum of the percentage. The square root of the quotient gives "a"and the smaller it is the more uniform can the sample assumed be. (iii) Schoklitsch Number or uk".

The maximum diameter of a particle that can be determined bv a siltometer is 0·6 m m., so that in practice the mass curve is bounded by the 0 and 1.1'6 m.m , ordinates and the line (Distribution Curve) may be taken to repre,en~ a normal mas .. curve. If then the area A lying above and to the lp.ft of the mas, cnrve, be divided by the arf13, Riving below the mass curve :md to its right the fraction AlB remains constant as lor g as the I mits 0 and 0·0 remain unaltered. This was pointed by Professor Schoklitsch, who found that this fract:'on worked quite well for specifying shingle~, lthough open to many theoretical objActions). This number is referred to as the Schoklihch numher or "K" and when not otherwi;;e l".pecifined is taken to refer to diameters lying between 0 and 0'6 m.m. Should it be desired to specify these limits more particularly it may be written as 0'< 0·6 in th~ same way 0.51, 2·0 would refer to mixtures whose mass curves lay betwpen 0-5 2·0 m.m. It has been often asserted that the presence of fine suspended matter in the watpr will alter the viscosity. so a series of rough te,ts were made on water containing from I oz. to R oz. of fine susFcnded matter per cubic foot. A plot of these values is "hown in Fig. 4 of the Punjah Irrigation Rpsearch Publication No. ] 5 Volume If and with the exception of one point they lie on a fairly good line, examination of thA wide point by statistical mf'thorls showed that Chauvnnets criterion ju<;tified its reduced (Brunt D. "He Combination of Observa.tion" 1933 pag!) ]30). Th~ v!sm>ity in~reases from 852to 914 from pure \\ater to oz. of ~ilt per cubic foot, which may be se'n Gn a reference to the approximate tables to be that produced by about 20 0 difference of the temperatum. It m'ly

185 be "Concluded, therefore, that the normal amount of suspended matter which rarely exceeds 2 oz. per cubic foot. in canals makes no practical difference to the viscosity. The temperature, however, is recorred at the time of observation so that suitable correction may be applied at any time, if found necessary. It might te argued that though the fin} suspended matter bas no effect on viscosity, it would exert some direct influence on the movempnt of bigger pa'ticles. Silt was, therefore, analysed in the Puj Siltometer using water w th increa5ing quantities of suspended matter. The f<'sults l,elow show that silt constants a e unaffected 1 y the presen~e of fir.e particles, TABLE Effect of Suspended Matter in the Water on Silt constants. (Sample from Lower Gugera Branch R.D. lEOOO). a

K

'2894 '2952

'892 890 '904

1'008 0'932 0'969

'2993

916

O'~99

'30(:2 '3022 '2958 '2950

'946 '988 '89(1 '862

1-001 1'015 0'972 U'367

:::'usj.>elll,ed matter

Ill.

Ounces per eft. ~------------

0 '12 16 '39

'3U 11

62 I'll 4'09

S'U

It has already been shown that L:>cey's silt f
.33

-~:- = ( ~~~).

·3

(

-~~- ), (-§~-)

,2

whHe X=C.v,R, W = Vv'eight of total silt charge carried and rolled. m=Weighted mean diameter of silt carried and rolled excluding soluble matter and clay below '67 diameter, Q=Discharge in cusets.

22, Wee:! Growtb. The weed trouble in the Punjab canals does not exist because they are fed directly from the riVf'fs. The weed trouble in the seepag';: drains in the Punjab is very acute. The Deccan canals fed from the storage reserVO;f3 usually suffer from serious weed trouble, A very authoritative account of this trou')le has been describen by c.e. IngLs C.I.E. Director Poona Research fnsti:ute and V.K. Gokhale. in Bombav P.W.D. Technical Pape" 1937-38 on "The I~radication of water weeds from the Dec:an ('ana1s." /\ brief summery is given here and the student should refer to the original publication for a detailed account. (a) During the mOll"ocm, the Deccan Canals obtain most of their supply from rivet flow; but for the rest of tl e year they are dependent on suppl es from IDrgE' artificial lakes formeo by the construction of ma,>onry dams across river valleys in the foot· hills on the eastern side of the W.,stern Ghats. These d'lms are ahout a mile long and vary in h~ight from 100 to 270 feet. The Canals, eXcf'pt the Mutha canals, take off from above pick. up~weirs constructed acros~ the Rivers som~'20 to 53 mill'S downstr~am of the storages. These weirs vary from 10 feet to 40 feet in height; and from 890 feet in len~ th in the ca.se of the Paravara pick-up~weir At Ojhar, to 3618 feet in the case of the Godavari pick-Up wp.ir at Nandut Madhameswar, Tn the caSA of the Pravara left, the canal when first opened in 19]9 was capaJ.le of giving a discharge of 500 cusecs with only 6 feet of water, whereas by 1922 only 272 C1!secs could be obtained with that depth and only 73 ~usecs or 15 per cent of the 19]9 fignre after the weeds had grown, within 2t months of a full weed clearance. Weed growth is not uniform throughout the yeaf. It generally starts in October, and by Deceml:er it is heavy and under the old method of

186

running canals, another clearance was required early in March and another ahout the end o( April, (b) The following water weeds are found in the Deccan Canals : 1. V::lllisneria spiralis, 2. Potamogeton pectinatus, 3. Potamogeton perfoliatus, 4. Potamol'eton indicus, 5. Ceratophyllum demersum, 6. Hydrilla verticillata, but for simplicity, water weeds may be dividen into only 2 groups :. 1. Vellisneria spiralis-a gr3ss like weed, up to 14" in length, whIch grows in tufts, and 2. Potamogeton varieties and associates-the worst of which is Potamogeton perfoliatus which gr()ws to a length of 12 feet or even more. No.1 is the first ,"epd to appear, and is comparatively, unimportant except in small channels-. No. 2 indicate~ a much more serious condition of wee). ,c) Factors which may be expected to affect the growth of water weeds. [il Infection, [ii] Temperature of water, [iii} Chemic
187 from Bhatgar being more constant tha.n in other year~). This canal has alwdo}s been more free from weeds than any other. The Godawari Right Bank was the only other canal in which weeds were, at this time, decreasing; and the disc rpading were also small. In 1930 there.was a marked increase of disc reading in the Pravara Left Bank Canal and thereafter weed . growth became serious. The worst canal for all weed-growth Was the Mutha Right Bank Canal in which the disc reading generally exceeded 4 f~et. (d) Conclusion:[i] In every case examined, weed growth and turbidity bore a close inverse relationship; [ii] No othM single factor inhibited weed-growth unner normal canal conditions. [iii] Where D>3d, no weeds grew, where d=Disc reading and D=depth. [iv] Where D>oz/2. only Vallisneria grew. . [v] Turbidity, which le:Jds to exclusion of light was the dominant factor controlltn~ weed growth in Deccan Canals. The growth of water weeds in the Deccan Canah h:ts hitherto interfered to a serious extent with Canal administra.tion, due to the fact that closures for weed clearance were necessary in the hot weather at intervals of 40 to 50 days. These closures, which took place when the discharge had fallen to minimum supply, necessitated an increa"e in the period between waterings and considerable dislocation of normal supplies, with the danger of mistakes and the certainly of water being taken out of turn by SOill'} irrigators. The consequent dislocation of normal conditions did not end when the canal was reopened, but persisted for about 2 rotations after each closure. These closures inevitably le
2j.

Lined Channei Sections.

K. B. S, I. Mahbub Executive EngineElf, Published a very cpmprehensiv0 paper No 260' on "LiniI:g of Channels" in the Punjab Engineering Congress Proceedings. 1943. A brief summary on design of sections is given here (.-\) Design of Sections, The best form of lining section would S(~em to be an arc having sloping sides, more or less at t.he same slopeas the angle ~f repose of the soil. The arc in the bed should b(! ta.ngential to the Side slopes. It can be eastly shown tha.t we get the mOst econoIIlical section, i.e., the

188

maximum area for the minimum wetted perimeter if the centre of the arc is at the F, S, Line with radius equal to depth, This section is also useful as it has a higher silt carrying capacity than a wide shallow one, During low supplies, heading up has to be done at off-take sites which would cause some silting. This in turn reduces the velocity and also the value of 'fL.' In the sp.ction proposed, however, with no level bed, the silt can deposit on and effect. the rugosity co-efficIent of a relatively small portion of the perimeter and hence cannot greatly affect the velocitits, The effect on 'fL' also would thus be corn.spondingly less. The side slopes may be kept as 1 : 1 for radii less than 1:2' and Ii: 1 for radii over 12' provided that the angle of repose of the soil is not flatter than I! : 1, as shown in. Fig, 16• ~~~~~

,

.

.

______________~~~~__________~__-,~L;~8-~.

"

Fig. 16 The sectional data would be given by the following ~ormulae:~ Distributaries Side slope, 's' 1:1 1'78 S2 Section area I • ' 3-565 WcUed perimeter 0'5 S Hydraulic mean radius (R) The velocity according to Manning's formula

C:lnals It : 1 1'925

52

3'85 s 0-5 s

III

=!:_48() R2;a 51/2:;:: !-~8~R2/3 (~_) N

'

N'

lU,OUO

where 51 is the fall in 10,000' with N=0-018 we have v=0'S26 R2j3 Sli 2 and its solution is given in nomogram Fig. 17, 2 3 /

' harge= A V= 0. 9 2s 2'-3 •5). :. D ISC 12 f or SI'd e s 1opes I' : 1-and 0 '995 2

S1 ~~ f or

Sl'd e

s 1 prS

v =0'40s t SI Ii : 1 and Lacey's fL=0'7Sjf 2

Graphs connecting Q, 5, s, fL and v have been plotted for side slopas 1 ': 1 with N =0018 (Plate XIV -A) and these can be conveniently used for design.' The free board may vary from I' for D=4 and :l' for L·= 16, which would be e::J.l,I.iY'!olent toO'S DO-5 ' / (B) The limiting depth, The limiting depth of this section for all practical purposes may be taken a<; IS' and so fot' discharges exceeding 2.000 cusecs, an alternative type as shown in Fig, 18 may be adopted. This was adopted on the Haveli and is also proposed to be used on the Thal Main line' , 'In this the sectional data is given by the following formulae. '

When

P=~.!C=~ D D

Side slopes's' Section area Wetted perimeter

aud N (Manning)-O'018

== 1 : , ' ' =D2(p+ 1'7854) -D~p+3'5807)

.I

189 LINED CHANNELS

HANNING's

FORMULA

.~" ""'~ f.:l"

.coo Soo

(.I;

C) ~

0

z.....

.,..

;Jl

\l

10·1)

rn

1&1

.::::: u :::: .......

~I

100

....

100

I

••0

!it c., 0

'Do reoo

....l

tn

f.r 4'0

0

......

..e p:;

z

~I

l.

.... 1&1 ....

f.:l :;?l

"-

c...:>

....

~

:Jl

IU

')..

Q.. III

.... .... \.I

3·"

0 -.I

\iJ ~

'·0. '000

.11"" SOOCI

fC

IU

I&..

.. ,

,_.,

,...

<1>.

~ooo

\'oao

eooo 0".

F~. 17,

~

....

....l

: 'til, fL 'I

< et:

A

>-

::t:

190.

;....

ii-

.::::1

i:"

~.

;f.. ,,..

..

,>'

~

._.-It ·f'

y.,locitv =0'826 R2Pl Sllf2 With 51 =1 Discharge={p+ 1'7854) 0'822501 3 D8!3

V2) = 0'511

Lacey ,s fL= (0'75 '---R--

Hg.)8

ell3 DI/S

(P+l'9248) 0'825501/3 D818 0'511

(1/ 3 Dl/3

p+3'8496 1'+1'9248 Graphs with N ='018 for side slopes 1: 1 have been plotted correlating the various data (PlatE-s XvII (b) Vol. III which would be found useful in designing any section, This section is better than a trapezoidal section, as it is more stable and economical and also does away with the np-ed of having a toe wall to support the sides. The slope may he kept as the steepest practicable subject to a maximum velocity of 6 per second and a minimum value of fL = 1'2. Iron or concrete rings, flush with masnnry may be provided in the sides every 1,000' apart, fixed vertically to enable any person who falls in the channel to come out. .

. P +3'5708 c= - --p+17854

(C) Kennedy, C. V.R,or Lacey's silt factor in lined section. Kennedv's C,V.R.(X~-,=l 0) "nil Lacey's silt factor (fL:c-~1 0) connote regime channel conditions in the earthen irr:gatJon channels normally maintamed with self-silted berms and silted bed, The roaghn"'ss of the perimeter of the earthen channel section is greater than that of the lined channels. The silt supporting erldies in earthpn chanBel sections are relatively stronger and more efficaciou<; to support and to roll the !'ilt charge in channel as compared with the lined channel. In actual practice 20 percent higher value of Ktnnedy's C.V.R. or Lacey's silt factor i.. allowed in the brick lined sections and 25 per cent more in the cement concrete or cement plastered sections.

23.

~uper-ele"ation

.in Water Road5.

(A) It is a well known fact that when a body moves in a circular path. it gets deflected from its tangent to the circle by a force acting towards the centre of the circle. In the case of canal sectLOns un circular curves, the centrifugal effect of the mass of water moviDg round the curve causes damage and slips to the banks on the concave side loutside of a curve), The curve, thllS Sdon developes into a hnrse shoe bend impeding regular regime flow and inducing silt deposits on the inside of a curve. To maintain equilibrium and to counteract this tendency of the water moving round a curve to attack its conC'l.Ve bank under the action of centrifugal force, super-elevation or raising of the outer !l;ide is most essential . The centrifugal force developed on a curve in the case of canals with velocities les3 than 3·Oft. per sec, (which is the li:niting velosity for side e~osion lor the soil conditions in the Punjab) is too small to have any effect on the concave side of the channel section. The centrifugal for ~c results in the eccelemtion of the velocity of water near the concave side of the

191: cut\'e and retardation of velocity near the,convf'x Sifh~ of the curVp.. The dischargp.' intensity er foot width of the channel section dops not remain constant as in a normal section in a rtraight reach. Both, the increase in the discharge intensity on the concave side and the ~cceleration of the velocity may result in producing velocity near the concave side higher than the sa.fe scouring velosity of 30ft per sec. The maximum safe-scouring velocity has been taken to be 3'Sft per sec. in extreme cases in the case of tenacious clayey soil crust. The silt distriblltion at bends is describp.d in paragraph lS(f} of this Chapter. To design the non-silting benns, the bed of the channel should be super-Elevated a'1 shown in Fig. 19 w that the discharge intensity is the same per foot width of channel. The depth of the channel on the concave side should be reduced according to the increase in the velocity If the developed maximum velocity ~exceeds the safe-scouring velocity of the soil of the bed and the sides, the channel section should be protected by pitching or by paving. . The minimum radii of curves in irrigation channel,; are fixed in practice based on the experience of earthcrn channe' sections and their valu&s are given below : Capacity of channel. Minimum radii to be given. above 3000 Cusecs ,j JiJ;tJno ocb ;ll.::w\W:'l ~\.dj k 3000' 3000 to 1000 " 3000' , 1000 to 500 " 2%0' " 500 to 100 " 1000' tOu to 10 ., So()' Below )() " (, ' 300' lAs far as possihle larger radii shoUld be glven. -Hi· l.I·~;U o. .i (B) Calculations.

,

It water be moving on a curve, the presiure varies front one stream tube to another.

The centrifugal force on astream tube is balanced by a ~ifference of

pressureq on the two end;, Let 'r' be the radius of a small strt'am tube of width dr and let 'v' be the velocity'in fep.t pet second. It can easily be proved that the change of pressure caused by the Genttifugal forc" shall be:-

G~ ~ ~= ...

r:::[:

S

,.

4 ~

~

"'~'::l ~ \..) i:; "Q "

dp. =\\1!~ Where w==weight of unit eft. of watet. dr gr. v- Velocity ft. per sec. ' -wr(wherew is the angular velocity in citcular units).' r=radius of the stream tube in ft.

~.:ti~f~1,;""ue. diffeeec," in(:; In a channel of WIdth B, the lUlllts of rare, Rand (R+Bl, Integrating equation (A) within limits Rand (R+B). p -p w 2 (, } .' ' .J".... _l_~_!:=: ~R+B/2 ..... R2 W 2a

'"

\oI~ ~ Q

4{

...

,-»'-'

~t'

\i <:)

-~4" Fig. 19

-'1

11\

...

F'=

ill 2

'"

- (B2+2RB)

2g

192

In the straight reach. let Q=total discharge in

cusec~

q = ~ discharge per foot. v=

bVelocity in feet per sec.

D=Depth in feet. Let VI aild Dl be velocity and depth at the middle of the curve on the concave side (outside of tbe curve) and V 2 ond Da be velocity and depth at the middle of the curve on the convex side (insine of the curve). F represents the total pressure differences on the outside of a curve relative to the inside and let us assume for the sake of simplicity that the water surfaCe is depp'ssed to the extent

of~ on the inside

and elevated on the outside by

~.

The depth D

reduces to Dl Fig. 19 near the outside of the curve in the outfall beyond the middle of the curve, .

(V 1-V)2

F

"-~g--=~r

Vl=V+v'~ IC) similarly depth D expands to D z on the inside of the cur l1e

:. v2 =v-v'-g-F

(D)

On the inside of a curve, the average velocity in a channel section, is retarded by the "ritical velocity due to net pressure difference caused by the centrifugal force on a curve and on the outside of a curve, vice versa the velocity is accelerated hy the same amount . .~.

a.nd D z= __
(E) (F)

va

super--elevation e=(Dz-D1 ) (G) In rhanne15 with sloping sides, the super-elevation can be calculated neglecting the slopes. In a large canal, the error thus introduced is extremely small and insignificant.

Ie) Limitations. It is evident from the above treatment that the design of non-silting and non-scourine bends with non-changing discharge intensity per foot width to avoid swirls downstream of the curve is governed by the following canditior1s:~ . . (i) Due to retardation, the velocity on the inside of the curve should not drop below the non-silting velocity for the depth there. (ii) The maximum velocity developed on the outside should not exceed thp. safe.scouriIlg velo~ity of the mat"rial whir.h the section is made of. . (iii) The full supply levels are not changing. 'i he first condition cannot at all be fulfillen in earthen channel section becanse, if the depth he increa.s"d more than the d~pth in the straight reach, actual velocitv must drop bf>low the n ·n-silting velocify. It is only in lined channel sections that this condition can be fulfiJ1ed. BI}.CaU5e these can be flumed with the available slope to about two-third of ben·width on account of the reduced co·efficient of rngosity of the lining m::tterial (brick wor1<,. In r.emeJlt plaster aT cement concret, even greater reduction of the section is possible. It is aJso impossible to fulfil the second condition in the sandy soH or silted bed conditiO'Il ber<'.u~e the velocity developed on the outside of the curve is certainly going to be more than the scouring velocity of the earthen channel s ction in the straight reach of the canal. If soil of the bed is day which is not liable to be eroded up to certain maximum velocity, say'

193

o ft. sec. and roughly assuming 20 percent increase infveTo:;ity

~(I)dmum veloeity in the normal st.raight reach j)e

3 '0

X.! =2·Eft. per sec, which is 1'2

Kennedy's

Vo

on the outside of a curve,the a channel could at the maximum

0

for 55ft, de)th It is evident that it is only '

.'

pOssible to design non-silting super elevated bends in earthen channels with depth less than 5ft 5 . The t h'Ird cand't' , f u Ilf'lIed only In . the regIme , 1 Ion IS channels. In non-regime chann~ 1s t h e design of non-silting bends on the inside and non-scouring bends on the outside is imprssible in arthen channel sections. e Let us assume that the bed is unerodable clay and will not be depressed on the inside o of the curve to satisfy the condition (i) and ~ii) above, then water surface on a Cllrve takes the shape as sketched in Fig 20. Depth Dl reduces to depth D on the outside and the depth D does not , 8 ", change on the inside. . 1! ~

f I

I

,

(vc.-:YL =F 1 2g

or

).

VI =v+v'2gF

','n

(H)

f'

~-

'1

"H: . D=.9.:.. v Super-elevation =e::::t(D~Dl)

!l'

(D) EXample 1. Design a super-elevated curve in a lined section for following data OLl channel:Discharge ,= 1000 Cusecs, Bed width = 60'0 ft Depth =6'0 it Slope ='175' per thousand. == ito 1. Side slope v = 2'64 ft, per sec. N =0'0225.

the

C.V.R.

Brick pitched sections or rough m~sonry- ~ =0'015 , neglecting side slopes for lined section, llsmg Mannmg,s Formula: .... Effeetive bed width:=: 62~_~'2.!.5=40·U ft. OU225

Usual side slope for economy is kept I to 1 in lined channels fot side soil compaction, Averacre velocity=. _1000 ___ =_~0~=__!Qo..~_3'65 ft' per Sec. o (K+D)D 46x6 276 .. Let the radius of the curve=2000 ft.

F=~~. 2RB±~~ 2g

=

3'65

R

2

'64T X

2x 2000x4~+46a (2000)2

.... 0·00955.·, ft~ say 0'01 h

194' vl=v+~=3'65 +V32'2x'Ol

.I :'

. 1000 DIscharge peT' foot run=~' 46 =21'8 cusecs. 21' 8 , D 1 = ----=5·18 ft.

i

421

21'S DS=3:06=7'03 st. Super-elvaJion =e=D 2 -D t =7·03-S·18= Ij85" 1'85 . Slope of super-elevated bed::: -_ =1 in 21·6

4Q

Since v2 =3.{)f) feet per sec is grea.ter than the

Kennedy's Vo far 7.01 feet depth, thlt is, 2'92 feet per se.:.. the nesigned curve section is nonsilting; and the discharge inttDsity shall remain constant throu~hout the width. The abo"e calculations' give the meximum super-elevation in the middle of the curVe. It !:hall be zero at the beginning and at the end of the curve. The contraction in the upstream of the curve and expansion on the downstream respective Iv shonld be 1 in 5 generally and 1 in 3 in the extreme ca.'ie. The exp~nsion sho',dd preferably be designed as per paragrph S(Fl Chapter XU part II. Example II. Design a super-elevated non-silting curve m an earthen channel sectian with the following data. Discharge = 265 Cusecs. Bed width = 20 ft. Depth J: = 5'00 ft. .h~I'.iI::j; ';~r-'f,"\i' = -! to 1. Sides ./ 1 Slope = i in 4444. Velocity - 2'35 ft per sec. and Kennedy'5 v,,=Z'3; Kennedy's C.V.R. 1'0 Effective bed width=B+ D 2

=20+~-=22'5' 2

Discharge intensity per foot wiljth= 2~~ = 11 '6 Cusecs~ 2",·;,

Let radius of the curve=lOOO y2 2RB+B2 F= 2g X. i{:F .

'"

it.

V1,=V+v' 2gF . ~t35+

From equation (HI

v'zgx (0 0041 .

=2'35+ O·SOs.c2·S55 'ft. per IJec-ond D1=

}~

Super-elevation

=4'1 it.

=5'::'4

say 4'0 It. But D=S'O It,

1"",0'9 ft. s-ay }'O"'it

19~

Thp. s':'ctinn designed is non-silting but the discharge intensity may not be exactly the same throughout. the width. It i;; not so injurious as the swirls (vertical rollers) which sh.all die out downstream of the bend of the curve in the straight reach. ~uper-elevation

in rivers.

The super-elevation in the water surface as calculated in the foregoing examples of irrigation channel sections is r::Jther trifling but in the rivers very hkh velor.ities of the. order of :to tc 25 feet per sec. are pos-;ihle especially in the boulder reach with steep slope of the order of 1 500 The Ganges weir at Bhimgoda, Hardwar, in the United Provinces, India, is situatd on a curve. Tn the flood" of 19~3 the differencfl of w::Jter level on the left side Flank was recorded to be 3,0 feet higher than that on the right side Fl::Jnk. In ordflr to counter-act the effect of the cross flow and the varying disch'l.rge intensity, the crest levd of the weir bay on the left side had to he rctised by 3'0 ft. the nc;xt bay by 2 0 fed and the third one by 1 () ft. There are 8 bays of about 500 feet each. fhis .. hawed that the velocities, which developed on the outside of the curve (left Flank), were of the o[d~r of 35 to 40 feet per sec. in this boulder-bedded river at Hardwar.

24.

Exa.minati()n QUestions.

1. Describe Kennedy's silt theory. A channel i!> silting badly in the head reach How would you proceed to determtne its C.luse and what remedies would you sugge
Use any method orformula you like that gives reasonable results?

Vg

(T.C.E. 1928) 4. What do you unierstand by (a) regime channels, (b) initial and permanent regime of channele? Determine the hy lraulic mean depth and water surface slope of a regime channel to carry 8 ') cusecs. 2-=0.8

Vo (T.C.E. 1935). 5. Complete the design of a channel on the enclosed L. Section form which gives N. S. level etc. [)raw type erO,lj sections of this channel at R D. 5000 and R D, 121)00. Inspection road will be at tlle top pi tlW bank on the left unto the fall and on the natural surface below that. "Work out the land-width reqUIred m the left from theccntre line from head up to the fall. (P.I.B.1939) . 6. A minor of 30 cusecs discharge and a bed slope of 1 in 5000 gives constant silt trouble. Give pOSSible reasons for the silt trouble and state what measures you would take to stop it. (P.I.B.1935) 7. (al What is critical velocity ratio? (b) Wnat are the velosities for various type of soils ordinarily met with in the Punjab? (c) VVhat points will you bear in mind in aligning and designing an earthen irrigation channel? (P.U. 19!2) 8. Describe a brief es,ay on the design and grading of irrigation channels. (P.U. 1942) 9. (a) 'Vhy d ) the irrigation channels silt most in the heacl reaches? (b) Wh~t do YOll understand by silt movements in irrigation channels? Explain their causes. 10. Compare Kennej'y and Lacey's silt theories, 'Vhy is Lacey's conception supenor to that ()f Kennedy? It Hr)\v do the diurnal and seasonal variations of silt charge in the irri ation channels affect their working? 12. Skdch the best form of a lined channel section. Design a lined channel section for 200 cusecs discharge, slope 0 3 per thousand, N =O'OHl in Manning's formula. _ . \ 3, A channel is to be designed to carry a full suppy of 600 cusecs with a depth of 4·:,feet. A velOCity of 3'0 fe. per second ;s considered suit.'lble. Side slope 1 to J, sketch a dimensioned channel and calculate the slope required for this channel. The co-efficient of velocity can be ~elected frOID the following table. H M D. 2'5 3 3'5 4 4'5 C 67 70 73 76 78 (F.S.C. 1937) 15. How wou ld you design a stable channel in coherent material? Describe briefly the factors jnvolved, t An earthpn channel of trapeZOidal section wi th sides,"\- to 1 has a bed width of 20 feet and dppth 3'5 feet ThE, slope is 000025. What will be the uischarge? Will this channel be stable one? (F.S C. 19H) 18. QllOt" :Yfanning's formula, explaining the various terms and say to what it .is ap~licable., A draiuage calvert ander a can'tl has a level barrel 200' Ion" faced with brick rnasonary. 4 ft. wide and 6 feet high The Jl~or is extended horiZontally beyond the end and the wings are splayed at an angle of 30 with the axis' There IS a vertical breast· wall at each end. Using Manning's or any other formula, derive an expressllu}

HI6 connecting the discharge with the upstream and downstream water levels. Also obtain an expression for the pressure urder th" roof of the culvert at a point 50 ft. upstream, of the downstream and, assuming the upstream water surface to be 10 ft. above the floor level. when the discharge is 140 cusecs. (F.S €. 1940) ]7, A canal lined with concrete has a section consisting of 45 degree side slope£ joined by a quadrant of a circle of 10 feet radius centred in the water course. Calculate its discharge when running full with a slope of I in 5000. 18. Derive a formnla for the depth of water in a circular pipe which will give the maximum discharge for a CQnstant slope. 19. State Bernouli's theorey. How would ycu calculate the velocity head ill a chano,el kpowing the velocity distribltion?

II

PART

CANAL IRRIGATION CHAPTER VII

Design an d Maintenance of Banks. 1. The; b~nks of irrigation channels should be strong enough to withstand the water pressure due to the depth of water in th.e channel. The earthen bank; are porous and, therefore, water can percolate through. them The normal pore space in the Punjab soil i,:, a\)Qut 40 ),~ by volu'lle. The bank; as originally comtructed are rather loo,e, hut whfn consolidated In course of tim~ in a couple of years, are compacteri better than the normal soil cm-;t. Tile width of the bank is cletermined from the considp.rations of the hydraulic gradient which is usually kept I in 5 ;IS shown in Fig. 1 . The actual gradient of flow is 1 in 2'5 to 1 in 3 as shown dottfld, and the permissible hydraulic gradient presupposes a factor of safety equal to about 2. The height of the -....\ . ,._F •... bank above full supply level in the channel L. is called free board. It is usually allowed 1 25 feet for the minors, 1'5 ft. for the distributaries and 2'0 ft. for the branch and main canals.

__,..,.....

2. Typical distributary cross sections. Fig. 1

Typical distributary and minor cross '1 . sections are sketched in Fig 2 to 4. (a) Fi~ 2 giv~s the cross section for a dhtributary when bed is level below natural ground surface i e., . N. S. 0(;

/' ';'in;

PARTLY IN DIGGING "'-.

1-'-4 Fig, 2 .,

The bank width=Z+D+

-~_ tv

)1

where Z=beight of bed above N. S. D =depth in feet B=bed width in feet Free

board=F=I+

~

t

,"·1

oWtlhl':'J a:):)/.~l :fli £1'1[011;: 2i; ,0

wit.

Hi ~)~?,.

i1bs:'

in feet and the berm width=D

The digg-ing is 1: I up to N. S. and the side slopes of the banks inside and outside 1. It i> assumed that the germs shall silt up to the dotted lines to a slope of 1/2 to L thus le'l.ving a clear berm of length equal to D at full supply level in the distributary. The inner edge of the berm is kept at wat-r level by cutting the lip. In course of time the other e1ige i" "loped up 1 in 10 by the earth made available by cutting the lip. The earthwork dug from tile hed is used on the banks and the additional earthwork required for them shall be obtain·~rI fro n :)Jrr,)wpits UJually pld.'2ed in the flelds at least 10 feet away from the canal land limits. ,lie

It to

198

The compensation for the earth got from the cultivators' land is paid according to the rules in force framed by the Local Government. The aim of the ideal design should be that the earth obtained from digging in the bed is eqlliil to the earth required ill the hanks. The chan nel is then said to be designed with th~ bJlancing depth. [f the digging is more than the earth required on the banks, then "ither th~ bank dimensions are increased or it is dres,ec! half a foot lower than the bank level as a spoil behind the bank on the side other than t lle bonndan or service road . . (b) Fig. 3 shows the cross section of a distributary when it is in filling with bed leve I above ground level. The height of the free board is kept the same. The bank width is kept to suit the permissible hydraulic gradient line of 1 in S. In filling with bed above N. S. : --:=::~~~~~-~:~~-..:_-=-o:.;_-::: -8 .• , ..,,--~...p-tf~~(l..i

'&

Fig. 3

. The berm width is kept 2D to 3D according to the requirements depending on the . embankment height. The side slopes are l! to 1 both inside and outside. All earthwork for banks is to be obtained from the borrowpits sufficiently away from the banks. In the case of large channels the borrowpits can also be put in the bed leaving five feet berm from the inner toe of the banks on either side and 10 feet wide barriers across the bed after every 90 feet. (c) Fig. 4 shows a cross section when the channel is iu digging with full supply level below the groul1d level i. e. N. S. ~! In Digging F. S. below N. S.

Fig~

4

Tn this case the earth obtained from digging is more than required. The digging is 1 to 1 on sides and usually a berm 2 to 3 feet is lpft between the inner toe of the spoil bank~

ani! the digging limits. The excess earthwork can be used to raisl! the boundary service road so that it is not flooded in rains as shown in Fig. 4 and the earthwork still in excess of these requirements has to be dressed in the form of a spoil bank on the right side as Shown therein. 3. Main Branch and Canal cross section. A typical cross section is sketched in Fig. 5. The free board is 2'0 feet. The bank widths are 17' to 22' on the patrol road side and 12 fpet on other side exclusive of the dowel which is 1 foot high ami 4 feet wide at the hase with 1 foot top width, sides 1'5 to 1. Usually thpre are two plantation lines on eithpr side with bounrlary road far cart traffic in between them as shown therp.in. Side slopes of b:Juks are It to 1 and digging 1 to 1. ; The inside berm dimensions shall change according ta the considerations outlined for the distributary sections in paragraph (2) above. 4, (A) Earthwork specifications. "~f (a) Setting out for earihwortlt.

On canals and large channels, preVious to

;\'

');li f(';;'

.'

.'

,

the edlt1ni(!t1c~riietit ~ \Torkl the ~Dtre Hrie 1§

199 marked by pegs at every chain, curves are pr"perly laid "ut, all half-breadths are carefully set \)ut, the top and bottoy? erlges of the excavation and the toe of all the embankments and spoil bank are clearly lockspltted. • (b)

Profiles for eartllwork.

Before construction, a complete profile should be set up on eVEry 500 feet of distance and at every chanFe of section. This profile should be a 10 feet length -.. .i. of thl' artual completed channel or embankm"ot, the excavation being n dug to the fJrOPI'T lewl, banks thrown up to the correct height and width,f. -. ... and all slopes dre~s~d to true form. C::Ire shol110 be taken that the ends of the profile banks are stepped so that they be picked over at the time ± ~ of construction of the banks adjoining them.

'<, \ ;?-~~

*(11 ;'

, .'

'

I

e

!

~~~

~

.

/

f

-+

,.

(c) Stripping soil prior to earthwork construction.

Before begir,ning work. the surface area of gr()und to b" occupied bv all banks "nd spoil shall have all its jungle and roots grubbed and be ...(- plnughed over. so as to completely eradicate roots and grass, and other ~ jungle, from it. Where the earth below the top layer is not suited for : making substantial covering to roadways and embankments, the top layer ... of good soil should be set aside for this purp(Jse~ U)

.):

(B) Excavation of channel.

(a) The excavation to be dug in lifts of from 2 feet to 5 feet, as may be ordered by the officer. in chargp., and-in each chain, each lift to bp. completen, as far as possible, beiore the one below is commenced. Care should be taken that the finally completed width of the channel is in no place exceeded. All gangwavs, roads and stepping should be left within the channel and not cut into the slope. The 11n<11 dressing of the slope will then consist of diggi.ng only and no filling or making up will be necessary.

0'"

~

(b) Deadmen.

Deadmen or such other marks as the engineer-i n-charge may direct sball be left at points indicated by him. These should remain in tact till measurempnts are completed, but final payments shl)111d be ~.l- deferred till all the marks are removed. Where natural surface is re~ular, deadmen or benches shall be left at equal distant intervals . .; .. .I- Note.-This paragraph applit's to borrowpits as well as to channel ... t. .. -t'4 excavatIon. 0 (C> Slopes for Ear~hwork. ~ The stannald:slopes, best suited for the ordinary avcrge soil met l -IQ with in the Punjab plains, are I: 1 in excavation and It ~ 1 in ~ vembankment, but where inferior soil is met with and in the case of flood ~ ..... ~ t.. embankments, special section shall be proposed by the local officers in the estimate~ for the work 01: reported for orders of sanctioning- authority wLen ,~ ~ I the work is put in hand if the estimate was made out and sanctioned for ordinary conditions. Fig. 5 0

... I

-.

,

.. ...

,~

(D)

Borrowpits (outside borrowplts.)

. (a) Borrowpits should be dug only wh"re unsvoidable spoil for the £onnatio~ or the banks being led along the chaDn"l, if possible, in preference to taking it form borrowprts. No borrowpits shoulrl be within ten feet of the toe of the bank and if its depth exceeds 2 feet, the distance to top edge of pit should not be less thau 15 feet. Where bortowpits exte~d for a considerable distance, a bar, separating them. 10 feet wide at the top, shall be IP[t l~ every chain so as to preven t drainage from running al mg the back of the canal bank. ~orrowplts sha.U beas shallow as possible, and they will therefore extend over the whole arua avallable for their

200

formation. No borrowpits sh,>ulrl b~ dug in th'l c1.111.1 b",d b",hN bed levp.I except under special sanction. All borrowpits should be properly laid out bV the subordinate-in· charge before digging is begun. • No borrowpits sh'JUtd at aU b~ m1.de in the berms of channels. Approximately 2t feet width of tile lio of the berm near tf-te wa.ter ed~e ma.v nOWdver be rlug away not in the form of borrowpit but it should be continuous without "ta-ti;s" for at lea;;t a chain. The lip c:m be dug to about half the full supply d~pth but not lower. (b) Table of quantities of earthworks.

In distributary estimates the table of quantities show, for ear.h 500 or 1000 feet length, the quantity of earth that NiH be obtained from channel excava.tion, and the quantity that must come from borrowpits. (c) Widening of distributary bed t() oMain earth.

In new construction extra earth reqllired for bank;; shall preferably be obtained by widening the hed of the cannel itself. The bed may be widened to thrpe times the normal width without causinf1 defects in future workin~ and m'l.intpn::tnce, such widening to be of the same amount through each length of low gnund. and not to vary frequently. (E) Emban~ments Laying.

(a) Alll'mbankmenh should be thrown up in layers which should never exceed half a foot in height, and to the full completed wirlth. Each layer should be commenced from the edge f~Tthest from the excavation so that all earth is thrown into the sloDe and not tipped over it. CaTe should be taken that the top of ea~h layer is level or slightly hollow in the cen :re ; any rounding should be dressed down level before the next layer isb egun. (b) Breaking of clods

All large clods should be broken up in the borrowpits and care should be taken that no clods larger than a man'~ list. nor any roots, grass, jungle or other rubbish are brought in baskets to be buried in the banks. (c) Allowance for settlement of banks.

The height of the bank should be in all caSfles one-tflnth greater than that shown on the drawings, to allow for settlement.

(d) Dressing earthwork. When thrown up to full height, the bank should be dressed to the slopes and dimensions ordered.

(e) Watering earthwork. Whenever water Can be lfOt down in a channel, the embankments of which are under. formation, the area reserved for borrowpits to be moistened to obviate aU risk of clods being introduced into the banks. (F) Spoil Banks.

(a) Spoil shoul~ be tipped as directed by the engineer-in charge, and spread evenly over the whole area avallable In layers of not more than 1 foot thickness. It should be dress0d to the slopes and form shown in the type ~ection of the work. Bad soil and sand where possible should be faced and topped with good earth. (b) Spoil banks for plantations. Spoil banks intended for plantations to be provided with long and cross dowels, forming compartments SO' X 501 so that no rain water can flow off. (G) Ramps (Earthwork). The plan;: of canal ma"onary works shall inclurle such a s:te pl:tn to a s11itable scale to show the ramps. Such site plans should sho Ti the ramps to any subsidiary work> in th

201

neighbourhood, such as bridges on nltch rlistributaries, mill channels etc. The plans of works should a Iso show how the ramps are to be arranged. Before construction is started, the ramps shall De marked on the ground bv lockspits. distribllt~ry m~sonry

{a Foundation pit (Excavation). The foundation pit should be dug truly to the level shown on the drawin~s. W erC the soil is strong and the pit is above spring level the whole area, may, at the discretion of the enginter-in-charge be opened out prior to the commenctment of c~nstructi')n. In such soil the bottom of the pit should be dug truly to the plan of the bottom of the foundations, and the side slupes should bl': as steep as is compatible with safety for sLps, under the shock of ramming. (b) Inspection of pits prior to laying of foundations. No cOIL<;truction to be commenced without the order of the engineer-in·charge and such order in case of all works in the cbannel of tbe canal or branch must not be given ulltil the pit has been inspected by him and passed as true in depth, form and len~th. (c) Foundation plans. For large works a foundation plan should be prepared by the Engineer-in-charge showing reduced levels of each part of the pit. (d) Watering of pit.

prior to the commencement of work, the bottom of the pit should be thoroughly watered, but all ramming of dry ballast or laying of bricks or stone over its area ahould be absolutely prohibited except III the case of slushy foundations, (e) i. Soft foundations. In laying concrete in slushy clay foundations it will be found that the lowest laver of 3 inches depth will on ramming sink into the Sl il and mix up with earth and be rendered useless as concrete. In such cases, to ensure the full thickness of concrete being good, excavation should be carried out to such extra depth as may be ordered by the officer-in-charge and dry ballast should be rammed down to form a satisfactory bed for the concrete to rest on. In the case of foundations in bad soil or below spring level, only as much of the oit should be dug down to final level as can be rendered safe during the day by the laying of the bottom courses of concrete or masonry. Extreme accuracy of form or level cannot be looked for, but care shall be taken that tne level is nowhere higher than that on the drawings, and that the edges of the lower course of concrete or masonry as laid are nowherE within outer footi~gs as designed. (e) ii Foundation Plt (filling). The backing of walls and filing of eXcess excavation should be carried up in level layers of w>t more than t foot in thickness. The top of the filling should be, as a rule, about 2 feet be low the top of the masonry. Before commencing any layer of the fllling, the surfa:e of the layer below should be cleared of all spawls, bats iLnd other debris, and each layer should be floodtd to a depth of 2 inches over. night so as to be consolidated and to prevent absorption of moisture from the new masonry or concrete. Care should be taken t.hat no clods. roots, grass or other rubbish, is buried in the earth filling which must be laId gently to prevent dust getting on to the top of the completed course of masonry. Where the filing consists of shingle, care should be taken that enough sand or finely broken up loam is mixed with it to ensure complete filling of all interstices. No silt or soil having angle of repose when wet, less than 2 to 1, should be used for filling. (H) Turfing earthwork. Turfing should be carried out over the areas in the manner directed by the Engineer-in • •charge. It should be done in all cases immediately after the setting in of the monsoon~. and should be kept well watered until the seeds or roots have sprouted. It should be protected from cattle.

202 Watering by spray being preferable to

~atering

lJy flow, should be adopted, where

possible.

5.

Earthwork specifications for repairs. (a) Repairs to banks (Holes and ravines).

All holes (gharars) and ravines should be, wherever possibl~, first fully opend out to the bottom, aU lumps of fallen e1.rth dug away. and the sides dug down in steps of not more than Ii ftet depth. All iungle. grass, roots, or oth0r rubbl5h, should be thorougly cleared and the work when ready for ftlling should be inspected and passed by the engineer or subordinate. deputed for the purp:ne, before fWing is h~guu. Filling shnulrl be done in accord'1.nce with the spocification<: given for fOilndation pits except that constant wettingduring the work may take the pll-::e of fil)odin:s elch 13.yer. Flooding the top layer of the ilay's work should. however. bO) done every ni~ht. ramming with wooden rammers while the wnrk is in progress, should be done when directed by the engmecr-in-charge. Ib) Repairing of banks by earth from berms.

Where a silt berm exisls, earth for filling and for repairs generally should be obtained far as possible, by cutting away such berm, care being taken that a layer of at )past six inchps 1hick of silt next the bank is left untouched, except under special orders of the Ingineer-in-charge and that cross dowels are left at close int~rval" in the silt berm, to permit· !,uch borrows silting up quickly. Any ba.nk which i5 to be widened, should be ploughed or cut into steps. ~s

(c) Raising of driving banks.

Raising of driving bank shall not be done with sandy earth from silt berms. (cl) Rep)'iring of banks by eareh from sp:>il banks.

If there be no berm, or if the s:>il o~)tainable from the berm be insufficient, earth shall be obtained from the spoil bank, if such exists, or from outside excavation in getting earth from the spoil bank b::>rrowplts on top shall be rigidly, prohibited, as in wet weather they form tanks and lead to damage by breaching. Earth, therefore, i5 to be obtained from the back of the spoil, or by widening the drainage gaps in the spoil banks, where such exist.

r J Repairing p

of banks by earth from borrowpits.

Where there i" no spoil. earth sh mld be 0 )tained by levelling do ~n any high lump~, if there be such, and last of all from borrowpits. Where borrowpits are unavoidable, tlley mu;t be dug as far from the toe of the bank as possible (the minimum distance to be 10) feet), must not exceed one foot in depth and must be neatly set out parallel to the bapks. The long slope which forms at the toe of all banks by washing down of soil from the top and slope shall in no case be dug away. (0 Silt Clearance

The spoil from silt clear :!.TIces of cha.nnels should be spread out evpnly in the b::n-rowpit.s. if s11ch exist. [f thev do not, thl! spoil s]lou:d be spread eveuly a.long the back of the bank thus widening and strengthening it. Care should be taken tha.t the spoil is n )t hoaped up on the top of the bank, or thrown in lumps on the outside so that it may no~ be blo Nn in by the winds. ' n')i~hbo'lrjug

6.

Spe3ificltions for puddle

. . The c.lay should be dug and exposed t? the air for two or thrle days. The clay contamlDl?' sodIUm c~rbonate (called sodium clay) IS the best for punelle. If nec-cssary. sand ShOllH be aoded until the mixture is suitable. and thfl whole should be wetted and" e1 \I 0 ked up in a rug mill or Ly nen's fect into .a. smooth plastic IT ass. The working wit;} a pug mill or kne'lding with fe~t tends to COvflrt !lodium carbonate into a colloidal s'Jlution and the cor ods tenrl to choke the fine pore spaces to make the puddle impervious ..

~;

7.

Construction oi

hi~h

203

embankment.

Special precautions have to be taken in the construction of high embankments, such as approaches to aquf'ducts in the case of large canals for example Solani aqueduct, of the Ganges canal in the LJnitpd Provinces. [::IJ Speci lcations of earthwork in genf'ral as descrihed in paragraph 5 above apply to the earthwork in high embankments concerning the layout, removal of jungle, the size of the clods, location of borrow pits etc. [hJ The u~ual section adopted in the good old days was as shown in Fig. 6 with a p1lddle core. The earth was laid in 6 inches layers a1.d c'JrHJlidat-:: i by w)odqn rammers ::Ind the puddle core abo'clt 5 feet thickness rose as the bank progresspd. The main reliance was pld on the efficiency of the puddle core as a water tight substance. . This efficiency of the puddle d"pends on the retenti()n of the moisture in it because the densification of the purldle is due to the chocking of the pore space by the sodium clay being pugged into colloidal state to fill the pores. The dried puddle 15, therefore, even worse than ordinary sdl banks becau~e it cracks. The dry soil arouud the puddle core extracts the moisture in course of time. reducing therehyits efficiency. It is therefore. th'l.t high embankrnents in the past have always he en a source of great trouble. . rc] The modren practice is to stabilit' the whole. mass of the soil in the bank. Various methods of soil stabilisation have been described in Chapter III part VI such as :'lij 1: 0 manipUlate the component paris in such a way 't'nat the mixture will. proGuce compact soil. . [iiJ Use of vario,ls admixtures such as electrolytes, chemicals, binders and adhesives. [iii] By the p.lectrochemi-al process such as the application of heat. [ivJ Campaction and df'nsincation at the optimnm moisture content. Only the last method is of practical utdity when earthwork is to be carried out on a larg-e 8cale. In this method the soil is made impervious not by chocking the pores but bV compaction. Compaction results in reduction of the film of water around the soil particlf>s. When the soil is compacted at the optimum moistllre content the dry density of the soil is maximum. Therp. are vari()us methods of compaction at optimum moisture content. The one described below can be used in the field in a la.rge scale. [iJ Measure the sand content in the soil by drying a soil specimen, then pulverising it and passing it throngh ~;ieve No. 270, calculate the percentage by weight of sand left on the sieve. [iiJ Calculate the optimum moisture content· in each case according to K.B.S.I.. Mahbub formula. Punjab Engineering Congress, Lahore Paper No. 257. ,. . W=25--14S where \V =percentage optimum moisture content S=percf'ntage of sand in the soil. [iii] Determine the hygroscoPi: moisture content of the soil_ The difference of the optimum moisture content and the hygroscopic moisture content will give the amountof water to be adrleu while compacting. [ivJ Lay th., soil in 6 inches layers and then add water as worked in [iii] aboVf~. With a little experience, thp. variations due to the prevailing temperatures can be easily allowed. [v] The soil should then be rolled by means of 1'3 ton dentated roller. The roller is .m~de of concrete having staggered teeth projectinl? three inches ::In~ d~iven by b~lllocks. The: sOlI IS supposed to be consolidated When the irnpres"lOn by the proJectmg teeth IS not more than iN deep or when the surface has been rolleci by 16 to 20 times. [viJ After consolidation of eaeh layer, the density of the soil is tested. It should be about 1~8 . . [vii] Each layer should be cover ted with' a couple of inches of sand. after consolirlation whi:h should be removed when the next one is laid. This is just to stop soil evaporation during the interval.

206 awl parallel to them, with cross banks at intervals of 500 feet to 1,000 feet apart. The series of compartments, which are thus formed, have inlets from the canal at the upstream ends and outlets to the canal at the downstrp::Irn ends of the compartments. A portion {)f the canal tiL5charge is passer! through each compartment by these inlets a:ld uutlets, and it is thus gradually filled up with silt.

(b) The 'Long Reach' system. Under this system (Fig 8) external parallel banks are constructed, ::IS in the first case, with similar cross banks, but these are at 4000 to 5uOO feet intervals. Head inlets and tail outlets are constructed,. and not only a portion of the canal supply but the whole of it is

Fig. 8 ,. diverted into one silting reach at a time. The canal channel contiguous to th~· siltini~r~;f~::;tn operation, is closed at its head and tail to prevent the deposit of silt in the canal. WHenr, thiS :' ';"1 ~" ~': ."::;'; system is employed, spurs also are constucted to encourage deposits. (c) Thc system of 'Internal Silting.'

Under this system (Fig 9) the canal banks are set back at a, little distance' frnm the normal section of the canal channel. Inducements are laid down to encour::lge the deposit ,..,f silt internally on the herrns This system is the simplest, the best, and the most economical of the three, but it can only be applied to a new canal which is so constructed. The papers give full details of the operations, with illustrations. It was found in the. operations of the Ra.kh Branch of the Lower Chenab Canal in the Punjab that in 22 months 16,000.000 cubic fpet of silt was deposited in a length of about seven miles. It W::IS found best to commence with the "long reach" system and complete the nperation with the 'In and out.' system. The proportion of silt deposited to Vi'ater passlng was ahout 1/2200. Tbe silted portions were eventually ploughed and sown wit h shisham very successfully.

, Fig. ;10

_··';-'·1"

"'H"..'HSAL

SII..TING

H

.

'_

$Y$TtM

,.If Q. k a-A /a:;:-h

To obtain the most speedy and satisfactory results with a long series of reache~, reach should be closed and made reasonably secure by olJtaining a sufficiently heavy deposit. Other reaches should then be taken in hand, and the completion of the warping in the reaches first opened, which being a.51?w process. should not be undertaken until all the r~aches have received their first heavy slltmg. The mner bank should, therefore, be made suffiCiently strong to withstand the he'ld of pressure when the canal is full and there is no water in the reach. One other point to be noted is that silting reaches should not be made too narrow. A. G. Reid says that the Width of the tank will of course he the who Ie of the Nidth between the canal bank and the boundary road, but it may oftpn be desirable to increase the usual width between the outer boundaries when passing through low ground in which silting reaches are contemplated. A.M.R. Montagu, Superintending Engineer Western J .lmna Canal ~now Chief Engineer] evolved a system of silting tanks on the Western Jumna Canal with a view to rtffiOVe 'he sik-

207 trouble of the canal. Clear wa.ter. after ~1ropping silt in the silting tanks, picked up silt from the reaches of the canals and dIstnbutanes bwer down and thus caused scouring of channels. This method gives a great relief to the silt troubl~ in a canal where proper silt Extractors and Ejectors cannot be constructed on account of the supplies being not available for escapage II. Accidents to canal banks. Breach~s in the ~an.al banks are .f~ir.ly common. They may be due to raJ Intentional cuts by the cultIvators to Irngate the ad]OImng lands or [bJ the mual causes for normal breaches . . . The ::Iccidents of the former case, can be avoided by patrolling banks at night, by levv of addItIonal charges for the water thus wasted, and by strict judicial action against th~ persons at fault. The breaches can occur due to the followIn!! causes:-·

(a.) wEak Bank. Insufficient bank width should be nnde good by period;ca1 strengthening of banks which is normally required after every fifth year. (b) Overflows. The overflow can also be avoided bv periodical raising of the to the designed sect ions.

banks

(c) Leakages. The leakae-es occur through insect or r::lt holes. Tl~ev take a considerable time usually more than 24 hours before they develop into a breach. If patrolling by beldars is efficient, no breach sbould occur on this account. (d) piping due to excess supply. Even though the bank be strong. the exeess supply over-topping the berms results in failure at t he banks by piping as explained below in Fig. 10. Let CD be the surface of canal wa.ter, where it normally run~ full supply. CG Fig. 10 rt-presents the saturation line in the bank. The bank as sketched above is extra safe. Lpt there be an excess in the canal so that watpr ltvel rises to EF. What actually happens is that the line of saturation is changed to EH. A breach should not occnr even if the point H be higher than the toe of the bank. At the most water should seep out from the canal. The velocity of the seepage cannot be high enough to dislocate the soil particles of the bank. A failure never occurs by percolation through th .. banks. Under normal conditions the soilof the Dank al;tQve CG is dry and has probably been never wetted. The Tise of the saturation line froIll C~ to EH wds for the· first time the soil of the trapezium CGHE of the bank section, Dry soil on tirst wetting contracts and the bank stands at places by arching action. Thus an open pipe is forme,i between EH and E'H' ai shown in the sketch ll.bove. Water flows out of it as a leakage "'S if an open connection exists from water in the canal to that outside. The water cornming out starts washing out the soiJ and eventually develops into a breach. If in the beginning the mouth E of the pipe EH coulq be located and closed. the breach would never occur. 12. Closing breaches. (i) Closing a breach in a small distributary or minor. Water of the breach spreads on the adjoining land~ and usual~y there is no place to take earth for closing the breach. Th~ earth has to be obUllned by cuttmg the outer slope of the existing bank. Enough earth should he collected on both sides· of. the breach on the . existing bank. The earth baskets should never be thrown in the water. All Jungle should be removed from the breach site by men in running water. The process starts from both ends by slipping the earth from the heap and protecting the channels sidE. by grass~ clods usually ava~lable .1rom the berms. No grassy clod should be allowed to be washed down mto t~e breach SIte. WIt~ a rush of earthwork at the end, the breach can be closed straIght away progressmg from the bank. f

208 (Ii) ClosIng a brelch in a mllor distributary or sma.ll Branch canal. fn this C:lse it is necessaTy to reduce the flow through the breach, otherwise a ht of earth will be washed away before the breach is closed. This is usually done by, driving a double line of stakes as shown in Fig II and then putting planks (,r mattrt'sses against them if available :l.nd if not then filling jungle in between the stake.. pressing it down with bags filled with sand and by men walking over them. No earthwork should progrr·si ,before C4NAl. the flow through the breach has been arrested to ---- ----.----.--some extent in this way. Mt'anwhile earth is piled up en bothe sides. The closing is starte-d from both sides by slipping earth from the heap in form of a ring bund as shown in Fig. 11. All jungle from the ring bund site s30uld be removp.d before earth work progresses. No earth Sl.Ol'e basket should be thrl)wn in water it must always be slippp.d from a heap. The last gap of about 10 feet shonld be closed with a ru~h when enough earth h:ls teen collected on both s·des. Straight closure in l .. rge Fig. t 1 channels is not possi bIe, •

(iii) Closing a breach in a canal The closing of a breach in a canal follows the same method of the ring bund but the jungle or planks do not servp. the purpose of arrpsting the flow through thc breach. The double line of stakes should he driven as before if depth permits and a double line of gunny bags filled with sand is put in. The inter-spac~s are plue-ged with berm earth, A temporary i)ank of gunny bags is raisecl in the position of stakes and bushing as shown in Fig. 11. Th6 closing of the breach is then done by constructing a ring bund behind.

t3. Examination Questions. 1.

How would you consolidate a new canal bank in filling if it has

clods and is full of ( P. I. B. 1941 ) 2. How would you in~rease the amount of silt entry into a silting tank inlet? (P. I. B. 1941 ) 3. Draw to scale the cross section you would adopt for building a two mile long embankm~nt (each from a new distributary of the fo.lowing dimen~ians; the soil i;, light and contains a small amount ilaUar 1

,f kallar.

Bed width 25 feet F. S. depth 3 feet Slope 1 in 4000. F. S. L. 5 feet above N. S. L. . Stace what precautions you would take on opening the channel and running it to ensure that the !mbankment reach would become safe and water-tight as quickly as possible. ( P. I. B. 1940 J 4 Descrihe What method you would adopt for each of the following operations:(i) To form berms on a distributary. ( P. I. B. 1939 ) (ii) To check side ero,ion on a large channel. 5. Give Specifications fOt" :(i) Repairing rat holes and rav:nes in a canal banlt. (ii) Deadmen for borrowp ts. . ( P. 1. B. 1936 ) 6. Draw cross sections of a channel of dimensions given below for the following cases:Bed width 20 feet, F. S. Depth 4 feet, F. S. Discharge 160 cs. (a) When natural surface is 3 feet lower than the bed level. (b) When natural surface is 2 feet higher than the bed level but soil is very bad. (P I. B. 1935) / 7. How much labour should be arranged in each day for the construction of a fall on a distributary In a ten days closurf'. having the following quantities of work to be done? Earthwork in foundations. 200 eft, Ceme:':'t concrete 400 cft. . (P. I. B. 1935 ) Brick masonry 1500 eft. Dry brick pitching 300 cft. S. Give sp"cificatiolls fvT Glzarabandi and describe how you would carry out and check this class of work to prevent fraud. (P. I. B. 1936) 9. You are required to make embankments of a channel leading to an aqueduct. Lay down ,pecifica.tions for earthwork, (P. U. 1942 )

PART II

CANAL IRRIGATION Chapter VII I

Lining of

Channels

t. The lining of channels has progressp.d only recently in India. It was brought up for the ntst time in 1917 by T A. Curry in paper No. 32 Punjab Engineering Congress. Messrs. R. S. Dnncan and Som Nath Kapur contributed their paDer Nos. 221 and 25::l in the Punjab Engineering Congress on the "Haveli Lining." F. F. Haigh Superintending Engineer, inchargr nf Haveli lining wrote various notes on the subject. A comprehensive paper No. 260, Punjab Engineering Congress, Lahore 1913 by K.B.S.r. Mahbub on "Lining of channels.' wasblicati)Ds published.forAabri'cf summary 'pu detailed study.is givcn here and the student should rcfer to the originai 2. Advantages of Lining. The main advantages of lining ate:(a) To save water for extension of irrigation or increasing the water already served. , supply in

area~

(b) To prevent water from reaching the water-table ;lnd raising it. thus avoiding water-logging. (c) fo improve command owing to flatter possible slopes. It may thus be worth while in some cases to line only the head reach of a distributary. So as tothe command adjoining high areas and leavd the channel unlined in the lower reaches where commandthe is ample. (d) The and alteration of stability outlets of section, which in tbe case of distributaries should reduce (e) Rcduction in maintenance costs. 3, Suitability of lining,

remodeIlin~

an~ bitumen linin~

The principal factors which have to be considered in deciding the suitability ot design are:-

(a~

Permeability, i,e.) reduction in absorption losses. Generally speaking,

or a suitablp. form of Concrete or bri;k l'ning would reduce these losses appreciably.

Th~

presence of any cracks, however) would also have a material effect on thfsp. losses. (b\ Co efficient of Rugosity. which will determine the carrying capacity of the channel. It is preferable to use M"anning's formula in designing the section as it is simple anf] fits closely to several Kutter's,observations. for which values of N have been determined by various experiments and deduced from The values of N generally accepted are :~ Svrface Perfect Good (p,ment mortar surfaces 'OIl Fair Bad '012 '013 Brickwork in cement mortar ,'012 '015 '013 '01$ Concrete lined channel '012 '017 '014 '016 Refer to article 23 chapter VI of this part for finding 'U18 out lined channel section al1(j Plate XIV of Vol. III. (c) Durability. This may be described as the resistance to the following dIsintegrating force!!: ..... (i) Weathering;_ This is caused by the disruptive action of alternative freeting aDO

hawing and by expansion and contraction rpsulting from temperature variations and alternatt wetting and drying. The resistance of any surface to Weathering is thus a fUEction of itt

210 water-tightness and volume-change characteristics, It may be remarked in this connection tha.t the co efficient of exoansion and contractin of brickwork is about t that of cement concrete or cement mortar. (ii) Chemical Attaek: - Thp. mostimDortant destructive agencies under this he:td are sulphate of sodium ann ma!5nesiurn, commonly encountered in so called alkali soils and water. Corrosion of concrete by alkali W:lteor can be m:J.terially reduced by the use of sulphate resisting cement. Surface coatin~ treatments are also gen<>rally effective in prolonging the life of concrete or bricks though this mav not be a permanent remedy, Alkali solutions inc:rease in strength in dry seasons when dilution is at the minimum. The United St:ltes Bureau of Stanrlareds specifies that concentrations greater than 0'1 of 1 percent enclanger concrete. (iii) Wearing: -In the case of concrete brick-lining this wearing action is negligible for all velocitits under ordinary conditions.

(d) Initial eost and subsequent maintenance. This would vary with 10cal1tv an,:! the availability of various materials. Generally brick ma'>onry lining wi)uld be cheap~r than stone eoncrete lining, (e) Structural Stability, The following factors may be considered under this head: (i) Reinforcement: -In America. it is a common practice to ninforce the lining concrete, Reinforcemeo t i<; dC3igned to reduce th"l siz~ of c::>ntraction cracks and to assist in preventing. failure of the lining due to settling of the sub-grade ar to back pressure from a saturated subgrade. On the other hann, this may delay relief beiag obtained by local failure in small patches, in thp. case of heaning up of water pressure. thus causing extensive oamage. flis was found to be the ca"e on the Haveli Main Line, (ii) Thickness of Lining: _-The side s of a channel to be lined should preferably be [,£t nearly of th'~ S'l.me slope as the angle of repose of the natural surface, whicn is of the following order: Angle of repose Slope Material 45° 1:1 Firm clay well jrain<>d 36°-33° Clay loam, awrage sandy loam Ii-It: 1 Sandy or gravel soil 33°-26° It- 2 : 1 Where the slopes are left steep~r, the side" have to b~ designed as sloping retainiilg wall~, Etchevery ([rrigation Practice anrl Engine~ring Vol: 11 by B. -\. Etcheveryl has work.... d out the following thickness of concret'l lining corresponding t) varioils depths of canals, based on Coulomb's lormula:. Maximum depth of canal in fect. Side slope of canal.

Angle of repose of earth.

-'--~~--.~.-----

1/2: 1 1}2 : 1 1/2: 1 1/2 : 1

1

:1

I

: 1

: I 1'5 : I

1'5 : 1

~o

1"

surcharge and thickness of lining. 2" 3" 6"

.

'

33

5'0

10'0

1-:!.

18

3'2

04 0'3

18 06

12 09

36 2'4 l'S

9* 8

4'8

19 08 11'3 6'S

97 3'8

U'S

23'0

5'7

29'U 11'4

1'7

2'5

5'0

226 5'1

3tO 7'6

68'0

53

106

160

16

3'2

4-8

10

2'0

0'5

1'1

3'3 1'6

9'6 60

15 : 1 2 : I 3 : 1

158 3'8 }'9

31'6

:1

370

:1

6'2

740 124

3'8

473 U'S 57 III °0 8'6

.---.,~-----------~---

0'6

1 : 1 1/2 : 1 2 : 1 3 :1

77

-

]'6

32'0

2 3

Maximum surcharge and thickness of lining of 3" 1" 2" 6"

11'4 2220 17'2

15'2

Thec:e results may be considered as useful for practical application only within: reasonable limits. The thickness required N()uld be much m'lre. if provision has to be made for any h ydrostatc press 11 re across the IininQ'. In the worst conditions, the lining is subject to pressure due to saturated soil and the

,.

differential water head across it. Assuming angle repose of earth to be 30° and angle of slope of 1 ning as 45°, the differential head that a lining of 6" and !::In thickness would stand, as obtained from calculations, is indicated in the graph in Fig. 1. It would be seen that with greater depths the lining would only stand a slight difference of hycirostatjc pressure on the two sides. This clearly indicates the importance of proper drainage so as to keep the difference of hydrosta tic pressure across the Ening as 10'IV as possible. (If

\ I

1\-+ .'

.~f\WI

II

,

I

\

I\IN " -1 I

a

i

!----- f--

'"~ ~

--

~~

•

~ r-- J ~

.......-

~.

.. I

1

IT,' ~"'CIC 4,",,,

..7.

eli

TH'CM

,'If' •

f---- 1----

rl

.,ffllE'HIAi

4

S

,

1

•

MIA6 A(HSI "NIN.

Fig 2

,

(iii) Strength of lining. Any reasonable strength should be good enough if the materials used are such a~ do not deteriorate. in course of time. A piece of Bik~ner lining shows on test a compressive strength of only 690 Ibs/sq. inch. The compression strength of l;~ cement. sand mortar after three months is conc;idered to be over 3,000 bsfsq. inch. Both cement concrete and cement brick masonry would thus give more strength than the Bikanet lining.

(i v) Eat th Backing. In the U.S.A. Bureau 01 Reclamation speci.ftcations. it 15 laid down that lining should only ce placed on an undist1lrbed material or thoroughly compacted back fill. It is also neces~ary to provide a.dequa.te facilities for drain"lge of rain water tJ ke~p the backing in proper form, The American practice is to lay open joint pipec; in gravel-filled trenches to serve as. longitudinal drains. I'eeder lines are brought from the sid~ slopes where n~cessuy and outlets are provided as required to discharge the acctimml1lated water.
Various type; of LiRing. The type generally u<ed for lining so far are:~ (a) Cement or lime concrete .. ~" to 6"thick. (0) Cement mortar-!" to If thick. , (c) Stone \1asonry set in cement or Hme mortar -6~ to 12" t~k. (d Road oils. (e) Sodium carb"nate plastt>c. (tl Clay purldle-3" tn 6" thick. (g) Brick lining combined with cement, mortar-3" to 6~ thick. (h) Preca,t cement concret{' block's. (i) Tar or bitumen imp:egnated cloth c.)vered by masonry

(a) Clnerete Lining. . This is a very useful type and is generally arlopted. Tt is dtlcable if lctid properly, and reduces the ahsorption 10sses by nearly 95 %. The co efficient of rng()sity is very low, and in: view of the high wlocities possible, tho section is considerably reduced. The All Am~rican Canal is a crmcrete lined channel ' On the Gang canal ~Concrete lining of Gang Canal by C. E. Jefferie5, Punjab Engineering Congress, Paper No. 102) whIch consisted of 6" of 1: 1 : 6 mixture of lime, grit and k.snkar balla.st, a value of Kutter's N =0'013 was adopted. The value actually obta.ined wa'l, ho~ver,

212 reported to be 0-0145 in 1935 and O'OJ f-3 in 1939. As all the ingredients were obtained from local kattkar the cost was quite low, viz., Rs. 22/8/- per cent sq: feet. The joints were made Vor Y shap;d and hter filled with bitumen i'n the ca~e of the Gang Canal. A Jap type is not desinble as it breaks at the shoulder under tension. A butt Joint 1" .wide und(~rlaid by a 1:4:8 concrete sleep:r 1'0' '.vide. and of the same thickn~ss liS the lining is conc:iderEd to be better thaa a V or Y shapad joint, as this would o'wiate the necessitv of filling with bitumen afterwards. and would simply mean leaving plain constuction joints at specific places. .' To avoid cracks, it is desireahle in sn..:.h .cases to lim't the siz~ of blocks to saY 20 I X 20' or 15'x IS', Alternate blocks should be laid and preferah 1 v an int(>rv"ll of seven davs allowed· so that the setting, contraction may take place. ,Alternatively, strips 51. wide may be left all round the blocks, and these strips rpay be con~reted' -after a week To avoid the subgradef ahsc>rbing moisture from the hottom portion of the concn'te and thus making' it spongy and pernicable, it shoulrl be thoroughly moistenp.d. According to the Bliearu of Re~lamati'm. ·U.S A. th~ proper moisture penetration is 12" in sanny soil and 6" in olher slils; except when this much moisture causes the subgrade to become muddy. Other alternatives are:-(i) Use of oil paper. This has been found to give very good results. The cost works to about Rs. 2 per c(>nt. square feet. ' , (ii) . Spreading of any crude oil on the subgrane so that the whole of the surface is fully covered. ThTs'may be usefully adopted whf're oil paper i, not available. The cost of using linseed oil at Rs, 3/- per gallon works out to Rs. 1/10/- per cpnt square feet. , (iii) 1:6 cement pla<;ter on the subgt:lde. The plastering need not be very accurate, and half tlre~labour tate~r'normallv paid for plastering should be good enough for this type of work. The cost ihdurling materials wou'd work out to ahout Rs.3i8/~'per cent ;:quarc feet. (iv) Spreading t" of 1:4 cement mortars and slurry a couple of hours before plaCing the concrete. The slurry can be poyred direct fr'lm the cans. This has teen found to be quite successful in' actual practice, and the cost wdrks'out to about Rs. 1/8/- per cent square feet. The consistency of concrete used in lil'ting is a verY important factor. The United States Bureau specifications for: canal lining lay down that this consistency is critical. . "The concrete must be fluid enough {
(b) Cement Mortar.

as

This type is naturally not very durable u~less suitably' prot~cted, and such can only be used in conjuction with some other protective mat~rial. According to Etchevery, 1" thick cement mortar stops 75 percent seepage. Actually. however, it is mue». more effective . .,,'

(c)

.

"J.::.. ,

stone Masonry.

This has a limited application mainly on account. of tpc cost imd thus should/ be used only where stone is locally available. Th;e co-efficient of rugosity is, comparatively higher in this' case, as stone cannot be very finely dressed. ". ",

(d) Road OilS. For using thpse the soil is rolled or burrowd so as to seCure a peti~ttation of 1/ to 3". It is estimated, that Ifl6". thjck.l~yer 9f erude ~~l (at about l/B,lfoi agaUop per hundred square feet) stop~ 15 p~ cent.se~page,.1Jl.)S IS thus not ,as 1mpermeabl1! ~s the other type~ The ~o-efficien~ of tugosity is falr,Iy ~lg1i: and Its effect is no~ durable. t~lS does nO,t, stop bliIrowlBi by a~lmals and wil1 prevent weed growth for only a few spasofis, ' .'"

(e) '~odlum:'eaTboDat( llnbig.

"Th~, h,.!~~~~ u_se,~~P1'1 :V\/atereotl~ses ai?-9. small chat1llds and consi~tS of i
213

up of clay, bhooso and s Idium carbonate in the proportion of 100 eft. of cl;!y, 6 mds of bhoosa and 9 seer::. of sodium carbonate. The cost to the zamlndar who provides bis own labour and bhoosa according to the figure given by G. R. Sawhney, in his paper (lin,ng of water-courses by G. R. Sawhney, p, E. C Paper No 24l;) on the subjPc t is Rs. 25/- to Rs. 40/- per mile. The author had an occasion to see some of this type of lining on the Lower Bari Doab Canal. The plaster was found to he damagfd in most cases ano could not he considered to have a mefullife for more than 2 to 3 'ieasons. The saving of water effected bv its arloption could be attributed more to the proper alignment and grading of water courses than to the plaster. The method was also tried in the United Provinces bnt was not found to be a s"ccess. Thev had founr1 that lining with u~ar (local salty SOLI containing lOq!~ clay and6% sodium carbonate) was more effective. A bitumen aud mastic plaster would, however, be much more durable than even Usar. If) Clay Puddle. This ha~ been in use fOT a long time as the only material required is suitable clay. Th'! selected SOli IS allowed to weather and then pugged throughly after saturating it with w'"lter, by men marchwg up and down. This pugged clay is then put in position and covered with about l' layer of Silt. This was considered to reduce seepage by about 80 per cent. Recent researches have d~arly shown that there is an optimum moisture content for each soil at which the dry bu.lk densitY': obtained 1S the maximum: We cannot, therefore hope to get the denSity by saturatmg the SOlI, as has be~n the practice m the past. as by cont rolling the moistu[p contf'nt and keeping it. as near the optimum as practical,le. This moisture content can be easily determined in the laboratory by us:ng a compaction apparatus An approximation can only be obtained by using the formula (paper 257 P.E,C. by K.B.S'I Mahbub). W=25-'14S where W = "/oobtimum moisture content and s= % of sand in the soil i.e. particles owr 0·05 m.m. diameter The percentage of sanri can be determined either by a Chain Hydrometer after taktng into account th"1 time taken by various particle5 to settle after dispersal, in accordance with Stoke'~ law, or by pas5ing the disptlfsed soil through a 270 mesh sieve, with water froni a wash bottle playmg over it. . Rolling can then be done in 6" layers at the optimum moisture content with toothed roller, as de,cribed in netail in Punjab Engineering Congress Paper No. 257, as these ensure a higher intensity of pressure anrl uniform kneading from botton upwards. It may .be noted that the deslrable placements ra?ge of moisture content i'l very much reduced WIth hlgher clay contents and a more ngld control over moisture is thus necessary in such ca!"es· . (g) Brick Lin :ng. This was used on a large scale for the first time in America in 1933 on the Southf}rn Texa"l Irrigation Canals. It was also adopted with smtable modifications for the Haveli Main Line in 1937. The Haveli Lining c"nsisted of two layers of tiles 12" X Srx 2k" laid in cement witli t" of 1 : 3 cement plaster sandwiched in between. [he botto.n layer of tiles was bedded on a 1" layer of 1 : 6 cement plaster. 1he masonry was reinforced with 1" M. S. bars laid in the 1 : 3 plaster, forn ing a grid 12:1:' X 12t' in the sides and 24!' X 24i' in the bed. This lining failed in several reaches within a year of its construction due to water getting behind the lining from external s~)Urces and. fro.m wave ~c~ion oVt'rtoppi.ng the lining. In one case the water cau"ed a ~reach ot the bank behmd the .hnmg. ~f.ter whIch t.he lining sLibsiced. In the other cases WhICh were many, the pressure behmd the hmng caused It to fail and fall into the canaL No lining of practicable thickness could have stood under 6ither of 'hese circumstances. The ddects urought about by the failure were :. (a) Inacequate compilction of the back fill. (b) Lack of proper provision for the drainage of the banks • . (c) Insufficient free board. Nothing was thus found wrong with the type and no similar trouble could be anticipated ift~e above defects were effectively r6ffivved in future dt signs.

214

5.

Construction of Brick Lining.

(a) The following are the main precautions to be observed :(i) The earth to be used in the manufacture of bricks should not have a salt content above 0 3 pew'nt and the quantity, of calcium carbonate should not exceed 2 percent. The clay content should range from 10 to 20 percent. (ii) Great care should be ~xercised in the moulding and burning of bricks No pilla bricks should be aHowt'd to be used under any condition. lili) The bricks ::;hould be thoroughly soaked before use. This is important as bricks which absorb water quickly lose it as quickly when taken out of water. Each mason should thus be provided with a kerosene tin of water in which his immediate requirements of bricks can be kept. (iv) Sand should have a fineness moduless of preferably not less than 1 2, and should be free hom (rganic impurities. The percentage volume of silt in it shoulri not excefd 6 per cent. \v) The consistency of mortar should be properly regulated by having slump tests. the masons should not be allowed to mix water in the mortar pans at site, under any conditions. ' (vi) The olaster should be allowed to sft properly for about two days before laying the masonry pn top. . (vli) 1 he 5ubgrarle should be properly moistened or oiled to avoid absorption of water from the bottom layer of masonry or plaster. Thl} bats obtained as a bye pre(Iuct while burning bricks can bl'! broken into ballast passing thro 19h f' ring and used in concre1e lining, which can, for ease in execut.ion, ce restricted unly to p~rti JDs'n ted .. . . Ihis concrete can be lald III compartments, as ~entlOned already and levelled and compacted by means of heavy screed~ or tampers fitted with handles weighing not less than 7 lOs. per linear foot. These should not b; les~ than 3" wide and should have !;" thick flat iron fixed on the underside. The surface can then be floated with a flat board IS' long and about gw wide, after which it can be rolled. if necessary, by light rollers, weighing 10 to 12 lOs per ft. run. (b) Brick lining in general has the following acvantagcs over concrete lining laid in situ :(i) Comparatively low cost, as bricks can be manufactured at site, thus avoiding long carriagps. (ii) Highly skilled or specialised lar-our is not required, as the work is of a simple straightforward nature, (iii) No elaborate or expensive equipment is nectssary as would be needed for concrete linings. (iv) Due to the large number of joints, cross cracks due to contraction are greatly reduced, and buckling caused by expansion is pli_ninated. tv) No expansion joints are neCessary. (VI) Brick lining can be more easily adopted to construction in circular sections. (vii) There is no risk of any undertected thin areas due to poor workmanship, as the thickness is controlled in this case by the thicknes~ of the bricks. __ (viii) Repairs when necessary can be canied out easily and expeditously. " 6. Compactions of the back fill and banks. (a) The importance of having a stable back-fill which would not settle behind the lining cannot be over-emphasized. This should be obtaiop.d by compaction of the soil at~ the optimum moisture content. This can be easily attained by rolling tht! earth sufficiently in 6" layers, with a 1'3 ton toothed roller 4' wide haVing knobs 6 x4" and 3" high, at the optimum moi~ture content, Generally, 20 t? 24 rollings would be good enough for the purpose It may be remarked here that the maXImUm dry bulk density would be obtained if the soil contain!:! I 70 per cent ~a~d and 10 ~o 20 per cent Clay I As it IS not pOSSIble to roll the ends properly. all extra ",idth of Ii' on the inner s:de may also be compacted and then removed before lining, 1

I

,--{

215

(b) Banks. If all the voids in a s~il are filled with water, the volume of water for a given pressure is called the natural volume of voids. The greater the pressure in the soil, the smaller is the natural volume of voids in it and vice versa. Settling will thus take place, if the actual volume of voids in the soil is greater than the n'ltura1 voillme when the soil gets wet and apparent co esion ceases. Consequently' the more permeable the soil, the sooner will it settle. The so 1 in a bank should thus be rolled to the natural volume of voids corresponding to the pressures wh eh will be in the bank to avoid future settlement. The density of the finished bank should be ehecked by measuring it ;n a s:lmple fOJ every 500 eft. or so of the bank. This can be conveniently done by taking out the sample in tho shape of V, so as to accomadate a wedge, 6" square base alld 8" height, in the hole. The wed~ is then placed in this hole and a measured quantity of sand poured outside it from a graduated cylinder, so as to fill all hollows. The volume of the soil would then be the volume of the wedge plus that of the sand and its dr~ bulk demity can thus be cal'~ulated. In the case of smail channels, it may he possibl~ to run the earthen channel for six months to ensure connection of the back fill and the consolidation of the banks before the 1inning of the channel is done.

7.

Drainage of Storm Water.

As alrf'ady mentioned, inadequate drainage facilities for the disposal of storm water were in a great meaSlure responsible for damage to the Haveli Main Line. The following precautions in this respect therefore seem desirable ; (i) No berm should be provided in the channel as it simply forms a receptacle fot wateJ . . which can work its way behind the lining. (ii) The dowel and bank should slope away from the channel. A sl:ope of 1 m SO for the bank and 1 in 20 for the dowel seems desirable. (iii) A suitable drain should be provided at the toe of the bank to drain away tm storm water. (iv) In cases, where there is a spoil, a berm at least 5' wide should be left on the spot) side of the drain. (v) 10' wide gaps should be left in the spoil 250' apart to dispose of the water in the drains. A typical cross section for a lined canal is shown in Fig. 2.

Fig. 2 8. Conversion of existing channels into lined channels. For canals and branches it wil.l generally be advisabJ~ to construct a new lined channel along with the old one. as the lining of the old channel cannot be carried out without intt>rruptint! the irrigation supplies, In the out case of small channels, the question as to whether the construction could b. carried out in rotational closures may. however, be investigated in detail, in each case. In view 01 the saving which could be effected by this m6thod, as compared with a neW channel, considerable expenditure would be justified on temporary arrangements for fpeding the channels durin~ construction. For instance, banks might be strengthened to permit channels to run with largro supplies for shorter periods and the rotational programme might be modified to meet construction requirements. 9. Lining in Reaches with High Spting level. The linning of tbe head reach of a cana.l having high spring level will not generally bt

216

a: velY economical proposition due to uplift pressures under the lining in closures. There may be circumstances, however, in which it may be desirable to line' a reach in an area of a high spring level. To enable this lining to be properly maintained and inspected it would be nece"sity to arrange a system of pressure relief under the lining, baving a gravity or pumping outfall, depending on the condi~ions at site This press'ure relief can be arranged by vne of the following methods as described' in a note on Confocal Conics applied to sub-soil to and from open channels, by F.F. Haigh:(a) ;\ contiI:uous inverted f,lter under the lining. (b) A system of drains or porous galleries. (c) A system of vertical reI ef pipt'~, In the case of (a) there \\ould be great difficulty in avoiding any leakage between the canal and the filter. (b) Thi" method also suffers from this defect to some degree, since all the length of the drain must be adjacent to the bed. (c) This method suffers the least from this disadvantage and is proba\>ly the cheapest to construct. The spepage dischaJ ge and thus the sp::lcing and size of relief pipes or drains can be easily calculated from the formula derived by F. F. Haigh. Whatever system is used, unless the outfall is through the lining, connection must 'be provided in the shape of drains or ducts from the relief elements to the outfall. 10. Losses from Lined Channels. F. F. Haigh bas suggested thA following formula for the brick-lined channels :K=l'25 Q.056 where K=lo!:s in cusecs per million sq. ft. of wetted perimeter~ Q=Discharge of the channel in cuseC5. Th:s formula gives results generally on the safe side (if there is no drainage). This means a saving of about 75 p.c. in losse, by absorption and percolation as compared with tte earthen channel section. . The loss in the Bikaner Gang Canal has been estimated to be about 15 to 2 cusocs per' million sq. feet. The tests of the losses from the Havtli Canal so far show similar figures. 11. Examation Questions. ]. Describe th e advantages of brick-lining over the concrete-lining. 2. Sketch a suitable section fer a lined channel in fillin~ and describe the precautions which should bll taken so that lhere is no settlement in the back fill and the banks. 3. (a) What are the advantages of lining channels? (b) What saviug in 101lSfS from-canals by absorption and percolation can be expected by lining them? 4. Describe the various types of lining usually used and say which type in your opinion il! suitable for (a) distributaries and (b) main canals. S. What additional precautions are nece~5ary when the lining of the canal reaches with spring level bigher than the bed is to be done?

PART

II

CANAL IRRIGATION CHAPTER IX

Cross-Drainage Works. 1. Thfl alignment of all canals and distributing channels are selected in such a way that they run along the ridge anrl no drains would thus be intersepted by them. However, sometimes they have to cross the drains wh n the country is irregular and uneven. Works necessary tn dispose of the drains are called Cross Drainage Works. fheyare usually classified as follows:(il By lateral diversion. i.e., by excavating a channel parrellel to the canal the stream can be thrown into another drainage line, for the disposal of WhICh provision has been marie. (ii) By passing it unrlerneath the canal either crossing the stTf'lam on a raised ; aqueduct, ()r, if the headway is insufficient for a clear passage, the bed of the stream is depresst'd below normal level, anrl the water passing in a tunnel underneath rising again on the further side. The latter is termed a syphon or a syphon aqueduct. (iii) The nrainage water can be admitted into the canal itself. This is termed an inlet. Uv) The, drainage can be taken into and cross the canal at the level of the bed of the latter, the inlet on one side and the exit on the opposite side. This involves one regulator across the canal and one at the further bank across the exit of the drainage. This is termed as a level crossing. (v) The drainage can be taken over the canal by an aqueduct. This is called a super~passage, to distinguish it from an aqueduct proper. (vi) The canal can be taken under the drainage ~ C line by a depressed syphon or syphon-superpassage. 2 Masonry Aqueduct (a) In Fig: 1 (a) we have an example of the usual design of a masonry aqueduct. In this work the canal bed is 25 fp.et above that of the drainage, giving sufficient headway to pass the highest flood, which is 18 feet deep. Like all masonry aque(lucts, the construction mainly consists of an arched bridge with platform at canal bed level. and provided with two solid parapets which retain the water flowing through. L

Fig. 1 \aj

T~ reduce expense, the waterway of an aqueduct is made narrower than the average width 10 .... -1 of the canal in earthen banks, Owing to the smoothness of the sides, the co-efficient of rugosity (N) !is much less thaI) t~at

Fig I (b)

applIcable to channels with earthen "ides and bed. bemg '013 in. the former against '025 or '0225 in the latter. This alone greatly increases the velocity, so thclt a. considerable reduction in section can be effected, even it the original slope of the current were retained. As however. that velocity can safely be incleased to 5 feet per second, if sufficient bed slope be given, a still further reduction in the width of the wateIwiY in the aquf'duct can be effected. In the exan:ple we are considering, the reduction in bed width is shown on the genera I plan in Fig 1. (c) (b) the thickness of the arch throughout is 2l feet, the radius being 20 feet.

218

The value of the co-efficient in the formula, thickness=nv rcan then he approximately increased in proportioI) to the depth of watn carned ; in ordinary cases :1=0'4 ~ The following rule tor deducing the increase to the value 1 - - - - - - \ of n will suit in most caSES (Bligh's rule). Let d=df'pth of ,water, then n=C·4+V02 (d-2). When the d"pth of water is 1:=::==c::J::::::-:::jrl 2 feet, 'n' will remain -4 ; with S feet depth n=U'46, with 6 feet """'---'-A-'-1"::J.4lI....-...... n=O-48, with 7 fept n=O'S, with 10 feet n=0·56. This is for large spans of over 25 feet. For smaller spans 'n' should be taken as 0'5, r.o matter what the depth of water is. In the example the correct crown thickness would then be, wita 7 feet water carried=O'S X '\I for 0'5 x 4'5=21 feet This would increase to 2t feet at the springing, The parapets, as is usual in larg aqueducts, are widened out to carry a roadway, as communica tion for cart traffiic must be kept up along canal banks. The parapets here are 7 fett wide at base and 6 feet at top. corbelled out to provide a 10 teet roadway, with an iron rail fence on either side. The Fig. 1 [c] , thickness of the p:papet in this ca!'e is excessive. It can be made half, but should not exceed two-third of the depth of water. In the next example we shall see that it is made about i f) in width, D being the depth of water in channel. p

(c) Tht> piers are {-- or :0167 S in thickness.

They widen out by offsets to 7 feet,

o.or U'23;;, at the base, S being the span. There is no definite rule regarding the ratio of the thickness of piers pIoportionq to the span in the casp of large span bridges. It may be taken to vary from

~ to~,.

For heavy works of this description the proportion;

as

in this case,

,would not be excessive. (d) The floor is composed of inverted arches with a wersed sine (If 5 feet, the thickness in the centre of span being 4 feet, and that at the !'pIing line of the inverts 9 feet. The object of this invert is evidentlY t( distribute the weight on the piers evenly over somewhat ,shallow foundation. It is very doubtful whether the inverted arch does really act in this way 'the use of an invert is more to prp,vent a floor from blowing upwards nue to water pressure , underneath, and it i~ used with advantage for this purpose in work SUbjected to a head of water. In case:. of bridges. howaver, there is DO appreciable, head of water against the work "consequently in'lerts are. apparently not necessary. The objection to their use is the great obstructiou they offer to the free passage of water, by decreasing the effe<:tive depth to the extent of nearly 3 feet. . : ,(e) Reference to Fig. I-c will show the disflllsition of the wings always a most . important point. In almost all aqueducts and super-passages double sets of wings are required, viz,:, Two long curvf!d land wings to form the connection between the masonry aqueduct and the earthen banks of the approach channel, and two water Wings connecting the face of the 'abutments with the river banks on either side. The land wings form really a continuation ot .the parapet walls, and are of the same section at the top.· Being subjected to hardly . any earth pressure, they can be built with verticalsides of the same width~lhr~)\:~~out as the top. (f) The length, a!! shown in Fig, 1 (c) is determined from :0' efficient.

considerations (" percolation The land wing!! and water wings should be long enough to permiJ the distance

219 Type Section

111 'UD/H.•

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DEEPER SY~UOH ---_._------

X to be more than the gradient 1 in 5 for the head frl)m the water level in the canal down to the bed of the drain which may be considered dry, the distance y in the bed of the canal is paved with concrete or masonry (impervious floor) to destroy the pressure of depth of water in crt'\ep. Solani aqueduct, of Ganges Canal is shown in Fig. 2. 3.

Masonry Syphon (Syphon Aqueduct). An in~tructive example of a syphon passing dra;nage underneath a canal is given in Fig 3. In the transverse section it will be seen that there is a fall of 3.5 feet in the syphon This will enable a large discharge to be passed thorugh the work. at an increased velocity. the waterway being considerably curtailf'd than what would otherwise be required. The spans are •.9 feet, the pier~ 2.5 fe"t thick, the headway 6 feet, and the floor 3 5 feet thick. The abut!llent IS of reasonable dimensions. The disposition of the wings is apparently good. The earth lines, so necessary to form a proper idea of the suitability of the win~s, are not given. VERTICAL WELL TYPE OF SYPHON

-------_--_ .. _-- -----_.

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The canal is 7 feet deep and the parapets are 3 feet 6 inches wide at base and 2 feet 6 inchs at top. The roadway is formed by an outer arch-way of 6 feet in width, the piers being lengthened to carry it. This provides a road way of 7 feet. The exit of the work has a sloping rise to the bed lev~l of the stream, which is as it should be. The head producing upward pre~sure is 4 feet. i he arch, with concrt'te covering at the crown, is 2 feet thick, and with a specific gravity of 2'0 will just balance this pressure. No exception can be taken to any of the details, except possibly that :t thickpr parapet corbelled out on both sides woulri provide an equaUy wide roadway, and thus save the lengthening of the piers and the external high level arch. A cross section of a l-ertical well type of syphon is shown in Fig 4.

220 5.

Super passage. Cases where the levels are such that rivers have to be taken over a canal, are comparatively rare, as thfy involve a verv heavy work, if the stream or torrent is large, and so they arc avoirled so far as possible. 'They" gmerally cccur in the upper st!e~-.a...,canal, the headwork of wh:ch is situahid among the lower hills bigh up in the course of a river. There are some very lan~e works of this descr pUen in the olel Ganges Canal. An pxeellent modern example is given in Fig ] (16 of the Budki Su)::eJpassage en the Sirhind Canal in the Punjllb. The length of the lVork is seven spans of 30 fett each, the width tet~'eeri parapets being 4()O feet The arches ha\e to l:e raised well acove tho (anal bed on account of the exigenCIes of navh!ation. and al,o of the level of the bed of the torrent. The 30 feetwirle spans are therefore suitable. The thickness of thl' arches at cro\' n is '45y'X::- TIle thickness of the piers' at springing is 6 feet or .2.S. ,W.e have already seen that a proportion of· \Is giving a thickn~s of 55 feft is sufficient. The piers are therefore, too thick. The' bottom width could be retained at 8 feet the piers ha.ving either a stra'ght or a eurved baUer as has >b~en designed, The foundation;, which are probabh' on good soii, are admirable. The abutment, at the Inok of thp. section, is dearly much too heavY, a very common fault among designeTs. To prove this the actual incidence of the resultant line of pressures on

Fig. 5(a) " .. of if.u:u '~~"\l'

.f; )i :

ba.si has bee., gr!l\phically found; the wethod of working, consists in first fi~ding the ce~tre', of gravi y of the ~alf arch and its load of water, the latter reduced in depth. as shown by the.,. horizoatal dotte<J; 1in~. to an fquivalent ma~s of masonry, This process is shown in Fig 5 (a). and, the reciprocal fUnicular polygon above. The forces 1 and 2 are the areas of the two halves in.to which the half arch has been divir1ed. Having found the centre. of gravity ot the half arch, a horizontal rne is drawn through the centre of the arch crown to intersect the vertical through this centre of ~ravity, and from..{t.e point thus found the resultant tne R is drawn through ~he centre of the arch at its springing, till it intersects a vertical line through the cen.t.r~~ of gr~vlty of the abutment artt'i its water had In the force· polygon the load hnfl, composed of the areas and 2, is continued down to,meawre 3( 0 square feet, the lIne, R is then drawn from "the tern ination of 1. and 2 parallel to its reciprocal cutting the horizontal P at a point. From,this

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point another line, RI joining the termination of th~ verticall(ad;lfn{T,;~~d;a"j1isi":obtallied· gives the final resulta.nt RI. This projected on the profile of the abutment in Fig. 5 (a) from it.

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,221 proper starting point, viz" the last intersection found. cuts the base of th", abutment at a point S feet within its heel. As no credit h~s been given to the weight of the earth. ba.ckin~ with .. water above it. the resultant line Rl need only just fall within thp. b'lse. This proves that the ' abutment is l1nnecf'ssarily thic.~ The line P represents the horizontal thrust of the arch, and if measured, will be found to closely ~orrespond with rt or 8 X 30=240. i.'ft the cakulated ho.riz'Jn. tal thrust of the arch, If the abutment were made 8 feet wide at the springing and 13 teet· at the base, it would probably be of sufficient section . As built. it is haH as widf! again ,as these , dimensions, and beside5, is provideri with a l~rge buttress of which no account ha<; been taken . Thi~ particular analysis is due to W. G. Bligh . It might be mentjoned here that the calculations for the effect of buttresses in an abutment or retaining wall are affected as follows:- The- wall should' b~ con.c;idered havjng a base equal to its normal thickne:;s plus the length of the buttresses, but formed of two materi~\s of different specific gravities. the solid portion being of the proper specific gravity of the material and the part behind of a lighter sp~dfic gravity, equivalent to that nf'a material spread . over the space of the same weigM a'i the solid buttrp.s, only. Thus, supp:)sing a walt 6 feat thick. is provided with bl1ttress~s projecting 4 feet thick and 6 feet apart. ie' at to fap.t intervals. and let the specific gravity of the \yaU be 2. then the spscific gravity of the 4 feet wide space be~ind ~ome

a,

, will be 2 X..!.._='8 and the effective base width of the wall would be 10 feet, not 6 feet . 10

The disposition of the wings is generally similar to that usually adopled In aqueouets consisting of water -wings as cnrvtrl continuations of the faces of the abutments and splayed land ... iogs which. carry parapets in continuation of those 1U' the aqueduct proper. These wings are shawn in the plan over all Fir S(c). As a further precautiun. the ends of the land-wings are connected by a cross wall at bed level. which a:pparently goes clown to the full depth of the foundations The hnrl-w'ng.; being in solid ~round ,are stepped lip Fis. 5 (e) in foundation, which is shown in the

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levation Fig. 6 ;a) .

Dhanal1re Level crossing upstrea-n v:e ',v,

Gang~s

Canal

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,6. Level Crossing. Dhanaure level crossing in the Upper Ganges Canal is a nice example of .this type of work which is cODstructed when the bed levels of a drain and a canal coincide at the junction. The usual layout is shown in Fig. 6 and Fig. 7.

7.

Author's Auto-suction Weirs. The author carried out a few experiments on the subject of cross drainage works to deal with small·seepagp. even-surface drains across canals. The results were published in the Indian Engineering, Calcutta, Febluary, 1~38, in an article. Three methods were suggested therein--(i) Auto- suction Weirs. (ii) Syphon Spillways, (iii, Venturi Flume. A brief summary of the said publication is given here. (a) Our knowledge of disposal of drains across canals is limited to aqueducts, level crossings and Syphons. In thp. aqueducts, the drain bed is required to be well above the full supply level in the canal. Level crossings are only feasible, when the drain bed and canal bed coincide Syphon requires that the barrels are not completelY choked up in order to permit initial waterway for the floods in the drain If the bed of a drain happens to be between the bed level and full supply level in the canal, none of these devices are applicable. A Syphon would be completely choked up and would have no initail waterway In a level crossing, the drain would tend to silt np the canal. Aqueduets and level crossings. are out of question when flood levels in the dra.ins are lower than the full supply levels in the canals. Even a super passage is not possible when 8. drain has got a small depth and bed level near about the bed level of the', canal. The sllbject of drainage works across canals perhaps has not progressed beyond where the primitiva hydraulicians had left it. (b) Remarkable advance has no doubt been made in the design of sucH on hydrautomats which could lift up small drains into the canals. A suction hydrautomat requires a minimum head of at least 50 feet. Similarly with high heads available in the canal, the small drain could by pumped into them hv the e~ection, of compression hydrauto~ats or hydro-electric pla,nts, Big falls are not generally available lO the canals mar the drams and all of these deVIces are anapplicable, (c) This subiect is of very great importance to the province of the Punjab where seepagecum-surface drains are a pressing necessity to relieve waterlogging. The contiguration of the , country is often such that these drains are inttlfcepted by the canals. It often happens that such drains have their bed levels above the bed of the cana.ls ann their flood levels lower than the supply levels in th: canal~ P1!mping into the canal by oil engines. has generally been tried pumping deals sahsfacton1y wlth seepage wat,er. but flood wa.ter remams acc1J~ulated for a long time till it is cleared by ~he pumps, The gravity outfalls are not generally avatla!:lle except by running the drain long dIstances parallel to the canal where seepage from the canal itself is difficult to co~tr,Ql. {d) fh~.,disposal of sma.ll seepage· cum surface drain .across the c.anals with bed levels above the canal bed and flood levels below the supply level m the canalIS not a subject which could be said to be of impossible solution. Such drains could easily be drawn into by the canals In all the above mentioned three conrlitions , the drain should not be disturbed but the canals should be t;e\lted ?n the line~ as described hereaftpr. (i) Auto-Suction Weirs. Model experiments were carried out by the writer on numerous forms of this device for drawing a natural dr']'in into a canal. The form of the weir in Fig 8 was found to have thfJ maximum effici~ncy and c?mparatively. low. working heads. The results .of two experiments were published In AppendIX I of the said article. The model was 2 feet wlde. The maximum dep1h on crest H was 1 foot. The length of crest was 2 H, i.e, 2 feet, out of which 1 5 feet was level and .5 foot was curved with radius of 2 H There waS a drop of 0'12 foot from the crest to the point where the glacis in 5 started The sl~pe below th~ orific~ for the drai~ was ta.ngential to the curvature of the crest. The control sectlOn of the WOlr. whu;h wa.s at a dIstance of H feet {rom the belZinning of the crest, was not affected.

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The drain discharged into the canal against a reduced prf'ssure 01 the jet of water down the glacis on i account of the pronounced effect of ..+C04'YA~. the centrifugal force around the curve of the crest. The design of ....___ ._i, the weir was the same in both experim~nts, hut discharges of the drains were varied. It is clear {rom the results tha.t in the first experiment the efficiendy of liftio8 dr
j'

(ii) SplUway Syphon. The canal could be passed over the drain by designing a low head spillway syphon 01 the form sketched at the next page(Fig_ 9) which is suitable for efficient prilLing. Low head spillway syphons are very suita.ble to pa"s the drains undisturbed undCl the canal. The spillway syphon can casil) be designed with the low heads so thai the pressures at the summit are equal to o _ '·I_C, or gr(;ater than the vapour pressure oj water. Average temperature of flowin~ wator in the Upper Jhelum Canal has. been found to be about 25 degrees C' iD condection with absorption experiments. The water vapour pressure for th~ temprature is about 13 feet head 01

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water. The pressure a.t the summit of the syphon may be calculated acccrdidg t. the following formula.:,-

H

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P=Pressure in feet head of water. . A-Atmospheric pressure-34 feet. '." . H=Elevation in feet of the centre of the summit .etion, above wa.ter level upltreo.m 0' the syphon. . v.=Velocity at the summit of the syphon. H!= Losses in friction. (iii)

VenturI Flumes.

The simplest solution to pass the drains over tho carta.l is to construct a Verttltfi

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flume in tho e canal as Fig, 10, Let the section of the canal be constructed' to I ' one half so that velocity of the cana 15 ',__ tinc7refased, say. froffi 3'5 feet per. :eco~d --., 0 eet per seCOlld , y ...... r .

Fig, 110

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Tho bed in the canal may not be depre5sed for the sake of cton.veltieat, . The uplift pressures under the top slab are likely to be ·tt~ubreicj~e but t_~ft" can ..nainly be managed at no additional cost, . T

---

(c) Conclusions, The loss of head roquired in no case is more than a foot if these designs are adopted in , canal of, say 4,000 cusecs discharge. Let the depth in the canal be 9 feet and the bed width 150 (_t. A drain of 150 cusecs diSCharge could be easily disposerl of hy adopting any of thp. al-)ove ,n.mtioned designs, A fall of about a foot coulrl generally be created because if the drain has got 'Md level above the bed level of the can'll. the canal would be in deep digging. ThA main dra:n'l ~ve hardly been constructed in this province yet. When the I'lrains are extended to fields, there .m be numerous cases where an ., Auto suction Weir," will provide a very cheap device to dravy tmall seepage drains into the ~rrigation c h a n n e l s . , ,. ,. t.

Example R. C, Trough aqeuduct. A distributary is to cross the main channel. Design an aqueduct with the following d,Ua.

Main Canal :Full Supply discharge :Bed width Bed T,eveI Full Supply Level Slope Main Velocity DIstributary :Fnll Supply discharg. : Bed width . Bed Level Full supply levd Slope Angle of intersection Natural surface

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t=60' fiC: 544'5 ,,=549'6 "'" 1 in 6666 _2' 1 tt,/Sec. tr:::409 cusec.,

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=550,1 1 in 6666 ==61 0 30' 13# =556,12

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Branch Canal Flume. Let thfl' seclioo be contracted to ~ It. having :J spans ()f 12 ft. with "3 tt, each. Distance between abutments=36+2X 'Z S=40 (; ft. Discharge r~ N'r It.

tWo-'pTets (If

'Nfdth=,~ = J~'~ CDsees. . ~

, The section of the aq-ue'drtct is ress than 60 Ct, as it IS' n'ta~otfry lliction is Ips!! and so- the velocity is more. '. '. _..., By doing this, we have saved the cast IJ)' 1 . f~

f

&Jj,iieaFdep'fh=tDc=~ q2_ ==~195X19'5 -=2.1tt 8 32'2 '

a.-n& the ~o-effid:ent 01

227

Let depth be 5'6 ft.

The depth cannot be lower than this. Then C in the discharge formula

Q==CB t H3/: ; or C=Bt~3)2 = HJ2 where q = discharge per foot width and B is 1 f,t. widt) v2 2'lx2'1 H=Head in ft =56+- =5'6+ " 2g 2x3~'2

5'669

. C=___!_~-- =1'44 .. I X (5'6)3': From curve in paper No 12S-Puniab Engineering Congr~~s·. (Fane's curves 'Piite IV. C=I'44 ",hen drowning ratio =0'99 :.Loss of head=5:669 X '01='06 ft. \0 , DP.pth has been tncrea.~ed by 0'5 ft. at the flume sectlon 5'1 ft. to 5'6 ft. Therefon the fioor will be depre;sed by O'S ft. The upstream approach in bed=I in 30. ,btl.• _ Tbe Hoar level is transitioned b the floor level of the downstre,am bed. Discharge Flumc. Lpt the floor levd of the distrihutary flUme be 552'1 to ensure clearance for the brand. can,al The be
~=37'5

ft. 10'91 Ag~in from Fallc s Curve3. paper No. , 125 of the Punjabi~, Congreii. drowning ratio is '97 for C=2.1 Los~ of head-'03x3='09 ft. Say 0'1 ft. D'esign of R. C. Trough of the Aqueduct shown In Fig 11.': Calcula tion for the bottom sla':> :Let it bA I ft. thick . The load on the slab is that of the slab and water. Wt. of sla.b 1 ft. thick= 150 Ibs. ' Wt of water 4' depth=4x62'S= 2501bs., . . (for wOl;t condition excess supply upto the top c)f tter~~. X! NP.t 1.lad=400 Ibs /sq. ft. , The slab is continuous over 3 spans of 12' clear . angle of intet!'ection =61°,30',15" ' , ~' . The reinforcement. is o~lique and parallel to the sides. '

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400 x 15 x 15 lu

9000 X 12 Ibs inches

_ 400 ~ 13'7 =2740 Ibs

M

tit" Let d be the depth. 9000 X 12=8'1-: d=c"MIO ='485X.t V I V 12

Let the depth be 12'/ with 1'5" covering.. 10'S'" is th,4fffective depth. Design of Reinforcement. H r "" a M 108000 . .V! Steel=ISjd =i800X'S78x--To-:-s-= 65 c to c.

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Bond. ::;; O=3x 1'77531. U=

2_?~0_ _ =68 tbs which is safe 5'31 X'S7l:Jx 10.5

Temperature Sieel=As =p. b, d='0025x 12x 12='36 sq. inch" 4 64($ pacing 6" c to c, both on top and at the bottom. Side Walls.

of'-l16 "

dia .

fhey are to be cesigned for the water depth of 4' including 1'5' free board.

Overturnmg ' movement due to water pressure=~6_ WW = ~~x~ 6 ==665 ft. Ibs. WH =62'5x4x4 Share= ___ - - ---=500 tb-s. 2

5,\

let d be the depth then d=C_!f_ = '085 X 665:>( ~~ = 4'2'" b 12 From practical consideration it will be kept 12" with effective width==lO 5'"

~s=~= _______ ~~~_X_1~ __ .. ='41; f, Jd 18000 X 'SSx 10'5

use 1/4'/ bars 6'/ c to c (for safety)

femperature Steel. A. =p b d='0025X 12X 12='3G sq. inch Use 5/16" dia bars 6" C to C both inside and outside. The side slab of the aqw~du:t is acting as a beam as the sido is monolithic with the bottom !lila':> capable of taking load so we put 2 bars at the top and two at the bottom to tab the load of 1he bottom slah np to a length of 6 ft. The bari are are 5/8 11 dia, ; 2 number. EXpansion and contraction in Fluming. (a) Let creep ro-efficient be I in 7 Creep len,goth required=7x 4'4=30'S or 30' (b) We contracted the upper ch:mnel to the flume width==37'5' /1 Actual bpd=41' ; and the difference=41-37'5=3'S' I The contraction on the upstream side and f'.xpansion D,S. side be \ "~J:j:~th 01 t.bI !><,cca protection= 3'5x~ =__!_~=S'75 2

2

The flaring is designed from vertical to 1 to 1 The Jf'ngth of the flaring wall for depth 4'4'-4-4 X5.. 22'

229

Total length required=22+S'75 =30'75' say=30' ~"" Difference on oneside=1.75'; Flaring on each side=4'4 It .~ Total expansion and contraction=S'15' .• Allowing it 1 in 5 length of pacca pro~ection on s.ide=5xS·15=30·75 or say-30 1 Sections of the walls change from vertical to sloplllg 1: 1. Percolation through banks. The percolation head=Distributary water level-bed of canal. =555'1-544'5=10'6 ft The safe percolation coefficient through banks is 1 in S. The length req11ired=tO'6 X 5=53'0 or say 55'

Questions :- Cross-Drainage ·Works. I. Sketch a design for a brick arch syphon to carry a discharge of 40 cusecs uncter a disty of bed width 50' wa.ter depth ~ '5', height and width of banks 4'0' R.L. of bed disty 560'0'. RL. of bed of dtain 556'0' T.e.E. 1933, 2. (a) What are the diff~rent methods of disposing of crOS3 drainage intercepted by canals? (b) Sketch a design for a syphon to carry a discharge of 100 cusecs under a disty of bed wiath of IS' discharge 100 cusecs, beds slope 1'2 ft. per mile, RL. of bed of disty 610 0, R. L, of drain 60S'0 maximum depth of W;l,te1 in draIn =4ft. T.e.E. 1934, 3. Briefly describe the various canal wcrks required for crossing a natural drainage. F. U. 1942. 4, An Irrigation Channel carrying 700 cnsecs, with 60 ft. bed width. 5'1 ft. depth. side slope 1/2 to 1 and bed slope in 6666 passes over a drain in a ma.sonry acqueduct. Design the follOWing if the archway ha3 a span ef 20'0 ft. (a) Flumed rectangular section for the channel with no loss of hea.d assuming co-efficient of rugosity fat brick masonry as 0'013. • (b) Archway for the drain. (c) Masonry Sides, waH and approaches for the aqueduct. P. U JQ.U_

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PART

II

CANAL IRRIGATION CHAPTER X

Falls and Meter Flumes I.

Definition.

A fall may be defined as a work de.signed to secure the lowering of the water surface of a canal and the safe destruction ot the energy so liberated. In Northern Tndia such works are commonly named as falls but in South India and America, they are called ;anal drops.

2. Necessity of falls in canals . . Canals arc earthen irrigation channels. They require to be designed with the velocities nep.end IDg on th.e nature of the soil of the bed and the sides so tha.t they neither silt nor scour thelr beds ';lnd sl des. Su~h a ve~ocity is known as the critical velocity. Lacey fixes the regime slope p.llrbcular for a glvpn. dlscharge. In every discharge formula, the bed slope is ::t predommant factor to deternllne the velocity of flow. In order that the canals Iun non-silting

Fig. 3 they can only be designed with the requirf>d amount of slope in the bed. If the slope of the country exceeds the slope which can be I!iven in a canal as shown in Fig. 3 below, vertical falls or drops have to be given in the canal be4 and the water surface.

3. Location of Falls. The foll )wing factors control the selection of the suitable site for a canal fan. Ca ) In the case of main and branch canals which do no direct irrigation, the site for the 1all should be determined from considerations of economy in the, digging of the canal and the making up of its banks. The most economical section of a canal is that in which the earth 1ug out from the bed is enough to make up the required eal thwork for the ba.nks. The depth of digging is known as the balancing depth of excavation. A suitable site for a fall would be at a place where the oepth of digging drops below the balancing depth, such that the reach with digging more than the balancing depth downstream of a fall is not longer than the reach upstream of a fall with digging less than the balancing depth. (b) In the case of the distributing channels, such as distributaries and minors, the falls are located from considerations of co nmand of the are I to be irrigated. Suitable location of falls with outlets taking upstream of them results in command of extra areas. (c) The combination of a bridge with a fall usually results in economy, because the floor and walls of a fall can be utilized to serve as foundations and abutments of a bridge. If there is going to be a fall near a road crossing, either the road can be diverted to the fall site or the fall may be shifted to the road site. (d) Where a canal has to be bifurcated, a regulator will be required. A fall should be combined with the regulators to save the cost of the masonry works.

233

4. Development of the practice of Fall Design. . When t~le grtat irrigation projects came to be constructed by the British Governmerit h dIa there eXIsted no theory of the falls to guide the desio-ner and there were no records of the successful pr::Jctic~ to be followed. These projects were t> the Western Jamuna Canal 1817, thl'! Eastern Jamuna (anal 1823, the Ganges Canal 1842 (now Upper) and the Kittna Canal (South India) 1852. (a) Ogee Fdll of Sir Probby Cantley. .

III

. In the design of an Ogee Fall an attempt was made to avoid the destructive effect of verbcal. drop on the downstream floor by providing a curve from upstream bed to meet tangentially the oownstream ted. The direct impact w~.s r 0 doubt avoided but it rf'~ulted in draw oown with excessive velocity lind ,cour upstream, which \\ as soon rectified by constructing the All falls on the Ganges canal are Ogee Falls. 1he forward crest as shown dotted in, Fig. 4 velocity of water remained excessive and nestructive in causil)g " the bed and ~ide era: ion downstream which necessitated the recurring addition of oose stune pitctling on the. bed and on the sides. Every f 11 possesses such protection more than a thousand feet in length. Fig. 4

(b) Rapids of Liert : Croftm R. E.

Ogee falls were followeil by Rapids where the drop was comiderable. Rapids following the weir design are still sllccessflll falls. because they utillsed the part played by the hydraulic jump (though imperfect in destroying the mergy of the fall without the designers knowing ;this inherent improvement in the Rapid Design). The rapids are very expensive. The western Jamuna Canltl Falls were made rapids with very flat glacis sloping 1/10 to 1/20 d<)wnstream to admit of Timber Traffic over them.

..

(c)

Vertical dl'op with cistern •

Rapids were folloNed by falls having vertical drop with cisterns as shown in Fig. 5 . .The dimensions of the cist~rns were put in arbitarily in light of the experience of the designer. Another device in,the form of grid was usually used in the cistern intercepting the dropping jet of water as slnwn in Fig. 5. Grid consisted of baulks of timcer either horizor:1al or inclined, spaced some inches apart. The grid became clogged with jungle carried by the stream and its clearance was not gen~rally practicable except in a closure. 1 he grid timber rotted and had to be replaced. This device has now been abandoned.

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Fig, 116

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"

(0) Trapezoidal Notch Fall (Ried 1~94).

This design consisted of one or more trapezoidal notches in a high breast w~ll ~cctOss ~ channel with smooth entranCf! !lnd a flat lip proj~cting downstre::tm to sPlay the drOpplOg let. The notches were calculated to give the required discharge at a Half Supp~y ~epth and Full Supply bepth, the error in between J-.ein.g neghgible. The dis.charge d~pth reJabon 10 the chan~el abo'Ve ~he work was maintained. This relatIOn means that the dlscharge III an earth~n char)J~el vanes ~ccordmg to mean exponential formula which is expressed as Q=k D513 were Q IS the dlscharge m cus~s.

~34

1) the depth in feet and k a consotant. A typical de,ign is worked in paragraph No. 11 of this chapter and is sketched in Fig 124. fhe object of the scientific des:gn m keeping the crest at the upstream beds level was to stop silting up of the upst~a!ll c,",annel in Llw supplies, The dr owned falls give a lot of trouble dnwllstream inspite of the provision of well de~igned cisterns while in the case of free falb there was no troublt! at alL Never-the-Iess the trapezoidal notch fall w~s so suc :essf .. f that it held the field in India for many year/? and was copier! ~ll over the world. There was one seriou;; def~:t in these falls that they could not be '.!sed as regulators in addition. In some cases groove" upstream of the notches were prov!ded (or inserting horizontal karries but they gase a lot of trou~)le by getting choked with debns •.

(e) Free OverfaU of the weir type.

With the general improvement of irrigation practice, the more economical and accur~te distribution of water became pss~ntial Engineers foun i them ;elves obliged to measure the disch:uge at frequent intervals in irrigation channels. fd.lls had to b~ designed as meters of supply. Nutch tall~ did not admit correct cilibration to g VA a di3clurge table depending on 11. gauge reading. Broad cre;;ted-weir., with fre~ overfalls supplied the necessary solution. Further research work on broad-crested weirs p·ov..!d soon that tile ire:! fall formula could be used even up to a drowning ratio of 85% to 90% when a hydraulic jump was formed downstream of the weir crest. The efficiency of the hydraulic jump as a very pJtent means of rle5troying the energy of canal falls was brought out clearly by the research work of the M"jamy Conservancy Board of Engineer;; in a publicatlOn by Sherman M Woodward on "Tl1eory of Hydraulic Jump and back water curves" 1918. This brings us to the modern designs of falls which are de3cribed in detail in this c.hapter. (f)

Contracted Falls.

The falls of the above mentiond types were gelerally c!)n,trltcted of the full channel width. In the case of trapezoirlal ~otch falls, the maximl~ n c )llstruction of the width at the fall was never more than lth of th~ bed width. But the Slltlej Valley canals in the Punjab were constructed soon after the last great war, the rates of construction were very high, and th~ ~olution for ecnomical Cl)ll3tructioll was found in contractin~ '1r tlu'ning tlu fall, and comhining them with bridges. The fluming wa3 done in some ca'ies mlre tl1'ltl ha f the bed wirlth of the channel. The resultiug action downstream was generally ser;o 1" and in mlny ca'3es disastrous. (Paper No. 147 Punjab Engineering Coug-ress, Lahore by E.L. Pro.heroe on Dam:lge to Falls on Khadir Branch, VJry Pakpattan Canal). This opellP.d up an interesting and a new field of Res,arch work indinting that there was still surplus energy even after the formation of the hydraulic j Unlp on a glacis or the impact in a c:stern which had to be destroyed further down. The developmpnt of th ~ subject took place in two directions, firstly to invent ways and means to arre:;t the destfl1c~iv(' PJtentiality of the high velocity jet leaving th~ fall near the bed in the for.n of hafflt! walls and block~ of different kinds finally devolping in the InglisJaU design. and secondly attempts were made to arrange horizontal impact in the hvdraulic jump instead of a jU'np OQ a ghcis leading up to latest :vlontagu's Fan dpsigns. Both these designs are des:ribed in the S~')5 'q:l~nt paragraphs. The I atter has proved to be the most efficient. / ~.

Classification of Falls.

Falls may be divided into four principal classes in accord:tnce with the purposes of the approach.

Cllss I.·-Fal15 designed to maintain the depth diScharge relation. It was believed at one time that a high-crested fall w;)uld ca'He Silting in the channel upstream of it. This is no doubt the case when a channel is run far long p !riod. at less than the designed full supply during the silting 53ascm A, the(~ is g'e.l.~ Vlriltlo l of the silt ontent OV..~r the year in the head reach of a channel, the pan lin~ effe2t of ;). hig\cr'::3te 1 fa.ll h the head relch mey have the effect of creating silt in the canal sY3tem below.

235

"

If the channels are run £1111 or nil supplies as is 11suaUy dJne in the casp. of distributaries and minoIs, and if the period of low supplies are not protractf;d, m()d~rn opinion holds that the silting effect occurs only for tte limited distance of the brl.ck water curve and that any such silt deposited in bw supply turns will be radidly swept out during periods of supply and eqn:ltJrium restored The principal types of the class are the trapezoidal notch falls and the low-crested rectangular notch falls. The trapez'Jidal notch falls are described in detail later in this chapter. The shape of the trapezoidal notch is rles;gned to give conect discharge at the corresponding channRI depth at say, half S:.lpp:y and full supply. Thp. error at intermediate discharg ~s is negligible.

..

Class II-Falls designei t) maint tin a fixed supply level in the channel abave fIe wor:. There are usually two reasons for cons'ructing a work of this type ; la) When a hydrauLc power station is combined with a fall, tke de5:gn of such machinery often requires a m)re or I S5 fixed Intake level. (b) When a sub.,idi:Jrv channel takes 01 t'le parent some distance above work. Such works do suffer from the defect of silting caused in the channel above the work by a raised crRst fall, and the constant level is only near the work just upstream. while Hle levels drop off in the chann"l according to the back water curve in low supplies. The principal types of the falls of this category are syphon spillways and high cre,ted weir falls. The syphon spillways are described in Chapter XIV of Part II. High crested weirs may be used when abs,)iute constant level is not requiIed, but it is only necessary to maintain a high level above the work. . Class 111- Falls designed to admit of variations of the surface level atove the work at the will of the operator. Such falls have also to serve as regulators. There are three m~thods of regulation usually resortEd to (a) Sluice gates (b) Horizontal stop-logs or karries (c) Vertical needles. In prac:ice falls of this class are confined exclusively to rectangular [!otches. The width of the notches depends on the size of the available gates especially when they are made of steel. Considerable economy is possible by the manufacture of such gatp.s in stanrlard sizes. The reduction in number of notches will increase the cost of gatt's. [he mcrea;t in the number of notches with the corresponding reduction in the discharge intensil y per foot run will result in reduced cost of the distribution of energy of the fall in the cistern. Horizontal karries are usually of deodar wood of 5" x5" section and quite strong for spans upto IOta 12 feet. The ewls are protected by iron straps. There is provided a groove . at each end having metallic rod across it. The r'lgulation staff is provided with poles with metallic hooks at one end which can fit in the grooves of the karries to lift them up. fhe water level is regulated bv removing or addiug kaj·ries according to the requirements, This is a very defective arrangement, bf'came it is very difficult to remove the karries in watJr. Moreover, they are often chokeri with jungle which has in many cases resulted in complete blockade of the falls accompanied by many bff~aches in the channel upstream and the outflanking of the fall itself. Regulation by means of vertical needles is very much superior to that by the horizontal karries. Their lower ends rest against an angle iron sunk in the crest of the fall and the upper end, bulking against the regulating foot bridge, and projects a foot or so above it. The needle3 can be easily pulled in and removed by a man standing on the foot br:dge. Moreover, they a-e put near the ends of the span witli free openin~ in the middle and. therefllre, they do not choke with jungle. Where gates cannot be procured, the needle regulators should be preferred to the horizntal kari rpgulators. Class IV.-Falls under this category are designed from special consideration without any referencc to the
(a) Cylinder Falls usually called well-falls.

1"

They are quite suitable and economical for low discharge and high dr )ps. Water il thrown into a well over a crest from where it escapes near its l>ottOIJl fhe destructi m oj eLergy is usually complf'te in the well.

236

(b) Chutes or rapJds which conduct the stream in an open inclined trough. (c) Pipe Falls.

Where a pipe replaces the chute.

~. ;

. i

Each of the first 3 classes of falls may be designed as. A. Meters. P. Non-meters. The trapezoidal notches can be calibrated to work as meters provided the . channel upstream does neither silt up nor scour. On the whole, it may be said that the trapezoidal notch fall is not a satisfactory meter. The rectangular notch falls can satisfactorily be designed as meters. In the case of sharp-crested rectangular falls the metering is limited by th~ free fall conditions available. Water level in the chanuel below must be 10
It i'l only the broad-crested rectangubr notches viz weirs which prove as su :cessful meters of supply. Tte design is described and discussed in datail later on in this chapter. Th ~y can be designed as meters with a drowning ratio of 85 to 90 per ce;:lt of the depth on crest.

6.

Destruction ot the energy of the tall.

The mass of water dropping from a certain height at a fall in a canal represents the f'nergy ~hich mUst be destroyed in the fall design. The following methods are usuaJly employed for effiCIent destruction of the energy thus liberated by the fall. (iJ Impact.

(~) Impact t)f falling jet over a vertical crest .against the dow~str~am Bo?r is ver):' efficient destroymg the energy liberated by a fall. Sometimes the droppmg Jet strIkes agatn,t the floor at downstream bed level and often in falls with a vertical drop the downstream floor is deprpsspd to form a cistern, which serves to add to the depth of water acting as a cU5hion and reduces impact against the floor. .

In

. (0 Impact can also be arranged between two strflams striking against each other. In a slUice regulator there may be rising and droping gates. Water pa~sing through the lower gates can be made to rise up meeting the dropping jet from the upper gates. (c) Impact can also be arranged between the fast moving stream leaving the faIt and the slow moving stream in 1he channel downstream as in a hydraulic jump. H.' draulic jump is now recongnized to be the most efficient means of destroying energy liDefd.ted at falls. (d) Similarly impact of hypercritical stream OJ) a glaci, downstream of a weir can be arranged against a permanent waH across the glacis known as the baffi~ as introducdd by Inglis. Impact.against staggered blocks on the gIaci'i bdore formation of the jump has also been tntld.

(e) The Colyer's Biff wall.impact of reverse flow in a. cistern has been tried with success as in the , case of (f) Lateral impact has not yet been trierl- The supply of the channel may be divided . Into equal parts and passed downstream from sides. High velocit.y jet issuing from opposite side walls should be allowed to strike against each other in a cistern or a wah. (ii) Aeration. The uspiulness of· aeration under certain' conditions appears to be generally recognized by engineers in practice, but there appears to he complete absence 01 theoretical treatment of this subject. This has been successfully tried in America by spraYIng tht high veiocity jet
It is usually the name given to the turbulence in a hydraulic jump ot that in a welJ designed-cistern. Formation of lot of standing waves dONostream of a drowned falll" a case of

IS:

... II> II>

pr ~

..,~,

::0 ~

S 0

0-

~

'"

Q,

en

::T 0

~,

::l 0T:l

en

M-

III

U~

at!

,.,'"...,

0. ~

I' c

~ fJl

::v c.h

~.

ciQ'

"

'.

l I

-f'---

1 f .·

.239

..

"'

~-

super-turbulence though inefficient in its objPci of energy destruction. It cannot be considered a separate means of energy destruction because it is nothing but amplific'l.tion of the impact.

7.

Methods of destruction of surplus energy downstream of falls.

The various forms of im :>act and other methods of destruction of energy described before, aim at the destruction of the horizontal component of flow of water. Water flowing especially on an inclined floor has vertical compon"nt of flow which generates dangerous pl:e,."ialitie<; in ero:i;ng th~ b~d and the sid~; of the earthen channel downstreom of the falls. Energy of the fall, d11e to this rea,on. is n:>t compl~tely de3trojed in either hydraulic jump or impact in a cistern. There is al~ays some surplus emrgy which mU5 t be destroyed before water passes on to the earthen channel section. The following methods have been tried with success in practice.

(i) Bltne Wall. A wall built trans"ersely across the line of thw of a strP.am firstly to head up water above it to such a denth that·a hydraulic jump shall form ann secondly to withstand the actual impact of a high speed jet of water and to dissipate energy. The height of the wall is merely a matter of jud~me:lt and so:netimes a seriou; trouhle results from keeping the wall high by creating a second falL (ii) Fllation blleks or arr3WS. They are U:;U1.lly b'~ilt on downstream floor of the falls below the glads or the cistern. Their object is to divin~ the hottom high speed water laterally~ They are spaced and staggered REINFORCED CON: "FRICnO~ BLOCK'- so that there is impact between water so (A) The Block (B) The Reinf. divided and deflected. They just serve to Scale I" = 1 foot. reduce the' bottom velocity of water SIDE ELEVATION lea:ving the pacca downstream floor of the fall. Height oithe friction blocks may be up to t depth. They are spaced 1·5 to ~·O times the height of the hlock. The deSIgn is shown in Fig. 6. The distance ~tween the successsive lines is equal to tWice the height, Several lines may he staggered in·relation to one another. The distance between the successive lines is equal to twice the height. Several lines may be staggered in relation to onE another. The distance up to which r01,lghening of bed is required by arrows or friction blocks is given by the following empirical formula given by Montagu. D 2312 H 1/2 .·5. L=C_ _L_ _.. Dl I

+,

..,

I •

..._ _-+

\

+.4---... ....... •• IT

i--.;._j

+ ....,

1.

where Dl =depth of the cistern . (~)

.

. D2=depth do,",:nstream• HL=drop at the fall . e :::a co-efficient.

Fig 6 . The co-efficient taken is unity for vertical impact. three for aix for inclined impact and eight for no impact. (.

horizont

(iii) Dentated Sill. A sketch of tbe Rehbock's dentated sill is given in Fig. 7 below.

240 ,!,he object to this sill is to deflect up the high velocIty jet from near the bed. This is built at the end

of pacca floor downstream of a fall. \i v ) Deflc~tor is built on the ,arne lines as a dentated sill. It is of uniform height unlike the dentated sill as shown in Fig. 8. Its obJect is just to deflect up the h:gh velocity jet near the bed. ' Fig, 7

(v) Staggered blocks.

The staggered blocks are usually rectangular, blocks as shown in Fig. 9 in plan Thy are of t1:e height not more than 1/5th of the depth They are staggered in pTan. The energy of hottom water is lost roth in impact against them and in intercolLsion by lateral deflections. Fig. 119 Ihey alfo deflect up the Ugh velocity jet. Taey are the most efficient form PLAN of devise usuallY!I,e.d downstream of the ,cistern ~E "" CII/f""l~""iIAl4 or the hydraulIc Jump to destroy thp. surplus c:::Jr---"T"-....,c:::J--"T"'"-__,L-.J..L.:..;;..::r-~~I:.:.::.:.=:::;) energy which escapes destruction in the cistern or in the jump.

:'~'_$1i

(vi) Cellular or RIbbed Pitching. (

Internal frktion of water in a channel is a negtgibl" quantity hut roughening of the Fig. 120 perimeter can ~ucce~~fully be developed to destroy • surplus energy downstream of the f~ll, This has. b~p.n t(ed in Cthe form - ••,c.~:: . ~4.. of C~nular to Ribbed pitching. ThIS type of pltchmg IS constructed by , •• u •• _ putting alternate bricks on end mstead of on edge as shown . cit.. .... in Fig. 12. ,i

.

(vii) Fig.

Bur wall.

1~

Colyer evolved the design of a Biff wall in the 'Punjab

,;F.

as

~~own in Fig 13. This is put in at the end of the cistern. The object

._ Js~~
8.

•

>

Contractei Versus Fall-wIdt] fall.

Fig. 13

Advantages of falls with full-width of tbe ohannel. (~) Discharge intensity is low. The energy desiruction is efficient in a cistern or in a hydraulic jump energy. Thf'! cost of energy de3trllction device~ is very low. Free falls with hill width can successfully bo constructed without cistern and othf'r energy destroying devices, as has been done in the c~s~ of falls constructed on the Sarda canal in the United Provinces ~b) The action in the earthen channel section is very much reduced necessitating very/ little elastic protectioIl in the form of pitching _ (c) Such falls are most suitahle for corr~ct gauging of the depth on crest of the felll. The error due to los~ of head in entry from the earthen channel upstream to pacca channel between the side wa.ll:; upstream of the meter is negligibly reduced . . lq) Wide faUs with no complications of contractions and expansions serve as free faU meters up to drowning ratio as high as 90 per cent when provided with a glaciS.

,.

Disadvanhges of full channel width falls.

(a) Haisrd h:gh crest i~ likely to cause silting up in the upstream channel if it runs long periods of low supplies. The silt when piCked up by water in full supply or When the silt content is low as in the month! of October a.nd November, will likely cause silt movements in the channel dOWDst '~'1lD.

24l (b) when these falls are combined with bridges, they prove to be relatively more expensive thm the contl"acted falls. Contracted falls can now safely he con~tTucted using the modern enel"gy-d,stroying devices described hitherto. fheyare compautivdy ec()nomical. when combined with bridges. .

Advantages of contracted falls are shted below:Cal They serve as ('foportional distributors with low-set crest, causing neither afflux nor draw down. (b) They prevent excess silt entering the off-taking distributaries due to dividing the flow at the sides induced by the coutracted entrance which tends to concen ,rate the bed silt in midstream. . (c) 5"fety of floors is increased as £luming increa"es the creep length. (d) The cost is very much reduced especially when they have to be com!Jined with Toad bridges.

9 Falls with cistern or glacis. The selection of the cistern or the glacis downstream of the crast of a fall depends primarily on the prev'liling levels. Theoretically there is no need of a glacis wha'(l the drop available is equal to or greater than Ij3rd of the total energy deptb on enst of a fa!!. tut in actual practice the energy destruction is very imperfect in the case of falls with a cistern when the drop is about:

as

shown in Fig 14 below :-

,\ "" ", ~:,

alOjai:!

" s.,.'.I..

Fig. 14

The critical jet leaving the weir crl\st simply skims over the cist"rn fnrming standing "'aves. There is neither nestruction of the energy of the f'lll in impact in the cistern nor a hydraulic jump is farmed because the critical jet is n,)n-adherent and un,table. The cistern design should be used when tbe downstream water level is up to or below the crest level. (b) In thf! case of drowned falls a; shown in Fig. 123 above, the glacis design is very desirabl~ to drop the critical depth leaving the crest to the hypercritical condition upstream of a jump. (c\ Glacis df.s·gn is essential when the drop is not enough and it is de'lired to use the raIl as a meter. The h~'draulic jump is formed on a glacis with a fall of full channel width up to a drowning ratio of ~o per cent, and in the case of contracted falls lip to a drowning ratio of 80 ~r cent. The provision of the glacis en~ures the hvpercritical flow downstream of the cre~t which does not allow the buffers of the jump to foul t~e c{)ntrol section on the weir crest.

m.

Cistern Design.

Th€'oretic~l treatment to work out the dirLensions of a cisterIl h
242

l , ,'i\~:'; .

I

"

".

:~., \

rig., 15

to d~stroy the energy of the drops, and thirdly to prodllce reverse flow by providing a suitahle , enrl~wall to ,ensure an imp::Ict in the cistern. , 'The impact against the fio)r depJnds upon the vertical drop. In Fig. 15 a fall with '. :.v,erticl\.l droP.is shown ,

_E___ be the depth of the cistern

Let

4

The drop without cistern =(I1L-Dc+D) Drop with cistern =(~L+l'25D-Dd Discharge =gl/~ Dc3/Z=309 H3(2 cusees per {ootrll.rt Impact or force against th~ floor is equal to the mJrnentum degtroyed per second M wav 2 perpendicular to the surface minus the pressure due to the depth = ------'-v-wDa=:~···~.~-wDa . g g .",~ ...... ",,~Jo

wv 2

v2

g

g

Impact per unit area=~---wD=w(_-D)

Impact wit~ no cislem=

;I mpllct ,

'wD

i'

'-4

} .

J

.,

.

. h' clstern=w~ . ( 2g(HL---D '250 c+1'25D) ~--.-___ ~~. I , L g

WIt

=w

~.

w)l 2g1!lL-g D,+ DLp) ~ . ,,' ,

( ,') =w ~ 2lHL·-Dc)+D ~

l

'\

1

(,

} .

{2HL-Dc)+1·25D ... '

/

Thc.re;is increase in imp::lct aganst the floor of the clst6ti by an iittlotifit' eq dal fa h . when t e depth of the cistern }is,D/4.

!be cushion is just the wpjght of volume of wa~er displatecl by the jet as shown itt Fig. 15 mmus the weight of the water dropping per sp.cond. This will naturally increase if W6 increas depth .. If we put a bucket below a tap, water strikes against the bottom but as th ~ eepth of wat~r In th~ bu:ket increases, thp. cu~hion increases andeventually no effpet i~ felt at. the bottolll:. 'Th.~ rdal a-:iv
243 (bi Dimensions of a cisttrn. 1 (i) Sir Proby Cautley put the depth of the cistern as one half the height of the fall wiF:o any reference to the discharge intensity. (ii) Captain Dy~s givec the formula x=yHL x~D-where x=depth of cistern in feet. HL=drop in ffet. D=depth of water downstream in a channel. (iii) Bombay Pra::tice P. W. D. Hand Book. x+D=E+EJl3XHLllj ; length of cistern "

~:

EY(HL+D+x).,-E

where E=total energy at crest. (iv) Following is in use "in Bihar and Orissa, India, known as Glass formula as u:>ed by E.L. Glass Chief Engineer, x+D=2'25 £l/Z'HU/3. Length=5(x+D) , ,,_,,"{v) Etcheverry formul:t as evolved in America. ..... .. .

.

,'

~

'

Depth=one sixth of its Length (vi) Montagu's formula, Punjab, India. Depth of cistern=t Efz when Efz is the energy of flow downstream. for the discharge intensity q over tb 'Weir and the fall HL from Plate VII. Length=l=4'Ef2 The formula gives the minimum length used in his faU design, but in the case of fallr 'with: vertical drop, it may be of the order of 6 Eft. In latf'st practice, in large falls the cistens bed is roughened by two rows of friction blocks one at '4l and the other'at '7l from the beginning 'of the cistern. ' 11. Trapezoidal notch faUs. ,,'

(a) Notched F~lls used to be generally constructed on canals and distributaries in the Punjab. They have many advantages. The notches are so designed th;~t, whatever the dischargo palsing down the channel, the aperture of the notch' is sufficient to pass tha t discharge at tho water level of the channel at the time. Tha following rules were drawn up by A. G. Reid for 'use. (Punjab Irrigation Branch Paper No.2, 1894.)' Notations. l=length of cill of notch in ft.et; n=2 tan a where a=angle made by the sides of the notch with the vertical; l+nx=width of notch at any point x above' base; c=co-efficient of discharge =0.78 for canal notches and 0.70 for distributary notches; Q=discharge in cubic feet per second H=depth of water in feet above cill of notch. and measured to the normal surface a. few feet upstream of the notch. . D=deptn of water in feet for discharge D in the reach downstream. Hd """Height to which notch is drowned in feet. Hl =height of fall in feet. ka =-Head i1\ feet due to velocity of approach= v! . ' . 2g Note:-In the following formulae Q1 and QI are the sptcial values of Q for which the i1()tch is calculated. Similarly HI and HI are the special values of Hand DI and D2 are th specialavllles of D corn sponding to the discharges Ql and Q2 respectively. Als') e1 and e, are the daphs of drowning of the eill for upstream depths of water d1 and de.

244 C&nai Noteh.s with Complete Fall. General equation is :- D=icy 2g (!H 3/2

+.!_n H5/2) 5

=5.35c H3/2(1+0.4 n:fI) This expression contains two unkown qnantities l aD.d n, and for its solution two values of H with corresponding values of Q must be assumed. Then for calculat1ng the dimensions of canal notches, with complete or free fall, the equations are 0) QaH 1312-Q H 3/2

Hlj2(~2-HI)

n=2.14cH;3/2

tai >

'fp:m.~

;,

1

\2)

. 'H .,(.,'

TABLE NO.1

,"

.11

Table of Oo-emcicnts of Formulre for :Discharges of Notehes with complete fall.

,

H 0'5 '6 '7

·s

.~

]'()

"I

dty

,It

. ;

1 . '01:

'2 -3 ·4

·s

tt

'15

-7 "8 '9

.J

"3 -4

0'05426 0'04740 0'04]70

()1)2'64of " 1'1:,

-t; "&

-7 -g.

'9'

'2

0'06260

"l!! ""

0'02387 0'02164 0'01965 O.OI79S 0'01647 0'01513 0'01394' f)'1j)1288

3'3 '4 '5 '6 '1

0'26688 0-2030Z 0.16111 0'13U19 0'11051 0'09435 0'08178 0'07178 0'06300 0'05683 0'05136 0'04727 0'04256 0'03907 0-03600 003336

0'03691 0'03286 (H)2940

-z

'1

,Oj~"

H

15'1405 X '7H13/2

1-33441 0' 8459 1 0'57538 0'41207 0'30697 0'23589 0'18588 0'14954 0'12242 0'10171 0'08560 0'07285

• JJ .(.,

2i)

3~

~.-[~-

6'0562 X '7H1 512

;!!~rl:J' j'''''.;._"

0'03100 0'02S9! 0'02705 0'02533 (l'02387 0-02251 0'02127 0'02014 0'01910 0'01816 0'017Z} 001648

L -1--

K l

L

K

~

·s

'9 4'0 'I '2

'3 '4

'5 '6 '7 '8 -9 5'0 '1 '~rlf

,IS,

'2 '3 '4 '5 '6

'7 'S

'9 6'0

15-1405 X '7H 1 3 11

6'0562 X '7fI 1 5/2 0'01193 001107 0'01029 0'00959 0'00896 0' 0083 6 0'00785 0'00737 0'00693 0'006:;2 0006 15 0'00581 000549 0'00520 0'00492 0. 004 67 0'00444 0'00422 0'00402 0'00382 0'00364 0'00348 0'00313 0'on313 0'00304 0'00'l91 0'00219 0-00261

h:

b,~:..

~

..

,4,.,

'jJ'zd

.

'-f

rb 5rii" J:I

eM"

£~!nl

:n liJW, ..l:' !;

".

,.,1

0'01574 001505 0'01441 0-01381 0-01326 o 0127-t 0'01225 001179 0'0113t 0'0109" 0010(10 0.0\022 000988 0'0095 6 0' 0092 6 0'00897 0'00868 0'00844 0'00820 0'00796 0'00773 0'00752 0'00732 0'00712 0-00693 0-00677 0'00658 0- _0642

Distributary Notebes with Complete Falls. Take HI any convenient depth not 1es9 than one·third or more than one half of th;J full supply depth in channel downstrerm of the notch. and let Ql and Qz be the discharges conesponding to' the depths H t and H2 in the channel downstream of the notcb. Then the fonowing equations mu<;t be ll<;ed ;-

n = K (Qz-'l.83 Ql)

{3 ) l=L (5.66 Qr-Qz) (4 ) where K and L are co··efficients tM [Ju1nerical v~lueg. of which of for dill~d'lt V.ltli6S' of given in the table.

&.


245 TABLE No.2 . Table of Coefficients of fortnulae for Discharges of Notches with Incomplete fall. M

,M l

°1

6;15 x'7H/'/2

15'38 X '7Hif3'

0 -~~l----

6'15 X7H1 5j2

H 0'5 '6 '7 '8

.

,

1'31401 0'83309 0'56661 0'39887 0'30229 023228 0'18304 014725 0'12055 0'1001.6 008430 007173 006455 005344 0'04668 0'04106 0'03635 003311 0'02895 002603 0'02351 0'02131 0'01939 001771 0'01622

'9

1·0 'I '2

'3 '4

'5

's '7

·s

'9 2'0 'I '2

'3 '4

'5 '6 '7 '8 '9 3'0 '1 '2

o ~1490

0'01373 0'01269

15'38 X '7H1 /3Z

•

0'26272 019985 0'15860 0'12983 0'10879 0'09288 (;'08051 0'07066 0'06267 0'05607 9'05056 0'04590 0'04190 0'03846 0'03547 0'03284 0'03052 002846 0'02663 0'02504 002350 0'02216 0'02094 0'01982 0'01881 001788 001702 0'01626

------

H '3

."

'5 '6 '7 '8 '9 40 1 '2 '3 '4 '5 '6 '7 '8 '9

5'0 .} '2 ... _.. '3 '4 '5 '6 '7 '8 '9

6'0

001175 0'01090 001013 000944 0'00882 000825 0.00773 000726 000682 000643 000601 000573 0'00541 000512 000485 000460 0'00437 0'00415 900395 0'00377 0'00359 () 00343 0'00327 0'00313 0'00299 0'00287 0'00275 0'00263

.~

O'() 154.9 0'01482 () 01418 (NH360 0'01305 ()·el.254 ()'0120G ()'Oll~.J.

()'01l19 O'OlO79 001041 ()'oHlOG

-o0097:J (j'1}0941 0.0091% "()'0088:J "()'OO855 ()'OO83() 0'00806 ()'007-83 0' 00761 o '0074
Distributary Notches with Incomplete Falls. , The following simplified formulae for incomplete falls on distributaries are app licable only when the following conditions are obtained. (a) The descent of the fall must not be less than one- third or more than one~balf of the full supply depth of the up~tream reach. (b) The depth for a givt'n discharge in the downstream reach must not be less than the depth for corresponding discharge in upstream reach. Failing either or both these eonditions, the formulae for canal notches with incompleto falls must be used. Let Ql be the discharge due to depth in the downstream channel equal to the des::an\ ()f the fall and let Q2 be the discharge due to depth of twice the descent of th~ fall •. (The not-eb will thus be just free with depth=HL in the downstream reach and drowned to a depth = Hl. when the depth of water down-stream of it is 2HL .) n=M (Q2-2.5Ql) (5) 1=O\5,37-l QI-Q2) (6) in which M and are co-efficienb, tbe numerical values of which fOf different values of H are given in table 2.

°

246 (c) Fig. 16 shows th", form of notch uSed in the Punjab. It will be seen that the plane of the profile of the notch is set back 1'5' from the downstream face of the notch wall. The profile itself is formed by a horizontal eill and by twr') equally inclined straight lines which arp. the traces of the crowns of two inclined surfaces of varying curvature The limiting radii of curvature are shown in the sketch. Ali arcs of C'Clrvat, re are drcular, and all centre~ lie in the plane of the profile. The same form maj be used for large distributalY notches, but in their case the plane of the profile should be set back 0·75' ollly from the face wall. and the unit of radius may by 0'33' in place of O.S! as shown in the sketch. Cn aU ca1!es the upstream splay should be 45° and the dowDsteam splay 22° Thp. height of the notch?s on distributaries should be in every case that of the estimated depth of full supply. and on canals it sh(mld, as a general rule, be aho of that depth. Thrre will, however, arise cases pn canals in which at times the volume to 1-e pa,sed i~ considlp greater than that dne to the full supply depth . .ElEVATioN which has been as';umpd for the purpose of caleulating the profile of the notch. and in such ca~es the notch ShOUld be carried up to the . surface level due to the maximum depth of water which will be carried by the upstream reach. . The thickness of the notch wall must be sufficient to withstand the pressure to which. it is subjected. Where two notches are separated by an isolateil wall, it may be laid down as a rule that hoth faces of· the wall being vertical, the thickness should not be less than half th~ height on canals, and 0'4 hmes the height on distributaries. PU.N The lip of the notch must be corbelled out beyond the face of the crest wall of the fall The edge of the lip ~hould' be an arc of the circle of radius such' that it passes through the following thrpe points :(a) On canal falls-At the end of the lip the two points in which the downstream splay of the notch meets the fare of the nothch wall; and in the middle, a point two feet outside the face of the crest wan. ',tit " (h) On distributary falls-At the end ef jb.&~n i the lip the t.o points in which the ·.1 [~dj ", downstream splay of the notch meets the surface of the n 1tch wall; and in the middle, a point one foot outside the face of the crest wall. <

(c) EXlmples--Reid gives in his paper the following examples ot thf! method of using

these

f()irrl\lla~_

Frae FlIlo, Cm\I-Ctl·~uht~ thl} dimension1 oi thl notche; for an 8-0 ft canal under the following conditions :-

fall on a

Upstream Reach Ped wirlth 100 feet Inclination I in 66666 Full supply discharge 1869 Cusecs Three rajbahas, with an aggr"gate full supply of 42~ CU>6CS to take off trom this reach. Downstream .Rc-ach. Bed width 87 {fet Inclination I in 5,000 ". Full supply (norm:! 1) 1,445 cuscct Minimum supply oYer the faU-770 cusecs.

247 Assuming side slopes at t to 1 the dp.pths of full supply in the upstream and downstream re;lches will be found by Hi~ham's table to be 7'0 and 6'0 feet respectively. We have first to consider the depth over cills of notches (Hm) at which the normal full supply of the downstream reach (1 ,445 ~usecs) should be passed. The depth at whicb a supply of 1,445 cusecs wOClld be passed in the upstr(}am reach is found, by Higham's tables, to ce 6'0 feet, or exactly the same as in the downstream reach: The limiting value of Hm will therefore be :(il Depth of full supply at head of up stream reach=6'O feet. (ii) Depth in upstrt'am reach due to a supply of 1,445 causes =6'0 ft. It we take Hm = 7'0 feet, the working of the upper reach will be perfect as long as all the rnjbahas are running full supplies (424 cuse~s\, but if one or more of the rajbahas are closed, the notches will be very tight, and will head up the snpply. If, on the other hand, we make Fm =60 feet or lO foot less than at the head of the reach, there will be a great draw under normal conditions, i.e. with all rajbahas open, which might cause a serious bed scour, and would lower by one foot the head availa'1)e for the rnjbahas immediately above the fall. The value to~e ascoumed for Hm will lie l::etween these limits. Generally it may be said that the nearer a falLis to the head of the canal or branch, the nearer should the value assumed approach the maximum limit. In the present caSe we may take an exact mean and assume Hm=6'5' The depth due to a supply of 1,445 CUSECS in downstream reach (Dm) has been shown above to be 6'0 ft.and ratio of full supply depth above cills of notches to full supply depth . .H 6'5 III downstream reach -~= Dm 6'0 The minimum working supply is 770'cusecs, corresponding to a depth (Do) of 4'15 feet in downstream reach, as will be found Ly the tables. The supplies Q1 and Q2 to be taken in calculating the notch will be those due to depths D1 and D2 in downstream reach, and these depths may be determined thus :6°0-4'15 D1 =DO+HD m -Do)=4'15+ 4 =4.'61 _

3

•

D2-Do+4\Dm-Do)=415+

3 (6'0-4'1

'l

The value of QI and Qz correc;ponding to calculated (from Higham's Tables) thus:Red width 87 feet Depth D1=4'61 D-D 2 -5'54 The corresponding depths over the notch

these depths in downstream reach ~a}' be , Inclination = 1 in 5,000 Q1=924 cusecs Q2= 1264 cusecs cills HI and H2 will be

H t =D1Urn =4'61 xAoS=5'0 feet; H 2 =D 2!f_lll=5'54 X 6'S =6'0. ieet Om 60 Dm 60 We have therefore to calculate the dimensiom of a notch which will pa.ss 924 and 1284 cusecs, at depths over the cill 5'0 ft and 6'0 ft. respectively. H 1=S'0; Q1=924; c=0'7:1; H 2 =6'0; Q2=1264. Q2 H 13,2_Qt. H 23/2 _ (1264xl1'181-(924x14'7') n 2' L4(;h~.3/2tr~3{2lH2--=--H~) -2 14 X 0'78 X 14'7XfF18 X (6:0::"'5'0) 0

= 548'72 -2'0 feet 27447

'~I

'L___Ql_

5';J,jcH13,'2

=

-04nH 1

924 -O'4x2xS'0 5.a5xO'78xlloU; = 19.81-4.0=15.81.

248 The above valu~s of 11 and l are for a single \. otch, if we design the fall with, say notcl.es the vulues for each notch will be

SIX

n=,~_:O =1; l= 15'61 =2'63.

6 6 The width of the notch 1'0 foot above full supply or 7'5 above cill, will therefore 1:e ! of L ..' I 7'5 +-2'63=5'13 feet and the profile of the notch will be as ! ' - s ..I._': in Fig. 17. """._.... It will be found by applying the gen~r::ll equation Q=S'35 c. H3 12 X (l+0'4 nH) that the full supply of 1,869 cubic fpet of the upper reach. which may be anticipated when all uppl·r raj bah as are closed, will be passed with a depth over the notrh d=7'5 feet so that the water will bl> just level with the top d the notch, as shown in the sketch, and there will under these extreme conditions be a heading up of 0'5 feet. If it is desirable to avoid this, or to leave a gnater margin, the height of the notch walls might be reduced to that required for the normal full supply passing i)ver them. namely 6'S feet, and exctssive supplies could pass over the whole length of the wall, hut there are few circumstances in which this could he recommended. (d) Calibration of Notch falls.

Fig. 17

Nethers-ol's Tables.

The late sir Michael Nethersole pre Dared a series of tables to facilitate the calculations of the correct discharges of notches for distributry falls. Tables give the dischages through the two side triangular portions of the notch as distinct from the discharge of th .. rectangular portion in the centre. These tables were published by him in 1903 at the Thomason Press, Roorkee, India. The velocity of approach cannot be correctly allowed for in the calculations. SometimQs the value of the coefficient is increased to allow for this. The calibration is nothing but approximate. (e) Trapezoidal notch fall is still the best type of fall in channel, in which variation of supply is very much and no metering and regUlation of supply is required. However, this type shonld be avoided when it is not a free tall. 12. Montagu Type fall. The design of the glaCis prnfile does not seem to have received the attention it deserves. The ... hole theory of the formation of a hydraulic jump postulates an horizontal velocity and it is during the change of this horizontal velocity from the hypercritical to the subcritical stage that the dest rurtion of t nergy takes place. 2. The fact that all water m lYing down a glacis haq a vertical component of velocity seems tel have been lost sight of. in evp.ry pUblication on the ~ubject. It appears that the high speed jet which so often persIsts below a Hydraulic jump is the outcome of this vertical component of velocity, the energy of which is unaffected by the occurrence of the hyilranlic jump. 3. It will be cle::lr that a reverse slope on a glacis such that the hyper-critical stream is moving horizontally. is the best solution (Fig. 18) The drawback is that the Hyrlraulic jump is extremely sensitive on an horizontal floor, and that I the level 0: ~uch a floor is only correct for one ideal set of conditions Any departure from the -conditions postulated, leads to trouble which may clttSr be serious. But for a varying discharge, the profile of the glacis should be so designed that the maximum horizontal acceleration is imparted to the stream at all states of discharge. By imparting Fig. 18 maximum horizontal acceleration, the maximum horizontal velocity is attained in any given length of work; such a design is thert fore conductive to economy in construction.

--_L

249 .4. It will te clear that a stream flowing on an horizontal bpd has no horizontal acceleratlOn because the reactien is norm~l to the bed. . .. I~ will also b~' cle;r that a Slr~am flowing- over a parabolic hed appropriate to the 1m hal hOrIzontal velocity \ , will have no horizontal acc" lpration because there is no rea~tion. So"'ewhere between thpse two there will be a path upon which the horizontal component of the reaction imparts a maximum horizontal aceeleration. It is this path which is the most efficient and ecnomical glacis profile. (Fig. 19). The equation of the ideal glacis profile derived by A.M R. Montagu is stated bplow and the student should refer to the original publication No. 10 Central Board of Irrigation bv Mo.otagu for its proof.

;/4

x=vv·_-- . . g

y

(v +y where

v=the initial velocity of water leaving the creest. X= Horizontal distance along the ordinate. y= vertical distance below the horizontal.

.m'&91iaawob !,' ,.abl.e tb~Qc'6'm:l:lf!' Example. Design and sketeh a fall of M mtagu type for the foll~~= lUi :It

I p\ 1 e'"

U'lt

Discharge=207'S cnsecs ; Bed width=3f-0 feet, F'S'D'=3'6 ft.

.'

783'94. 78034 F'S'L'= '--'---, Bed level= .~--' Fall=20; N'S'=784'72 7~ 1'84 778'34 ' Calcu :ations.

2.0 fall at R.D. 2.000 Kokri Distributary Sirhind CaOlll Data. Q=207'6 cusecs; B=31'O feet; D=3'6 feet. 207'6 Mean velocitY=(3-f+--:-326136 -=1.761 ft. per second. 'f'''; ~j,:

~

783'94. 780'34 . .. ' F .S.L.= 781'84' B.L·=77tF3T' Fall 2 0 feet> N,S',=784 2.

7

1'76 2 . v2 (1) Flume:-h a =-2g =-64-:~f =·OSft.

8" S. D Downstream=3'6 feet; Ef.,=3.6+·OS=3·65 fpet. From plate \II for HL =~·O and-Ef 2 =4'65, read q=U'6Cs 2076 =17.89 Say 18.0 feet. 11. " (ii) Crest. Q =207.6; De = 16ft (critical depth); B = 18.0 and q = 11'4 es. Efl = 1.6 X 3/2=24 feet, R.L. of crest=783'99-2'4=781'59 Length of crest=2'S H=..l·Sx2·4=6·0 feet. i (iii) Approach. Side expansion each sine upstream=(31-18)·i=6'S feet. Expansion 2 to 1 length=2 x6 5~~ l~ 0 feet. ='--~6-

B;

~.

Cistern. Dppth~~*Ef2=3. 6 5= l'S3 •

2

feet: R.t. of cistern bed=t778'34 -1'8~j=776'Sl

Length of cistern =4 xdepth=-t X 1'83=7'3 ft. S

Glacis. X=V

(4

/y- +y

ygy

(I)

.J

250

q = 207'57 = 11'53 cusecs; Dc = l'6ft,; IS

q 11'53 7' 2ft,/3ec. v= -=----=Dc.

1'6 ,)'

, .'

Substituting value of v in formula (I) above x=7'2x'3524xy'y + y =2'54vy +y RL of crest =781.59 and RL. of cistern floor=776'Sl . Ditlerence=S'08 feet.

y y'y 1 1 1'0 2t 1'4142 3 1 '7321 4 2'0 5'08 2'252 Horizontal length of glacis is IO'S feet

254y'y 2'54 3'59

" ;1q

x ~'54

8'59

4'4

7'4

5'OS

9'08

5'72

10'S

Departure downstream.

.. 7.

Departure on each side =i (31-18)=S'Sft,; Splay 3 to 1 ; Length =6'5 X 3= 19'5ft.

8, Exit Gradient. For minor works founded on clay soil, the exit gradient

m~y

be 1 in 3 to 1 in 5

Exit Gradient GE =_I:!_

I vide Plate III ; where, 7T'y'~ d=depth of cistern wall at the end of pacca work =2'15 feet. " d

b 56 a=--=--=26'5 d

2'15

,',,'

Head=H=worst when water level is up to crest and downstream bed dry='jSl'59-778'34=3'25 feet 1

"'YA

='086; From plate III, GE

== 3'25 :us

X 'OS6='13 which is safe'

/

i't

Upstream pressure. (1) Upstream curtain wall.

Corrections of thickness; total drop =15% .J.. _15X30_ ,- 01 't'c~ -~.- - 4 " 10

d= 1'4 feet, b==56'O'

lUU

a='0225

,pc =85 pc,

.

from Plate II

,

4'5x'9

ProportlOnal to thIckness= _ - 2'S6 1'4

In terference of Glacis toe wall

!~'32=19 /-l'33=~~~ ::::,6°/ . ¢c corrected=85+2 86+ '6==S8'4G 0/19 /(J y' 29'8 V 29 8 56 /0 (2] Glacis toe wall, d= 1'4 ; b,..:56 0% Correction for slope of Glacis;

b b

_j._

29'3 56, ---' =.53;a==- =40, 56 1'4

;C=48

%; 9D=48 % ;

For slope in 2 read from Fig. 68; .

.LE=48 == ]0'8 X6'3=2'3Q~

't'

:l.9'1

I"

Corrected 9~=4S%

o~ II

(3) Coerected ¢E =.pD=48+2·3=50·3%

Downstream curtain wall.

Corrections Thickness of floor ; drop = 1%8 30 =5'4% rpE=18,-< __

0=2'15 feet

~=o b

100

!_= 2.15 ='038-\

a

56

Proportional to thickness

.

Corrected ¢E=18-2'27-'37=lS:360/0 Thlckness of fioor. Soil Mlow the floor is sandy .mixed with kal1kar and'theretore pervious. H=3 25 feet. '1

Worst

Table 3. Description.

Percentage.

:1

Full seepage :'ei: . . .jJ:l· , ,irhn flow pressure . , iT 1

Thickn'ss provided

Thickness of floor calculated

j'

:

50'3%

Unner cistern 10'25 from toe of glacls 19'8 do

Ii

J

·'::~.:fi:;i~:i

1'64 1'4

;"'
1'64 1'4

14

'9

1'15

1'9

tc;·!i

'9

Th;ckness of the glacis.

The thickness of the downstream ghcis has been designerl for the worst conditions of the trough of the hydraulic jump and it oc;urs when the supply in the distributary is minimum, Area of trough at the jump=8~4=16 sft, per foot width. Area of pacca floor under trough of the jump=S'S X average thickness=*S·5 X l'f)== 16'15 Hence thickness is sufficient,

sft pe) foot width.

Curtain walls. Upstream curtain waIl=1/3 Downstream curtain wall.

t

of downstream depth=

F.S.D,=1/3x3·6""'1·2~ft.

¥=L8

thickness=l'4 ft.

':.tt -I

• __ ',

":'_:_,1

it,

thickness provided at the axis of the channel==2'15 feet as the bed is bowed, as per Centra) Board of Irrigation Publication No : 6 Fluming Page lO~ ~ ~

,1

. ~ !>

Bowing of Floor downstream of cistern.

It is raised up 1 in 10 to RL, 771,57 petmitting a bowingt>f_!_to .~belowthe designed, 40 30 bed. End curtain walt is also bowed,

Let. it bt.1!..in this Case=l,O ft. (:$(J

252 Downstream bed protection.

LONGITlJDINAL SECTION. SCALE {HOR: ~£R:

Fig. 20

I

2.ft thick loose bats far a length of 4 to 5 D 3'6 X 4= 14 4 say IS feet bed and 10 fflet on sides in bed. Roughening of the cistern bed.Cistern bed is roughened by two rows of friction blocks. Side walls. Side walls are flared from the vertical at the end of the crest to a slope 1 in 1 at the end of the Cistern Fig. 20. 13. Inglis type Fan. The inventor Jf this type of contracted fall iC.C. Inglis M.I C.E. Director Research Station Bombay) described the essential features of his design in paper No: 44 Technical Publication P.\V.D. Bombay and paper Mo: 170 punj ab En~ ineering Congress 1933. A lucid description of tne nece~sary points is gi ven in Appen iix V of the Central Board of Irrigation Publica'ion No : IO.A sununary is presented here.

(a) Notatj( ns

Q=di ;charge in eft. per second [cusecsJ q = }ischarge per foot width of a channel or flume. qo = Discharge per foot run of overall throat width of flume i.e., including piers. \' =velocity in ft, per second at any selected point. d1=Depth of water in upstream sertion of achann~l [e g., ahove a fall or contraction~. d 2 = Depth of water b'l.ffle pavement at toe of fall [assuming no standing wave has formed d 3 = Depth of water in the downstream section of a channel or flume [e. g .• below standing wave.] dx=Depth of water downstream of standing wave above baffle pavement level in a parallel sided channel, dy=Depth of water downstream of standing wave above baffle pavement level in expanding flume. j,;j.>'(d d z = Water depth in cistern. downstream of the baffle pavement D1 = Depth of water upstream, above sill level. D=Effective .depth of water a00ve sill upstrGam =D1+ch x hv = Head causing velocity H= Fall in water level i e. difference of water levels of upstream and downstream of fall (below standing wave) Hx= Fall in water levels with parallel sides. Hy=Fall in water levels with expanriing side". h2 =Difference of level of water upstream of and on baffle pa.vement at the toe of the fall. assuming no stancling wave i.e. the effective head for downstream velocity v 2 hb = Height of baffle B=Bed width of a channel B 2 =Bed width of flume at the contracted section rexcluding pien). Bo =Overall teil width of flume at the contracted section including piers. , Lh =Dist:mce of the upstream face of baffle from toe of falL (b) Description of the Design. ' 'I ,;}I

i:

A section and a plan of the fall is given in Fig 21 Des'gn consists of ; (i) A standard long -throated weir flume followed by a glacis slope and a pavement on which a baffle is fixed to dissipate eneTgy A cistern downstream of the baffle with a deflector at the downstream pnd of the cistern is provi~ed. pacca pavement ends at the deflector There is a se{;ond cistern downstream of the deflector the section of" hich need only be pitched,

253

-.-.,t-~ j_

..rT

'Inn

..... I . II

,...

~

I

I

()

,.~

;:

:ce

-

III r- -t oo

"

..

I I I I

~

"

r-

c: t)

I " ~ I ...'"~ lIo. r.. f

I ,..i

.. ..:: ~

,

-

~

M

<:

I

UJ:

'Il1

,~!lh

;{!

,.."b Jo.

<,..

....'" n....-t a

-

::}

nr \ £"

(ii) At the toe of th.~ glacis, very high velocities aTP generated, and the energy in excess of th.e persist :lnd the rlistribution of velocities downstream of a fall does not approximate to the distribution in a normal chan nel. It follows that when the materials of the channel bed are erodable, heavy scour results, and this is a('centuateil where the sides diverge sharply below a fall, because cork screw eddies are then generated. Where the height of fall exceeds l/:;rd the depth of the channel, conditions are markedly improved by adding a properly designed baffle. (c) The maximum dissipa.tinn of energ~' by a hydraulic jump occurs when the jump forms at the toe of a glacis. In practice, if there is a sloping glacis, the hydraulic jump may form: [i] on the glacis, [iiJ at the toe, or [iii] downstream of thp. toe. ~

Fig. 21 (i) If the hydraulic jump vouId form on the glacis, where there is no baffle; i.e. if da-the normal depth of water in the channel downstream would b~ greater than dx (or d y)the optimum depth, the baffle should be fixed on a platform at a higher level than the canal bed level, so that the natural wave would then form at the toe on the platform. (ii) If th .. hydraulic jump would form at the toe of the fall i.e., when da=dx (or dy], the baffie should be fixed at pavement level. [iii] If the hydraulic jump would form downstream of the toe, i.e., if d 3 would be less than d x or [dyJthe glacis should be extended and a ci,tern provided of such depth as to bring the wave to the toe and the baffle fixed on the bed of the cistern. Plate XV enables us to detem1ine the level of the platform on which the baffle should be fixed for an overall discharge of qo per foot run bet Neen abutments for a fall of Hx feet when the channel has parallel sides and when the sides diverge" The height of fall Hy ca.n be turned into equivalent height for parallel sides Hx -vide Plate XV and kilO wing Hx we can fine dx from Plate :XV and as Hy+dy=Hx+d x , we thus get d y , the depth of the baffle pavement belOW the water level downstream of the fall.

254 The height of the baffle should be equal to l'3d 2 ; d 2 being giwn for any qo a.nd Hx on graph of Plate XV and the distance of the baffle from the toe of the fall=S'25 d 2• It is important and interesting to note that as the position of the standing w:;).ve depends only on the discharge per foot run and the head available. it is immaterial whether there are piers or gates in the throat. provided the piers do not cause afflux and the coefficient of gates is unity; but if the coefficient is les. than udty. then the head available is the difference of head upstream and d)wnstream (Hg ) less the energy head destroyed by the gates or piers; which can be calculated. The baffle ceases to be effective when Da/Dl exceeds about 0.60. because then it begins to become ' drowned" . The graphs shown in Phte XV allow for nornmal (IO%i losses due to friction and the graphs in plate XV allow for the part of the prc:snre of the standing wave which is balanced by the side walls. (d) Even though the energy is effectively dissipated by baffle near the toe of a fall, the distribution of velocities is not normal, hence a chtern and deHector are provided. At the point wh~re ~he downstreem flume width is equal to 3/! bed w;dth of the channel, thl'! nepth of wate WhICh IS necessary to give the mean velocity of v=cXO'8! dO 64 is calculated. The difference ?ctw2en this depth and the norm~l depth do vnstrcam giVdS the amount by which the pavement IS su:-!k below the downstream bed leVel. Plate XV show;> the value.;; of L in terms of Bo for' various values of BalBo and divergence of 1 in 4 to 1 in 10. A deflector is fixed at the end of the chtern i.e. at a distance L from where diverge'lce ~tarts, the height of which is 1112 of [F.S.D.+depth of the cistern below the diagonal canal bed Level downstream.] [e] Side divergenee. The side divergences should not be sharper than those shown in Plate XV otherwise a return flow occurs. A cistern with a semi·elliptical cross section gives a much better distributi n of velocities than a cistern with a flat bed. The side slope deflectors are bel1eficial by caus.ng • the bed roller to form over the fclll width. thus preventillg the formation of lock screw eddies [fJ Seour downstream of bed ddlector. Experiments have shown that where a deflector Fig 22 was fixed, the material tended to bank up behind the deflector to a slope of about 1 in 3 to I in 4 and for the deflector to be fully effective this scour should be allowed to occur because flat pitching prevents the form'ltion of the beneficial borjzontal bed roller. Protection should be laid to the natural slope of 1 in J

[gJ Examples Design an Inglis Type Bumed fall in a channel with the following data:Discharge=700 C1lsecs; Drop=6'63 It; Bed width = 60 ft. Depth 5'1 feet; Fun supply level= upstream downstream

t

4R-~,,'

·;':·~':-·':/:;~I'i~,;;·;~;,!;· ,~

.........., . _.... ::.

".0

~ .1.\

622·S9. Bed levels= --_, 615::16

_. ,.::'-.: ; . : : :....

Fig. 22 (i) Design of flume:-

Mean

secono: N.S.=624·O; Side slope

5-'

Area of the channel section-S·l(60+--1, =319 sit. ~

velocity=2"19 it per

t to 1.

255 fL{from

V=

l'15v' fLR=O'81

Height of the hurrp in

throat=_
l:l

Dl=7/S d a=7/8 xS'I=4'46 feet. d)=height of the hump+D 1 = 64+4'46=5'1 ft. v l =veloclty of approach=2'19 feet per second. hv=head due to velocity. of approach =

~0~ .086 ft.

},'ote:-Instead of 2g, c.e, Inglis adopted 50 to calculate hv. D=Dd-hv=446 (-'09 =4'55 it. Q=3'09 BDl,0=700 :.B=23 4 ft. say 24'0 ft. lt is desirable in l'ractic p to design the throat in an exact multiple of feet s() that the ;pan width is about 1'5 D 1 ; let there be 3 S?arlS with two piers of :2. 5 ft. thick each, the di"dn;g,) co-efficient reduces in that case by l.S P c. . . ' 700 2/3 .. The new D (. _. ) =4.52 feet. 24x3.0-l This will give Dl =4.43 and the height of the jump='67 •

[iiJ

~en

mouth ups tream approach,

4'52 1 '°= 19'2 feet, The curve shou'd su;)tend 'an angle of 600 and then continue tangentially till the wall penetrated the side slopes above F.S.L. . The sill of thrO;:Jt may be formed to upstream bed level by a sloping pavement. (iii 1 p05iti:m of ga'lge cha ill cer, The posltion of the upstream gauge chamber from the end of the thi'oat=4D15=3tVi feet say 38'0 feet. Radius=2Dl-5~, 2 X

iv. Throat Length=2'SD=Z'SxS'l=1I'3 feet. Throat width=3x8+2x2'5=29 feet. qo

=--~OQ=2!'14 cusecs, The glacis slope will be 2~

2'5 to 1 and will be joined to the thro'lt .

and the baffle platform by radius 2D",,9 04 feeL

Side divergence B3 = _~Q_=1l'76 from plate XV for-:§___=ll'16, the side diwrgenc6 . da 5'1, d " , ;, should be 1 in 9'2.

In the design, it may be adopted as 1 in 8.

(vi) B::l!fte anI Baffle platform Hy ='0 rs ttP.:l u wcl.ter-level downstrean1=ctest ievel+d.,l-, 6.21·oa=o~:a2·59 r511-:--3~1 '0(1 Fr,):n pIa!',· ;{ V fur q 1 =24'14 and Hy=6'63 01' from 'qU'lti'>n <1 2 =' J I q) Ih:l 5 (.-\) and x= 7:3 go .5! : Ix ,',1 (B) '="663 ft.

fL an d sram·,' Btl

()II

• =2'07= ,'CK'U2=l [2 'N ' .

•

dx form equation (B) above=5'S6 feet. h6=height of the hottle = 1'2 (Dc-D 2 )-1'96 feet. / -----;;;-

/ 24 '14 2

D ={I-_={I--=2 63 ft. o g g The baffle should be 1'96 ft. high in i length and should have its top sloping down at the ends. The dbtance of the baffle from the toe of the fall=5h b =5=1'S6=9'8 feet ;,Hy+dy= Hx+dx; dy=4 87. R.L. of the baffle platform=downstream water level--dY =621'06-4'87=616'19 (vii) Cistern downstream of baffle. Minimnm length of the cistern is given by L=6'3 Q.3=45 feet. The bed width at the end of the cistern expanding in 8=48'78 at the end of the cistern = 14'36 cusecs.

~..et

q per

.loot widt\}

Depth of the cistern is given v=-Q-='84 cd 2 'u

q2

of fL ='81 and then C='9 :. d. =6'02 feet. Actual length of the cistern is usually kept rather liberal. Let it be 76 feet in this case, 41 fee,t with pacca sides and bed and 35 feet downstream of the deflector with pitched bed. The cross-section of the bed of the cistern is bowed. The amount of bowing in ;nidstream equal to 25% R wnere R is the hydraulic mean depth. The actual bo\\ing of cistern ted can best be done by letting a string held across the section touch the three points, two ends and the middle. The curve obtained is catenary The depth of watel in midstream at the end of cistern=621·06-614.82=6 24 feet. The bed deflector will be=6.24 =.52 feet say 6' high. Side deflector =~264 =1'04 feet 12 . say 1.0 feet. (iii) Vanes.

It is usual to provide vanes in the continuation of piers to stabilize the hypercritical flow The vanes may be 6' R.C. walls with 6" free board, Sometimes in addition to the deflectors, staggered rows of nctilinear blocks say 4 in nnmber are provided to stabilize flow downstream of the pavement and to reduce scour. In this case the second cistern can be omitted and only one cistern of about 41ft. length at the worked out level will do. h This type of fall is considered to be v'ry efficient, for distribution of energy hut the cistern element is unnecessarih' elaborate and very expensive. fhe position of the gauging site is defectivf because it will be opposite an earthen bed, which is liable to silt in lows upplies. In this the correction due to velocity of approach cannot be correctly applied as will be !>xplained later.

e4.

Meter flume.

The correct design of meter flume received thp. first impetus fn m thp. experiments carried out hy E.S.Crump I.S.E.punjab Irrigation, described in papTr Nos: 26 and 30-A of Punjab Irrigation Branch PUblications, Class A 1923.25 Th,,"e experiments brought out three points very clearly· \i) The discharge formula Q=CB~H3f2 was applicable to the long- cCfst(d weirs and that the value of the discharge coefficient C was 3'O~ whidl is its theortical value (ii) The length of the crest sh"'uld be 2H. (iii) The value of the coefficient was constant and indepenced of H in a long-throated weir flume upto a drowning ratio of 91% (model L of (tumpe contracterl flume with? length of crest 2H and Expansion 1 in 10 downstream on both sides}. In ca,e of flume with vertical drop it was constaut upto 66% drowning ratio

257 (b) Discharge formula.

Let q be the discharfe per foot run: D be the depth upstream. Initial Enugy E=D+~~ 2g

Depth on crest=Initial energy -Rise of crest H=E-x Let y be the depth of water on the crest and the motion in a frictionless channel. Fig. 22 The discharge rer unit width of the wier q=A.v wit h respect to y

for the maximum value of q for the values of y;

~~

=0

1 \. -Vi This is ju~t the necessary condition which gives the maximum discharge for the kn·)wn value of H. Therefore discharge.

(H-y)1/2_IrY-H--iT2 =O, or H-y=ty:. H=3J2y or Y=iH

q=iH.V2g~=iv/l.

=3'088 H3 1 2=3'09I{3'3 we

obt::~ :itil~~~ep: jfm~r {I <

gi

.

A

H3/2

J:r:"'l' llf3 g

.

SubStitutillg Yc in terms of H in equation q=

v/~g~'H~-Yc J3/3=gll2 yc 3'2= v~

8 =(

27 H3)lJ3=iHor H==iYc

[A] (B)

It is therefore that the critical depth is the de)th of water ff·quired at the crest to give the maximum discharge or the coeficient 3'09, provitied the flow is frictionless in a rectangular channel. It has been shown that the water surhce profile in an open channd, is parallel to the b~d profile in the condition of critical ffow. This is the section of a weir, where parallpl:sm of flow is attained. It is the section which gives the maximum discharge so long as the parallelism is not fouled by the conditions of flow upstream and downstream. Any ilisturbance of this control section results in the reducti >n of d15charge of weir. It is to attain this condition of parallel flow that the crest is kept levd (c) Length of crest Advant~grs of long length of crfst. (i) A long length of cr{ljt a~ usuall) ad opted in weir flumes ensures a constant cQO)fficient of discharge with all depths on crt}~t. (ii) A lcmg throat provides a considerable increase in the modular limits. Free fall formula is applicable to as high a drtlwning ratio as 90%. (iii) In long-throated' weirs. the ce~sation of modularity and the disappearanc~ of the hydraulic jump occur simultaneously, so that tll'~Y o:1er this !!reat advan tage over their shortnecked brothers that one can tell at a slance whether a flllm~ or a weir is dE-livering Its full m<)dular discharge or nl)t, . The water surface profile shown in Fig. 23 i, convex in the beginning. then attains

pnalbl!sm in the critical C);} iitialS of flON (uSHlly c1Hel flu point of Inflexhnl and lastly drops belo", the critical con iitions in a c!)n~aV~ curve. fhe convexity connotes a CUflrature of fila'l1'~nt.; wi}ich is ngth downstream of the critical section, so that the buffer of the hydraul c j Imp in the case of meters with a gla~is and the convexity of the dropping jet in the case of falls with a vertical drop do not foul the critiC'll section. Hypercritical jet is adherent and not liable to prpssure inflations. It has been ohserved that the control section or the point of inflpxion occurs in the IT idater than 2H, The author wo~ked out the length of level crest from c)U)iderations of a stable ann an ~l(lherent hyp2f(~ritical jet flropping in depth by 5% from the critical depth in his Article in Indian Engineering, Calcatta, December 1936. The length of level crest worked out to be (~quaI to H downstream of the control section with f='0066 and if the crest was of cement . concrete or pla"tereil masonry it shoul
259

(iv) Correct Gauging of the depth on creSt.

~

f!lO.' ~

('

~

It would be very accurate if the depth at the control section where parallelism i'l attained ___...-....:'=-R=t.;;;:$~T CJuld be accurately measurf'G, because there

~.

3

the discharge will then re simply y'gDc and no correction for the velocity of approach will be rpqnired. The control !"ection is simply a point of inflexion on the surface curve and it is very di ffi :ult to loccte it correctly. The de pth on crest has, therefore, to be measured UDstream of the Fig. 24 n:st ann the correcti m for the velocity vf approah has to be applied. The es'e:1ti 11 fen nre:; f1r 'he correct Gauging of meter Gauge would be :(a) The surface pro'lle sh rm 1d l'e very nearly horizontal for an appreciable distance upstream and downstn am of the Gauge hlle. This mean'> that there should be no change in tl:e section in this length The change in section shall produce a slope in the water surface. A Gauge well in the bell month approach to c -est is, therefore, Ollt of question. (b) The velocity of approch should be correcty calculated for the section oppos:te th3 G~uge ho:e. This is only possible when the section (!oposite Gauge hole would neither silt nor ",cour for the range of the v triahon of the discharg~ OVd the meter. In the ca"c of contracted meter flumes with bell mouth approach up to the crest, the gauging has to be done in the earthen channel upstream where the bed level changes by silting in low supply and the velocity of a'.lproach cannot be calculated correctly. Such falls serve a; meters only in the full supply conditions and even thpn the results are approximat~, as they neglect the energy losses from gauge well to the control section which is a consider abe distance. In the standard meter name design de~;cribed by the author in his paper No. 154 Punjab Engineeing Congn~ss, 1932 the floor level opposite gauge well wa." designed in such a way that it rt~hlained free of silt even with half supply. fhe method is illustrated by an example in this chapter. The type is shown in Fig. 25. (c) The design of gauge wel! and gauge hole shottld be such that the surface pulsatioll3 in the channel are not cc nveyed to the water snrface in the gauge well. This suggests the use {)f a sill§ile g'1uge h\)le locatt'd below the crf'st level. In the standard meter flume desgin lmntioned above, it was prov:ded to be a circular hole in a metallic plate fixed flush with the wall outside. A 3" X 3' hole in the wtll as shown in Fig 26, and the area of the hole in the If. iddle of the iron plate from 1/2000 to 1/5000 of the gauge well area. The position of t.he gauge ho!e from the beginning of the crest in the standard meter flume design is kept 3H while there is provided a straigt reach 2H least upstream of it. Thus horizuntal !'urface pr0file o.)po,ite gauge well is ensured, The pUlsation on the watFr surface of the chamid are produced by action of the wind on the sllrface. It is advisable to d:vidd the large flumes into compartments by constructing thin R B. Walls 9" thick projecting '5 ft. above F. ~.L. and to construct gauge wells on both sides to take the average gauge reading for accunte gauging. U~.8tfl

~

-'4-..... -

_ .. _ .. ___ -l

·~R-;FI

Plan of Meter Flume

.~"t . "'1

"'" ; "

~

r-t ' l:\

- _.L',

~ig. 25

. ___ :.r-:-'

'.I$/",t:.=.

,.. \::'::'LOOA O • .
,,.

0.• ("4.'.;

260

'dJ The water s trface in the g:t~ge -w:eII should be accurately measured. It should be M"easured by neans of a. Hook Gauge whIch IS n ~t usually practic:tblp. bl'cause f'ducated. gauge readers capable of handlIng sl1ch gauges are not available. The accurate record of gauge IS now made possible by installing automatic wat~r level records. Legget's water level recorder IS usually used in the Punj!l b. This instrument I which giws a chart of ihe water surface level 1>10 .. ,- . . _ in the gau~e well is manufactured i~ th~ Central Irrigation Workshops at Amntsar JI~7077zr.~--pt~Tli~~ F up-jab, tut it is a costly instrum"nt and cannot be inst<>lIeu everywhere. It is U!;~~l to put in sloping gauges in the gauge we Us <;hvlded accurately to th.. second place of decimal of a foot or showing cusecs. A sloping gange provides enough length for small Suh.divisions Fig. 26 l6.

Calibration of meter flumes.

The formllia of discharf e as worked out for a longo-crested weir tiume in paragr" ph 14. of this chapter is b"sed on the assumption that the channel was frictionless. Let hi be the loss ()f heae" from the gaug~ site to the c,mtrol s 'ct;on on the weir crest. rn the case of raised crested meter flumes, the approach curve in bed is usually circular as de~c~ihed bpiore, Even if it L omitted or if it is a short slope, the stream lines are curvred irom thtl bed upstream to the cTe,t The curvclture in the stream lines cannot be avoided exc:pt by giving <> very flat slope, say \. in 10, which is nClt po,sibk 'in the practical designs. The effe~t of circular approach in bending the stream lines alld therebl producing centrifugal force, wa~ worked out by the author in his article Ddcem")er, 1936 Page 199 Tndian Engineerings eulcutt... Let it he dt'noted by F, so that F =5 H. The discharge formula q =3.09H3/2, can be writton in the form q=C (G+h.-h+F)3/ 2 per foot run of the weir, where G is the gauge reading and 11. is velocity of approach head= ~2 and C is the coefficient of dischargE'. If hf = F, C will be :lg equal .0 its +heore~ical value 3.09 but if hr is greater than F ac; in th~ case of small channch, the value of C is loss than 3.09 and in case of large channels, the effect of the cen ~rifugal force is very pronounced, the value of C being more than 3·09.

..".

~

..,

,_

I

J

:;;;

._

l;'

"

~

C/. C(G+ho.) ~= C H

V

-

..

'- ....

J..,..

~ I-

!-,_,...

/

~'-

••

V

..

WHERE G .. GAUGE READtNG. .,

;t\,";:'

--r-I-

,

-I'

...

20.

'J

U.

OtSt!HA/fC' PER

-'0.

n.

40.

.

....

FOOt RUN II' Iif£TER nUNE.

The author had to carry out large scales observations on Lowe.l Jh~ lum Canal 0 mpter flume! with the Standard Crump-Sharma approach e." with silt-free floor levels which were opposite gallge hole site up to half supply conditions. One interesting pCJint in these

261

observations was that discharges were obsprved oIPosite the gaug'e hole by running of traveller on two ropes stretched across the side walls in the section which waS always free of silt and Jpvel. The vel lcities were taken with current meter. The value of actual cO"fficient was sensibly constant for every m~ter flume with respect to H but varied with the size of the channel, viz., the discharge for the different: meter flumes as plotted in Fig 27. (b) After the value of C has been actually observed for a meter flume or taken from the graph opposite, the discharge table for the meter flume can be work eo out with the help of the table No.3 of thi!'> chapter or the graph in plate IV tB). The o;)ject of the table is merely to provide a readv means of performing the proce"ss usually referred to as "c()rrecting for velocity cf approach," in other words. of applying tt e ahove f.ormulaQ=Cb (G+h a )3/2 in view of the difficuhy arising from the fact that the term ha is itself Q · h arge. pende:a t on th e dISC

We have

1 Q2 _ ----.~ 2g 2g AS 50 that the formula for di::charge may be written . t(G+ 1 Q2) 2/3 Q=CBI zg-'_A2where Bt =width of meter at crest (2] The values of C.Bt., G and A being known. the value of Q can. of ~ourse. be d~termine.d by trial and error. It IS, however, a tedious and lengthy pro :es~ from ~hlCh the pracbcal engmeer would be glad to be saved. In the attached table No.3 and curve, 10 Plate IV B, correspondmg CI and CBt G values of ---c ~ are given which enable the dis~harge Q to be calculated directly and rapidly from the formula. Q=C 'Bt Ga'2 [3J in which the value of C / is obtained by mUltiplying the known va.lue of C by the value 01 C' [ C ] taken from the table or curve. The calculations of corresponding values of _~ CBt G have been made as follows:C and A From equations I and 3 above we have Q=CB t [G+ha ]3/2=C'Bt H3 /3 whenc CI G+ha ]3'2 [ 2/3 ha. (4) ~ C=( ~ : er C] =1+ G I (C'Bt G3/2)2 But ._ h a = _I. Q2 ______ 2g A2 - 2g A2 V 2 = h = -"_ a

£

~

"'~=21 (IBtGt=(C/)2_1_(~)

G g whence from (4)

A

,Cl)i =1+(C')2_1 C

C

2g

C2g

A

_(CBtGi) A

_(5)

putting~=y and CBtG =x=__£Q_ if Z=Height of crest above U.S, flOQl. C

A

G+Z

Eqnation (5) becomes :_yf =1+y2

~2 ; or x=_!_y2g(y2/3-1) y

2g

which enables us to calculate values of

X=

C~G for

various values of y== ~' •

Corresp mding values of these two quantities are exhibited in table :3 attached in Plate IV (B). By way of example we will take the case of weir where :~ G= 16'0 feet; C"",3'40; Bt=240 feet, A-4500 square feet.

We have x .. CBtG _3'40X240X 16 0=2'90 A

45UU

and

cur~

262 From the table or curve Plate IV (B) we find the corresponding value of ~I

y =~- to be 1'42.

whence C'=1'42 C;

=1'42 x3 40=4'83

and Q=C'BG3j2=4'S3x240x (I6'0)3/2 ; =74'200 cusecs, TABLE No, 3 CB,G Table of corTtsponding values of Y= ~I and x=---:t\ CRG

C'

C ,-----..-,-~.-

C'

-A..

1020 1'030 1'040 1050

l'oeC) 1'070 1'080

lr09c}

l'wa ]'110 }'lZO

1'130 l'14() 1'150 l'16() 1'170 1180 1'lSO 1 200 1'210 I'220 1'230

~

-

C

CB,G

0'907 1'\)99 1-251} 1'390 1 507 1 6! t 1705 1790 1'8(;9 1941 2007 2069

)'240 1'250 1'260 1 270 )'280 ] '290 1,3('0 1'310 j-320 1 330 1'340

2'541 2'571 2-6()0 2'626 2'8':;2 2'676 2699 2721 2-741 2761 2'780

1'350

Z 798

~'127

1'360 ll70 1'380 1'390

2·815 2831 28!6 2861 2874 28S8 2900 2'9'2 2923 2934

2181 2231 2278 2'323 2'365

l'~OO

1 '410

Z 404

1'420 1'430 1440 1'450

2,441 1. 477 2510

-A-

C

-~.~-----------.-.~-~--~--

-

---

y

CBtG

C'

--x---

=_1 -yl2g\y2/2_1),

---~----

1460 1'470 1'481) 1'·190 1 500 1 510 1 520 1,53 ) 1 540 1'550 1'560 1'570 1 581) 1'590 1600 1610 1620 1,630 1 6~0 l'S50 1'6GO 1'670

---

-

..

"..,

CBtG

\..-

---x-

C

-.-~----

..

-~---~...__-.---

29H ~ 9;; t 2963 2'972 2'981

I '6~0 1'690 1'700 1'710

2'98~

1 730 1'740 1 750 1 760 1770 1'780 1,790 I'SOO 1810 1820 1'830

2'996 3·()O.3 30!0 .3 016 3'022 3'028 3013 3038 3'013 3047 30;:;1 3055 3'0';9 :3 062 30(15 3068

1,720

3'071 3073 3 ()75 3'077 3079 3081 3'082 3084 3'085 3'OBC) 3'087 3087 3 (J8R 3088 3'Oil9 3'089

17, Meter Flume Design Examples (Author's Dovelopment of Crump's DesigIJ ,) [AJ Design a ro, ter flume in a channel with the following data:( Discharge = 150 cusecs, Depth=38 feet; side slope=l to 1; Bed1Vidth=-20 feet Drop= loS feet, Range from full to half supply, [a] Crest level :-Width of the flume Bt=:lO 'feet. f;.

' h arge per f oot run= 150_ D ISC -- = 1'5 CUiecs 20 The value of C from Fig, :~7 = 3'045, Let total energy depth above crest=H :,H=

[t1iiI3=[/~h ]2 1 3=1825

; Depth in challnel=3'S feet.

7,5 velocity of approach = 3-8= 1'97 feet per second

f ,

v 2' t 972 ha = -- = ---='0652 feet. 2g

644

The depth on c est=- }'825-'065= 1'76 _ . ow: Let urst earn water level=500 0' The crest 1'wl=500'= 1'76=498'24 (b] FloOI level oppo,ite gauge hole half supply discharge=15 CllSCCS. 75

,.

,

Discharge per foot run=2j)'=3'75 cusecs' per foot rna,

I.

Scour depih or non-silting depth D= I'll q 61= 1'1) X3'75'61=2'S feet. Total energy depth on crest for half supply 3'75 )2/3 =1'15 feet H={ ___ 3'O-!:i 3'75 Velocity of approach= - - =1'5 feet per MCond. 2'5

t 52

Approach head=~='035 ft.

. _.:.l.:..~,:?

Water Ievp.I in half supply=49S'2t+l'I5-'035=499'3S--- - . TLe floor Ie-vel opposite gauge well=499 36-:ol'S =496'88 : . (c) Length of crest=2H=2 X 1'83=3'66 say 36 ft. Radius of upstream aprroach curvp.=2H=3'6 ft. Distance of gauge hole=3Hh:3 X 1'83=5'5 feet. Straight distance beyond gauge hole=2H=3'6 ft. ., ~,:~" Radius of the curve of the side" aUs is 2H, Keep 5'0 ft. in this cue. [dJ Glaeis, The glacis slope I in 5 Critical depth=i X 1'83= 1'22 ft. Crump's L=I'5 ft· and_!:_=J.:.?-=I'24 C 122 From plate V for

-~-=1'24, K+F =3'4;~='42 and-.!-2'Oa

CCc c .) F=3'4X 1'22-183=4'14-1'83=2'31 Jump will take place at a di,tance from the beginni~g of gla.cis b 5 X 2'31 = 11'55 say ll'6 ft, Depth upstream of jump='42x 1'22=0'51 ft. Depth downstream of jump=2'02 X 1'22= 2 46 ft, Downstream water level=SUO-15=498'S The bed level downstream=498'S-;"8=494'7 Drop from crf'st to downstream floor level 498,24-4947=3'54 Length of glacis=3'S4 x5= 17'70 feet The jump is at a di3tance of 1]'6 feet and, therefore, well within the glacis. (a) Length of d"'wnstream protedion=5D=SxS'8=19'O say 20 feet. This may be partly pacca if staggered blocks or friction blocks are added, but in tho case v mlaU channel this may by only '65 feet thick dry pitching 10 ft, long, The level floor u,ill be followed by loose bats protection I· 5 feet deep in bed in a slopt of 1 in 10 for a length of 10 feet and sides bats-filling 1'5' slope I to I. (b) Design a meter flump. in a channel with the following data:Discharge 700 cuspcs. Drop 6'63ft B~d width 6U,O,Depth 5'1, full supply levels Upstream

627'69

= downstream =612 U6

Upstream 622'59, I 2' ~ft·~'· '=6-- -;sldes-to.I.N.S =6 4,0 • downstream lS'96 2 . Calculation, The d,op in this c,se is more than the dopth, rhe meter num': s!)all t,e with vertical drop Bed width downstream =60 ft. The width between the side walls downstream of the crest shall bo 60 tt. The width at the weir cresb.. 60-1 "'" 59 it. .

Bed fl

levds=~~--

264

When water drops over the weir crest, the drop causes convexity in the stream jinf's. The jet Jeaves the crest with preSSUTf' at the bottom below atmospheric pressure and at the surface at atmospherk p:essure. Ttie actual water level below the jtt is at C'D I instead of ABCD. Fig, 28 the differen Je has been observed to be

The convexity results in the distribution of the prefsure,

F,S.L

Q

S p·e.L

Fig. 28 ,1

about O' 5 foot in thi falls of the s;ze as in this example. As the jet is being discharged against a pressure varying from about 0'5 foot below atmospheric to at .nosph(> ric , the discharge co-efficient of meter flume varies and increases more than the theoretical. This introduces another uncertain factor and the remedy is to keep the cistern width 6 inches more on either S101;: than the crest width so that free air can get below the jet.

The discharge per foot run of the crest width; q= 7_QO = 11'9 cusecs 59

The value of C ir c.>m Fig. 27 is 3'065 for q = 11'9 1]'9

2.

Toial energy depth above crest H={3'Oo:t ='2'47 feet Velocity of approach (approximate as the floor level is not yet fixed}' II'.

=~---

v2

.

"'H-:;;n

2'4 2

=2" feet per second; :. ha=c-. = -2~ ='09 feet 5'0 ~g g The Gauge Reading=G=2'47-'09=2'38 feet. . ;jii~'d:"'" Crest level=F".S.L.-G=627·69 -238=62531 J i

(ii} Upstream floor level. . Half supply= 119 -2 = 5 '95 cusecs per foot run.

According to Kennedy's formula, non-silting depth=::" D= 1 U'q·Sl= 1'1l=5 95. 111 =3 3 feet

HI = (

:'::5 )i- = 1'585

feet

5'95 1 ~o Velocity of approach=~3'3 =1'8 !t./sec :. h= ~~ '='JS! Gauge roadin~=Gl=1'585-1 05=1 535 feet Water level III half supply:ocrest level r-G1 =S2531+1'54=*62685 Tho floor level opposite gaug.3 well =626'85 -3 3=628 5S tUi) Length of crCl~t=2H=Z X 241 =4'fH say 5'0 feet ~"'L The distance ()f cauge well hole from beginning of crest=~H=3x2·.~=7·5 feet The straight portion llpstream Gauge hole =2H =.) feet . . Tho rise in bed to floor";622'59~-621'06=1'53 feet aUowing a slope of 1 in S=l'S3X;S .0

=7·6 feet

.

.

•

265 The radius of the side wall ~t upstream=6'5ft. [iv] Cistern. Etcheverry formula:Length=3y1tCL H=3x,,/t:F6:fx2'47=12'15 it say 12'2 leet Depth=one sixth=1/6 x 122=2'0 feet MOHtagu formula : From plate vIr for HL=6 63 and q=l1'9, the value of Ef2=4 25 ; Depth=4 25 x !=2 12 say 2'0 feet Length=4Ef2 =4 x 4'425= 170ft. (v) The protection downstream of cistern:The total length 4D or 5D=5 X 5'1 =25'5 say 26 This consists of 10 ft, level floor with a curtain w;ll1 at the end and then followed by 15 ft. of loose bats fill:ng 2 fept deep in slo;>e 1 in 10 bed and sides 1'5 feet deep in slope 1 to 1. . (vi) Floor design (Bligh's method) Fig, 29 :The design is simple, using Bligh's theory, A creep co-efficient of 1 in 7 is enough for the usual Punjab clay soil, and in some cases it has been kepi 1 in 6 wiih success. The worst

----

III

- - - - - - - -17 - - - ---,

NDN SII.TIN(; fLOOR TOR HAL'SIJ'I'l'f: '. GONDlf/ON

.,-. -.f _ . _ _ 27.0'_,

'40

.-n.':"__.-t

Fig. 29 condition for the creep is when water level is headed upto crest level a.nd the downstream bed is dry, Creep Head =crest level--downstream bed level=6Z5'3l-6IS'9(l)_ 8'35 fee t, Creep length required=7x9'35=66. Actual creep leogth=89'9 which is enough, Fig, 30, The upstream floor opposite ~auge could be :heapened by making it in dry brick pitching 6 feet deep and need net be changed in this casco The actual creep up to begining of dstern=54 feet. Head lost=54j7=7'7 feet. The thickness of floor=!_ X ~~--=-_7_~=~ X -_!-~-~--- ='Z'20' 3 p-l 3 2'0-1'0 Keep 2-75 for half length and 1'75 feet consisting of '75 feet masonry· of brick on concrete for the remaining length of cistern. (vii) Cistern floor Des'gn Khosla's method, , Depth of downstream cut off=3'5 feet, Total length of impervious floor = 52 feet. 0.=

_52 3-5

= 14 Sand H =~ 35 =2'67

1

II 1 -'115:.GE==-.--_ =2-67x'l15='318 d ?tVA

--~

?t VA

' d

on~

foot

1)(

3'S

increase the masonry depth to 3-25 and

cOD(;rete"",'75

~

for

the end 'Cnrtaln

."

,

wall then

266

52

a=--IS' 4- " ,.

1

-nv',\. from plate 111='12

GE=9'35 X'12=28lthe safe value is 1/6) 4

Fig 31)

This is safe mough for the Punjab clay soil. Note that on account of clay in the soil the pressures calculated from Khosla's theory are reduced to 70% Pressure at the begining of the cistern. b=27 +25=52 d=12':;S feet p 27 -!. =~='52 and a=5Z/IZ'38=4'Z b 52 ,pE=64%, ,pc==35%, ,pD=49%

The correction for depth=drop (49-35) = it X 11'38/12 '38=: 12'85% The other corrections are np.gligible. pressure=47'S5 X 9'35=4'46% The soil being a mixture of clay and sand, the effective press'U"e ='7x4'46=3'122 feet Actual depth of floor=3 7,;it. is therefore safe.

QuestIons, What do you know about the Standing wave meter flume, Fxplain the ase of It. (T.C.E,1933), '2 Discuss the advantages and disadvantages of a V notch'versus plain crest in the case 01 canal falis Show by a sketch tbe effects of extension of impermeable platform in a weir (a) upstream of the drop wall (b) downstream of the drop wall, (T.C.E,1934)" 3 (i) DiscU!,s the advantages and dls~dvantages of a plain crest versus trapetoidal notches in the case .1 falls in (I) Main Canal (ii) Distributaries (3) Drains and escape channel. (ii) Calculate the height of a crest required for a '2 ft. fall in a OistY,with full supply discharge of 150 ~usec'. bed Width 25 ft. bed slope 1/5000, lengh of crest being 20 ft (T.C.1935) 4 At a certain point OD. a Disty, the channel dimensions are as given below:Discharge = 1l0cs. Bed width=20 feet. F.S.depth=3ft. Top width of bank 5 feet. Top level of bank 1 ft. 6 inch above F.S.L. Full supply level at natural surface, It is desired to raise the full Supply Level upstream of thIS pOint by 1 ft. 6 inch. Design a broad crested meter dume fall allowing for the possibility of somt slight silting occurring downstream, Give dimensi ned sketches not necessarily to scale from which a Draftsman could prepare working c1rawiDgs. The thicknes~ of wingwalls will be fixed by the Draftsman. Giye reasons for the particular ratio of width of flume to bed width of channel ;ond of depth on crest to depth of channel. (P.LB. 1 HO) 5 Describe a method to check beavy bed scour immediately blow a fall in main canal, (P.LB. 1 ~39) 6 Design a broad created meter for a distributary carrying a discharge of 91'S cusecs with full supply depth 3'3 ft. and bed wid th 13'75ft, Difference in upstream and dowmtream level may be taken as .75 ft velocity .f approach sbould also be taken into account. also, draw its dimensioned sketch (which need not be to scale) thowing plan of the meter with position of the gauge well and its L. section with downstream protection etc. All dimensions relating to the d'sign sbould be clearly shown. (P.LB. 1938). , 7 Prepare the pr~liminary free hand dimensioned sketches and calculations for designing a broad __ _ (P.I.o.1937) created meter flume for thebead reach for channel with A. F.S. 300 cusecs iD sun dry loam soil. ·'>;Ii· (. 8 Design and sketch a broad crested measuring weir for a channel with the following data:(I) Discharge = i 00 cusecs. (2) C=3'1 (3) Difference between upstream and downstream wa.ter levels=O.8 ft. (41 Depth of water in channel 3'1 ft. (5) width of channel = 17 0 (P. U 1942). (6) sides=l to 1. 9 Describe briefly with help of sketches the various types of the canal falls. (P.U 1942) 10 De~c!lbe the vuious methods of destroying surplus energy downstrea.m of the canal falls. with sketches .04 give reasons why you consider a particular device superior to others. 11 Describe the signilicance of long crest in a long crested meter flume and explain the essential nquillites in a good meter flume design;

267 12 Describe the advantages and disadvantages of contracted falls. Explain with sketches the chie., characteristic of Montagu type fall as used in the Punjab. 13 Deduce an expression for determining the discharge over a weir with a clear overfaU. How wow. the above be modified if the weir is partially submerged during floods? (F.S.c. 1935). 14 The' upper and lower suTtace water are 6'0 ft. and 2'0 ft. respectively above the crest of submerget weir 70 ft. long. Calculate the discharge; take C=O'S for the drowned portion and C= '557 for undrown~ portion . (F S c. 1937) formatioa 15 Explain the phenomenon of standing wave and state the condition necessary for its Draw a sketch of s,tanding wave .fll!me carryiq.~ out its essential parts ~nd expl.ain the functio~ . of eae) Deduce an expreSSIon for determining the discharge of a channel on which a standmg wave flume IS Install. State assumptions m a d e ' . (F.S.C. 1939)

PART

II

CANAL IRRIGATION CHAPTER XI

Silt Excluders And Ejectors 1 Introduction.

The idea of silt excluders originated with the late H.V. Elsdon, Executive Engineer Punjab in his paper No. 25, P. W.D. Irrigation Branch Publication L922. Three ejectors or extractors and two silt excludf!rs were designed and cl)nstru ~ted in 193t -35 on the Upper Jhelum Canal by E.S. Crump, Sup'rmte!lcling Engineer. ~alampl1r Extrator on the Upper Doab Canal followed soon after. Khanki and Darlnpur Silt excluders were constructed recently, and the Hnt than the silt excluders at the head of a ('anal. [iiJ The other most important feature of design should be to provi ie saperati(m of the bottom water charged with c mcentrated silt from the uP?er watj>r wi~hout anv dist'lrbance, This requires that water should enter the approach to the chamber below the Diaphragm slab with the same velocity as it is flowing in the canal aDproaching the work without disturb.l.nce, (iii) Lastly the high silt-laden water thus stealthily taken away from the canal should be es-ap d through the tunnels connected with approach with a velocity which does not disturb the entry of water a.t the approach. 3. Approach Channel to a Silt Ext ·actor.

Undoubtedly the o' ject should be to provide a long straight approach chanl'leI. in which the silt can settl"! into the lower lavers of the water, Ula thu~ increase the efficiency of the extraction. Anything affer the nature of curve, whir.h will dispbce the silt ('oncentptiotl t,) the s;de of the channel as well as reduc':) it, or any obstruction on th,~ sides or had wnich will set up turbulence and hence destrov the b@d conc",ntf'ltion. should be avoided. The great arlvantage that an extractor has over an eXc!11der i'.l, that the approach channel can generally be securpd without difficulty in the cas~ of the former, while in case of the latter it is usually necessary to turn the water through a right ~nf I.. hend before separation is dfected awl in a o.y ca~e, the approach channfll, which cf'nsi~ ts nf a natural river bed, will probab;y haye curves iD it and will certainly have very inegular boundaries.

269

(i)

The approach channel shQuld be designed with the flattest slope which will carry the l,eaviest grade of silt likely to approach the work. (ii) It should be pitched or lined up to 3 to 4 D (depth in the channel) upstream of the work. (iii) If possible, the bed may I::e depressed upto 1-0 ft. by a gradual transition curve in the bed. There should be 110 change of section on the sides. (iv) The minimum length of approach channel below a head rpgulator to ensure the stilling of the turbulence down-stream of the head and then the restoration of the normal silt distribution, may be taken about 1000 ft, for a canal with about 6000 cusecs discharge. .

.4 Escape DisehaI'ge above

Ex~racter.

TIl''' efficiency of an excluder may be defineil as the reduction per unit of the silt intensity in the caml supply when comp:ued with that of the water approaching the work. This, though the onlV practical standard, is a fal"e criterion, Th~ true measure of efficiency of an excluder is unity minus tht ratio of the silt entering the caBal to that whi ·h would· enter it if the excluder were not working. The pc int about this dIstinction is that the addition of the escapage to discharge the canaIrdischarge increases the silt aflprnaching in the canal and increas··s it in a proportion greater than that of the discharge, because in Kennedy's theory, silt transporteilv aries as D ol3 and discharge varies as D5/3. We mmt not, therefore, bl ndly a~cept the idea that the great2r the escapage the greater the efficiency. Research is neces;ary to determine ",hat the optimum proportion is 20 % or below is suggested a3 rach design of the Extractor.

The St paration of the escape water from the canal supply at the edge of the diaphragm should obviously be arranged without disturbing the silt distriJution. It is easy enough to arrange this for fixed canal and escapage discharges by placing the diaphragm at a height such that it divide; the normal stream into the correct proportion. In practice, however, it is always necE'ssary to vary both the canal supply and the escapage and if the height of the diaphragm is fixe i it will generally nlt suit the varying prop::>rtion of the two. In the ideal case, water near the bed should en.tar the ejector with the same velocity with which it 'approaches it and in the full supply condihOD, the stream lines will be horizontal for the water passing OVAr the diaphragm. If. however. it is required to unr the canal sllPply full, while sufficient wat-~r is not avilable for the discharge escapage or if theescapage is run full, when canal supply is low, we shall have stream hnes what some as Fig. 31,

~~-----------------"71."

,»,»; > »

?/ ) ,.>/) .'/J /

A.

Flg, :3

»); .'))';;,/7,',' //) ))~,.

B.

In the region AB there may be a certain amollnt of turbulence set 'Up which will cause a less favourable silt distribution. The question is, is this disturbance serioUi ~ According to EIsden it would be as shown by his proposal to have the height of the edge of the diaphragm variable. In praetice this device bas not been made use of and little attention has b.e,~ paid,to the point in the design. This point needs investigation in models.

270

'0

(a) TUDnel Entrances.

For f'conomy aud to avert any danger of silting. the velocity in the tunnels must be Iligh. We have, therefore, to transform the comparatively low velocity of the escapage at the approach entry to the high tunnel velocity. This must be done without allowing the draw of the tunnels to affect the velocity distribution upstream of separation and in certain cases when escapage head is valuable, a gentle transformation is necessary to avoid loss. The former point can always be secured by. placin~ the entrances a s?fficient ?istance downstream from the edge 'f the diaphragm, but thIS may mvolve an expenSIve cantlleverd slab. The method by which this is usually arranged is shown in Fig. 4. (b) Tunnel DC Ilgn. leu

The tunnels them"elves must be arranged to evacuate escapage at high velocity. say not than 10 ft. per second. They must aho provide contr01 of the discharge sO that the sam'} velo-

SALAHPUR EJECTOR ~ ~ U.S.D. CANAL '''&Ll.-&,

,

~ ~

•

Pig. 4

-

t

my is secured at the entrance to each tu~nel. This mlybe done either by keepingthf saille tbtu'UI iimeasions and varyiog the width of clnal served by each tunnel. o.r by keeping the widths fi(fTv4fd

271

273 and hence the discharge the same, and varying the tunnel sectional dimensions to secure the !:ame discharg.. with the varying tunnel lengths, The loss of head in ~ach tunnel may be calculated hy Manning's formula. At Jaba, th~ widths served and the tunnel dlln~nsions are the same and the discharges are equalized by a varying degree of contraction at the tunnel exits. At Dadupur, the nischarge of each tunnel is the same and the tunnel dimensions are varied. There is a control weir at th., end of each tunnel, the crest llwels of which are varied to suit variations in width. At Khanki and Madhopur there appear to be no devices for equalizing the tunnel discharges. The tunnel roof ~hould be designed to take the fnll water pressure above it with the minimum pressure which may occur inside it, assuming the entrance tn be blocked, If the tunnels act as weir for the canal supply, the possibility of uplift occuring with the tunnels closed at the downstream end, and a velocity <:iepression oyer the roof should be studied. The oocapage, if less than full supply, is regulated by gates on the down·stream end of the tunnel. At Madhopur , a surge chamber is provided at the down-stream end (If the tnnneis which serves to obviate any danger of water hammer. Thh arrangement also pnrnits the regulating gates to be placed with the chamber and enables gr()OVei. with only onl! face machined, to be useo. At Dadupur. the gates are placed on the outeI' ends of the tunnels and the grooves are machined on both faces. the gates, against the upstream face. At Khanki, Bhong and Jaba the exillting undersluice gates were used to control the tunnel discharge.

Cc) Tail Race. The channel from the ejector to the river for escaping its dhchar~ should be designed with Somewhat steeper slope and relatively higher value of C. V.R. as comp'lred with the canal. 7. Extra.ctors combined with a Meter. At th~ h~ \d of a c<\nal a silt ejector can' conveniently be combined with a meter fiu""e wit h crest higher than the diaphragm level. For accuratA gauging it would still be better if the fioor level opposite gauge wells be kept higher than the diaphragm leveL For idea.l conclitinns, it should btl th~ top level of the diaphragm slab. The meter flume shoud be with fn II width of the channel without bringing in coml)lication of the contracted approaches. There has not been any serious trouble with the existing silt extractors resulting in thpir choking due to jungl p getting into them. There is usually no arrangement in the form of trash-racks to remove jungle. laba had a slight trouble to begin with. 1.

Effect of

ex~luder

or

extra.~tor 0:1

the Ca.nal regime.

So far the silt excluilers have been hu.ilt where the silt entry has bep.n affeding the regime of the Canal to a dangerous extent. In the case of the Upper Jhelum Canal, the canal capacity had been reduced conSiderably and was still diminishing, as a result of silt entf\'. In th., case of the Lower Chetlab Can~tl. excessive silt en try at the head had caused the hed uf the main line to rise. and was giving great trouUe in th(~ branches and distrihutaries. In all these ca,es, therebre, it was obviously neces!-ary to exclude or extad silt from the canal, as much as possible, and the excluders were constructed as a methOd of affecting this; but in cloing so, no attempt was made to consider what grade or (,}uantity of silt was suited to thp. canal regime, and to regulate the silt entry a ;cordingly The excluder has alwa"s been designed to be as 6fficient as local conditions would permit at reasonable cost. It is evident, of course, that if the excluder was too effective and resulted in too rapid retrogressi:>n of the canal, it could be dimsod or worked intermittently and thi~ had actually to be don~ in the case of tbe Bhong excluder, where the retrogression caused endangered masonry works in the canal. On the Upper ]helum Caual the efied of the excluders has bf'en so far to stop the progressive silting up of the canal which was in progress, and to restore its capacity to that desi!;ned. On this canal the capacity is ruled by a minimum gauge of 11'3 at JlggU. The discharges given by this gauge in different years are as given below:1934-7695. 1935-7875. 1936-8160. Tn 1937 the gauge of 11'3 was never attained. In January of that year a gauge of 11'25 gave a disc harg~ of 8::lS5 cUlLecs which appears to have been the maximum run. On the Lower Chenab Canal. the progress of silt erosion is about l'S8 ft. in the head~ reach upto R.D. 40,000 and '93 ft. upto 140,000 The. effect of silt excluders in the case of the Western Jamna Canal and the Upper Doab Cabal has not yet been felt.

274 The amount of silt exclusion in illl cases wag arbitrarv. No attempt hag, howover. so far.been made to reguld.te the silt
9. Efficiency of silt excluders or Ilxtractors. There has been some doubt in the past as to the best method of calculating the efficiency of excluders. The one in general use gives only the reduction of silt intensity in the canal water

as compared with that of the approach flume. On the Upper .lhelum Canal, howev€r, it was formerly customary to take the ratio of the total silt escaped to that of the approach flame as the efficiency, and tbis method is employed at Madhopur as well. If Q, I and S are the discharge, intensity and total silt contents the SUffiX P5, f, c and x denote the approa~h flume, the canal and the escape respectively, the efficiency is given 'by Haigh's formula.

E= IL-Ie = I I,

l

(A)

I

1£ observations of the approach flu,ne are not available, the efficiency may be obtained from the canal and escape observations by the formula. :E=- Q_,JIx- Te)

(B)

Ie Qc+1xQx

According to the second method referred to above efficiency is given by :E'= Sx=" _Q-,,~= QJ, Sf Qrlt QcI.+QxI"

_Q1Tf-QJe QII,

whence E' =E+ QxIc

(B') QfI f : It is clear from this that the latter method gives a greater value of efficiency then that calculated by the former. It may also be noted that if the excluded efficiency is nil, i.,e., if the~-­ intensities in the two downstream channel are the same as that upstream the latter formula" would still show high efficiency while the former would correctly ~ ive a nil value • . Ql, In comparing the efficiencies of excluders it must be remembered that the great"r the proportion of the supply escaped, the greater efficiency. As has been pointed out abo 'Ie, the, efficiency will not vary directly with the e3capage. Since the intensity de~n:asf)s rapidly with· depth, additional escapage will increase the efficiency, but !lowly. . Anoth.r point to be borne in mind in this connection is that the efficiency mmt re: affected by the grade of material carried by water. Since that grade has been found to cause .:. trou.ble .in practice, effor~s are .ma?e to exclude everything la.rger than ~'2 mm. diameter. T?e i proportwn of the total SlIt whIch IS great"r than 0 2mm. and the ralatlOn of th1l coarscst s}'lt;. carried to this grade will, however, vary at different sites. ...J

gx

275

JABA S'L.T £XTRACTOR ',.

'111 '

tl(l:

SqLE,j'so

PLAN MANHOLE. (OVER BOLTEO OOWN

T~J~PI"T (J:PlIFT IlY W~TER

--.. 6·0

Fi

.,2·o.,....~-----

This same .excluder may be expected to work more efficiently where the proportion of KH A111(1 (XC, UOER PLAN OF TlINNElS s"M"'V~' . • ~- .....4'"

Fig {1

276 Th:! same excluder may be expected to work more efficiently whtre the proportinn nf coarser silt is gr..-ater than wbere it is small. but on the other hand, the coarser the grade of silt carried. the greater the slope and velocity ann consequently the les:) the concentration of
10,

TypicaIDesigns.

The typiral design of a silt ejector is shown in Fig. 5 alf usel4~t, Jaba. tle Upper Jhelul1l Canal, and a different design of a silt excluder is given::f~::Fig'~H~!! !i~ti IL

Automatic Silt Extractor Without loss of Water.

The author described a design of such extractor in the Indian Engineering, Calcutta, January 1938. A brief summary is given here. The silt movements take place after the Monsonn in the months October ::Ind November ,a~d the silt ejectors would be most effective then, but on accout of the Rabi sowing penod, they have to b ~ kept closed as nnt a drop can t hen be wasted '. [aJ Different types of silt extra tors or ejectors have already been tried. Tbe silt ejector at R.D. 1,00,(00 of Jhang Branch has simply got slits a couple of feet below the silted bed leveL The depth of the channel is about 10 feet. The depth of silt above the slits stands by mutual cohesion 0 t particles and no silt or water flows out. If the silt above the si Its is disturbed, thl! canal 10 Sf'S more than one-third supply under pressure head of 12 feet. Such ejectors wor ked by tt:e pre~sure of thl' depth are useless ou account of loss of a great amount of water. Improved ty; e of silt ejectors have been constructed on the Upper Jhelum Canal where the discharge lost throngh them is controlled by means of gates on sluiCf~ valves. Chak-Sikandar ejector is a nice example of a very efficient type. The maximum discharge is reetricted to the dIscharge of the canal up to 1 f00t depth. Even 1he controlled discharge is as much as 250 cusecs whiCh cannot be spared for escapage thrtlughout the year. [bJ The principles of silt exclusion for distrIbutary head regulators as described by the author in his Paper "A Silt Selective Distributary Head Regulators" published by the Punjab Engineering Congnss 1936, are equally applicable to the silt extraction from the canals 1 his paper describes clearly the detailed experiments wbich were carried out on full size modf'Is made of glass to determine the dfe:t of streaml;nes in each case. About twice the normal silt charge in a cubic foot of water ~oulO be extracted if tbe red water of the canal be stealthily extracted without the slightest disturban~e. It is very essential that no disturbance should be generated in the act of stealing the b,.d silt-laden water. \Vater should be taken away with the s:'-Ime velocity with which it is approaching the silt extracting device, which ShOUld not in itself be an obstruction or a disturbing factor, (c) If the supply which e~capes in such a case is, say, 10 per cent, the silt extracted by weight will be. one-fifth of .the. total silt charg~ of the 'channel This is. an appreciable.exclusion as it mostly consish of the obJect·onahlt COHse sIlt. In order to further lDcrease the efficIency of a silt evtractor, the eftorts should be ilin~cted to concentrate the silt charge near the bed of a canal. This could 1 e attained by reducin~ the roughness of the approach channel sectlon.--The reducing in rough/lPss means eliminatIon of vertical silt carrying eddies. Cement plastered sides and bed will do upstream of silt ejectiug aperture in bed of a canal' up tn a lengt h of. say,S times the dl'pth of the channtl. The concentrated silt charge near the bed will thus be led to' the apertures "'ithout disturbance. The degree of concentration of silt charge near the bed depend, upon the reducti"n in ronghness in the approach channel. Glazing or even covering the perimeter with mica 8r celluloid !'hf'ets will be more efficient than cement plaster. The author thinks that ~uch expfllsive measures are not in fact necessary. Even cement plaster will reduce the roughness of the channel section to oDe half in comparison to an earthen section and consequently is lkely to double th.. etflcier cy of a silt ejector which is sure to ml'et the requirements in all cases. 1he scientists having res"urses of Hydraulie Research Institutes should help the engineers by evolving some cheap methods of hydrogen ironisation of water reaching a silt extractor to concentrate all silt charge near its bed.

277

(0) After providing suitable approaches for efficipnt silt ejection, the design of the ejector should inv@Ive a.. little los;; of water as possible. The aim should be that there is no loss of water as there is harrlly enough water in winter for the crops and no water could be spared from any canal for purposes of silt.ejp-ction. Tbere is bound to be some loss of water if the silt-ejecting device is worked by the hydraulic pressure uf ' depth. Unfortunately. all existing ejectors are worked by pressure. They invariably entail a considerable loss of water. We cannot afford to waste a single drop of water in winter and they have to be closed down for six months. We should, therefore. think of SOme other property of silt or water to work oat silt ejectors. Laboratory experiments could be usefully employed ,(' dis~over Some dev ce to eject silt from canals adoptbg some simple principle such as variation of viscosity due to difi(?rent sitt charges in water. As described bdow, the writer has worked out a design for silt ejection from a canal, utilizing the difference of specific gravity of silt and water. This device essentially aims at little or DO loss of water in the proce')s of silt ejection. [e] Suitable Design. A suitable design of an automatic silt extractor without loss of water is: given in

It is drawn to scale for construction at R. D. "0 of Mancher Distributary. Lower

Fig. 7 [aJ.

AUTOMATIC 51'-1 EXTRACTOR

."

WITHOUT LO'S OF WATER

'. or

~~ .... ....... ~

Os

.,

...v .......""'-'NCHER" ... ______..

. '"
IIY~

-

«I ,.~

I

: i.'

1,.0

F.

:ul

RERM

:'I!L.<~~~~'-ll -<

;!I

Chenab Canal, the discharge of distributary being 70 causecs. Regime slope cannot be given and the available slope is 1 in 5,714. The designed depth is 2'5 feet. Tbis distributary takes off from one bay of Chenawan escape which has got a very low bed level as shown in the drawing and which can easily take eway the silt extracted from ebe Mancher Distributary. Smooth approach in cement plaster is provided upstream of silt extracting apertures. The width of the channel is not restricted. The reduced roughness of the approaoh channel will thus concentrate the. silt charge near the bed. -

., Water will leave itsi eargo above the aperture as a suitable O&TAIL. OF CH ... "'aE~ expansion is provided for reduction in velocity. A guaze deflector is provided as an additional factor to catch the silt. The automatic device consists of a swing gate which is permanently loaded on the other side for the head of water above the gate which is 3'5 feet in this case. Additional loads are provided for the weight of silt on the gate. The additio.lla Fig. 7 (b) . . weights could be adjusted in such a way that the swing ga.te should open when the SlIt, 15 say 9 inches over it. Provision is made that the gate opens just enough to drop. awa.~ the slltThe gate will then automatically close the aperture till it is again loaded w1tb. sIlt upto a. stipulated height. Very little watpr will flow out when the silt is dropped. InspectIon ehamber is provided as showh in sec tion. A very steep slope of 1 in 20 is given in the tunned :so that th.e Fig. 7

278 silt moves out into the escape with the least amount of water. There are no sensitive moving parts needing special attention. The ball- hearings of the swing gate shall require to be oiled occasionally This device provides a suitable design which could be installed on canals which have got syphons with good outfaIls. The working of this silt ejecting contrivance is automatic and without much loss of water. 12. Example (f Desine:- (silt Extractor at R,D. 600 That main line) {i} Tunnels. Each tunnel serve~ 80 feEt of the bed width. To ensure correct ilistribution over this width there is proposed a diaphragm separating it into two orifices, spread 6 feet apart, each taking 1Z cusecs under a head of 0'5 foot. The ar"a required for this is given by q = 7 Ay'H ; whence A=2 4 sq. ft. i.e. 2'4 X I': the orifices have been stream lined. The tunnel on the left of' ' the diaphragm is 4'x4 ior which a=16, f=1O'6 and m=l. The dis~harge in 1his channel a~ ' compared with th"l t in the right channel loses additional head in a length of 30 '. This is ca1culat ed an below. From Manning taking h=O,0165; v=O'9m2/3 SlJ2 where s is the drop in 10,000' s- 0 v

2

81 m 2 '3

;

now v=3'75, m=l; whence 5=0174%. Loss of head is .

This may be compensated by raising the velocity in the right (v '-:_-_~~~

64

301=.~ 100

xO 174=00522'

channel to

VI

so

that

-0'0522 -

v= 1'83+3'75=5·58 ft. Area of tunnel at the narrowest section=

60 5'S;; ,

= 10'75 sq. ft.=2·69 ft, X 4 ft. The length of tunnel downstream of thA end of ,diaphragm is 76+170=246'. For the tunnel, a=32; Pw=24, m=133 ft. Loss of head per % ,foot=O'1l5 ft . . ', loss of head in 740.' length=O'29 ft. Between each tunnel there is a difference of about 60' in length. Loss of head in 60 ft.=0·118 X

60__ =0'0708 ft. 100

Difference in length,

2nd tunnel 61). ft. 3rd tunnel J20 ft. 4th tunnel 160 ft,

Maximum velocity Difference in required in tunnel Area required loss of head. at the paint of sudden expansion. 0'0708 O'141G 0'2124

rotallo~s

5 ~9 6'71 7-4S

20'4 17,1 16 1

Depth.

Width,

4 4

4

of head in any tUl1I1~l. therdore, is =0'500 Loss at entry Loss in 4' tunnel """OOSZ Loss in 8 1 tunnel =1) 290 Loss a.t exit "",0219 1'061 ft,

(ii} Out talt, (a] Surface fiow:-J The minimum river level with which it will be deCessary to ,work the' extiactdfs may be taken as 675'0 The normal discharge per foot of tUn'u-el IS 15 cusecs which is reduced to 12 cl.1secs in the cistern. Assllmin§ the final pond at R.L, 69! 0 and a T.E.L at the tunnel exit of 693'OJ H-693~675=18 fept. Hf~~..:: 52. Hence it wiU suffice to' put the cistern floot at R.L. 670'0

279 With a pond level of 690 and tunnel soffit level 582 of at the downstream end, the head will be 8 ft. and the discharge 1400 cus"cs

:.Discharge pp.r foot in cistern=34 cusecs. Downstream T.E.L.=683·9 The minimum downstream level required to keep the standing wave on the cistern floor is 677 4. Keep cistern roof at R.L. 678.0 to provide ior this depth. With a pond level of 692, the tunnel intensity will be 49'5 and the maximum downstream level consistent with the discharge about 682'0 With a rlownstream level of 685 corresponding with about l'5lakhs in the river, the extractor will take 1300 Cs. . [iii] Sub-soil flow and pressures. With the extractor closed and the mllllmum downstream water level of 6'i3'0 it is estimated that spring level will not exceed R. L. 682'0, Pressure at the back of pile line will be governed by spring level a.nd may be taken as 3/4 of the head from spring level to outfall i. e. ;)/4 X 9 or say 7'. The depth of pile line required for an exit gradient of 1/4 is given

H

by;-GE=!= 7\d

1

·VA. -

whence d=9'3 say a 10' pipe line,

As reg:nds pressure, the alternative, of an open cistern involving heavy wing walJs and roofing the cistern has been worked out and the latter is found to be considerably cheaper. [he maximum pressuri' under the cistern floor will bil abont 9'. It is necessay, however, to provide for silt depositing on top of the roof for which a level of 590'0 is suggested. The preSS'lres resulting from this are greater than the sub-soil pressures and hence rule out the design. The roof will be loaded to the level ab initio to take the sub-soil pressure. The thickness of the barrels, walls and roofs will be approximately as shown in the drawing Fig. 8. (iv) An eeonomieai thickness of a slab. Thic~ness ?f a slab does not appreciably affect the cost of form work, hence in workivg out-an ecnomlcal thIckness of a slab the cost of shuttering and centring is not considered. Let M=Bending moment. t=effective thickness of sla.b. c=cost of concrete per eft. s=cost of steel per cwt. 1'S" =Concrete covering for steel. Futther assume that distribution steel is 25 per cenl of the main ste!l;and the area

. 5 tee l'm square mc . h es=-----_ M af mam , 140UOt

Cost of slab per sq. It :-

,!

Steel= 12'5~ X _.i90s ___ ~s ; 0 C ... (t+15)c 14000t 144X 112 ;;68000t' C n rete

--u---

Total cost per sq. ft. =K=~~~

368000t

From

+ i!_+l'S)~ 12

K to be minimum dk=O; i.t'._l_ X Ms+ !.C::l:O dt

368000

t2

or tt =_l_xMs; 01' t=O'OOS1 /}'1s-, 30670

eVe

12

2M

Q it

Fi~~

I!a

..

. 1.

8

281

. At Kalabagh Headworks s= 15'25 and C=O'4l . ••

1'1.<;-'2'

t==O·C057X./ .------"U4_;

Xl

jM=Ol0822x y'M-

v.1

Que;tlons. I. Descril-e briefly and explain the working of any existin, work. which should be named, if p,",ssible, for c:<:cludingsi]t at, • (i) Canal Head Works; (iiI Branch R~gulator; (iii) A Distributary Rf'g lalor. (Pb.I.B 1941). 2 Show by ilimensional ~k .. tch~s a tie~ign for ~iJt coptrol at a Distributary Regulator taking off 300 .. use~l\ at right llnglf's above a fall discharging 200 cmecs. Explain how your design can be altered to TeduG~ proportion of silt taken by the Disty; offtake. (P.I. B.1941). 3. ExpJain any device for reducing the in-draft of silt into the head of a canal or disty; Also explain a.nv form of dltometeo. IP.I.B.1938 , 4 A channel is found to be silting badly in its head reach. Describe how the defect would be studied al:d remedied if due to a defective head. _ (p. I. 8.1935

CANAL IRRIGATION ~ .,..i'

- CHAPTER XII 1.

,~·e;.,~·f>

.

DefInItIOn. \.'

'"

,')u'm,.,
~y!

"

Fluming and Headless Meters ~.~ ..... ,'.

1'1";"

'.

" ; ' . :

.~_~ ._;..

;

.<,~:_~~, _.

:~'

A flumed work IS one, huilt in a stre;Jm, the waterway of .which . is reduced below the nor.mal. , Tt is necessarily accompanied by an increase in 'velocity. ,." ,,... ,;,' This result may he obtained in a variety of ways.; , . (al A reduction of width. The discharge per fOr)t of the width nece;;sarilv in :n'ases. This may be accompanied by an increase or even recluction of the depth. Examplf's of this type of flum{s are lined channe I section, contraction at the aqueducts and the flumed bringes. (b) A

reduction of depth.

This may bp acc)mpanied by a cnmtant Width. Works falling in this category are weirs, flumed or contracted falls and heaclJess meter flumes. A fe"" examplf's of ihe clesign are given here and the 5tudent should refer to A M.R. Montagu'g paper No 6 Central Board of Irrigation, Simla and F.H Burkett's Paper No. 125, Punjah Engineerin5' Congress 1929,for a detailed study 2 Classification of flumes Flufl1es my be dividerl primarily in to two main c1asses:Class 1. Flumes with' frep,"water surfacej.e,a water surface open to the atmosphere. In such cases the pressure on the free surface remains constant. Class J[ FJume!: with' sealed"water surface, i.e. of ~ hirh a roof forms part of the desigen The eS~l'ntjal hydrauLc difference between these two types rOTH I'tim' we is expillined l~elow :_. In class I thp, surfilce is open to the atmo~phere and the pressurp, on the surface remains cpnslant. A],o the area of the cross o section i~ free to alter with t he change in velocity. Fig. 1 I Consequently. BEO

Bernouilli'~ equation in the special fOJm Z+ D+

J

Fig. 1

Tf'mains sensibJy true if the effects of curvature are. nea;lected. But in fpe case of Class 1I the surface IS not free. -----rj--.:.::.:..;~~:.::.l~=~_ Provided the surface pressure does not fall below zero (when cavitation takrs place) the above f'quation has to - - - ._~/rY ..€.!!..£.f!.rj;l:_J,Ib.L_ :;n z be modified. (Fig 21 ." ~4 ",%) ~ y._"" R I I D ! ' mass a t a d'/' l Considtr a part cle 0 funIt cp th D below' the surface moving with velocity v. \;,,,,1;7 The potential energy=Z-j- D-d "'''TAL

ENtRy'"

LINE

l'

r

~ ,~I

'j.

.

v2

SID

t z.

Kinetic energy=-.

2g

Let Pr be the pressure on the roof. Then the pressure on the particle=pr+d:. the total energy' per lb.of the particle, measured in "f{et head of

Fig. 2 2'

v2

watet"=Z+D-d+ v_ +Pr+d=Z+D+ +pr 2g . 2g

283

Since total energy remains constant (save for the reduction by friction, etc, represented

by the slope of total energy line), it follows that :_ , If the velocity energy in 'feet he,ad of water" be plotted above the roof, the pressure thereon is represent"'d by the intercept betNeen ,th~ ,veloci~y en~rgy line and the total energy line. .

3.

Bed profile. (A) General . .. . Conditions of flow.: . .

; Water has Inertia. It follows tbat any sudden appli'cation of any extet'n:\hforce,?;lilVill bririg the laws of impact into p l a y _ ' ,J l >_ f:'" All {orce5 tending to a)ter'the, direction of flow must therefore be applied 'gradually if mpact and .the consequent loss of energy are to be avoided. The gradual,application of It force is followed by a change of velocity or dirtction-the stream lines are curvt d. - .

'.'. It w0:tIld appear tha,~ thi"i curvature may be increased by in<:r~a~ing the' external 'Impressed 'force upto a limit at present unknown. ...'' . .

~.' ,If the lImit be exceeded, thffniture of flowi~g ~ater exbibits the property of t~ying to .c'prr:ect ,the impropC!r c 1lrvature, by tne' interposition of a layer of minute eddies, in the form of 'hprizontal or vertical rollers, The 'eddies consump, energy and the total el}ergv of the stream is reduced. ' . If the curvature be still further increased, the eddies are. no ~onger effective in correcting the cu~vature of the boundary, tlW stro::am IllES b'e'ale and pure impact results, , . A vertical o':>struction across a channp.l.if! -t.~e, fo~m ~of a wall, will prolitlce horizontal rollers both up"trea,m and downstream of the' obstruction", If the o\;lstlUctioq. is excessive, there will be pl1reimpJ.ct, fl,gainst ,the wall and also between water pil:s;;ing_, oVl':r it and that moving' slOWlY ahead of it, It implies that all changp.s iIi the profile must he gra.dual. (B) The forces actIng upon a stream of flowing water ,are:(a) Gravity, ",hich is c:mstant in v~lqe< direction and sense. ,. . (bp. the velocity , of the stream always acts against the . dire~tion of flow:, ' " , , , , . , ' (c) 'The reaction of the envelope" which (wheI1 sep:lrated from friction) acts normally to . the surface 'of the' en velope at the point. Its value depends 6n anum )er of factors. ,. It is the variation in the reaction of tne en ~l<;>pe that causes .curvature.

down

(C) Ideal Bed ,profile, The chan~e in ~ection should be such that the jet remains adherent so that vertical compon<;;nt of the reacti,m at any. point IS t:qUa,l to the pressure due to the depth at tha~ point. Although the qualitative eftects of curvature In the stream lin~s are well known, our knowledge of the qu lntit~tive effects; t l1t is the '~qlld.tlon5 defining thp. fundamental laws, is practically nil. Consider a r\ct ang l'ar , n chaunt:! of which the hed risp.s and falls while the width remains con"tant, Ideal chang-e in section _,~____________• .u4W~I~.~.·.7$.aLr~,w~·_______ would bp, in the fo:m sketched below:~ Fig 3, It is comb'nation of double S curve to avoid all corners, 'The stream _ - - - -......_. " line upstream of the crest shall be curved upwards connoting vertical component ~ of flow due to cl'ntrifugal effect. The reac-, 1 ion 51 all be l's5 tt an that due to the depth of water at any point The ;;vater sur[aCfl Fig, 3 profile sha:I J::e convex. The convexity COU'iotes that the jet is not adherp,l1t and is liable to pressure inflation,., A very t asy. approach upstream of the crest IS, theref, re, reqnired. On the down-stream Side the stream lines ar" lonGave and, therefore. adherent.

-_

284

The convexity upstream of the crest, can be removetl (or rather renuc(':d if friction be taken into acc"11nt) by providing an easy uniform negative slope. J'rom experience one wo tld suggest a suitable slope C'''l'sr from I in 3 for low velocities to 1 in 5 for high velocitif's. fi}' Tn thp case of the uniform slope. the corners need to be MD _ $.C_ _ transi tioned by introducing short circular curv"l tangential Fig. 4 to both plane3 as shown in Fig. 4. The upstream curve to crest with radius 2H as introduceo by Cr,.mp in meter flume nesign looks, no doubt graceful, but the e.ffec~ of c~rva!ure i~ prcdu~ing Cfntrifuea) efff'ct is very prononncei as calculated by the author In hiS artlcal In Tndlan Engllleering (alcutta December 1935, On the downstream side S curve shall t-e ideal and the iDclease in d~pth may le arranged even in a relatively shorter distance liub-critical stream and hypercritical stream for type Critical stream, the Montagu's design of bedprofile i! ideal. (Para 12 Chaptu X).

_--==__f -" i

4. Approach or contraction upstream on sides In this case, a curvamre on the side, will no doul,t intronucp. the Cf~ntrifugal effect which usually result!' in heaving up of the surface about the middle of thf' stream and which also accounts for the concentration of the silt charge about its middle, but the jet is perfectly adherent to the sides due to the inertia or the momentum of the approaching water, There is no chance of the reaction against the side-wall being less than that due to the depth against it. There is r.o possibility of the forming of vertical rollers which usually occur in the expansion downstream of the crest. The design of the approach should aim at the following requirements of a suitable approach:(a) Thue should be no sudden change in section to produ.:e the losl of head in f'ntry. (bl The change in section shoulcl bP. gradual to avoid clirect impa~t against the wall. There is no mathematical solution yet possible to work out the conditions necessary to .

~ ~'

"

. '

- ' , - , __

--....

I.~

~

•

.

J

/

fullfill the above-mentioned requirements. One could only say that to avoid impact. the forward . . .. I . component 0 f the incommg water shouId be equaI .~ to the centrifugal effect so that the rea ~tion tit· f !(If.... _t_ agaInst the wa II is not cbanged H owever, .rom _ I expt-rience it can be ~uggested that a splay of ---, 1:2 for low \elocities and 1:3 for high velocities " will do for the approach on sides. In plan it • _.shall be ot tne form as sketched in Fig. 5

-........... ··........... ··..... "1 -.. . -:1'

I-~ ..J /"

---'

• . --'

..

C,"N~._

~n ideal cur!i~;uld be

with infinitp. radius in the beginning "Ind the end as shown in

Fig. 6. However, it is not possible to design such a curve which may ce lllid out with precision hy 8n average Engineering Subordinate. It will be enough to design a drcular curve as ~ / shown in Fig.6. ~ ~ ~~ • \ • I II I~. The radius of a (ircular curve ..~ ______ . _____C~.~IN' can ea"i1y be worked out assuming it 10 be tangential at the point where the Fig. 6 contraction is complete. The curve needs to be transitioned in the beginning for a short distance, as shown above. to avoid loss of hE ad in entry.

,..,.". ! "

.

• #-..--._--

Departure or Expansion on sides downstream of the contraction. (A) Expansion and dispertions of a stream of water is another Hydraulic Phenom~noD which has recei'led the scantiest consideration of mathematicians. Even experimentally lltt16 work appears to have been done on the subjed.

5.

285

An ideal expansion wOl1ld be when the stream is just arlherent on the sirles. If it is l'ls<; than the ideal, the jet will no doubt be arlherf'pt on the sides; but thp. work will be expensive. If it is. more rapid than needer!, the jet will not }Je adherent and low presiure pockc[s near the side wIll cau~e the formation of vertical rolh-rs with the consequent loss of energy and with the eddy-mJtion causing scour on sides in the earthen section as the stream leaves the pacca work. The reverse flow on sides is the clearest inqi~tiol1 of a too rapid expansion. [B[ Forces acting. The forces acting on a stream flowing in a section are as given bclow:[iJ Reaction. Thp reaction of the 'led and the sirles is opposed by the internal pressure of the water which can easily be romputed at any point of the perimeter. [n a rectangular section, the reaction aRainst the bf'd will be equ,1} to the-pressure due to depth, and against the sides it will be variablll according to the depth. In:tn kleal expansior1 the jet should remain adhere!lt to the side. Any factor tending to increase the bed reaction will help the lateral dispersion.

[iiJ Friction. . The effect of friction can be depicted by giving a downward slope to the total energy lme, The effect of friction on total energy line elm easily bp. calculated. Friction always acts aglinst the direction of flow. It may bp. considered as a component [resol"ed along the bed] of the reaction. Its effect is to ileflect the reaction against the direction of flow and the total value of reaction. The net effect of friction is to ittcrease th<' rate of lateral expansion. In a frictionless channel. lateral expansion of the jet or oispefsil:m will be nil on this account. [iii] Gravity. h e c ange Of momentum per second is a measure of the force which a stream is capable of exerting. Any struc. ural change in a channel section tending to retard the inertia shall produce a change in the internal prpssures and the consequent disper~ion of the jet. The in tertia acts in the line of the direct· ion of the motion of the mass. Velocity on the line of floN has no bearing on the inertia transverse to the line of flow unless there is something to change the line of flow with the consequent change in the internal pressures Tn a hypercritial jet leaving a crest of a free fall weir. the forward momentum is prerlominent, and there is no lateral exp'lnSiOll, even though the side be suddeuly removed. There is no lateral expansion of the jet, if it follows its natural parabolic path, but if the bed profile is flatter than the parabola of the dropping jet, there is lateral depression because the line of the velocity has been changed which results in redistribut:ion of intt:.rnal pressures. The dispersion in hypercritical j .. t will be very slow. If the stream Ipa'ling the crest is subcri tical. the parabola of drop will be steeper still with this low velocity. The departure introduced by a slope will be more pronounced resulting in the relatiwly greater de pres ,ion. MoreovPr, the forward force due to momentum is in this cass 'k:ss than the side pressure, the jet will exp:n1d adherent to the side. Ml1Ch more rapid expansion or dispersion of a subcritical stream is, thl'refore, possible. rhe water surface profiles are governerl by tha conditions of flow as described in Chapter IV Part VI. The effect of friction and the bed slope flatter than the theoretical parabola of droping water is essentially to disperse the jet laterally. The condition of flow may be subcritical or hypercritical with level. downwa.rd (positive) slope and upward (negative) slope; but the expansion against negative slope cannot in practi~ he arranged unless the surface is curved. The dispersion necessarily means the reduction of tbe discharge intensity with the consequent reduction in the critical depth. A mass of

water [M1 moving with a velocity v has a momentum

gMv

Th

[C) Conclusions. (a) The greater the discharge intensity, the higher the \'elodty artd the less the dispersion in both subcritical and hypercritical coI)ditions. A stream flowing with lower initial velocity

28~

will expand its cross-sectional area by a given amount in a shorter length of the work than the stream flowing with higher velocity, other things being equal. . ... .. [bJ fhe flatter the bid slope in the outfall, the greater the dIspersIOn In both the subcntlcal and hypercritical flow. . . (cl With. hypercritical stream leaving the crest, the radim of curvature .In the, !)utiull should be infinite at the beginning of the lateral expansion. The radius .of curvature may decrease as the expansion proceeds dep"nning on the first two conclmions.. . A straight line expansion, howe \'er gentle, i~ not satisfactory, because a stream will not adhere both in the beginninO' anrl at the end. In the caie)1 su'lcritic'll flow, a ·circular splay tangential at the contracti~n is likely to serve the plrpJSe, if a decreasing. radius cannot be araranged. . (d) Il'l the cas. of flumed bll" the expan5ion should bnil or very slow upto the jump of the ~lacis, but may be rapid after the jump in the subcritical flow. The rOjJghening of the bed by artificial. device such as· friction blocks, will help thA rapid di<;persion. . (D) Length of Expansion. . . (a) The f::lctor that remains unkown is the lene-th. Owing to the existing· ignoraJilce of the manner in wh;ch the varyinJ pressu es act on the inerria of .1he m.S3, the accel~ratinn of the lateral expansion cannot be predict([d at present. Experience ahne must be the 'ginide in determining the important factor of length. The departure splay is of t~e. order, varying fram 1 : 5 to 1 : 10 as usually allowed in practic'll dcsigns. . (b) F.R Burkett dealt with the question of expansionfrom considcration of pressures a lno in hispaper No. 125 Punj ab 'Engineering Congrpss, Lahore, on headless meters as given btlow;., . ':Now it appears obvious that, a ch'lnge il~ the direction of fhw along the side wall.is used hy water pro,sure at right angles to lh~ lattt~r. It should, therefore, be our aim to keep this pressure constant and as the ve10cllY of .vater drops, the radius of curvature of the side wall sho~ld decrease. As shown in diagrarn 'Fig 'j! RA2 should remain constant, ,where R is the radIUS of curvature of the sine wall~ ana A is the area. of waterway. "If the floor downs tre'llll folhwed a cons t an t lila pc' a du'fcren tial eq nation could be obtained connecting dista.nces nonwstream of the crest with off-sets to the !Dide- walls, but in practIce, this i<: not po.;sible, a!> tp.e qlhstioIl, Qf.critical velocity upsets the uniformity of the Jl90r 'gridH;nt' .;.. "''0 1 ""',',.. . . . ..•• .. .. )(

-"

¢,=_ R, 11 , tfJ. 2)(- (If, - R.) 5/~

SIN 51N

:&

-

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Rz

SIN

y,. • Yz ..

l(

TAN~ z

. . Fig,7 Fig. 7 5hO\, s how these walls may be la'd out for any initial radius." IE) The Aut~l()r'S lVIet!1oi . ' .. , _ . (I) The rate (if expan ion is to be d~temined from the graph give;) in Fig, 8, Th;s will 11'( 1he length of the outfal', Tn t'lt~ Ca.,e of Ilbcritical flow downsteam of the contraction, as u;ually available ill. thfl ra'!~ of flamed I I :dgos or hearlldSS meters tlw expa,!lsion may be circular, tangen ti.ll to the eo[,traction •.

287 '$4

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BED

In the ~as~ onhe falls wh,en water leaves the crest

I 1

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:m.:)1 j1

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with hypercriti0al flow, is then

foll()w~d by a jump, on the ~lacis a!ld listly, t.he subcritical-flow, an ideal shape of an expansion is Bernauillis Lflmmiscade used In the d p slgn of the roof block )f the A. P. M. outlets. . It

as

has lot ,\-I-n infinite rad ius in the. bf!ginning and then it decreases towards end of the Expansion as shown in Fig. 9 below: ' The curve recommended is the one f()lmed by bending a uniform flexible strip of some homogeneous material (such as (~teel or celluloid ~ in the manner indicated above, Knowing the length of expansion as determined by its rate of change as fixed beforehand, the curve~cJUld ,'" J td it,' l~e drawn in a plan to 3. reduced scale ,nd th, 14,:'0 percentage df pr-rture read at suitable .distanc~~s \ .. .. from the beginning lind then accordmgly laId . - - - - - . _ _ _£'.1J.!i£_. _ _ . _ _ _ • _____ at site Fig,9 (ii) Flaring. . Tn flumps, long vertical walls are Df)t only very expensi ve, ,but also ,they cause consi<1erable reduction in w"terway pven w'hen t.hey are 't uilt' at -the toe of the side slope. The usu;:;,l sid@ ~1()9" allowed in p;tchi ng is t to 1 in distributaries and minors and 1 to 1 in Branch and Main Canal~. The chAnge of vertical section to the normal means considerable contraction upstre::tm and expansion dnwnstre<\.m. J t is. therefore, usual to fine the sid€ wall from vertical at the crest to the permissible side Slot e at tt·,e he~inniT'fi of the contractio-l'l upst'eam a;q,-d that at the end of e:>ipans;on dowDstrearrl, The typical sections of flarid walls are ;shown ~ p~~

XIX_ : The sections (h), lC) (d) as comparocl with section fa' show considerable saving in the sectio. of masonry and concrpte. The saving of cost in a long wall is about 40%. 7. Example No: 1 Flumed -\queduc;t. A channel with the followin~ data has to pass in a masonry aqueduct .flume with

v€rtical sides with N ='013 with no loss of head (with the slope of the channel), De~jgn the fluming. . . .' F. S. Dis?harge 70~ cusecs: Full SUPhly level 549'6 Bed.width 60 feet; Sl()pe 1 ~D 6666 ; :8ea level 594'S ; Slde lope! to 1 ; Depth 5'1 ft. ' . ' ... . [:tJ Assume width at the contracted section as 42 feet: Sectional area=A=S'l X 42= 214'2 sit.; Perimeter=42+2 X 51 =52'2 feet.

288

A 214'2 . f--. R=H . M• D . =_~_ ---:::041 ~. P 52 ~ Using Manning's formula:-

104~: X4'12/3X(_1_)l{ll=-3'3 ft./sec, N I~ 6006 iat Dis~harge=42x~'1 x3<~=706 l::auseC5 which is nearly the same as required. 700. v= 1'48;; RlI/3 51 /1 ;=

of contraction up<;trealb allowing 1 ; 3 FLUMED BRlDGE-Srale IllO()

tb) Lf'ngth

=-3X 6~-42 =27 feet; Radius of circula.r C!;)ntraction (2R-9)9=27l :. R =394 feet. 2 (c) The departure downstream I in 5=-,,5 X ~~2=45'Radius of circular expansion' =(2R-9;9=452 :. R= 117 ft.

Jq> The walls shall be flared both lJpsirt'am Fig.IO. S. Example n Flamed Bridget (Montagu)

31}0

00 v.ostnam to } to J sjde

sJl>j)I'A9 J»

It is required to flume a ch~nn~l with the d 1ta given below withou t txceeding the critical velocity to a width of 10 ft. whIch is fixed fOT an existing railway bridge. Find the fevel of lhe bottom d girders allowing a freeboard of 15 ft. with 100 as bed level of the earthen channel. Di~charge 250 cau.ecs; Slope 1 in 1000; Bed 25 feet; Depth 4'1 feet; Velocity 2'3 it per seconci: 1 to 1. CalCUlationS. LbJ Throat under the bridge with vertical sides. the discharge intensity=250/10=25

cuse.c~: Critical depth=t1-i;r- =2'89. Th~ actual depth must remain well above the critical by at least 10% say not les, than 3'0 feet. [c] Up~tre'lm side contraction 3 : t ft. Let it be 1 in 3 at bed level; The length of 25- to . f upstream approar:h =3 X _~_-=22 5 t <

Rarlius=f2R-75] 7'5=2l5 2 :. R=37 33 feet. The wall shall be flared t to I slo~ with I foot free board.

The radius of top of well; contraction each ~de=7'5+ ~d-=10'05 feet; .

. a.

_

R=«%R-·-IO 05) 1005=22 5 .. R -

22 ..:;2+ 110 '4 ------:rot---

615

=-2[--30'0 feet nearly,

(dl Downstream Deptarture. Let the !'ide splay be I in 5 at bed level; 25 --_ -10 =.37-f Leneth of oJ,ltfall =05 x -.;) t.; ~

~

Harlius at bed 1~vel=.2R---7·5 7·S,,,,3752 :.R=97·13 feet. narc!c t~ h:.l.H !:::: or.;:; slope with 1'0 it. freeb:mrd. The expansion at top

The wall shall bl"

289

4'1+1 . level=7'5+ - - =1005. 2 The radius at top leTel= ;2R -1&1'05) 10 05 _37'52 .' ,R=75'2 feet. (e) Throat length, This depends upon tqe straight portion required for the bridge,let it be 1(1 fpet Three mp.thods ,)f solution are po~sible in this example, only one of which will be illustrated here' (0 The bed may be sketched in a.nd wing wal's designed tlaerefrom, (ii) ThA wing walls may be fixed and bEd designed therefrom. iiii) Sketch in the water surface and oesign the bed and the sides. It is prol osed to illustrate the 2nd method here. (f) From Efs Diagram of Montagu Plate Hr. Discharge 25 cusces; Depth of 30; Ef2 4'08 ft, Total energy level in the open channel

.....

-

.

!

'!

o

v'

=100+4'1+ - - = 10"'1 2g

, +23 2g

2

= 104'18

Of--

Bed level ill the throat=lOt'18-t'08 =100'10; F'S'L'= 100'1 +3 = l031 The hed need to be raised by 0'1 ft. oaly which is tri !ling Now work out the design with no chang!> in b~d level. Read depth for Ef 2 =4'18; Depth=3'28; Water Ievd= 100+3'28= lO'j 28 The botton'\ of gilder= 103'28+ 1'5= I04'7~ (g) Friction bss.

Velocity in contracted section= 25 =76.J It 3'~

:

...

J

0.

• '-..-r--f--

per second;

... -

Velocity in the bf'ginning=2'3; Average veloc:ty 764+2-3

110:::-------

.

2

---WJ-:-·,1 _.. f

.

=50 ft, nearly

~

1 .'!== 110'9 say 111'0 -3·H1; R=!_!LQ- -3 25 ft.

H.Y.D. in the beginning; Uea= (2'; +4"l) l'erime.ter .... 25+4·1 x 2 yll+5'j

3~

17

°

~~

290

H.!t!. D, in the contracted

5

10;< 3 28 3'l:~8 'ction= - -' - -, = --, = \.97 ft. JO+2x3'2816 56

A H 'MD 52'2 nverage I' ' =3'25 - - -\-1 297 - =-2--

=

""61 /I

ft,,'

For N='OI5 J'n

Manning's

furmula

w;th

'l

R= 2'61 and v=2 0 from Nomogram PIette XIV S= _1 __

]400

"

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U1

11

-

225 --=' 0 I 6 f t.

' approac h = Loss m

14UO

37'5 Lo~s in outfall = ~ ='Ol.7; Rate of loss in throat for R= 1'97 and v= 7'6~ 1400

1

S= 6C.o X 10,-'016 ; ~et 1055='06 ft, 5ay 1 ft. The downstream water level may be shown 1 ft. lower. The Totahinergy liDe will have slope of 1/1400 in approach and outfall and of 1/000 in the throat, This slope is f\\ther very small and there will be no change in the design.

9 Example III. Contraction with depressed floor, (MontagH) In the above example, contract to 5 ft, width with vertical side

.Montagu's Solution C. B. I. publication

walls (A, ~f, R

No, 6), Then mean velocity enfrgy Ev=

~

"2g =0 OS2;

~fean value:,f Et =4'182, Assuming the win~ wa.l{s of thp. approach and oeparture to be vertic,d, I.e, the sectlon rectangular. then on the section at entrance to apPloach tran!'.it)on, Fig, \ ~ , Qo=250 cusecs: Bo=25 feet: :,discharge per foot width q=lO cusets; E t =4'182; :,D o =4'09 fect; and Vo=2 44 f P.t pef second, The Throat Assume a flurning ratio of one-fifth width of throat, Bt=5 fect; Discharge per foot of width, q = SO cusecs, The velocity is n)t to exceed the critical ve~ocity, Exrerience dictatfs t'Jat the designer 5hould k-eep well cltar of the critical point. Examine the curve appflpriate to the value of q=50 cU!'ccs Sp.!ect a point thereon, '...·ell cl,~ar of the locus of the criti :a\ puint. Let ~he point selecte(\ have the co-orclin"tes. Dt=7'O; Eft=' 7'8 Then tht line of the ted may be set off downwards from the Total-energy linl, 7-8 ft.

anj

tl:e line of the surface u~t up froUl the bed, 7 feet; The TraD.;iti.DJ ;-Begin by assuming

Vt=

qt

-_

Dt

=7'14. This is satisfactory

an approach transiticn of ];2 splay in

pia-no

Its length will be ; - L a = Bo-:-_~t X ~"",20 teet.

'2 1 :. The slope of th~ bed from level of normal channel to le vel of the throat

Eft-E{c - --. ___ = 12

La

%;

wi}}

be

..-

' Let the :length of tbroa t L t= 10 f eet. I

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The design (resumed) ..Refer now to FIg 11. Assume any nUin1:er of sections X Y Z etc. on the plan and elevation and proceed as follows, t~ construct the tabular statem<:n t shown' at t ne bottom of the plate, The total discharge Q remams constant.

291

Measure the succeisive bed-widths B on seection XYZ etc. ano record them in the table. The di5char~e per {not width q at the successive sections equals Q divided by B at each section. Calculate and -record. ", The value of E f appropriate to each s ction is determined by the intersection of the appropriate q curve with the "curve of transition characteristics". Record this. The depth at the point is read off tile' Hydraulic niagrams at the same time as Ef and 0

r~corc!~d

The R. L. ()f the bed is determ;~ed by subtracting the value of Ef kJm the R.L. of the total-enugy line at the section. Fig. it.

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Example :'1. Hel:lle3s meter fiun1'3 (Burkitt's paper No. 125 Punja) Engine-ering Congrfss) (a) The theory is sim[lle. ff at two sections in a strca:u dose t06'cther, where ~here are no sudden changes to upset a str{am t"ne flow, the breadths are b o ,md bl and the ce:}ths Yo. a.n? ~ l' the dtpressi~n in water surface between the tWI) sections b':ling h, then tile djscl1~rge Q IS given by the eq_uatlOD:-

Q=8-025 ho Yo Yl 't'

~'bo2~·~~2-'. 21 t Yo

. ~2 •

-,h.

· ,'- 29% For:- v I_V 1=2gh' 1

G

'

° 0

°

Q! _ Qf =2gh' ° 0Q!

All!

A02

'

°

h

:.Q=8·025 b. Yo b l YI { -b 2 2 b 2 11 o Yo - 1 Yl ... 8.025 b o Yo Yl

2

2

Ao2_A1 1

}t

l.t

h

Ibb~2o 'Y0 -Y1

2i!h AoJAl'

2 \

(b) Hearlless meter at R.D. 103076 Mithalok Distributary

F.S. Discharge=3~'1 cusecs; Bed level=6~2'ol~ 62 ' ;) 624'85 F.S L'=624 75' Allow a loss of 1 ft·

Bed width= 10 ft. ; Sides t to 1 ; N S. 622'74 Velocity 1'3 ft. per second; Depth 2'7 ft. (c) Calculations ;Velocity of approach= 1'3 ft. per second Velocity of approach

v2 head=ha=~=

2g

1'3' _ ='03 ft.

84'4

, ietthe crest be level with the downstream bed; Depth upstream=Z'S It. Depth downstrl'arn=2'7 ft. ; Drowninng ratio=~_:_~=='964 2'8

The co-efficient C for a drowned weir (rom Fane'~ curve Plate ta.tio==2'S2. Let B be the width at the maximum contraction ~:

,/

.;

tv

for this dtovmi1lf

~~-

fd) Width opposite upstream gauge for nonsilting conditt. .....-'·Depth*28 ft.; vo=.84 d "='S4x2·S· '4 =l'63 say 1'1 ft/see, . ~c_

Width=Q-=

38'1 ==8'0 ft, 2't; ~~ 1'1 There will be one gauge where widt.h IS 8'0 {to and one where width is ~'5~. (e} Draw·oow:n to upstream gauge. Total energy aepthz:2 8 +'03=2·83 . - - ft, =H; Let depth at the 6rst ga-uge->wen~pH; The drdjY &; Dv

-i -

(l-p}H ; .; Velocity=v' 2gh1; DIscharge ptt foot /-"-' . _pHxy!2g (1-pJ H==p. Vi-po

-v

/

.Jl-~==3S·r

. 1 ='1265. The solution olthis' equation is g:ot (rom ffiowli 3 /Z s Xv'2g -x2'83 Pv curve Plate IV in Punjab Eng;ineer:ng Congresg Paper 125 1929; but it can eotsily be If){ tty the use of slide

rure.

b:

"Set the re-v-ersf'fr sIi'de to '1265 ot'! the scale anrl then read under the cUrs~1' 6ft the' II- and C scale 80 that total of p and I-p is one," '.' I-V='011 Draw down=h1 - 017x2'S3'=.0476 ft. (f} DrawootlowB to s{cond gauge.

• • as'1 · 1.. arge In D ISC1J t en 51 t" = ·--cusecs per ft.

Draw ·down =hs={l-p)H

3'52

J

'Where H=d+haa::2'83 feet;

38'1 py'l-p= 3 S2

X

1

v2g

-tI-

X 2'833/3

'd . with sli e rna,

solving

I-p-·I03.·. nraw·down+ha=2·83+· 103=29 •• (g) -Depre<:sion or difference between the two gauge readings h=h 1-h 2; Depres<:ion='294-'047a= 247 This will be the difference in the full supply conditions the discharge for other . obs~rved values of depression 'h' being according to formula in raJ above. The design is shown In FIg. 12 11. Example V. Ra~ed crest headless meter Hume. (Authn(s] In the last example, tne width at both gauge· wells should be the same: but the crest be raised at the second gauge·well . (a] Let, width=8ft. o?posite'upstream gauge, [b] HeIght of crest The depth upstream approach=2'SO' Lpt CTfst height be R Depth on crest= H-R=2'SO-R Depth downstream 27-R Drowning ratio= 27-R . Let 28-R ' Drowning

e . <

ratio=2'~-I'!' 2' -1'

R-t'''. ..

'928

from Fane's curve=2'9

~eb\~c~~r;::t2'91~48~'1'~~:~:'3 c~ 11an(~~l~ 38'1 '~W~'~:'\lien R... l't . ,.m: " ,.

ft. O. K.

I"

,

•

-

-4-'--

.j

/

294

(c) Draw-down to first gauge as bdore='0-l76, 1 be pH where H,-.:}'43 ft. :,PV - p =

Let depth opposite the second gauge

8.~~';X8Xl'43~/2

Solving with a ~lider u1(~ I-p='2 \ , : f Draw-down to s;c0nd gallge= 2x I 43=':?86 ft. ,dl D"pression in thp. design. of full supply h='2R6-'0476='238! ft. 12. .i:;{H' ..., 12' E J ample VI. Authors's Improved Headless meter Flume. ;:j) (-\) DeLcts in Burkitt's Headless Meter t~ lumes. Ii) BUlk tt's Headless Meter Flume app:ies to vt'ftical secti ms and therefore, entails expenditure of heavy wall sections. (ii) The correction for vdocity of approash is rather very cumbernme, only p03sible by trial and error from th~ gauge rearllng, of the first gauge s;ection. (iiil Expensive gauge-wel's and ina curat~ ganging. (8) 1mprovcmen t in author's improved Head les<; I-Iume. A flurr.e of this typ@ was designed and constructed by the author at R. D. 1206:~5 of 8hudinala Drain, UpPff Jhelum Canal comprising the followin.g speci'll fCatures:(a.: The hydrauLcs is developed to suit the trapezoidal ~ections so that the sides need not ')e vertic:!!. (b) The op.c:ign is v{'ry che'lp with only pitching for the side walls. (c) Thf'! gauge wells are suitably locdted in the central pier divided ill t .vo parts. 0116 ,:-ecorrts the gauge at the contracted s~ction, and the other upstream onl'! is s,o designed rlS t,_) teeOf@ the tieDth and velocity of approach head serving as an open Pitot gauge LJr the 'lDstrcam Sec:iOIl. (d Tte correction for velocity of approach is automatic. (e) A difierentirll gauge was installed in the fom. of inverted U tll'oe ::lnd water ~'as suc:ked ur from both gallge wells to glVtt a direct reading of the differences tl-!at is,' H' nea;! causing floW b"tl"een two section, .\ vernier ~cale lias provided to give thl'! rea,lino correct to thinl pl::lce of decimal. 0 1/) T1.e formula of Discharge is very simple. If H is the refad:ng of d;fferentiaJ gaugp., ri.e dischargp Q=Ay''lg I-{ where A is tHe sectional area at the c()ntra'~ted section.

(g) Data.

./

<~-. r':- =t='--~~

l' S Channel Data. B= 19'0 ft. ; d=7.0 ft.: s= }'5 to 1 ; Q = 700 cu<;ecs. A=/

0(19 0+lC·3)=7·Ox29'5=20S'5 sq,ft; v=2 v2

:i':i9~

'tg

6'1'4

=~ =----

h d

Flumed seetion:- Design

£Ol

L=fF-

~~~

-.~/~.{.'

=3'39 ft/sec,

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.... "1

~

=0'178:> it

.

F,S. afflux of 0 3' Try F = I 0 (R.ise in 1ed)

A=x(B+x) . and w=B·t2x,' ',h= A_=_x~*x) , '2w 2i:3+4x v=.J"2gh- =- ."")'}:") y'h ; H=x t-h; H+l·O=7.3 TO,178 . J'fi8; x+h"=6478

.: Fig. 13

) .,..h·=S·478 ; i.e.,

,

:-18+5:<,

!('-fi:f+ tX Fro:r-;

d)

x+x__:_~+x =6'478; x(l +_~±;<-)~-o'4;8 2o+4x

2B+4x

),,8/l(B+x)3/l

G'478 (1) : ---~V2~:; 4x

7110 -

8'025-

(2)

3Bxt5x2 = :'05: ' ,.:o'912x ; B(3x-12 956)=ix (25912 -5;,;)

-

295 2S'912-5x B =x ,-----3x-12'956 -

,

4'A~n2-9S6-2X4'6,312

(i) Let x=4'6; Left hand expresslOn=-- -

-________ 31<46-12956

=182'5

(U) x=4'7=Left hand ex-m"sslon= 4'7'112'PS~-2 '>(4?__,!_lz =129'4 .

JX47-u,t!:6

_

(iii) x=4'S; Left hand f'xpression = 4~~~(1_3__~_5~=3.~_i_:~~= 98'( 3.-<.48-12'9:6

liv) x=4'716; Left hand expression=4· 7tR2(1'1956-2x4716r_: =123'4 __ .. • J ,,4'716-12'956 , • 25912-5x 2332 - - - - - =4716~ -=924 ft, 3x-12'956 1'192 (C) Solution x=4'716; B=9'Z4 A=x,B+x) =4'716 (S' :4U+4 7 \6)=4'716x 13 956=65'816 B=x

w=B + 2x=9 420+9432= 18'672; h =

~ = ~16_= 1'762 2yv 31'344

V=V2gh =8 0'15 x 0-762= 10'65 ; Q==va=IO'65x6S'82:-;-701 H=x +h=4'716+ 1'702=6'478 correct. Variation of Working Head. Assume Manning for C1_ annel.

.

,.

CU$eC1l.

i.e .. v= ~~~_R21~S1l2 ',i e VXR2/3. v=K.R213

N

'

Q=700; A=206'S; v=3 39; P=19'O+3'OOBX 7 'C=19'OX2S'242=44'24 R= A = 206'5 =4'67 R2J3=2'794 ; K= 3'39 =1213; ~'794 P 44':B '~t

,,,-I

A

d. l'u 20

30 -40 50 50 70

2 :,w'_)U 4400 7050 100,0 132'5 168-0 206'5

P 3 'l'l6l 2621 29'82 3342 3703 40'64 44-24

TABLE I R 4 0907 1'679 %-164 2992 3580 4 )30 4,670

v=}'213 R2J3

Rt 5 U 93b6 1'413 1 775 2079 2'313 2575 2794

v I;

1'136 1'714

2 ];;0 2'250 2'840 3,124

3390

Q 7 23;3

--~--

754 1516 252,0 3764 525'0 7000

(D) Section opposite U, S. Gauge-Well. The section is arbitrarily selected to Ie IS feet wide with slope 1 to 1 and the floOJ level, viz" one foot raised above earthen channel section upstream with the object: that the floor . remains clear of silt undp.r all conditions of flow Actually the discharge is obtai!.l_e,d independent of the measurements of the sectional area opposite upstream gauge-well unlike Burkitt'f -headless Meter flume Fig, 14. (El Flume Conditions.

A-x\9 24 +x); W=9 24+2x; h==+w; v-S'025v'i1'; Q=vA

296

TABLE II

w .,

~

4'0 45

10'24 Il''ll 12'2t 1324 14'24 15'24 1624 1724 18'24

.. 71fl

rR fl7

'5 1'0

I5 2'0 2'5 3'0

35

P'24+x

A h=-H=x+H 2w

A

v=v' 2gH

d

4

5

6

7

974 10'24 10'74 11 24 Jl'74 12'24 12'74 13'~ 4 13'74 I~ q"

487 10'24 16'(1 22'48 2935

0'238 0'456 0658 0'849 1'032 1'2U5 1'373 1'536 1'696 1'762

0'728 1 456 2I5S 2849 3'532 4'205 4873 5'536 6196

3'914 5 42 651 739 8'15 881 9'41 9'95 10'45 1065

3372

4459 5296 6181 tiS 82

frt

fi ~7S

H

Q 8 19'0 55'S 104'9 166'3 2392 3232 419 5n 646 701

,.

Working head=floor level+Column 6 of table 11 -(D.S.bed leveI+Colum 1 of fable I) The flume will work in free fall conditions upto a discharge of 323 giving a working head .t 16%.

Galibration :Read H from th~ differential gauge installerl in open pitot GaugeWell which registers the ",ater level at the first s. ction plus the velodty of approach head and also the Depth "x" from the (ange rf~ding in the Gauge Wtll B. Dischar€e=(9 26+x) XV2>;H CUStlcs. A difference of gauge reading C and B is denoted by G; the formula for discharge ?ecomps with H=G+h

Q=R 1 "-2V':!gH y' A 1'l.-Aa 2

10

13. Example Vl[. Weir spillway sYp'hon flumes.-Fig. J5. Cl)nversion of R. Culvret @ R. D. 54,600 of P.R.K. drain into a weir spilway syphon carry 200 cusecs. Data.

Section of the existing culvert is as shown in the sketch. 8ed width of drain= lS'J it; F. S. depth=4'Z ft ; Bed level=73Z'07 F.S. L.=:::l733.'Z7; Length of :ulvert is 47.4 ft. ; floor Jevel=7~'7.23 Depth above floor level=736.27-73.t23~4.04 say 4 ft, Upstream $ide. Q~3.0x6xH3/!;

154=lBHM; H=4.IS ft .

..t the lowest point of the roof p= 12.5; assu:ne depth=x

A=125

2 154 = 12.32 v' - = 12'32 I 2''l55 v """ ............ _- ._ - x~--~,. 12'Sx x ' 2g x 2~ x2

X'

But for a free surface x=deqth=4.1S

_~~~5 X· .

.

Let x=3.9: R.H.=4.025 x=404; R.H.=4·091 Position .

1st try W=11.0 ActuaIK+f'_ -2.378 .

01

wave with )5~ CJ!eCl, .~.

Q=]54 cusecs L=4.JS+.16 -359 =4.34-a.59=,75 ft. K+F =4'18+'16= 4.34

1826

't'hitl> ~. ~ore •

2nd try W-I~

297

., I' I

I

L '7~ _'-\jhJ -_ = - - ='43b l. 1 7 L~{ ':

K--1-F C

.

,.

.

r~'~

1'"~:t ...:; ""'_.....""/ \I'"

.

·=2303

"' t: :

,'". .

I· • I Q 0

1J ! .J 3rd try w = '0 feet

q=

(Ii' ,ft

~ --- = 1;,'4

154

4:r'

10

,I

If

,

,

I

:,~

,.

•

I

",

.... .

K+F ··='2228

~

'.' ...

J

L

..

1'946

which is equal. Wa"e shill! iorm wheA

,.~.

eli J

'J "

x ='545 In'

W=lO'

r c':

~G

m.

·}:H :)',

x=106' Farrel depth='l:8' "':' Reinforeem(nt. (\" I,,; ' . ' . . • • Maximum vacuum pJtcfJtial=5'9- r&: ...· j 2

S,,-2

4'54= '·36lt.; v=' ,.~ :Lg

tg

=

S

".

1 86

.~}:.\ iefJl.IT'gF

Pressure dn~ to vacuum =1 S6x6~'5= 116 Ills, Add v;eigh t of cov; 1= II) 1\)5, ero wd luad = I W 1[IS,

Total " say

296 !lB.

3no lhs.

Max, span=7'O feet;

72

300x .. =18101Ls. ~

I

"'t

I I

• ~~

, 1

. against 434 ='22'2g

It)

\

';z:

<:> ~ ~

,_"

\)

"-l \t\ WI

I I I I

,f I

....


Qj;;

1.i;

298

R='555%

= 1840 Ibs.; d=

M =)25=5" max. 6" max. .1 v74 .

. 12x6x'55 and use thIs throughout; Iron=--lOU--- =.4 4 bars

of,r dia: max: '44 which is ample.

"I'

Neglecting the effects of curvature we may arram;e for the upstream lip at R. L. = 736:23 i.e. 4'0 feet a JOve H:e fic or of the culvert. Regarding the lattf'r as an open flume wl:ir • we have for the priming cischarge; Q=3x 60x 40312 = 144 eus.cs.

R. L. of D. S. Up. Depth of flow in the earthen channel for 144 cusecs' (144)3/5

d=42---- =345 ft. 200 The downstrp.am lip of syphon must dip into tht level to ensure sealing; surface 'level in drain for depth=3'45=732'07 +3'45=73552. We will therefore keep 'the downstream lip at R' L.=735 SO Position of wave at point of pri::ning with discharge 144 Cs We have L=drop=36'23-35 52='71 ft. 1st assume widfh= 180ft. q =

, [q2

C={I

/

82

-!~ =8 cusecs. 18

·71'._~.

. _ ,L

g= {I g=1 2,,8 Ie =)258= ,,6;),

from Crump's diagram

Kt F

==2 488 ; K+F=2'4S8X

,·258-3·lS tt,

Giving a floor levd [limiting]=736'27-313=733'14 The designed bed= 733'03 This shows that the wave shall form U. S. of 18'0 feet width of the flume 1the end 01 the syphon). No speci"l precaution to form a ·"ave is necessary as thp. floor is already low enough. WP. could on the' contrary reduce th width cO some extent in order to bring the wave nearer to the lowest point of the cowl and then extenrl the cowl at an upward !tlope to downstream F.S, expanding at the same time. This expedient would give us a higher coefficient for the syphon, 2nd Try a width of 15 ft, p

144 19 '6 2 L 7 q=~_-=9'6cusecs: C={I--- =1421 ;L='71-=_':__!_='50

K+F

.... --C---"-2,·395 b g C 1'421 .'. K+F=2'395x1421=3'4 It. ", l ,'~ , This gives a limiting floor level =73623-34=732'83 against 73207 i.e. R:"'L. of bed of drain, 3~d. Try a width of 12 feet.

144

q= -,- = 12'0 cusecs. J~

122 c= v~/(-""" 1'641 g

L =--F6!7" ·71. 'from Crump •S d'lltgram C K+F =2'295; K+F=3 78

C , Giving limiting floor level=736'23-3'78-732"45

299 We might go further in this direction, bu t to do so would involve a risk of wave forming too far downstream. By adoDtins- a width of 12 feet ot the l'wesr point of the cowl we shall be on the safe side with a nief'ly b::llanced design. Dotted water line shows conditions of flow for a discharge of 144 cusecs when the priming just starts D'>wn<:tr"am priming conditions. Down"tream end will become sealed when the water surfac p tou 'hes the low st point of the roof 31ab at R. L 7395 @ 16 itet from rlown ~tream face wall, fhe cross section at this p0int= (735 5-732'07) X II =:3'43 X 11 ~37,73

Q

Q

v="-A' v 2 ha=_l~=

2g

0. 2

X

[;;7 73j~

A t crest, the width

.

='~"F73

c .

Xl

lC I l

J

{l"l,i·.'/,

1 :lg

= 17

f~et

\ , = II~d ; ve 1OCl't y= ..O· se;:tton ::,'., 17d

,.

V 2

lace level

V 2 2

1

.. Q

~17UU

2g

:Lg

,.,..Q2( .. J ...___' _ ) in depth at ~h 7 UU

18000<.11.

, _" 1 [2J

lboUOd3

'

For \ he .!rain in f III <:llDiJly we h \IT" Q=200 cusecs; d=4'Z ft. a.ssume .

_SL =[.....~.!

20U

15 [3

[3]

J

,Try d=r 3'5 feet; from L3J Q-l·47-6 R. H. from equation !'l: Ii'

d=343.l.H3'6 2 [ .. ' . • 91700 =3572 ; d '-0 =: 'Oi2 Try d

n=

__ ~..

1

J 8600 X

1

..

'.,

91100

1 l~tiul) x:J jVli .. )

~

1

345; Q = t44'S; c>'=e.;35S3; d'-d-'1I3.Try

l ... 3'i5+154 2 (

,

3 StJ

Fig 15

,'=3'59 Q=154

which is the same as aS5umed.

3()O 14. Example 8. Surge Tanks and Chambers. (A}

Surge Tanks in w, ter supply.

To cushion an parts of the water conduit against the full eff.'ct of forces dlie to VI attr it is variously equ:pped with ff~lief valves, bursting plates, and surgl! tanks. A surge tank is "

Types of

~urge

Tanks

doubt!y valuable to -e penstcck hecause it wili not 0111y ahsorb energy during deceleration but it will also provide a ready reservior from wh'ch th~ turbines can draw temporarily, as when they are starterl, or, during normal opera tion, when a sudden heavy demand causes rapid oprning of the turbine gates, Surge tank t) pes are illustrated in Fig. 16 "', The simple surge tank often lives upto its name when a resonant (aDdition canses succeeding surges to become ever greatu until the tank spills over. (B) Surge Chamber Lr Jump (Crump).

controlled Hydraul c

At Dubbiwala culvert. Upper ]he1um Canal a silt ejector was t uilt and the escape supply of 200 cusecs had to be dropped in the arljoining Jhelum RiVEr in which H. F. L. was 75 feet lower than canal F. S. L. Water was carried in a 6 feet wide flume with 1 in 10 slope and the hydraulic jump was allowed to occur Fig 16 . in a chamber covered by a reinforced concrete slab which was ancoored and weighted down as shown in Fig 17. The idea of the chamber was to destroy the energy of fall of 7() feet with a depth of 4'00 fed in a chamber downstream of the hypercritical jet. 15.

Example IX. Rigid Top Flumes.

(Hypercritical to sub-critical without a jumn) Fig. 18 Suppose the origin:!l velocity is v l and D 1 . If the channel is open at the top, the static head at the point K is D1 and the velocity head is V12/'lg. Suppose the channel to be of uniform width and the bottom, level. In order to secure the gradual smooth enlargem~nt of cross section, supposp a rigid top to be added 10 the channel as shown from E to H, rising along s straight line. We know hy experience that if the angle is not made too big the water will cling to the inclined plane anli as the cross spction increases the vl'locity will be smoothly and gradually reduced, as exemplified in the expanding tube of the Ventnri-meter. ' At point B, where the depth has increased to D and the velocity has decreased to v. the velocity head will have diminished to v2j2g. By Bernoulli's theorem the static pr"'ssure at B then equale . >i

In general, this pressure at R would not equal D exa.ctly, but would be something greater, as BF. Bv means of the above expresion, the static pressure corresponding to eacHl depth can be easily calculated for given conditions.

301

....... •" .... ,...e:-

~'.

~ frretotc. MJI:lt:;NAI':'I' I,e J1/-4.'fCI(

,G(:f!"'il$ ........ , ... "

~

...

Fig. 17

The resulting static pres~ure, as shown in Fig. tR gives the r.urve EFGH. This curve which crosse, the surface (d the water at E and H indicates relations of gn'at fundamental, importance which should be ~arefully noted. At E the static pressure on the bottom is exactly that due t~ the depth of water AE. As soon as the velocity is rpduc~d and part of the velr)city head is· thus converted into pre'isure, the pr'l5>ure on the bottom is the greater than that due to the depth of the water at"ng. Thl1s at P thl.! pressure is that caus?d by a head GP. Tliis means that at the PJint N there IS a pressure afainst the upper bounding surface of the water eqllal to th::lt caused by a head GN. If a small piezometer tuhe shoulrl be inserted through the upper surface at N. the water would ri:;~ ill i.t to the hwd of G. This pressure tend .. to burst the cover of the conduit. The curve EI'GH is really the hydraulic grade lim through the expanding section. The interior bursting pressure against the upper surface begins with Z'3fO at F and increa<;e!", very rapidlY at first. and then more sl )wly, until it reaches a maximum value such as GN at N. From this point onward it gradually decreases utniU it a~ain reaches z:~ro at H. The pressure on the bottom at M is ltgain exactly that. cau~ed by the depth of the water. As the velocity decrpases betwpen E and N, the corresponding dimunition of velocity head is more than enough to raisa the watH ::llong the rigid. ~lanting. uprp.r houndry surface, and hence there is an accumulation of excess static pressure. As tt'e velocity decre::ls.es from N to H, the gradual conversation of velocity head into the pressure is not sufficient to raise thl'l water, and hence the previons accl1mulation of pressure is gradually drawn upon in raising the surface to higher and higher elevations. If the whole apparatus is open to air, the water at H would nl longer follow the uppt'r • I. -- slanting SUJ face but would break loo!e t--.,r-......;_-::;::::::::==========-=::;'liP1~- and flow away with level surface from this point. If the air were excluded by suitable means 1 eyond the point H, it I , would be uwler a vacuum increasing in I 02 intensity with the coutinued expallsion : -Vz of the ·:ross section. Tbe cross section at which the upward pressure on the surface E R is the maximum at NP is of a particular ........... _ m •••*_ •• M • • " ......m ...... interest. At this place a tangent to the Fie'. 18 curve at G is parallel to the water surface at N, and the change of velocity head is just sufficient to produce the change in elevation of water surface so that there is neither accumulation nor reduction of pressure, On account of this particular balance between velocity, head and depth, this particular section may be said to mark a critical point or a condition of critical flow. vc 2 Q1 It can prove that; Vc =gDc =g Q.; and Dc = _ = --

,,:~

~

g

g

302

The curve EFGH, it extended according to its mathematical equation, has as asymptotes the straight lines OL and OK. The curve EH need not follow a straight line. Any smooth curve would do and Bernaul', Lemnscate provides the ideal surface expansion. fhe curve EfGH would change correspondingly in shape, but would have the same properties as pnumerated above, and WOuld, for each depth of flow, be at the same distan~e above the top fhe df'pths at E and H always have a definite relation to each other because lilt these two points the sum of the depth and the velocity head is the same. Depths so related are called alternate depths. Let Dl=depth at E; D2=depth at H; Q'-"-vIDl=v 2D 2 V1 2

V 2

--- +Dl= 2. +D2 2g 2g .' $ubstituting for velocitie3 their values in terms of Q and transposing.

2~~li -2g~~i-=D2-Dl;

%. g::--:%~:i=D2--Dl

Dividing thrcugh b:y D 2 - Dl and substitutin~ Dc3 for Q2Jg Dc3= _~Iy Dl+D 2 If the values of any two of the depths are given the value of the thi.rd can rea.di:y ce oh~ain,d. .1 his device in th~ simple form was uspd by the author to reduce M.M.~, of the Onfice semI module as published in paper No, 2::S7. punjab Engineering Congress 1940 and described in paragraph 5 (e) chapter XII part II.

.

,

.

PAr
CANAL IRRIGATION CHAPTER XIII

, Siphon Spillways and Hydratamats 1.

IDtroduction.

Instead of alfowing wat::!r to spill over the crest of a dam or weir the surplus water may be dtalt with by a siphon spillway. This m::J,y comprise one or more siphon units. :\ siphon, {I,ot syphon, :IS it is sometimes incorrectly spelt) is a pipe or tube bent to form two legs of unequal effective length, by which a liquid can be transferred to a lower level. over an intprmediate elevation, by the pressure of the atmosphp.re in forcing the liquid up the shorter leg of the pipe immersed in it, wh;le th~ excess weight of the wattr in the longer lpg [when once nlledJ causes a continuous flow. The flow takes place only when the discharging extremity is lower than the liquid surface, and when no part of the pipe is high"r above that surface then the same liquid will rise by atmospheric pressure [about 34 feet for water near sea-level]. As applied to a dam the siphon is usually formed monolithically with the dam. Such a siphon is illustratt'd disgrammatically in Fig. 1 wherein are shown the names usually given to the various part;;. As the re"ervoir overflows, water flows over the crest of the sipt on as in a plain spillway, bnt the design is such that the air which is contained in the upper bend is shut off from the outer atmospheTe either by a water seal b<>low the downstream leg, or by a curtain of falling water. If now t he air is exhausted from the upper bend the siphon will run full and is said to have "primed" The discharge now very much greatpr than could be obtained with the same reservoir level and ;to phin spillway of eq\lallength to the siphon spillway. The air may be drawn from the upptr bend by an air pump, but it is usual to arrange Hat priming shall be automatic, the siphon being so designed that the water flowing over the cre,t itself carries away the air from the upper bend.

Olt

DAM

RE5ERVOJII

In all siphons the inlet is bell-mouthed or funnel-sha ped so as to fec uce loss at entry and minimize surface ,iraw-down above the !'iphon mouth. Usually the upper l'p of the mouth of the siphon is carried down below crest level and in this case it is necessary to provide air-vents in the hoon of the siphon just below the level at which it is de:;ired that siphonic action shall cftase, Fig. 1. If these were not provided. a siphon would continue to function until the reservoir level was reduced to the level of the siphon lip and mu~h storage would be lost.

Fig, 1 2.: Discharge formula.

Jhe

. , The umal syphon formula is:- .' .'.. Q=Cd A y'ZgH where Cd=Co-efficient.Head; A=Throat area, The value of Cd has bren taken to be'S in some of the low head designs ,adopted in Punjab for platn siphons used to keep a constant level in the channel. ',1,

304 A. H.Naylor, who built the Laggan and Dunalastair Dams in Scotland. considers in his book on "Siphon Spillways, 1935" that the head should not be introouced into the expression for the charactenstics of a siphon. His opinion is that in view of the lack of knowledge of the priming level before construction of the actual siphon, and in view of its variability according as external conditions vary, the performance of a siphon should be assesed a<; the ratIO of the discharge to the discharge of a "perfect" siphon of the same throat area. By a "perfect" siphon is me;:jnt tl-}e purely theoretical conception of a siphon with a perfect vacuum across the throat. This ratio, it i, suggested, should be called the "Efficiency" of a siphon. Efficiency = '1 -y'Q=- - where Q is the discharge of the siphon; A is the throat area; a is A :Lga; the :ttmospheric pres"ure in feet head of wa ter units; feet and second. At sea level a=34' and the expression then becomes: 11= Q

~

47 A

Q can be calculated with a fair degne of accuracy or may be measuren by means of a In a few cases it is pos"ible to check its value against the p:rf?rmance of the actua I slphon, though this is usually rather difficult to measure accurately. ThiS IS a true efficleny and can never attain a value of IOU per cent. It is a measure of the intensity of di,char6e ,.rver the crest. The only shortcoming is that, like the coefficient of discharg" it can take no account of priming level. But it has the advanta:;e of defIniteness for this very reason. A further dis.advantage i" thp, disappearance from consideration of the somellVhat indefinitu H. The .,"oefficient.of discharge" diverts attaintion from the true desiderata of :t siphon. It snggest?, that the dischuge is proportional to the square root of the head availablp. in any particula.r design, wherea, It depend.;; rather upon the vacuum attainable at the throat action. Type of ::liphon Spillway. Siphon, may b" classitipd according to Head as High, Medium or Low Head siphons. . High Head. Consider a ::.iphon whose area of cross section is constant from the throat oownwards. If the lower limb be imagined to be lengthened, tt en, as the operating head is increased, the degree of vacuum at the throat will ·increase. When the head becomes greater than 00 feet (the actual figure depends upon the design. barometric height and the ameuat of air in solution iN the water) the lower part of tae siphon will not flnw full, or altern;:Jtively violent "{:ulsations of flow will begin to take place. It is desirabl~ to avoid this, and therefore for greater operating heads the outlet area should be reduced by a nflzzle, or by tapering ttw lower ~part of the siphon, or in some other manner incre::tsing the resistance to flow. Such convergent siphons are conveniently designated as High Head ~iphons. Medium Held, With somewhat smaller heads a ~iphon of constant cross sectional "rea is suit able. Such siphons are often used where a greater discharge could be obtained with a divergpnt lower I'-g. !'hey have the advantage that priming occurs at a lower level and t hat from the con"tr"ction"l point of view a unifrom cross sectIOn is the cheape; t. Siphuns in which a lower Lmb is of const:mt are'!. may be designted as Medium Head siphnns. Lo·.v Head. fhere remain the siphons witt! divergent lower lim::'s. These are classed as Low Head siphons. The clasaification into high, medium, or low hea d siphon s accord ing a~ the outlet <1rea is is les~, equal. or greater th:tn the area at the throat, does not allow definite ranges of head being assigned to each type. There is a :ertain amount of overhpt>ing. It is <:uggested that the classification acccrding to head sho1l1d be, over 20 feet. 2() to iO feet, npto 10 feet. This is purey arbitrary. However, for heads les"> than ahout 20 fr.et \c"epcndent upon the design) the dis,--;harge may, in general, be ;ncreased by the u;e of a low~~head type of siphon. In all siphons the maximum discharge is primarily limited by the de:iign of the upper bend. Unlp."s the available head is very low, it is usually pns~ib:e to design t~,e rema:nder of the siphon so as to utilize the full capacity of the upper bend. With a llW head" thp,re are tWJ m'l.in reasons why it is difficult t) obtain the full discharge of which the thrr'at design j.; capable. These are ti.6 difficulties of ensuring priming at the df:cirefl watf>r level and the loss of b~ad:n a divergent (,utlet: 4. Priming methods. No two syphons are alik~. It IS usual to elassify them accor ing to thp methods adopted t'l en
305

Fig. 2 Laggan

~iphon ~howing

the nutlets and end siphon

1fi

action.

, . r'

fig 3

La~gan

..' .' I

Siphon sh?wing t4e effec.LoI the Jet disperseri;n . thil ?Utltts . ·

raj

AIr Pump.

The air pump or Pjector is the suitable .ievice by means of wh'ch priming mav be initiated :'It will with the water level below the crest. Provided that th,l mouth of the siphon is situated s·lfficier.tly JOI)l1 to remain immersed, the coiphon can be primed with He water-level many feet beluw the crest, thp criterion being that thE' vaCuum at crtst must n<Jt ex:eed about :t4 feet of wa1er fa complete vacuum is unattainable owing to Lbcration of dis.;olved air at low pressures]. Th" air pump can be applied to any shape "f siphon provided that there is through-out the priming a water seal to the lower Ilmh_ The great disadv;Jntage of this type is that, ~hould anything happen to impair ihe prorer functioning of the air pump or ej Clor, the dam wOllld be fhe air passages bping sm<>U, the po_;sibility 0: choking by rlebns or freezing endango::red_ cannot be rulpd out. An intfresting application of the ejo>ctor principle is to a battery of siphons To avo'd shock ann undue vibration it is usually arranged th<>t th ... siphon units shou!d prirne at different times. This is easily ('nsured b; the t-jector principle In the pal Uion I ttWtt'n a( j acent siphons a small inclined passage is formed above the Clest. After the first siphon is primed, the vacuum above the crest causes air to be drawn from the next siphon untiH this p;i1nes an,1 so on successively throughout the battery. The time lag between successive primi ngs can be incre<>sed IIV renucing the size of air pa~sages ; whj ... h must be small, as otherwise the priming of the tirst siphon will be hindered. This system cannot be recommf'ndpj, as it makes the priming of the whole battery and the safety of the dam dependent on the priming of a single siptlOn. This wethod was used at Mittersheim and also for the Oswego lock on the New York State Barge Canal U.S.A. In the latter case it is controlled and priming depth on crest is d

3 where d is the depth at the throat. (b) Auxiliary (Baby) siphons.

In some siphons a small auxillarv or "baby" siphon is formed just helow the crest This will, of course-; flow ·full by the time the water reaches crest level The sheet of water issuing froll'! the baby siphon is arranged to shoot ohliquely across the lower limb of the siphon so as io seal it and prevent ai r entering from below. The enclosed air is grad ually carrie i a wa~ \. y the surface of the falling water until priming take" place. A good example is the Maramsilli siphon insta.llation Tht'l baby siphon is one foot high and 8 feet wide' at the throat against t! feet by 8 feet in ca;;e of the main siphon. Priming I)f t ... baby siphon occun betm~ thp. water level rises to the crest of the ml.i.n siphon. With the ?etter design of the two types of baby siphon u ,ed, Fig 4 priming of the rna-in siphon followed In 15 seconds .. While the bab" siphon obv-ates th~ ne.;d hr a scaling basin b I',,. the lower limb, it h'ts many disadvantages and it i~ pro'nble that equally good results can b~ att'l;ne'l by one of the methods descrihed later. The NAItAMS!Ll.l effective tvp water-bvel for the considerat ion of storage of water is not the crest of the main siph on, but the CTPst of the auxiliary siphon. So -hat fLOm the point of view of maxim1Jm discharge the auxillary syphon must l:e looked upon as an t ob,truction placed imide the siphon. The minimum size for the auxill ar\- syphon is axerl hy the considerati"n that througliont priming the sealing' jet must function as such. As the flow over .:r__ _ _ __ i the main siphon crest increa<;es, the jet from the baby siphon is increasingly depressed and the combined jet will strike even lower down on the outer cover, The baby siphon must

ar!

Fig. 4

307

re sufficiently large to ensure that the combined jet never falls below the lip of the lo·....er leg. Thill !
8

•

d

is

the

di'pth

at

the

throat.

The

babby

siphon

is expensive and difficult to construct. as it must extend unbroken, the full width of the siphon. Any p'l_rtition would cause a break in the issuing jet of water. It is a source of weakness. Its cowl must, if necessary. be thin at the crest section and yet the outside wil,! be suJ.jec;t to a partial vacuum with possibly cavitation and destructive vibrati0n. Th3r,! is a dang~r of choking of the rel:l,tively sm'lll air passages. ~c 1

Priming weir.

The priming \\eir

fig. 5.

W"S,

introduecd to ensure priming where for some rUSon ·it WllS desirab'e to form the lower limb of a siphon at a flat sl'Jp" Fig 5. Tn this devictl a weir is constructid at crest level from the crp.st hack wards along the side an d acro,s the hack of the si ph(ln so that when overflow C'JllltEences, the falling nappfs complptelv seal the air in the crown of The siphon. AIr 1; th'!:, gradually carried away by the fall'ng water until pr:ming ensuf's. rests on the Bear River Siphons of the MokelumoJ.

Project indicated that the primin~ weir h, itself e0uld not he rdied upon to pronuce priming with the perm::i"ibl~ hed a'J,w ~ the I:rcst of O'3d The outhll of this siphon wa<; theJl modif ed so as to ensure priming illdeppnrlently of t:1~ pr:m'ng- weir. It was then fO'lnri • that by its e'f ~ct of d m')ling the lengtfJ. of \V'ir the prirniag weir (ansed th: siphon to prim'! 'uith a little mHe t7a,1 half the f.se of water-levelnece5sa. r y. Nhen the priming weir wai boarded off. fhe tarbulence ::l.od re,jll~ttOn of di ic!11.fge cau';ed l)y th is d-:!vice probably nentral ZH its arIv,mta{e i . l'or t~le sane fduon t'le pjm ns wei' Cionot be rega,ded as a sati~factory device (d) Heyn's Flexible TJngue P,i nin5 D'llvi3e. An ingf'nious app1ication is the system suggested hy H~ y"Tl in which a flexible steel tongue directs the over, n"", across the siphon until priming i1egins when the we ight of watpr prcsses down the stefl tongue ag"ins~ thl" inner wall so that an unobstructed flow ensues Fig 6. bU,t it is well to avoid moving parts.

(to) Priming Stf'P or Tooth. Fig 6

If the sloping lower limb is not too Stf'fP then, by surldenly turning it dcwn' near the lower end,

rr,mlng may he bro 19ht about without auxiliary oevice. When over'flow commpnces the ,h~et of running W
30R

napT e c1ingine to the lower surf~e. This can be avoided by a definite disconfinui,ty such as a small step "g. (7)

This device is known tn ensure priming with depth diG as used in Germany. The lower limb is often terminated.in a sealing: basin, the cill of which is I vel with the bottom edge of tae siphon cover. Examples of this type have-' already heen mentioned Ihe lower p)r'iofl of the siphon should be steep, but lnmt not in thi .. case be quite vertical, so that any air carl ied down into the sealing pool will bu) ,Ie up cltar of the siphon, Thus the spajing pool acts as a non·return valve for the air and ensures the steady evacuation of t~ siphon. Fig 8 An evil of a submerged ouqet may be noted. Consider the upstream water level to b~ ~t the level of the mouth of the siph!)n ur, if air-vents are provided, the level of the top of the air venti. An} ri,e of the upstream level will now compress the endosed air sJthat the water surface inside the mouth' will rise by a smalL r amount and therefore, priming will be delay~d, A rise in the downstream water-level wilt llkewise compress the air and may even depress J the upstream water-level inside th~ siphon sufficiently to prt'vent priming, In It such cases an air relief valve should he providpd iLl the Grown of the siphon. 1 ig 7. A simple flap vahe is all that is TequifEd.- _' -, '

' .1

Sealing Bas.in .

(J) Vertical or overhanging crest to ensure J}rimiDJ~. Water flowing over a weir the vertical profi~e of which. is an 8.rc of a circI~ will spring cleat- when It reaches a point about GOO from the vertical ~xcept in the case of a ~ery thin adherent napp~. Fig. 9, . In the Verona siphons constructed by Greg()tb, the crest is an ve. the crest of 2 inches to. ~. inches, 1. e. >

_.__~-to ~~', pr~dudng priming in 12 '8

1

'0 2 minutes. ' .Theje .

.

'.

, are h~avy hydr;:uIVc JoSSI'S .in. sllfh a sipho~ an~ the is only 0'40, .. . . Other instances are the Canberra West Lake '. Siphon, which primed with 2 inches over the crest,

.. >coefficient of discharge or_d_ ,

27

leaburg siphons.

to-~ ..

The, last'Gamed were.

above the crest level

'

so~e of the

siphon., at Huntington Lake and the

~f various siif's, b~t

.

.

all primed )"1th head of

!

from .-;-_

;i

The g }od priming (juafitit1~ of SJph,6tiS with ~yerhatJglng crest ate obtaIned at the expense of the disch:trgei which i~ somewhat reduc,ed by the large changes of dir~ction of ~.w .

(g) Comparison

at Ptiming Devicesl

. The air P11~ti is .bY) l:y~s1titable wher,e .tt1af;iu:'ti (!()htrol i_9 desJred. 'Pfiming by ~his ftiMn~ takes place at a steady tate. dependent npO'!l fhe capacity of the .{lit pUitIp (except whE!n a yacmtn1 ;tank is provid~d), So that it is' suitable wp.erEi the rise 01 water level may be very rapid. . , A weU des.i€ned a\1xili~ry siphon can ;nd:~lce 'priming .~ith a l~eB:d jlbo_ve crest level Qf J.'

••

309 c1

S· The priming weir is not very relia ble as a priming I

device, but in conj unction with other priming devices allow!> of priming taking place with a reduced size of water· level. The capacity of the siphon. is. however, reduced ry the increase of resistance due to the presence of ttl' weir. A water seal reduced the discharge. but used in conjunction with a priming device it makes prim· ing more certain. A few inches oVf~rflow usually ,suffices ttl bring ahout priming. If. however. the lip ttrminating the lower limb of the siphon is deeply immersfd in the water seal. priming will be retarded and mly even be prevpnted; Provision mllst be made to pr~:vei1t corr,pression of the air enclosed in the siphon or overflow at the crest may b(- reduced 0r even stopped.

"" I I

~,

Fig. 9

A joggle or step in the 10 IVer limb of a siphon can be arranged to cause priming with a height of the water surface abov~ crest level of d/3. In conjunction with a water seal to the lower limb this m:ty be reduced to diS or less With the lower limb steep, vertical or with ovp-r hanging crest. provided that the design is sound, priming can be relied upon with a head of water above crest·level dl3 and will generally take place \\ith a head of d/4 or less. . ' F )r good self priming qualities there must be sharp curves. large. changes. of direction or projections in the siphon The requirements for a high discharge are easy curves :and small changes of direction, so as to minimize hydraulic losses. A compromise must be struck between these opposites for good design. Priming must fint be ensured with the permitted rise- of water above crest level and then the shape improved as Imuch as is compatible with this c<)ns;.deration. 4. Design of sIphon S ?iIIwaJ tor High Dams. (a) Throat depth.

, The crest of a siphon' may be sharp as in the Verona siphons designed b} _;rogott or it may be wide. In the form~r case, the ?riming depth would be,lessened and tlle crel;t, heing sharp. would not take mnch space, a large outer radius could be adopted, at the l!>ame tIme containing· the whole siphol1 top' inclUding it's inlet within the limited top width of the' darn. But it has been found that a sharp crest reduces efficiency and ,therefore ,discharge. and also causes cavitation and vibration to the structure and is therehre undp.sirable, though welcome for a reduced priming depth. . ,: Experience has shown that .in a siphon design,. the minimum permissible -vacuum should not exceerl 24 ft of. water, because wIth lower .pre,ssures too .much air in sohltion is released from the water passing through, which ca1J~es vibration, cavitation and parting of the water from thfl crest. If we tuu, limit the vacuum to 24 feet, 3:nd this at the crest of the siphon, evidently if v is the

~t the stream lines'at the crest, then; v~==v'2gX'l4='8X2v6=36 It per second . '. No~ the flow atthe throat ~f a siphon. as proved by professor Gibson .. Davies and

" velocity

others ;in the papers contributed by Ylem ,to ,the, Institute of Engineers, London, approximates to a free vortex flow, which has the iwell-known property, viz, v x r.or the product of velocitv and the radiu!l at any point in the stream equals a constant. Fig. IV , Therefore at any section. where the. radius,,::;::[ and \Telcicoty=v; vxr=voxro (at crest)=39Xro

:.v=39~ r :. the discharge through the sli:t of height dr.. and width· t foot==dq "

=V

rOJ

Xd A;";'~rox r

dr Xl'

,

~

\

"

310

Q= Total discharge through the throat R=

i

I

R

Lro

-~~~Odr.=39 r

ro log

B_

ero

.', the discharge q per foot width of siphon throat is=39 To logp.}{__ '. r. Efficieney '1= -- ._Q_~ =~Q_­ A V 2ga 47A A =( R -To)x·1 per f 00 t

WI'dth""

•

R _39 Tolog;r 0 '1-~------

47 (R-ro) Discharge per foot width of siphon tube q=nx47(R-roJ

Negative pressure at the crest==24 feet; Velocity at the

crO~Il~39!? :) ;·'·/C •.. , II'> "

;-~fT'~<1!:~.<

1

(39[<:.J

R Pressure at the clown={R-ro)-~igft,

(b)

Width of siphon.

The throat section must be rectangular in oropr to get a maximum area if! a given height. The width of each unit is determined chiefly from strnctural considerations. Then~ is llsllally a high vacuum pressure acting on the outer cover. However, if the cowl is curvcd,a fairly wide siphon is permis:,ible without making this unduly high. Thp. effect of vibration must be borne in mind. During priming there is a likelihood of violent vibration of the water column and jf the sbhon cover is thin :md too wide, it may vibrate in sympathy. No rule can t e laid down, but width of about 2d gives good proportions. If the width is 'much less, the hydraulic mean radius is !'lensibly reduced and friction lossps ~nd th,' cost of construction are increa~ed. The discharge p~r foot width is worked out and now the discharge of each siph(JU is got by multiplying it with the throat width The number of siphon tubes can thus be worked out by dividing total discharge cap~city by the capacity of each siphon. tc)

Level of the outlet.

High head siphons are ohviously indic"lted Whffi the drop exceeds 34 feet over the flam, Water should be shot clear of the toe of the dam in the fvrm of jets. Since the discharge is limited by the vacuum at the crest :lnd since the lower the orifIce the greater t hp, jet 'velocity, the orifice must be reduced in ;lrea all the mm p • A low orifice with its greater Vf~locity and its proximity to the toe of the dam can shoot a jet further downstream, so that the jJo-,sihility of its affecting the dam is reduced, A low orifice ha~ many disadvantages, h"wever, Th.e extra length of siphons me'! ns extra c( st. Th ~ gre'lt"r construction of the passa{!e inrreasps the posi bility of obstruction. The down;tream toe is weakened in the region of greatest c)mpre~sive stress. fhe hig h velocity about 700 feet per second with 120 feet head might damage the surface of the C'Dcrete. In this connection it should be pointed 011t that there is no fwidence of deterioration of smooth, dpn<e concrete ullc~er velocities as high as 60 feet p(r second, if there are no irregularities to U?:;~t tlte Sm nthness of flaw and if the water is fr,~e from grit. Let it be limited to 50 feet per second in the case of con :rete and assu:ning co-efficient discharge.= 8; v=8V~gH'" H=60 feet. The level vf the outlet c011ld be 00 feet lower than crest. In ord .. r that the jet should strike the ri ver bed at a maximllllJ. distance frum the dan, the jet must be inclined upwards. Let 8= inclination of nozzle: x=height above river bed; l=horizontal travel of jet; v=initial jet velocity.

,----

Neglecting air friction, which will not be important fot' a large jet. i~ is easily shown that for 1 to be a maximum: Cosec then

e=V'~!~- + 2 and v

l=-~cos e~ ,in e+y'/~n2B+2~~---\ g

~

l

J

The area of the orifice at the outld ; Ao= Q-Sq. ft. . 50 \ (d) Verlicallimb . d) Th~ cross section aru at throat is /I. sq. ft. and that of the outlet is Au sq ft. It is desIrable to r~duce A to Ao a; quic::kly as possibl ~ from cl)nsiderations of the strength to give the maVJmum thickness between tht siphon units. If pressure is kept constant, the ratc of inc-ease of Kinetic energy will equal the rate

of loss of potentiai

~nergy ; d(--~~

)""'--dh

Integrating within limits hl and h't.; hl-h't.=9

2

2g

(

~0

_

,:~ ~

.n.

This gives the length of the transition for the cho.nge of the sectional area. (iiI Shape of vertical limb.

.

From the hydraulic poin.t of view 3 circular . shape of the vertical limb's as having the least wetted perimeter. From the point of view of stress in the dam the concrete between the :;iphons should be as thick as possible, and free from sharp corners. This would suggest an ow.! section or a rectangular section with rounded corners. But the extra expense is not justified 3nd a circular section is usually adopted. (iii) Bend on the vertical limll. 0' As in ve:itigated by Professor GIbson aJ1.rl Davies. there would be sone loss of he'l.d a~ the. lower bend and it has been found that, in a pip(', the minimum loss of head occurs when thl} ratIO of twice the carlius of the bend to that of the pipe is=5." lIi~al

(e) Inlet Cowl. We shall now consider the design of the inlet. In the early siph'lns, the lip of the inlet was kept at the same level as the crest of the ~iphon, so that, as soon as the wate~ level w"nt down. t) the Cf<:lst, sip honlc acti m ceased, air rushmg in as soon as the lip was uncovered. But this arrangement has the obviously great disa,:ivant;:.ge that the surging of tile water Cue to waves would prime and deprime the siphon, caming intermittent wnrkillg. Also, even when the siph n primed. the shallow screen of water ""ver the lip would t~nd towards the formation of a vorteX. sometimes e"en a hollow vortex, resulting in , air being SlIcked into the siphon and prevent-ing its priming even when the water level was far above the lip levd. Thi" wa". therl'fortl, remedied by carryir!g the siphon lip weli lJ~low the crest level and by providing air-vents at a suitable height to deprime the siphon. N( w the usual practice is to give an area for the widest cross section of the inlet, twice that provided for the throat of the s.phon.

[fJ Air ven ts. As already stated above when the l:p of a s;phon is catded 50 deep below the c~est ot ,jthe siphon, ior purposes of depriming, an air-volt of ;:. ;lui table size mnst be provided in th~ hood with its top at a level where it is de~:llfed to stop the siphonic action. The air-v,nt is lIst}BLy rectangular with its wicHl equall to the \\idth (,f the siphon and its height not very large) b,C>I,use the gradual uncovering of the vent by the gradual fall of the flood level would result in partial operation of the siphon over a long period, causing noise and vibration, With a high vent thpre is

" . .- \ . 312 . ','; _. . -..' ,.' a.lso te_ndency of vortex fortn:J.tion with the ri.;ing water levp.I a.nd this would either prevent or delay ~he pnming. Information available regarding the size of an air-vent ll'ee3SHY to deprime a siphon · IS .very mellgre. We h.ave got some experiments conducted by Inglis at Poona hut better than ,thIS we have t.he exp~nen:e of the siphons actually working in different part; of the world. The are~ of the aIr vmt IS generally expressed in terms of the throat-area. Stickney, the grandf~ther of SIphons and w.ho lOI.g back designed and ~onstructed siphons in different pans of the world, says that th~ raho should be 1(24. The ratio in case of the M~rmasi1li siphons has deen kept at l/t'6 by Davies. In the Lake Fife siphon, however, it is a, small as IllS and this has been found to reduce the flow: The larg~st ratio is in the C'lse of the Wood Creek siphon and this is 1/~·3. The HetchHetchy.slphons have a Jatio of I/IO,the Dunalascair larg siphons. have a ratio o,f 1/16 and the Laggari .slI?hons recently constructed in England have a ratio 0 f 1/ 11.5.Except in the cas~ of tu:o .the rabo In case of mOst d the siphons of the world ranges from maximum of 1/4'3. to a tIl1mmum of 1/28. The gener"l practice is, ho\\ ever to err on the safer side. Scalemodel expenments may also be co~duc~ed but the results though cannot he correctly representative in this respect, on account of VISC0Srty surface temi m etc. We normally migut keep the ratio at about 1/1 'l. the ,throat area. 'The shape of the lip is also important. If it has a sharp edge, then, under a strong . draught of. aIr, a~ th~ ri,in,! w,lter rea::h ~i th"! lip. the draught will depre,s th} water surface b~low the ltp and It would r,nuire several in:;hes of ri3! of wlt~r leV'el a~.)ove the lip bflfore the alr-venH.. llc~ually sealeil and thus priming would b€' delayed, though, of course,for ,the very · ~easons explaIned above,ddpriming would be fairlv quick If, on the other hand, th€' ltp surface IS broarl. and rounded, then. '1.<; soon a, the rising water reaches the lip; air will be cut off, as' there Will be no water depre,sion n'lwand the priming will be satisfactory. But as the wate~I.. vel falls below. the lip th:! air rushing under will be. at sub-atmospher~c pressure llnr~ thIS. would su~k up the water, which w,muld throttle the ~ur flow and ~h~ slp~on Will not stop working until the water lweI fa.lh some distanc~ below t~e lip. The depnmmg 15 thus delayed and the water in the r~servoir would bo. wasted. Thus, WIth. no draught of air, a sharp-erlged air lip is ideal; but where the rise of water level is to be stri(;tly I ' . limiteel a broad lip is better and safei:'; but ·J.I1~ P.t.LHSl. we m~st.. on the other hand. be prepared fl.r..p to lose some storage,: due to the delayed depriming. The actual slope to be useel, therefore, depends upon the co?ditio.n of l~e reservoir working.·A compromIse IS alNaYs desirable. To pnwent the interference in priming and depriming, due t~ the sur,ge of waves it would be convelllent to pro"lde . an exterio'r air lip as shown in Fig.It. though tbis would involve an extra cost.

"

Fig. 11

[g]

Jet Dispersers.

The rock in the' hed of the river downstream of the dam may not be ha ~(l awl m::ty intersected with a numter of cleavage planes The iets of water. ~ith a. initial.-ye,locity of about 50 feet per spcond are likely to, ¢i~inte~rate or re~we the~ !~C~ tn th~ bed '. by theIr 1Illpact fhe present day designerg, who have t') deal WIth such hIgh vclO",1tle, and s~ea large ma:~'ses of water; use, what are called, "Jet Dispersers." These have been used for th~:sluIr.es in the M~ttur dam al1d also, in the new L10yd darn Su:h ~i9persers h:we been us~d' also 10 the ~agg~n s1phons, recently con~tructed in England. These (itspet;;ers ~ave been patent.ed by Mes?rs, (jlentield and K~nnedv and they "con,ist essentially of a set of rarhal v
,., "P-\,

be

313

Hence, it would be better to design for a slightly larger .outlet vent than usually necessat y ;by about half :I. foot ciameter. 6. Graphical method of design. "According to usual hyrlrndynamic theory for two dimensional flow of an irrotational fluid, such flow c:m be expressed by the equation: ' ¢ +i :J_, = f (x+iyl ; when rP is the fluxe ; =1, 2. 3 .......... and 1>=1.2.3, are drawn. the Q) plane will be divided into a netNork of eg1lal sqaarps This represents a s:ra;ght, uniform. pu;tllel flow from left to right. Now suppose w=¢-f i 1.=1" (t)=F (l+i /J, where F is any function. The l ann 11 lines in the t plane corresponding to the 4> an(L,,:J_, lin~s in· the w plan~ wlll,inter,;, ct orJhog.)nally to form squares,but in general, the sides will be curwd and the squares unpqual III size. To every p'lint in the w plane there is a corresponding P(jlflt in tte t n1ant and 'I lines repre' en t a possible distribut on. of str~amlin"s. By successive in termf'diate , transformatiolis "f this nature the relationshi p cI> +i:J_, = f(x + iYI is finally reached and it is sometimes pos;ible to oiJtain a distrirution of stream lines and velocity-potential lint'S which will fit the boundary s rfaces of the How under comideration, Sch \1\ aTZ anrl lhristof1Po[ have • shown how such transform'ltiol1s may be mathematically performNi. b"t a solution is only po~sible in a few <:imple caseS Nhere the solid boundariPos are stnght lines or circnlar arc,. . ' " Hy virtue of thp properties ot the 4> aud ~O: lrnes of intelsecrin~ orthogonally and of dividing rp.gion of flow into cnrvilinear squ'l.re~. jf it is always po'slole to 0 "tain a graphIc" 1 solution provided that the boundary conditions are known. Consider the case ~f a siphon the cross-section of which is throughout rectangular and of cons.tant breadth so that the flow is in two dimensions onlY. Tn orrler that the flow into the mouth of the siphon be two-dimensivnal also. it' will he considered to be a unit in a battery of siphoIls all in ; operation at the same time. The inner boundary forms the "(;.i,stream line ';'=0 and the outer boundary . the stream line 'i =n, "here n is an arbitrary number of stream tutes, The :;; difficulty lies in finding two known lines of constant velccity, J:1( potential, or what amounts to the same thing. the directIOn o~ oi the stream lines over the remaining two bounnaries. Tf the reservoir is deep as compaTed ",ith the diameter of the siphon. then at a distance of several diameters the IjJ lines will be radial to the mouth of the siphon and the 1> lines will be concentric circles, as BB. [t is necessary to fix the remaining boundary before attempting to trace the stream lines. If the siphon includf's a lon£;. straight. parallel leg Fig.12 there is little error in as,uming that the tiow is para.llel to the leg at the centre of its leIlgth i. e, that the 9. lines at the centre are normal to the sides. as AA. Fig. 12. Now divide the area ABBA into stream tubes of equal flow. Four is a convenient number. These are sketched in by guesswork. At AA the lines will be equally spaced. At the cre:.t section, where the flow will approximate to a free vortex, the line, will 1e more closely spaced at the crest then at the crown, Finally at RB the spacing will again he approximately uniform. Sketch in 1he 1> lines so as to intersect the 9 lines at right angles. It save!'; time if these are spaced at interva1s along the strea. m tllbe. whic!l is near~st to tile centre of tne siphon. equal to thE: th:ckness of the tune. ft wlll prolnoly be f )lind that mnst of the elernental area~ are by no mean' square', the mear} distance between the 4> sides being unequal to the mean distlnr~e befween the 'y side~.: rhe lines should now' be adju<>ted so as to make the elements between adjacet t ¢ line" a, nearly square as pos~iole. 1'h"n new 9 lines call be "ketched in crossing these ¢ lines orthogonally. and the process should be continued until the accuracy desired has be0n attained. It ic; a 1vi,able tt") sketch in the whole flow netw.)rk in the firs': place. however approxiwately, as the terminal conditions affect every y and ¢ lioe. The flow in the upper

may

I"

314

bend never quite attains a simple, free vortex: flow, but unless the angle of the bend is small, the approx:im'ltion is very close at the centre of the bend and the cen tral rp line may with little error he assumed to be a straight radiallme. 7. Etlect 01 siphons on the dams. 1 be flowing water ext-rts a centrifugal force at all bends, a longitudinal force where. ever an acceleration of the strt'am takes place, and in addition tangential frictiun forces. The effect of these ann the lightening of the dam by the replacemf'nt of masonry or concrete by air !lr water throughout the !:iph'ln shollid be calculatf d whm considering the stability of the dam, The stabilitv of e:lch sectIOn of the darn between contraction joints should be considered inrlependently. The general effect of th"se forces is to incTfoase the overturning moment on the dom • The centrifug .. l force at a bend of angle 0 is in a nirection bisecting the angle of the bend and ha<; a magnitune of 2 "-'--Qv

,

.. '

g

sin~where 2

v is the mean

velocity. The accelerating force

wg

excrte
ov, but only one half of this is exerted

by the siphf.n walls. The longitudinal friction is given ':>y wAh! , whf're hf is the head lost in in the part under consideration In Clmsirlering the stre~s in the siphon cowl the centrifugal force cannot be used, but rather the actual distrihution of pressure on the underside of the cowl. Where the siphon is carried throu~h the dam, the possibility of the maximum shear or compressive strf'sses heing increa;ed must be remembered. Where the water from siphons flow down the face of a dam. there will be an increased pressure on the rlownward curved toe. Where the impact is below the dam, the nature of the rock must be considered. Not lfast important is the possibility of vibration ann its dfect on the dam, Thin reinforced concrete stTUctures are particularly susr.entible. Vibration only rfsults wheu a ~iphon is not flowing full ann free from air. so that its elimination lies in depigning to avoid sharp radii with consequenent vacua and vflrtic~s and in arranging for priming and beaking to bl! compli>ted in a short time. The an anging of the siphon units to prime ;l t different levels and the me of mech:lDit:ally-opcrated valves are of partkular advantage in tnis respect. A typical pre~sure diagram got in experiments by R. M Freeman is showr. in Fig. 13. ~riction

4

Fig 13.

~ "

P",SSllll'

S15

8. Ice trouble in siphons. One of the grp.'l.test fellrs ill connection with siphon; has bep.n the dan~er of freezing. Ttere should be no horizontal projection und!'r which an ice sheet might catch. A spell of hard fro<:t is always accompanied hy reducp. run-off. which. in thp. case of a hydro-flJectr c scheme. means a fall in wat"'r level Before a l'se of water level can take plac:e a t~aw must ha~e set in, and long before there is any apprec'able overflow. any ice will have dlsapp~ared .. fhe pipes supplying the still-water VI ells would likewise thaw out befJre any apprecIable nse taken placo. :, It is highly imorobable that the interior of the dam win ever reach a t lmperatnre ~pproachi~g freezihg. but the horizontal limbs of the siphon, are drained as a. pre~aution again,t Ice fcrmatlon.

9. Hydratomats. The Hydratomat in its many form; converts the pncrgy from low falls of wllter in canal systems and rivers to air power eithe" compr.essed air or vacunm and such air pown is transmitted . to lifting units some distance apart. principally for the purpose of raising water. . From a cursory study of the followi11g, it will bp. appreciatp.d that the system from beg-inning to end is free from any working parts and thtrdore. superinrlende lce, othe·i. ~~an that required to start and stop. is eIim nated. \{oreovpr it Cin be 5afdy aBullt"ci that th~ mltlal cost. construction being mainly simple reinforcfd r.onr.ret p • is low. . In the inste!!atiou of the Upper Chenab Canal Punj abo the system may be considered In two parts, where it bllS been uSl'!d to lift a seepage drain into the canal. . (a) Rarefier or vacuum power unit which is situated at the fall (b) Lifting or pumping unit which in this case is raising water from a drain about 1 500 feet away. The Rarefier as illustratpd in Fig- 14 comprises a ;iphon which is raised to a hf.i~ht slightly aho"e the VdCuum required at the lifter, In this instance the siphon Rarefier;s built ifltO existing maisonry pi.!r:> an 1 is ~ f-!ec 6 inches wide, while the entp.ranc6 water.vay is 6 feet deep. In the cen.tral or p'lrtitio:l wl!l "B" are fixei thl'p.e P(illin~ Ports "F'" whic1.. whe'l starting up, are u'> ~d to pri m ~ the sipho:1. When SWuUE~ open by lever~ from the out-;id~, t h?s~ ports E!ive a free pas<:age of water from up~trealll to downstrea n, Taking the lowest port, which IS alwa\s submerged, water pa,;ses from the upstream leg and on Spli"hin~ on t!le down .. trea'n. traps much air frorn the in'>icie of the sipao:1 fhe air pa'>sc!s out of the siphon a 1.rl i5 freed to atmosphere. This has the e'1ect of creating a putlal va~nUll inside the ,iphon and the water level rises until the next highH port comes into action and so on until the siphon commenr(,s running when all priming gates are closed. For quite a large siphon of this description :tnd to. a vecuun:of 16 fept '-\ith a fall of aeout 5 feet, the priming is accomphshed 1Il a penod of :to mmuh~~. Flow can take place like an ordinary siphon npwards in pa~sage "A" over the putition wan "B" and thence dowawards in passag~ "C" an" so to downstr.. alll. Aspiratin€ Fins "D" which aTe perf )rated, are arrmged in the throat of the siphon at intervals ac:ross tile width. The~e fins communieatf' with an air d ICt "E" huilt into the top of the partition wall or crl!st < B" which"com'lluilic:ttes with the air main outside, connecting- the Lifting unit. Now the water in pa<:s'ng these perforated fins draw:> in air from the air main which enters the water in the f'lrm of small air bu lbles. This emulsion of air ancts the Rarefier to tht lifter an.t thus the Rarefier is continuously extracting air from the Lifter and maintaining a partial vacuum.

316

H

'!nUli ?'J' "':,JfiJi~,

v: 1e:;',:1

,lfHi ).11;(1'; , f'll f

"",p;;;"it

to ,~j;l,;.te 5;

y'1C

mOll ft:dl 1701;> :

Fip'.14

'.:J

1: ".

:rr:

.4

317

HY~ratomat Lifter.

,. t'A(.(VM

AIR

MAIN

To ~AR£-F'F.R

OUTLEr

Fig. 15

W. L.

318

Referring now to Fi~. 15 it is observed that units consists of a concrete chamber having an inlet at the lower level "A" communicating with three lift pipes "B" and an outlet from chamber "D" to the higher level "C" lnsin .. each lift pipes "B" is pla"ed an air inlet "E" communicating with atmosphere by air pip·s "r''' rising through the roof of the Lifter. Assuming that the air is shut off from the air inlets and the main air valve on thp. vacuum main is opened, the water level inside chamder "D" will rise up aDd similarly inside thp. lift pipes ";3" The air pipes "F" are now opened to atmosphere with the result that air enters the water through the air inlets t'E" which are placed Slightly a JOVe the lower wa.ter

'..

~.'t- ,_, ,.,•..1 _L . 1-, -I. _,...,Io!--,.,-'-r

rI1 m~' M: I : I~·t

~.

.

\

-,-i: ~~-~-~ ~~J_-1't" I I"

~ " .1;: , .. ,

I

b~.-II,

II<

... , 01.:"1,

t

\

4-~

! I I c .•. HA~

....

~

I I

,1

I. I1 I

I

II

II

l'

I

,I.

,

'2

'.L_.-.J 1 '1-4..- ,.lII 1. 4·., I"ol.t! 10,.,"1 I' I I, I I I I I

AT THROAT

or

THt:

SATTIRY OF ""ROH

,,,..,r.:".L61'AT',,,,..'" '" ''': A..... 0. •. .,"",. U.&L. : .".

~.Ht

AT

.1._-.

$I:crloNAI.

.'.VATI." .•.".

1,""011

Fig, )6

$/(~rc" $I(OWiNS

1''11&

5n'HDN IN REI..ATrON rill /

TkE H61GHT OF D ... ,."

leve Y. Aerated columns are thus formed inc:ide pipes "B" which having a loWer specific gravity tun the Mlid water column inside chamber "D," rise and overflow into the cbambe·r "D" and 50 tf1 the higher level "C",

319 The air, which was contained in the water, is liberated in chamber "D"and is continuously fextractf'd by the Ralefier. Flow in the lifter is continuous and wide variations in head and quantity can be given. [n this instance. pumping is flom drains and the Lift is variable, in fact, the plant i!: arranged for pumping from O' to 10 feet and in order that reason ably efficient conditions will prevail over most of the range the air inlets can be raised or lowl'red to follow the lower water level although it is not necessa.ry to attend strictly to this adjust m en1. The type of Hydratomat may be used in irrigation for pumping water into higher level distributaries, pumping water from drains etc., and in works connected with watl'r supply. On the other hand ther~.are sy.. tems which compress air in similarly simple mamer and the air pow!'r is c ln~yed t) batteri. s of tube wells whele pumping is car1'ied out by aiT lift pumps. Hydratomat Limited, of Victoria Staticn House, London. S.W.!., are responsible for these developmtnts. 10. 11.

Efficiency of Hydratomats. The efficiency of Hyrlratom ats is rather extremely poor usually from]5 to 20 E)"ample II (Laggan Dam Sip.l0D\Uy A H. Naylflr).

%.

(a. Data. Flood dischal ge 380:) cusecs with priming head 1.0 ft. Dam section given in Fig. 17; Height 120' Base=51.0· rop width = 15 ft.

(b) Throat Depth.

In an actual mndel test it was found that the priming depth rquired was dJ4 to dIS Keeping it d/3, the throat depth will be 3'0 ft. Fig. 16. (c) Radius of crest.

This depends on the space a'lailable. Keep it 6 feet for the crest and 9 feet for the crOwn. (Fig. 16). (d) Discharg" velo :ity at the cre~t for permissible 24 ft. negative pressure=v'2g~ 24=39 it per sec. R _ Q _ ~~~r 0 log r0 _ 0 _ _ Efficiency '1 - 47I- 47(l<-ro) -6810 where ro -6 and R-9 Discharge per ft. width=.68 X 47x (9-6) X 1=96 cusecs; Velocity at the crown=39x~/8=26 ft. per second. . Pressure at the

crown=-3-v~ =_~_~62

= - 13 feet head of water 2g 2g (e) WU.th and number of units. The width of ~iphon tubes at crest is usually 2d. Tn this case it is kept 6 ft. to incheS Discharge of each unit-6'S3 X 96=650 cusecs. To give 3600 cusecs 6 units are required. (f)

[i]

Outlet. Level of outlet.

Permissible velocity in concrete=50 ft per sec. ; ... Head =r: ( ~ 50 _=~y-oo feet, '~Y2g

The outlet shoul'i be at 60 ft. below crest level. [iiJ Inclination of the outlat,. r-~"'

cosec ()=y .lg~ +2 where x=height above r""er bed ... 64 it. say. v

320 8=3160 say 30 0

v=50 ft· per second;

r

r~

"'---'-,

l=~!.cosO~ sinO+v sinzOX 2gx ~ = 128 ft. 2 g .

[iii]

L

v

J

.

Area of oulet.

Q =so-=I3 ~ Area=,; sq. ft.; Keep it 4'-6" dfa (16 sq. ft. area) on account of Be ,nd immediately behind. (g) Vertical limb of the outlet and for fixing jet dispersers. (i) Transition.

The area at crest=20 sft.. Area. of the outlet = 16 sft. Length oftransition=h1-h 2= Q2( 1 _~)= 650.2 ( ! _ 1 2 )=S 2g ,<\"a A2 644 162 20 1:.1;, It is kept 10 feet in original design. '() 1

H.

(it) Inlet cowL

The area of m luth equals twice the area of the throat. The velocity ot entry 650 = 16 ft. per second This is rather high and has caused vortex in the actual. = __ 4u

The area

and eotry mOLY be increas ..c from 2' 5 to 3 times the area of throat.. (ij Loss .. of head. The most impjrtant los"e;; of head are due to bends. There is no satisfactory information on the subject and it is hrgelv for thi" reas 'n tha.t scale mfJdel flxperiments are Sf) advisable. The loss is not a property of the bend itself but of the whole assemblage of bends and str::t.ight pipes. Tilers is a certain amoult 01 loss due to the redistrhution of velocity on entering a bend until an approximation to free vortex flow is pstablished, Then there will be eddy losses on the inside of the bend, additional to ordinary friction loss, especially when the bend is of a small radius' and finally there will he loss due to the readj ustment of velocities in the straight piDe succeeding the bead. It would not be pxpecteri. therefore thl- the los;; would be simply proportil)o-l.l t·J the angle of the b~nd. Bonchayar and Vlallet found the relationship between lo~:s alid angle of bend to b. very irregular, the less being less for a 6\.)0 than that for a 30~ bend. t

•

After a careful considerat'lon of avatla')le information the following values have. been ch0seIi : Upper bend angle about 135°,

2R

~d-

=5, 2R

v2

v2

loss=0'35~;

4g

=0'30· 2g "...• Outlet bend , angle 30 0, d..... =6, 1088=0'15

.

2~

Lower bend, angle 90 c' - ·:-=5, loss U

v2 g

.< . •

The distribution of velocity across a pipe is not uni.form even ;n the case of a straiaht pipe. Therefore. the kinetic energy of the is.ming jet wJl be greater than the kinetic ene~gy corresp:mding to th" m~an vdoci~y. O.ving t) the rligh value of c. the kinetic energy is taken as 1'05

VZ 9

~g

instead of 1'12

v2 ~g

as recommended by Professor F.C Lea for normal velocities.

It is now possible to proceed to the calculations, we have; Total Head H=Los:s at entrance, he +-]053 at bel ds, hh+frictiol1 loss, hrrR. E. of jet. ho

321

raj H=t6'

[h} H';"66'

VI

v' =O'02~

=0'02-'2g

'"

Lower Bend ,0'30 \,5_, L;l)oz~ "

2g

=0'30 X I 62 v' __2

va'-

-0"35

IT >!\lmq) ! ' ~ fP,011· ~l_-' ~, n(i. ~JrlT ,8(,~

2"

2g

2&'

..

.1

_

2g 0

30 Bend 0 15

va

L,

2g

-0',15 "

h f (Q being 125) Mouth 0 to 1 : 1= 12 v'=O'1 JV 2 2 m=I'94

I

X

1'62

v

t _2,_

2g "

)~!J{) J S-X j 0016'.

\,1'

-0'24 .!~2_ 2~ ,1 !'~<)~ 1€Q, _.,9, i'l':':' }JTt~- - An-

,/; iiil=

p.

'

\

'.

(,.'

'

V l

_l_ ,. '.-.n,o", -:Jg

[b] tr.87

•

-ftl_!!_

'l~q

I'viI1

2g

~:;)=1~5~!-1~1~ X64~" ~~s";':'{:

'·_.~i

hv- 1 05~82 = l'05x 2 63vas ~g

,a

ib2 76~

28 . '3<

.

2,

'=~'39 'v 2'

2'" 0

" >.i ',tiy'l

."

i

5

~

3

I

"'::2"'6 'vi 2g

"

raj Total H=S6 ... 4'26

V2

2

[bJ tola llt=66=4'31 V~2 2g whHe H is t11easured from 'the upstt~aIl1 water level at priming to the centre of the Doade Hence " " , ,; ,,,E. :, ' [a] vi=29·L.·~ Qlld:a 2v.=203x291_59t cusecsJ' ,J :: ,/,' e,,!j ,:

•

[bJ vll ==3j'3 :, Q=a.vi=20·3x31'a"",640 €usees

2,

.,'

322 .IE' ,. r] 590 62~ [ 640 The ewClenCles are La 20'3x47 = % t)J 20'JX47 67

%

These compare with a permissible efficiency for this design of upper bend of 68 % [i] Effect of the ciphon nn the dam. The effect is shown in Fig 17, 12 Exampel H, MaIikanve Dam, Inlia. (Prof. K,D Josli Mysore) Design a spillway siphon batttry from a flood discharge of 2n,,000 cusecs for the Ifarikanve Dam of the section given Fig, lB. fhe priming head not to exceed 15 ft. (a) Throat Depth. d=-3X 1-5=4'5; Top width is only 16 ft.; The radius of crest=4'S ft. Radius of the Crown=90 ft,

The crest shall be a full semi-circle. (b) Discharge.

For 24 ft, negative pressure, the velo~ty at crest= 39 ft. Sec, 39r loge

Q

r-R

~

'-

{?J: t

";II·

\ \ ~~vJ ti-t==i '°0=.,,,

PJIO:#.fficieD.cy -'ilA"" 47({-rf =.aB?~ w]Jere r=I-S Ji.; R-9'/)lt. (

~

..e r"':;m

Di~charge =·58 X 47 X 4' 5 X 1

Velocity X

4~ = 9

at

the

= 12~ cusecs, = v = 39

crown

195ft· per second. . pressure

v· 19-52 at the crown--4 5--=-4'5-tg 2g =-105'

(c) Width and number of units,

1 1

WC"HTJ

0". COIYCJI£TE

-W6/tiNT " ,

WA.-ell .,,~

.2

Ij

f

..

Let width=2d=!!x4'S=9 ft.; Discharge for uni t=9x 123=107 cs. Number of units f Ir flood discharge of 20.UOO cusecs is 19_ (d) Outlet.

(i) Outlet cowl.o."r _', The c)-efficient of discharge as given by eftlciency=-58; permissible velocity in concrete st'ction =50 ft. per second, Velocity with 100 ft. head, ='58 X v' :tg X 100 =46-4 it. per

say 50 ft/sec. Fig 17 (iii Angle of exit,

Cos 8

== .y / ~~~+2 v2

'n,

~,

; x=32 height ot outld above bed

-8=37° ; v=50 ft. per second. 'iii) Horizontal distance from Olitlet, where jet sheet meets the bed

f= v· cos 0 {sin () g L

+

./sinZ8+ v

-~~~ 1; V=50 and ,,==32:.1=132 fl., ylJ

lie cond

or

323 [iv] Area of the outlet A.=

(~)Vertlcal leg.

-~

=

1

~f =2,hq.

ft.

I

V·ngth ot trllnsition for :rea change from 40.55ft. at etast to 225ft' in outlet.

b~_hl=g2( __!_:.... 1 )_~I07J Lg Az

AI

64 4

_!_ '- -~)=28ft.

(

40

222

5'~

T----

The dia.meter of the outlet: -D=v~ x2=S'3 7\

Fig. t8

:L

tf] Inlct cowl The an'a at entry =twice Velocity

entry

of

v2

over the top = --

2g

th~

area at the crown=2 x9x 4'5=81 sft.

. = 1100 ---= 125 tH

f t. pet second.

ne head req 11ired for this

velo"ity

12'2 =.----=2 5 ft. nearly :.!g

[g] :\Ir vent. ;

I 12

1 · " 12

Afea of air vent=-·of area at throat=<- X9X4 5=3484 ft 3'4

• I

31; ,

height of vent =-> ='4 ft. say=5 inches 9 Note: The crest nep,d not be a e )a1plete semicirde but only upto 60& are on the tcservoit side. This will give )'6 ft. atiditional thickness behind the tube instead of 1'5 ft. only. The entry area at the entry should be increased to 2'5 times to avoid vortex tonnation.. 13. Example III. Plain Siphon~. Fig. 19. represents a sipholl in nature. the velocity of the wator in the siphon in

. meters per seeond IS

'1=

2gH V /- - --r (l+t)+>.. -(t-

in which H is the difference in wlter levels in mebrs, ,( ( is equal to 0'4 fnr a plain sharp-edged circular orifice and is equal to 0 1 ,for a, well-rounded mouth-pif ce," A is a frictifln factor, dependent on the nature of the matenal, L IS til. length of the siphon in meters. d its diameter in IT;eters,

Also ps, (Ule pressure at the summit) is

Fig, 19 _!'-,5!._ .5 Ze for the siphoR to operate

or

~,I

- :E w) in wI ich ho= 10'3 g . meters, the pressure head due to the atmosphere; HI is the height of the summit of the siphon above the upper water sm face. measured in rr eters; v. is the velocity of the water at the summit; and :Eill is the total losl in pressure head up to the summit due to the rf'si"tance of the pipe. Ps must be equal to or ~reater than e, the pressure of the wattr vapour if the siphon i. to onerate. This is, PS,5e for the siphon ,to opeTate

Ps=,,{hCl-H,-

" "

Values of e alid for Ze for water are to be found in the followinr tabJe.

PreSitare Tempera1 ure T"ble for water Vapour. TABLE I

,/

Temperature in degrees Celsiu9 (T) e in atmosphere9 Ze in met".

00

20n 0'023 0'24

O'OO~

1'.",P'06 ~ _ , -~.

.. ps'~

400 0'072 0'74

.

600 0196 2'02

80' 0'462 4'81

1000 1000 1'0:1

Thus, if water at 400 is used,.y must be equal to or greater than O'!."'-,neters if the siphon is to operate.

1=--2i H;:---'

In the monel,

Vm=

1(l+O+Am~ll1

V

dill

Where Hm= H -; Lm= t__ ; Om=.-d n n D

,(

~

.x. ~-w.jff

C as. before, lies between ()'4 and (J 1 and $houtd the sarrie as in nat tire. probably not be the same as X since the 1rictional tesistalu:fi to fio" for the modf}l .lid for nature will not necessarily be' ihe ~ame, x (1

5 ) III

for the model

• IS"

~ . 2g- _ ( ~(»)nt

11 ) m - . (vs)1m (ps) m = y (hO'-nl

(Ps) m mnst be eqnal to or greater

t.han-~' if the modei siphon' is tcY opftatf/( n

,

~.

tps.)m:> -» for the model t()' operde'" ..

,..

325 or (pg)m i'

f

5~for the model to operate. n

, Example. If the temperature of the water in nature is 41)1) and n i; 10, will the . For water at 40°, Z·=O 74 meters (see table I).

Hence. (Z .. ) m =

mo~cl op~ra' ...

()'7~ = 0'074 meter~ which would indicate a temperat.ure lO

fOT

the wafe'

less than 5°~ (see table) which is i\l1practicable. Example. Assume the fo lowin~ data fnr the m)(el of a siphon:n=10, Hm=06m, d m =008m, L".=80m, (H 1 )m=0'4m, T=T m=200C:=O.t and A=Am =C'025, and

~O>=( :6O»m=Am

. 1lon, as well as, tht , Dettrmine if. the mode1 Slp

IV<'m .

Lm dm

2g

nOli'll" 1 d;

,,;;

;

1a~n:) , li;; \0 ~3·. :,

.

f"

=

Now(ps)m 'Y

ho-(Hl}m- (vs )2m -(~ w)m; 2g

=9'36m. From the table,

~p_s)mof ')'

page

345.

•

1,

lSi:)

( .•

or(p~'m = 10'3_0'4_I'i4~ -O'025X~. = 1--',[,)-l!:)'6~

y

for

T=20o

0'U8

C, Z1=O·7·h.

Since

19'62

the value for

g'36m if greater than the value of Ze of 0 74 m the model siphon will operate. .

vst

~

Now -y-~. ~h.-Hl- -- . ~(lJ '(

2g

,__ ~ ,ij1£() ~IH

·lhen

f)'

J~~ == lO'3-4'O~ S·5Q.2__:_o-\)2f'~· ~~:() X 159~~-2!\:

19 62

d~1

?n

il

~tl

!~l' I~

..

0 t!

0

;:(",;

-10'3 -4'

"

r-.. .. ~3 9=0 9m from"'~~e , ~;

k

i·I'th ~

" . ' ',"

,

:tablel page 345; bt r"",zoClC: Ze ~ O"-Im. SinceLhas a value of O'9m. ,which is greater than . A 'D.... the value for ZI!:=of 0 'i 4 tn. the siphon in nature" ill operate. ". 14. Example IV, Siphon to maintain a const::mt ll?vel in the parent channel (Crump): . 1 hese are plain siphons as described above. Tltey are constructed to mainta;.n a constant level in the parent channel either to feed a high level off· take with fluctu tting supplie; in the parent a'S a siphon at RD. 61,000 Gnj rat Brinch, Upper Jh~lum Canal Punjah, or to fe~d th~ tuthil e plants constructed for Hydro~dectr'c tnstallation at a const~nt hea.i with varying supply ~o!lditions In the canal such as at Renala Khul'd. Lower Bar( Doa~ Canal, Punjab, f

• •,

(5.

Example V Gulping Siphon (ern'1lp). Rasul Siphon of UpperJhelum Canal.

~

The Upper Jhelulll Canal TUn') in the reach along the steep slopes

C

01

'abbi hills on the

I)ne side an-i the river Jheluru on the other, about 75 fPoet beIllw. There are a lot of barrel-type

,iphon.. under the canal to pa.ss the storm watp.r frllm these hill si
Data.

Siphon under canal 12 ft. wide barrel: 320 ft. long with segmental 'Invert arch in flow lIld semicircular arch above top. Flood disch~rge= 1400 cusecs; Flood level 'lpstream of siphon =786'25; Crest level of 31 ft. wide w(!ir=7S1.7S; Siphon width=6'O ft.: Sipbon depth =6.0; Crest level of siphon=781'0 . A. Calculatbns.

B.

Discharge=3'09 x34 x4 53 / 2 .... ~ XV2g x6 X6y'S'25 = 1000+420=1420 cusecs. CalCUlations (or sip 10n reinior ced concret•. Roof of siphC'n.

This is at all times subject to pressures less than atmospheric. The greatest DPgative "ressure occur when the upstream water~level is low,Ht' namely at R. L. 776'50. With this level the maximum working head is about S.O fpet. Assuming the siphon formula see Fig. 183. Q=5Ay'h; the velocity v=5Vh; and the kinetic energy VI =~5h =25 X 5 =2 feet say; the 64 .4 2g tH.4 itatic pres"ure at the crown is that clue to a heihgt of 7870 -776.5= 105ft. of water The total negative presure is. ther~fore, that due to 10'5+2.0=12.5 feet of water or 1'Z'5x 62'5=782 lbs!~q ft. Add for weigQ.t of slab= 118 l~s/sq ft. Total=900 s:q ft. lbs ft . . ,C.

Sides of siphons

The average pr.,sstlre on th~ sid-s at the crown of the siphon is that due

to 12.5-

6~

"d}·Oft. of water i. e. W .=9.5 XSl5=593 Ibs p6r foot.

D. These will be su'-jected to earth pressure fron the earth below the existing floor. The prpssure intensity may be taken a, 30 d Ibs1sq. ft. at depth d. TM resultant per ft. run for 'hft depth d will, therefo:·e. be 15 d l . Instea.d of blllding a retaining wall it is proposed to reinforce the sides an'! support tlv~ vertical sla':>s by R C. beams placed along ,he upper edgp", of the pit and normal to the siphon roof at the siphon exit. The tloo,. beam will be 15 ft. long and loaded at intervals of one foot measured from the downstream ~d I, 2,5. 10, 25 50. 90, 15(1, ISO 220, 250 280. 320 and ::n0 lJj, rp.spectively. Total m!)ment= 10885 ft. Ibs. .

The redul'tion R at the upstream end is thus given by R X 15'0=20885:. R1392 Ibl At 5'0 ft. from the upstream enc tLe bending morr;ent is 1392 xS.O - (320 X4+320X3+280 x2+:lS0x 1) =69(i0-~050=.3·)1O It. lbs. At 6'0 ft, from thc end it is 3910+ 1392-1390=3912 ft.lbs' These heing practieal1yl equal indicate that they are near the maximum value which may be hken as 341 ~ ft. Ids.

827

Fig. 20

~

'~ . /hICIl IN f:£NttI'T ... /os

"

For a beam of 9;' in width this

per incb.

give~

an intensity of .

"

/., S70;YS 1hl;~'X'c

~9~~=5.l13 ft.

QI~

llls lYet foot 5213 ia

It.

~28

..

r;

/5213 " GIVlng:-h=v'74=V~74-=8 4

The beam "ill be9"X9" with 0.555 p~rcent reinfo~C3ment i.p.. a= .00555 X 9XS 4=0'42 sq in. \llow 3 No J /2" dia bars. For the sh:::rt beams of O'U span. we may assume these uniformly loaded" ith a load of 3(10 lbs per ft.

Fig. 21

"-s tUs Is less than the loading on the sides of the siphon at the ctO\l n, the reinforcement already DTlJvirled is a.mple to take this load, provided the vertical leinforcemtnts alrearlv provirled ar,> also ample to take thi5 load and are ,nade to olerlap the last three of the incliLPd roads. The lat ter roads ~re placerl on 5" centre", so that Wp may assume that the terminal re ctions from the t'lO heuns Rre spread over the low&r one ft leng:h of the 8 roof, slab rhe total compres~ion on th's strut :ln1ounts 1392+900=229~ Lbs. The ct,.ss ~ection of the strut is 8x12=96sq, inches so that neglecting the assistance given by reinforcement

the

compr6'ssive

stress

229l

is only ~-'2-S--

,....

241bs sq ft. which is very small and calls for

no further rtinforceml'nt tl'an that already proviced for tpe roof slab. 16. Exampl~ Vl. Use of siphon as atomatic Mak€'.and.-brdk arrangement, Plain siphon designed ,I:; shown in the sk>tch Fig 21 wa5 us~d by the all thor to eliminate the errors in tank '1Jeasurements of the outlet d:scharge dUll to varying levels in the supply channel as descriLed in the Anthor's paper No,237, Punjab Engineering Congre.s. lahore, .940 The relea'ic valve arlmitting air at atmos;>hpric presmre is opp.ntd an(1 water from the channel let i7jto the tank and the stop-watch started, . /' '

PART II

CANAL IRRIGATIO~ CHAPTER XIV

Distributary Head Regulators and Distributors .. .

1. Introductbn

A distributary head regalator is an important feature of the pro')le:ns of distributioR of supp~ies. ~t is. m )reover, a n ~.>~",ary lillk hetween all p.arth'!n parent chafl1ul and an Off-taking distributary .. rli,;tr.blltary head is a r,·guiator. a meter of supply and a silt s ~l~ctive st~ucture. A ilistridutary he:ld 'Na.'> designed in the beinning slmpll1a> a r~gulator [t llsed to have a floor or a. Cfe3t at beel I ,vd of a p He,lt .;ilannel with ga'e" to r"gula~e supply . The regulator was undershot. I he dist.rihutries were boostf'd wirh E'xcessive silt charge and their di:icharge tabl,ts, based (In gaug~s tixed in their he4d r"ach~s, had to b..l re"i;;ed occasionaHy. To begin with, silt exc1u,i'lU wa" the first to receive ~ttention. A silt wa.lI in the parent channel away fr·Jm t"e gates was the fir_;t dt Circle NI-re so;)n provided with R.C. slab~ with a tunnel IJellw tlle;n. fhis devdope.i tIle design of the skimming platfom a<; a d
Pi: Metering of supplies at the distributary head regulat.)rs was the last to rece've attf'ntion. I'his was arranged in the form of open flumes as de~cribed by Crump in frrigati(JD Branch Paper No. 26 CI.ss A and as improved upon vide paragraph 15 Chapter X of this p.ut. 2. Old und6r-3hot dlstribatuy

heacl-~e:6ulat)r.

A typical cross s~etion is shown in Fig I The reguhtion wa.s done in this case on tne crest which used to be at the btd·lev.. ) of rhe parent channel and in some CaSQ3 a foot hig
330

The crest wa') foil wed by a cistern t to 2 ft. defp and about 10 'fl'et long. There used to be a ory brick (n.B.} pitch;ng downstrf'am of the cistern. The upstream wings were sloping 1 in 1 and splayeo'at 4",,0. In some cases D.B . • jlitching in I~ed in par!'nt channel was .1 .put in. as shown in plan awl section. • Thf' Iron ~ates med. were Hted by ~windes rising in groovps about 6' deep .a'l shown in the plan The regulation was eione on a gauge uSll:l11y fixed some 50 ft. eiown-stream of the head and in '§: !lome cae~s fixed against the down~~::==~~)-_::!:= • - , Ii •• Fig strpam 1. return \\'al: at G in the plan

'SI.C·TION

I

__

'1;'

Fi~.

There are no experiments on Ttcord which would give the silt conductive 'oC power of t lJe head but it t:an easily be f imagined that it wouH be of the ()rder 1.1. of 125 to 1~0 per cent by weight of the ; i silt charge in the parent r.hannel. The silt trouble was most acute in the off-

1

taking channels fitted with such regulators, These head regulators were provided with silt wall; as shown dotte,l in the croso:: sl'ction, but serveri nJ u ,cful pur,)p5e bjcause the draw towards the head was so great that the silt cnuld jemp over these walls. 3. Wood's rising eill gate (overshot rezulators), A regulator of the type which existp.d at the head of th~ !l'a1am disributary Lo\\cr Jhelum Canal is shown in Fig. 2. The distributary takes off at R D, 21700L of N Jr h~rn ·'Branch. It had a raised crest with a rising gate behind it after the desigll of W.)o is. The Insic principle in this d~sign is, that top water in the parent channel contains relatively low silt charge aDd 5hould be takfn into the distributary. . Results of an experiment on this type of head were pnblished by the author in pilper ~;.;

._,.,...,.,r;:;:;:;;;~~=~~~~m~~ \.

oj

Fis,2

.>..\i~D

.. ,;,'1

~JL i ;

I..

,.No. 189 P.KC. Lahore. Silt takvn ,,, by 1he Head Jegulator i<; 110'4. % by 11 !cH; I weight on the averagp. and si.eve ,!,~ analy;isshows that the dhtriLutary to k at leas t as much coarse. silt as that in the rarent channel. Alth:mgh it took very nf'arly surface water of the parent channel, the !>ilt conductive pc,wer of the )lead was very high. It was due to " ! disturbance and eddifs upstream of the gates cau'led by unsuitable approaches. Even coarse silt easily jumped over the vntical crest and the ga~es The Salam distributary was, theref· re, a bad silting channel. .It was 180ft. ",ide with 10 foot depth for a ( ischarge of 30 cusecs and had a slope of 1 in 2080. This expereriment showed that· in oreet to exclude silt it was not 1Iufficien1

3~1

to take simply surface water from a parent the channt'l. but also 'imperative to provide suitabie approaches up-stream, so thlt there was no disturbance u..)stream of the crest. 4 .. Gibb', drstributary Head Regulator. The existing design of the Fatehpur D:strihutary Lower Jhelum Canal head regulator is a Gibb design given in Fig. 3. The Hearl is an open flum'} and i~ provided with Gibb's groyne wall 011 lines of Elsdon's slIggestions described in paper No 30 of the Punjab. Head regulator of Fatehpur Distributary off· taking R D. 83,800 of Northern Branch.

L. SZCTIC,.,

Fig. 3 Engineering Congress 1916. The basic principle underlying this design is that the cross Wolves of silt srrould not bo allow;ed to enter the distributa,y by constructing a Gibb groyne ~ all and the amphtude of these waves &'1ould be incr"ased by providing pitchIng ou the side np;tream of the head in tft,} parent channel. [he wa.t~r"'ay a.t the entrance to the chamber, enclOsed by the groynf', is alloNed comidering the effectiv depth as two-third. A hOIL: of three feet dia.meter is provided in the G,b'j wall to (HCap.! the additional supply from the approach cba~nber This hole: is at the hod-Iev,}l of th~ parmt cha.nnel fhere is a dry brick Side-pitching 30 ft, loug upstream of the head in the pUClJt ch'l.nnpl. The velocity is increased on the sides nn account of the presence of the side pitching This reduces thll dittcrence between the side velocity and the meiln vplocity of the parent channel.. as water approacht's the hoad ; iJut incrt"ases the amplitude of the waVt;S of cross flow of silt near tho bed, from the middle of the channel towards the sides, Cross Waves of silt, thus, miss the entrance of the head and a~e intercepted hy the gwyne wall (Para 15 (d) of Chapter VI Part II), Silt observations wew carried out by the author as pu lishcd in paper No. I ~9 Punjab Enginne~ring Congres. SLIt taken by the head regulator.; is about 8S'7~% of the silt passing through clownstream of the fall at R. D. 641)00 Northt'rn EnDch, but the silt taken is some.vha~ tiner than that in the Northern Brandl Mlthalok Distributary is situated betvteen the Fatehpur Distributary head anrl the fall ~ilt exclusion at tt.e head regulator of this distrir,utary influence to some extent the results of this experimrnt. It is concluded that the design of the Fatehpur d'stributary head is just a suitable des:gn to give a proportiona.te S11are of silt to "n off-take. 5. Klng'e sUt vanes. 1h se have ler>D used with !'UcCess : in some cases in conjnnction with design of the distritulalY head legulator as described in paragraph 2 above. They are shown in plan in Fig 4 Tte basic principle on which they are designed is that the water near the bed of the paren

332 channel conhdns relatively a high silt cn:lrge, Fig 9 Chapter vr Part VT, ano shoulcJ, ther~'!ore, be deflpcted away without disturhance. Watl'r entering the distritmtary would thus contam a a relatively low silt charge lind grade. The prindple is very souno, but it failed in some cases where there was a violent approach with a strong draw towards the head picking silt· over the

.

v~a

, ~:

30

A Fig. 4 B j . • rhp si!t vanes are usually thin R· B. or R. C. -wall,; 3" thick constructerl on the paCca platform as shown in Fig 4. They are sometimes metallic :1$ in Fig. 4 (B). The radius of van':s is kept nlore than ~5 (lr 30 ft. usually they are cut short when they are inclined to the straIght dow at an angle of 300. The re'ght is 1 to! depth. The spac'TII! htween them is Ii time the lleight. The number of the vanes ne! ends on the di!lcharg~ of the channel to off-take relativ,~ to that in the parent cl:anrJel "he proportional bed should be covoed by vanfS with a minimum number of ':t. Th",re are nt) &ctual observatior,s on record to give the silt connuctive power provided ~ ith this device. . 6. Head witb a ~kimning platform. H~ad Regulator of the Satehara rlistr butary off-takingR D. 760()(I of Northern Branch.

. .....

-.:c< ,_

,-"

from

experiments described by

He author on this type in rapfr num!-er 189 Punjab En~in~:;rinl! Congress, i~ giVen lJplow:(a) This type is constnlctf'd ~ t the Satghara DistriLntary hf'ad If'gulator t;>king ofI. at ·R D. 760(10 L Northern Branch The ne~ign of the hf'::Jd is giYen ;n Fig 5 It is an open tlurre head regulator provined with a Giilh wall ann a "kim~ QJ min£' phtform. A circular groyne wall is providfd with w1jnst::Jhle regulating shutters ahove the reinf(lfl'ed I'oncret~ platform. The depth on the pliltform is I !- ff'et ag'linst normal ., 0 supDly depth in the p:lT.'nt channel of 70 feet . . Shuttf'TS are adjusted in snch a way that .i5 no· . dra w down at the Ilose of the groyne wall. A surface float in the parE'nt channel put in line with the nose of the groyne wall comps straight to the nose. lhere is no fl:sturbanc6· in the supply appro'lching the a:'proach chamber abwe the platffllm. There is a fnrther clarifiration ot silt on the platform by_ escaping the supplY "traight bE-low the shutters; In. this case the hf'ad, has the maximum efficiency Fig 5 as a silt-excluding nevice and the tunnel below the platform is nev.'r choked. the experiment was carried out in two parts. The first part consists of three

",j. ~

:)£1

An extract

of heads

~

333 observations with shutters w':,rking, and the second part with th~ shutters down; ::IS, if the groyne wall above the platforlll was a sailo one. rn th'se experim~'lt" the silt of the, ~orthern Branch was measured at the fall at RD. 64000 Northern Branch and th~ silt in the distri,butary was measured from th~ hydraulic jump downstream of the 'hpari of the distributary. ' , Result of the fir,t pal t M the experime:1t a, pu')lished in JHper ~o. 18-) f'. E. C, show that the silt conduction of a lwad regulat,)r with a skimming platform wr;; a" low as 729% by wpi~ht and that. it took distinctly fiin'~ silt in comparsicn with silt in the parent channel upstream of it Result's of the second part show that even a skimming platform Ill1gtlt fall to achieve high silt exclusion by its defective working. I he waterway at the entmnce ahove the pll.tform is an imporhnt factor controlling the entry of silt into the chamber enclo,ed by the groyne. From the following practical eonsidcrations it has genff 11y to be more than that required. 1. to suit the ave -g: supply conditions in the parf'nt channf I, 2, to allow for ri1hi a"rI Kharif supp~y ltwels in the parent r.hannd. 3, to allow surface width between the pier and the toe of the sides so that the tunnel is not choked. Supply of I-he distributary is limited to the authorised discharge at the meter flume El()wn~trearn of it, and thp excess supply turns round the nose of the groyne wall, Th;s causes a considerah!e draW-down and d stUi'hance near the nose of the groyn". wall. Snrface fioats from near the berm or pare,nt channd do not f'vpn enter the approach chamb~r Water appro'lching the head gets a tlVi~t. and there is pro iuce,j a horizoatal roll~r with axh parallel to th~ central line of the pJ.rent channel. Muddy watpr at the bottom of theparent ch;jnne[ tnu; enters the hfad and surface, water ,escape" into the parent channel. The conduction of the head was, thprefore~ 89'7% in comp"rison with tbat in tIle parent cll1.nnel Round eddies are produced jlolst at the entrance of th':l tunnel, and work, rotatiDg with their axil perpendicular tf) the bed, btlhw the platforn RJund eddles cannot carry dt thr,Jugh th 1 tun~el. When the tunnel gets choked to an appreciaM~ extent, the efficiency of the head a~ a ~l,t­ excluding de".'ice falls, . The remedy is to provide shutters aCtually dom in the case of tile head regulator,

as

(b) cantilevered skimming plai form. This type is ctnstruct~d at tbe head regUlator of the Khunan Distributary taking oft at R D. 207,000 of the Northern Branch, Lower Jhdum Canal. Tho:: d. sign of the hea,l is given in Fig 6. It is -;imply a flume regulator provided with a centi-Itvertd skimming platform.

'-:;

Fig. 6 The head ~ook silt 72'4% by weight on th~ average in comparison with tliat in the parent channel. It was evident from the ~ilt analysis by sieves that tat f'ilt taken by the head was distinctlv finer than that passing in the parf'nt channel.

7.

Auth.nr's silt-selective distridutary head-regulator.

The. hasic ~riciple on ,which the hpad is .d('signerl lies in th~ fact that in a fJowing~ stream carrymg SlIt 10 suspen~10Jl, the concentraclOn of the SIlt charge in the lower layers is g:oe_ate, than that. m te u~per on~s. Fig: 9 Gh. _VI ~ar~ II. Cons(:quently, If we can escape the Lowe) s!-Ipply Wlt~lOut hmterferlDg WIth the SlIt distrIbutIOn. the water remaining will have less silt in 1t per Ull1t of volume than the water upstream of the hearl,

33t (i) The essential features of the design shaull, thHefore, be to provide concentration of 'silt charge mar the bed hy some such devices as reductioll of friction by pitchinf! or plas 'ering the bed and the sides. (iii Thp other and the most important feature of design s hou ld be to provide sf'parati lD of the bottom water charged wIth concentrated silt from the top water without any disturbance. ~his requires that water should enter the approach of the head with the same velocity as it is flowing in the canal, approachIng the work without disturbance. (b)

Design descriptfon.

A typical design of a "Silt selective Hp:ld Regu!ator" is given in Fig. 17!. The structure cal'l be divided into three parts-approach chamb~r. regulator in the form of l{arries, and weir fiume. The approach chamber selects the silt. The supply is regulated upstream of the weir flume, which meters the supply. The student should refer to paper No.IS6. Punjab Engiueermg Congress. Lahore for a detailed description. Pitching upstream of (he Head in the parent channel on the sid~ a~celerat\!s the side velocity, and it is further increased by the reduction of depth pr'Jvided by raising th~ bed of the puent channel in. front of the head. The difference in the mean velocity in the Mindle and the side velocity in the parent channel, is reduced. Water on the side, simply swe~ps straight along the head without at;ly disturhanca. Cro3s waves of silt near be'd of the channel Lorn the middle towards the sides are cut off by this q'lick-moving W'lter in front of the h)ad r~gulator. Th~ floor of the approach is kept higher than the bed of the p lrllnt ch~nn"l ann e)(clude~ bed silt of the parent channel according to requirem .. nts. The pri)file of the side t; I is kept the same from bed of the parent channel to the floor of the approach chamber as the vdtical wall is likely t'J cause disturbance A sTTooth entry is providfd into the chamber b)th upstream and downstream on sides. Th~ watArway at the entrance to the :lPP;O'lC'l c!1amber i:> th"! c3ief factor which controls the silt-selective power of the head. It is convenient to maintain the required supply level in the parent ch'lnnel hy regulation at the olontrcil point. A needle reE!ulator ii the most su~tabll devic:! wh;ch interferes the least with the sIt clfnage in the puent chunel a ld i1 ea3Y and c mve lient to manipulate. However, if the distributary h'~ i-regulve,. [n thii c \se a. straight length of at least 'ZH is nquired from the regulation K ,Tries to the gaug·~ hole of the meter flume. This distance will be increased aGcording to disturbance caused by uguiation by means of Kanies. The regulator i" follo.ved by a IU}ter flllm~. fhe depth on crest of the flume j.; kept' about i the depth in the approach cha.mber. It has g)t a !engrh of crest equal to 2H and the distance of the gauge hole fron the beginning of the crest is 3f-{ The a;>proach curve in the bed is hid with radim 2H. The crest is f )llowed by a conv~nient gla :is, Watp,r to the gauge well is admitted throngh a single h Ie. the area of whfch is about 1/ L.OOO of the area of the gauge well. The hall': is provide.l in an iron plate secured flush with the wall and lo:ated an inch or two below crest level at a distance of 3H from the beginning of the crest

[c] EXPJrimentaI test of an existing head of t)il type. The head Tegul-.ter was huilt at the head of Melay distributary at RD 83332 R Southern BranCh, Lower Jnelum r:anal. fh;) d~sigtl was similar to the typ~ design given in Fig 7 .. The s:lt of)servations pUl)lishp.d in p:lp3r No 189 Punjab Engin'lering Congre3s, s'lOwed that tillS type of h ....d regulabr took 702 % silt by weight in. co npuis m with 1 hat in the parent ~bant1el dowllstream of it. It took distinctly a finer gradr at silt in comparsion with that in the p:lrent channel. fhi'> proved as e:ncient as a h.lad with a skimnlng p'atform. (d) EXperimental rq ult of models.

Very detailed experiments were carried out on this tYP:1 of head nn full-size glaz d models to trace the silt laden stream lines entering head. fhe fol!oNing conciu,j.Jns were arrived at : . (i) The silt conductive power of a silt-selective h 'ad regulatol w,)rking under ideal . conditions does not vary with the discha: ge of an o:I-tak'1, so long ai the depth in the approach

335 ~hambeT is not. changed or. in other words, so. long as th~ ~atio of the depth in the approa.~h hamber of a sllt-selertlve head to the depth

10

front of It

In

the par€'nt channel is not varied.

Silt Selective Head Regulator.

t.

Seetion on A. B, C. I~" ~ ;

Fig. 7 Ideal conditions of working mean that the wi ith of the entrance to the apprl)ach chamt)er has been suitably selected, so that the bottom wa 'er of tre parent channtJ' flows straight along the parent channel along the sloping t to I crest and hao; 'no tenrlency to ri5e into the appr 'ach chamber. Thpse conditions are available, where no rolling bed flouts rise up into the approach chamber an d the surface floats indicate neither drawdowri at t1',e entrance, nor eddies in front of tIle bed. . (ii) Under ideal connitions of working, the silt conouction varied with depth jn the approach chamher. In other words silt conduction vdrien :lccording to some power of the ratio depth in the approach cha.mber to the d ~pth in the parent channel in front of the head on the pitched floor. Results of the experiments satisfy the following rdathn : - , .,

'

[A) where Pl = Silt conductive power of the head (e:xpres,ed a'! percentage) in ideal conditions

H.=Depth in the app~oach chamber; D=Depth in the parent channd o?posite to the head. The value of index x in these observations is nearly t. (e) Advantages of this type.

li) This is a very efficient excluder of silt as compared witQ other types of head regulators de,cribed before. (\i) This can be designerl with any required silt conductive power to suit th~ silt conditions which could be safe~y allf)wed in the oft-take with the aVl\ilable slope and C.V.R. (iii I The design is very simple and free Irem the encnmbrances of groyne walls anl\ platform which often cause disturbance and reduce the efficiency as a silt excluding device.

336 Example of design of a silt selective Head Regulator,

(8)

NotatIon for Fig. 7. D;scharge in canal U5 of th~ orf take=Q : Depth in c:tnal=D u ; Be 1 width in canal =B ; Discharge of the offtake q; Bed width of the offtake=Bt) ; Depth in the offtake Do ; Depth on pitChed floor in front of head = D =0'9 D" Permissible silt conduction of the head=P )/oJ From Nomogram Df'pth in approach clJamber = H. Hate No. X [[ I l'r< j,>ction of th~ dowmtreem wing S=.q/Q (B+DuJ:l) ; Width of approach=W,,=K

.S ~ D where K = I 5 to 2; Radius of DiS :;ide wall of appro ach= Rl =3H.i ; Width of flume

•

Jess than Wa/2); Depth on cre,t' of tltlme = H = (q/ ~Bt)2/1 (from i H. to H.. ) Straight pnrti '11 up "tff'am he",mr] Gauge holc='L 5H : DistallcH of gauge well h lie from beginning of crest= 3 5H, Length of crest=2 SH. (b) Des gn of s lr-sel ctive Distributary head Regulator. fur the parent channel conrlitiom :Slore=1 in 5715 F.S.L.=61S''! CV,R .98 BCG=6W'2 = Bt (not

B pc" V= OJ

'D ept h5 = '0

=(.

Discharge: 520 cusecs ; B=8~6)<5=43'O ft. and v=2'29 rt. per second.

Off-taking Channel, Discharge =63 cusecs13.=p=45; Slope=l in 4000; Depth=2'6' B=2'7x4 5...,120'; D " ," . \'0= 1'0 v = 184 ; 1'.S.L.=61I'4 ; Bed= 11 4 lci 1'0 determine the required silt se~ective power of the head. Silt index of par"nt channel=C,V,R,=.98; Silt index of off-take=C.V.R.=l'O Rc=

~'\T:_~:_i__l1 off tak~_ =!_.OO =1'01

C.V,«.

III

parent ctlannel

9,s

A=.r!!P~~;ih-~a~('ti~a~~an~~l=.: ~O = 1925 ft=silt selective power of h 'ad: R c ,,=r 1 ·3 . r 2 3 . .\.1/6 awl asstl'ning fl =fa=r, R:=how that the ratio of the average diameter wa.~ very nearly the same as the silt conductive po\\er by w~ight . (i) Depth in :lp;)foach r:ha'nber for 85% silt selection, reI",tive to silt in the p.Hent,

p~ 100 (~''--~

1/'

'but D=.9 x D ,=45. '85=

=.6 or H .. =,6x4'5=2·7 it .',

Rl"",3H.~~8

(-~..-)

1/3

1ft,

4e) Set} ack of the npstream wing .

s=

$;-.{B+-_D..!'_l=_.?_3 (43+5 12)=55 £t

(f)

Widtb of etpproach=W

6g}

RadillS of upstream lpproach curve=3 H.=3 X 3=9 0' say .10

~

:l

;.;:"u

.

' W ~K_i_xO =1'5X5·S·1~Q=15{t.

a'

a-

Ha

:l.,.

337

(b) The lVidth of tiume= 15/2=7-5 ft_ say S-O ; C from Fig_ 27 =3-03 2/3 63 ,. 63 2-91 2 I H=(-------) =1'89 it. ; v.=-- ~-=2-91 ft:/Eec and h = - =13 8 x 3-03 . 2-9 x 8 • ti4"4 _',G = I ~9-'13=1'76 It "~ Length of crfst=2 5 H =25 xl'9 .,,4'75 ft. Gauge hole f.)rm the beginning of crest=3-S H =6-7 ft. and Sl raight portion upstreaQl~2'5" i,f H=4-75 ft. say S·O ft. 11. Practical lieU t(lsi of all silt-ax:chding device~ (a) Tt;s e:lsy to work out the pr )portional surface width of the parent channel for the discharge of the offtakf'_ A surfar.e float shnuld be allowed to flo:lt in the parent channel from 15 feet upstrea'll of the hear! of the ofi-takf' at a proportional distance from the watar edge_ If it jll<>t enters the off t:lkt', then it is taking its due share of bed and surface water. The silt conductiv(! pc:>wer of the head will be about cent ppr cent. [f the surface float dropped from even beyond the prop )rtional share of the surfacp. width, gets into the offtlke head. it is then working ~s :l silt excluder. a'ld silt-hden water :It bed is entering th... head less than the projJortional. This applies to all silt excluding devices di.,cribed in this chapter for distributary head r"gulator.; and also to distributors. PropOl;tional Discharge and silt Distributor,

...

I.ONGTUDINAL SeCTION

Fig. 8

338: " [h] In the c~se' cia si1t~selective distiibutary head regulator,; the sat' seledive power Can easily be predicted by 'simply running the surface floats, DetermiJte' the distance from the water edge upto whkJ:l the floats euter the off-fake head. It should be the same as the width of approach allowed in thedesigo ,for .the stipulated silt co~ductiv~ power for whi~h the head is dEsigneg .. If it is less, the !'ilt selective, flower, will ,he correspondingly reduced m direct proDortion 'rhe fact was established in Hie experiments des'crihed by 'the author in Paper No, 189 Punjab Enl!ineering Congress, Lahore i ,12,

ProporUenal Distr i butors,

[a] (n dist;ibuting ch~nne i~" proportional di~Jribution of 'sllp,.pli~ja: is ~lesira'bi{ a~d ,il! yery much appreciated by the qlltivators It i, a goon. practice to combine 1:hepf,f-takhg tI)inor~ an,d outlets into one distributor. lhe proportional distribution of supplies is' at once: arrang"q by, m~king all off. tak"s includin!{ the parent channel into open flume wein with their 'crests ~t ~he ~arr,e level, There are two arra~gements 'usually adopted a<; shown in F~g.. 8. and another ln. Flg. 9. When the off-taking mlDQrs and outlets are sm~ U as compared wIth the parent ;channel, ; tl:te arrangt')ment shqwn in Fig, 9. is suitable and. economical.. Wb(m the off-taking channel carries a discharge more than 1/4 of thp. la.rent channel,' the arrangemeut shown in Fig; ILis dEl~ire:l ble thongh usually somewhat expel sh e. . ib] The proportional distribution of the silt charge of the parent channel can eaSily be att:!ined in th~ arrangement a.5 shown in Fig:8 '6y dividing proportional water-way of the ch;Jnnel approaching each flume by extending the partition walls upstream of the cre!'t. In f'let !he partition walls can continue as silt varies with height equal to t to' t depth tQ ..r!l~trict or lDcrease the entry- of bed silt iato any off..take according to the requirement. When the off-taking minor is a small one as. compared with the parent channel, the arrane-ement shown in Fig:9 is convenient and economical There is enough p.xpoimepJ<.ll work on record (Khan Bahadur Minhaj·url-Din I.S.I:. experiments on silt di;tribution Indian EngiAeering, Calcutta . 1928) to show that the right-angled off takes a~ shown in Fig. 9 take relatively high silt charge a'> compared with the parent channel due to. the curwd entry of water, This can, howf>ver, be set right at liltle cost by constructing there . " a silt vane as shown so that only proportional bed silt en trrs the off-ta'ke. ProportioFlal Distributors with silt vanes. Scale 1/200 ,

~. .-.-...., .. ~.--'.----.. .......... ~.-.....,

Fig, 9

.-.-~-- ).I':~:.·'·:-,~:~,~ -.,"'~"~;""::-::f:::;;:i =;::::~:::=i:::=:j~_3ro=Fk':~;;:BiiI!i1:"~13~!~..$i'~""", <;,

'- 'u.,

.

c,!,'A-'31f-..

:.""

339

,

The calculations of design of distributors are given in Fig, 9, are as per standard meter flumes design as given in para 1S Chapter X. 13. Examination Questions,

The structural details

Gi'!e a sketch of an escape and a regulator f9r ;a.distributary having a discharge of 150 Cusecs a bed width of 20 feet and F. S, depth of 4'15 ft. Thecescape lias 'to take a discharge of 100 cusecs and will hav; a bed width of 14 ft, and wa.ter depth oHJ 54t, R, T•• of bed of,distrib,ut~ry 560'0. ~ L. of bed of escape 557'0 Explain a Walton gate:·fo,r ~pin~l head regulator (:P. B, 1:. 1937) ,,' 2, Work out and s;{etch.the design for a proportional silt and discharge distributor for a trifurcation with the following data:Parent ,Discharg~

" Depth .,' Bel width '. Slope per thousand C. V, R. Sides

ch~nnel

520 5'65 340'0 '2

1'0

ii to

I

Left off-take at right angle

, Righli off-take

'. ;'

,

at 60 0

!120

3UO

100

4-6

3-5

,28 '2

14(3) , '23 1'0 ii to 1

1-0 to I

~

',·a·s lUI -235 10 ; to,1

(a) D~scr'ibe the ba.-ic principles 0n which the problem of silt exclusillil,. j .." base!l, (b)' Wha,t are the advantages of silt selective heaq-regulators over other types? ., (a) Explain how you would determine by funning sur'fa.ce fl.odts in the patent c,ba;llnel ,'r.ll~i.h,er ,a head is working as a silt selective and silt excludil'l~"'device. ,'" " " (b) Explain the basic prjnciple on· ,which the desigll. 'of King's sile vl'nes' is based" ' " 5. (a), Why,did.\Vood's d<>sig" of riSing cill gate. fail even th'Jugh it aimed at taking, surfa,ce ,~ater hy oV,ershot regulation? ".', " ' , , " (b) When do the ttlnupls below the skimming platforms c11~ke and why? Sketch and explain the conditions when th .. y will not choke. ' 6, Design a silt-selective distributary head-regulator for the following data : Left off-take at ' , righ t,~,ngl e,

Parent channel Discharge Slope C V. R. Bed Bed width depth ratio Velocity.

520

63 ' 1 ill 4000 1-0 ' 12-0

I in 5715 '98

43'0 "{!'S

4'5

l'S4

2-29 1 . , ;:,

. ,. '7. Whal are thiltbree iu'nctions ora d isfributatyhe'adAregulatot ? modern distributary head-regulator designs?

y

..., ' _

!

, : . , _I

'. ~ ~.'

'."

",'

,

"

"

~.,

$ij>l;l.in their devel<;>pr;nelit lil the "

'

.

,

.'

'\'

.'

',:

.

PART II

CANAL IRRIGATION CHAPTER XV

Outlets and tail clusters . . .1. The masonry structure throlJgh which water is admitteil from a government dlstnbutmg channel into a water course (cultivator's channel) is known as an outlet ur mogha. In America it is called a turn-out. An outltt may be a module or a non-module as defined below:Definition. The term module, in hydrauI:c~, was originally applied to a contri \ ance deviserl to pass a fixd supply of water independent of \\ atel surface levels both in the supply and delivery channels. With the invention of the gauge-outlet and similar devices it would, however, sp.em more- convenient to broailen the term "moilule" to include the latter in \'fntions also. and to defin~ it as meaning "a device arranged to pass a supply of water incerenden c of water surface level m .the channel into which the supply i~ deliverEd." With this definit rn. modulEs fall into two maIO classes:(a)

Rigid ModUles-Passing a fixed supply.

(h)

Flexible modulfs-or (Semi· module") Passin{=! a supply which varies in some characteJistic manner with surface ltvel in the supply channel but whirh is ind.e.pendent of the variation of the water level in the dtl,very channel (water cour~e).

(a) Ameng rigid moilules are GiLb's Vortpx Modules, and the Kent "0 " (a plessurefloat device) ; Glllfur and KharJna's rigid modules. (b) Flexible modules m::!y be sub divided into :_ (i) Orifice type-The K .G.O. (Kenner:y Gauge Outlet) and the original Harvey Stoddard Stmning wave outlet. Crump's A.P,M. (Adjusta1lc Proportional Module). Sharma's jmproved A.P.M. (".S.O.D) (ii) Weir (or fiume) type. Various forms of oren weirs e g that used by Gibb for tail clusters, short-throated flumes as used by Harvey and Lindlt-'y fnr tail clusters ; Crump's open flume outlet., minor-he::!ds, proportional distributors, meters, and IODf -throated flumes: Sharma's narrow open flume outlets. (iii) Combined type - The Harv, v Stoddard Improved (proportional) Outlet, which is essentially a combination of su I merged orifice ann weir. 2. It follows from the definition of a flexible me dule t11at a vertical gauge, or scale, fixed rela~ive to the module can be calibrated to show the disch::!rge oi the module corresponding to aT, y mark on the gauge at which surface level in the supply channel may ~tand. The height in feet, measurtd to this surfact level from the zero of n,f' g"luge. will be designated by the :etit:f G, it being uncerstood that the zeTO mark repnsents zero discharge as calculated from the formula used to express module discharge in terms of gauge. In fleXible mC'dul(s of orifice type, for instance, G is measured either from the centre or the upper surface of the jf-t, ace >rding as the jet is rated all round Of only on the upper surface lind discharge varies as Gl12. In the weir type, G is mQa~ured from the weir crest, and discharge varies G3 i2. In this combined type, I

2,3

the zero mark is at wt:ir crest leyel, and t1.e di~charge is given by(.9 ) = (_g_) k K and k are COllstants for anyone module.

= G where K

341

For rigiil modules, the gauge G has no meaning. "inee discharge is inoependent of gauge. 3. With varying field levels, and with the zamindar at literty to silt clellr his wafer course, whenever and as often a~ he wishes, thp ~u Jply orawll by a non-moclular outlet is fur ev"r ...:hanging independently of surfac~ \evel in the s'~pply channel, and thereby affecting the general distri ution of supply in a ma''llttr entirely l~eyonrl the control and manllgement of those responsible for distribution. On a moduled channel, on the oth ... r hand, d:strihution IS render~d entirely indepenrient of the arbitrary ch:>nges in water C()urs conrlitlOllS, and is dependent only upon conilitions in the supply channel5 under G'JVernment control. Th;s gfl'!at llilvantal e of the monule is by O'o,w generallv r~cognizQd : the old non,n0dular outlet, except a,; a pu~el'y te ..i~)Qrarv expp.dient is noomed to disappear, and in what follows, it will be tac: tly assumed that we are c mcerned only with monult'd channels. 4. Following the defin'tiop of the term TT'odule of paragrllph I, all mGdules-whether rigid or flexible-may be more precisely classified. in relation to the supply channel, in term.; of a single characteristc ratio :D

,

~q-/ ; '!9..

r=

representing the ratio between tte fractional deviation oq in the normal supply q Q q q of the modu'e, and the correspondia.g fractronal devia.tion

-~Q- in the

normal supply Q of the parent, passing below the module.

This ratio 'r' will be calkd

the FLEXIB [U TV of the modllie. For a rigid module, the FLEXIBTLITY is zerO. For orifice types lik'! the K.G 0 it is usually IllS, than unity; while for weir [or flume] types it tends to l;e greater than unity (b) When the "r" of a module is just unity, thp. module is proportional, i.e it shares, proportionaUv with the parent, in any slTlall deviation in the normal surply of the parent; so that on a distributary fitt,d throll~hout-including the heads of its minors--with S1.1 h modules diurnal fluctuations of supply would affect all parts of the distributary to the same extent i e by the same percentage inc' ease or dt crease of supply. so that if these fluctuatiolls were the only difficulty to be overcome, the pmportional module would offer a simple hut ptrf, cb s')Jution of the problem of distribution. fhe proportionai s 'tting of the orifice type semi-modulel i" when G='3 D and for the wei! type outJe·s is when G='9D where G is the gauee and 0 the dep1 h in the chann!'!l The proportional setting of the crest of the outlet, therp.fore works out to b3 6/10 D and 9/100 in the case of the orifice type and weir type outlets reop ctively. The mlthemltiCJl proof of this was workerl out oy ES. Crump in lois pap~r No. 26, 1. B Publication Punjab. Ie) The problem is, ho\\ever, more c(,mplicated, as changes in channel regime, coupled with the usual rlls ..-ridion of hearl supply to within a prescnbflrl ma dmum lim;t. intru tuc~ a secone" difficulty. with which the pnporti onal module is poorly adapte! to cop" [he rigi t mooules, on the other band, behavrs in a directly 0ppo~ite manner ; while completely imm'llle from effect of regime cIllnges it take.; no share ...,hatever in fluctuatuatio(ls of supply. In lact. the proHen 0f distribution presents two independent difficulties the requirements of which are in direct opposition: the first is met by proportional modulrs, and the sec<'nd calls lor rigid modules Whether the K. G. O. or the A. P. M. set at bed or belr,w or modules of simil,r f1exiblity, which occupy an intermediate position betweell these two extremes' offer, for this reason, tJ e Lest solution of the pro'.Jlem, ,remains to be considered. 5. Every rf'ach of a channel pnns in what rnav be called a "COlttrO} point ," that is to say in a masoD>lTY work usually so desigued a;; to maintain (a) a permanent relation between upstream surface and di<;charge, and (b) parallelism of ~urf,.jce and bed lines with varying discharge. Fluctuations in supply may, thfrefore. be regarded a" causin5 a general raising or lowering of the smface line without affecting its slope. Regime changes. on the other hand, result in a steepening or flattening of the surface line, and their effect on disHbution is rearlily appreciated by visual sing the surface line; of llnV r~ach as swinging slowly about it'! downstream end i. e th~ "control-point" as pivot. All off takes in the reach (l,re affected in the same WaY ; but to an extent increasing with their distance from tl e 'control point." Th~ 1"1 ach as a whole benefites or loses, as the case may b accordjn~ to the los~ or gain of the reaches below it. The advan ta€e of frl:qu~nt control points in reducing the effect of regime chang~s is at once evidt nt; the effect is nduced inver~ely as the n11mber of sub-reaches into ~hich a silting reach is divided, I

A

,

342 .-

.~;

\ 6. The sensitivtness of a module to regime changes 6h~iously' varies nirectly 'with its FLEXIBILITY as defined in paragraph 4 above. It will, however; lYe useful and cond:uciva, to clearness, to distinguish between the two term> and to oefine the sensitiveness S of a modul.e.r as' the fr'l.ction increase(or decrease) of module supply per his,;a ris" (or fall) in channel surface: : With th'is definition as per ct:ump's papor No. 26 Class A,P.W.D Technical Irrigation Brandl.' Publications S

= _L_ applies to all modules,

and enables the precise effect of a, given regime, 6D .' . , change to be calculated in terms' of the FLEXIBILITY of the modules concerned, and of the, normal depth D of the c h a n n e L . , , ': ' ' For e(ample : applying tl,!e above relation to the case of d head reach of 2·S feet average depth, in permanent regime, and subject to an averag~ surface swing of±O·t foot; the percep.tage. season~l variation in the total draw-off of the re::lch would be abollt±6 per cent f01: pr()portiona.~ modules, ±'l per cent for K. G, O. Or other .orifice modules having a setting (G/D) of 0'9 (a falr average for such modules) and nil for rigid modules: Tn other words, Ie G 0s were used in th~ h~ad reach, no re-setting nf them would be called for; ;vhereas if proportional modules were subs-, htuted, they would have to he readjusted every three months or :sO, to maintain a well-balanced cistribution throughout tl;te year:. . , , 7. The idea of adjustable modules is not neW. wifh nrm-mod ular outlets •. :r~e~ad}llst:ments meant reconstructton. In the cae, of K. G. 0 .. it t;lkes the form of resetting on a masonry \'Jr c?ncrete foundation. By adjustbility is meant the provision of some suit'fhle means of altering :the s ze of the orifice'say, of a monule, with a minimum of trouble to the se empowered to make f'e-adjnstme'nts, but with a degree of difficulty suffi~ient to prevent re-adju,tment being· made il} :>n ·ilIegal or unauthor:zed manner, by the zamindar or petty official. In Crump's opinion, the nght mean between facility and difficulty is to b" ol;>tained by means of a key of solid masonry or concrete, substantial pncugh to defy tampering, hut at the Samfl time' small enough to be reAsonably cheap in renewal. Such a key, WOUld, of course, have to be dismantled and rebuilt at each adjustment of the module. It is assumed and regarJed as feasiblp. that re-adj ustments wo~l(l be carried out under the sanction of higher authority, by the Sub-Division?-I Offi~ef concerned, and that he would be.held responsible for the correctness of the re-::IdJustments : made anti recorded by him. As regards the rreq'lencv of the re-arljllstm~nts, it must bl.'! • remembered that all regime changes:"'an'd it h tht'se aJJne that call for atiju;;tahility-take place slowly, so slowly tha,J:., even if propo.rtional mcidtlles were used in head-reach~5, ,{eadi,!!stment would ordinarily be neces'ary not mort' frequentlY-than once a crop. ClUmp brought ,', forward , tne idea of adjustabiiity alld proportionality and therefore his outlet is ;called .'\djustable ' , , , , Fropo tional Module (><\.P.M). ! 8, Modul:u limits and minimum modular held (M:M H ) AU modulES, whether r:gid or flexible, require a cNtain minimum head to ensure , h~odulatity ..In th~. ca~e ?f rigid module~. there is alio an UppH limit beyond which const~~cy of ,dlscharge falls. ThIS ltmlt must obviou~ly be high enough to avoid trouble, within the range of running conditions. In all modules the advant:ige of low M. M, H is self-evi"'ent, since it means , le~s. evpense .in earthwork both in modulil1g ~xisting channels add in const-ructmg Lew one~ with ";a VieW to modul<\r equipment, and.in the fl)rm~r cas dess distilrbance of. existing regime. In ~ m od,.l~ng existing. channels it is usually found n
'

'

343

outlets

Fi~.

1 . l>15tHARGE OF CAi'JAL OU rLETS Q=KAy' h

5 I:

~. i

,.. .,

"t

. .i

.,

.

I' . •.,.

.,

,

. •.

.f

. .

".'

~

, 10"'" A~It.U .,c •• ~ .,.... .4

e-=

... ..... ""

..

..... ... ::! '"-=

J

NUN

.If

...

'?' ewllf

.,AH.r,,, All. LEN.'II

'

......

"!I

~.,/IU

,.(',IfT FM ,.014 ,.,,.E

$CA~' ,elt

'"'"

~

Wlrtf

t..

~

!l

.~

.,

''I

.,

•

~ ~

'1.;

4

~C.U. " ••..

Ii;. SA.re.. ,:,

. .......

,

EXPLANATION

"

Q

.&

.,

.y

.,

,."

~

~

::t

.,1 "~

j4

I··

. :, -If :

'{

.1' .'

...

~ '. 1,;

......

;;

•1 .

...

..

..

.

344 distrihutary.

They

may

be circular

OT

rectangl11ar

in

section .. The

discharg sqnare fPoet ano h is the working hea i in f~et (Difference between the water level ill the parent channel ami the wateT ievel in the watf-r c mrse) and K is a constant" hich :is taken as 5 in the case of masonry orifice" and as 6 in thPo case of wooden and iron orifices. There j<; umally providpd a face wall on the distributary side as shown in Fig. I and drop wall at the end of the bank in the case of pacca outlets. The wooden sho )ts are usually put in during the con<;truction of a ch'lnnel Thpy are simply put in the bank with puddled earth around them. They are meant to be temporary and kacha out lets and are replac~d Ly permanent ou tlets aftH rnnning the channel 3 to 4 years when the chak boundar fS are established by usage and some idea of the actual water levels in the water c mr,e" is availabh·. It is apparent form fg I that th" discharge of t~e outld can eaoil. be increased by digging the water course ~nrl thereby JO\~ering the water level in it. Thi~ Will increase the value of h and. therefore. the discharge Equitable di,tribution is not p'1ssible with this type of outlet when the cultivators can increase the discharge by simply digging the water course which is a form 111a is Q= K A

v h - where Q is the diich'uge in cu>ecs. A is the sectional area in

::aminddri channel The solu'ion of the formula Q = 5 Av'h is giv.-n in Fig. 2.

1 [.Tilt~ pipe Outlets. (Free fali pipe out1ets) The masonry ot pipe drownf>d orifices as desceibed above were re,>laced hy tilted pipe outlets as sketched in Hg 3 The pIpe is supposed to discharge f 'ee fall above the ~ ater lev-el in the wat~r course. The p;pe may be tilted as shown in Fig. 3 or horizontal Thf! discharge furmula of this outlet = Cd. A V2gli- where (.1=06 co-efiicient of the Aischarge: A= sf'ctional area of the pipe in sq ft.: h=head from F. S. L in distl : to the centre of the pipe at the outfall. fhis type of outlet is no coubt a ~erni ·module and the discharge TI1_T &:.0 PlltE. C)U'T LI.T

/

it creased by digging the This succfeded very well for some time. but the. cultivators Soon invented the method of constructing a ramp in the water conrse by heading up water to the top level of the pipe. The discharge increased by 15 to 20%

c:Jnnot

be

water-cour~es.

(:\-~.:=-~I!.!itJ~'"

Itoo, Ot• .,:

Fig. 3 The long pipe outlets do not usually rlln full at the exit and the r1is~ha.rge eo·efficient is mostly a measure of the co efficient lit the contraction of the free fall Jet at . the v~na contracta By drowning the pir e. it star ts running very nearly full ~ore. I he contwl,sectJO.n shIfts frorn the vena contracta of a falliIl~ jet to the s. ctional area of the plpP. a~ t.he eXit. 1he dlschar~e c,,-efficient inc. eases to L'S and even more in some cases, I he d;s~narge IS lllcreased e \Ten th:mgh--the head is lost tqual to half the diamtter of the pipe by drowning.

./'1

12. Kenreiy's Gau~e Outlet

Th is was the earliest type of semi-module used in India. I~ is ~ketched _in Fig_. 4. I t was invented hy R G. Kennerly. Chief Engineer, Irngatl?n. Pun~ab. I he outl~t is PJo\'ided "ith the bell·mouthed approach into an exp:mding cellvery p.l~e as shown m hg 4 .) he jt t in the air chamber is a. rated all round. 1 he discharge formula q=cd y2g A v' G- where G=the head mea!'ured from F, S. L. i~ disty: to the centre of the PI ific' ; cd= '97 = Discharge co efficient; A =St ctional area of the onfice at the end of the month,

Fig. 4.

This outlet required in. practice a Minimum Modular Head of about '22 to '25G and its discharge was independent of water level in the water course when the working head exceeded M. M. H. This m'Jdnfe ha~, however. bep.n supflfo;eded became its di5charge could easily be increased by closing the air holf's feeding the air cha.m ber. After the air holes are closerl, the air of the cham 'Jer is sucked away by the jet and it..; prc·ssnre in the chamber drops below the atmosphere The pres·;ure head cauging tlow increase, to (G + '\ -A') where A is the atmospheric pressure and A' actual air pressure in the chamba below <J ·.mospheric pressure. 13 Harvey Stoddard imprJvei outlet. fhe Har \ley Stoddard improved oatlet (Fig. f) was an early design to attain proportion. ality. It consi"ted of an orifice outlet coml)ined with a raised standing wave flume iri L. SECTlO:-'; continu::ltion. The loss of head was ToP 01' wALL relatively more than in a standing wave flume. M. M H. was about 22 to ~:; 'j',. A standing wave flume gives proportional discharges with a small loss of head, so long as thp. ;;3 depth of the parent channel is small . •• _.: 0.'50 j._-- /.77 - - - + - - - J"7--~LL___ Whtn however, the distributary is Fig. S. a deep one, the flume, which would have to be approximately the same depth Ito he on the right side of proportionality) would have to be made so Il"rrow that practical cOnsidf'rations would rule it out. ]4. Kirkpatrick Outlets. , Jamrao tl/pe open flume is shown in Fig. 6 atd the Jamrao orifice semi-module is shown in Fig. 7. Th" open flume of Fig. 6 has no level crest and has a short throated section about 2" or 3" wide, where an angle iron frame IS nxed. The up,trearn approach is 2 ft. long and has a splay of 1 in 4 1 he downstrt'am apprna"h f1urne is 10 tr lung ::Ind the width of the flume at it~ downstream end is ~~ H. hi, kp<11J L k f ULd that the shapes of the upstream and tho downstream !lames were n)t cap::tble of further improvt>ment and that any further increa~e in their length~ or L. SECTlO2'< I . iates of diverg"nce cou rI not Improve upon this tyr>e of nesign. Th" values of eo· efficient K in w_. - the formula q =:= KBGl.5 was not found to be _ constant for f1iffc'rc'nt values of G but if the inde~: 1'5 were changed to j'6 the formul::t agreed within a per cent of the actual observations. which c;)vc'red a wide range of both Band G. fhe discharge formula as pvolved by Kirkpatrick for this tyPfl of open flume outlet is· q=3'2 BGI 5: The M. M. R. o

found to bp necessary is=

Fig. 6

~

It will be seen that the M. M. H. requil"ed for this outlet· is more than that required for the Crump type of open flume outlet,· also the

246 narro '< as the open flume outlet suffers from t,:"o ot?e~ defec:s : [a] The control section does not remam wIthIn the angle Iron frame depth on crest i ncreasf'S. L. SErION lbJ rhe'e outlets are more sU'iceptible t() gettIng choked with jungle than the long W.L thro3'ed open flumes. Orifice type outlet in Fig. 7 is an attempt to reproduce a K. G. O. in Dl
M.M.H. with 6 Baffles.

8"

7"

He

He

4'1

48

He 4'1.)

He 39

4"

He

4'7

He

4'0

H

He

~:F7

4'5

~'5

4'4

3'3

4'3

He He

15

M.M. H. with 9 Baffles

He

He

C.. ~mp's Adjustable Propotional Module.

The setting of the crest for proportionate discharge is 6/10 D. The structural details aTP expHned in Drawing iri Fig. 8. The immunity from tampering is provided in the form of cast iron base ~nd cheek plate 1 0 foot wide with a cast iron roof block. The adjustability of the outl·t IS arrangeti by providing bolts passing through the roof block and the cheek. Tnese lJOlts can be removed after dismantling the rnas:>nry on top of the roof block and it can then be lCl1,ed dud Ic.,wered according to reqnirements. The masonry above the roof block can again be jlll' i'L l'he ~st of adjustment of the size of the outlet is very small. It is an orifice type outlet "Ifh tlie additional advantage of a
247

q =edy' 2g B. vv'~ Where q= Di~charge'in cuseC5; cd=O 91 =discharg~ co·~fficie It: B=Width ; y=Height of opemng; h=depresslon of roof block. H=h+y=depth on crest. The head" h "is measured upto top of the jet leaving h.e orifice under the roof block T~"re is levell~ngth H provided in be'tl after the roof.to ensure that thf jet of water Ieavin; with y depth should exert pre,sur~ on the floor. It IS, therefore a submergp.1i orificp.. It I~ semi-morlule becauso the dischuge is supposed to be indipendent of th", condtions in the wat .. r course and tile m ,dularity IS indiclted by the forllution of the hydraulic jump downstrearn ot the orifice A.P M. is, tberefore essentially a submerged semi-module . Crump in his experiments suggested ;:t coefficient Cd=cdy'2£ =7'3, He al<:o gave a table (f th~ minimum modular hmits based on his experiments in paper No 26 P.W 0 Irrigation Rranch, Punja=> pUJlicatio[ls c ass !\ His e'(p~riments werp carried out with width 0.5 ft, ann depth on crest '2'0 feet It was soon found th'lt the co-effitient C and M.M.H. as given by him did not apply to all cases. :::rumo's A. P. \'Is. have been manufacture i and used in eight standard width '2,25, '32, '4, '5'63, '8, and 1'0 ft. This outlet is used all over the Punjab This has proved to be a very succes<:full outlet on account of the immunity to tampering and tf-te adju3tability. The cultivators have been attempting to increase the discharge by raising and tilting the roof block [his defect is ven' easil~' (etected and set right. They sometimes construct a covered drain behin~d the side wall below water level in the parent channel and then drop it In the out-fall downstreo m of the ro) f block by piercing thf' side wall which is only It brick thick. Though difficult to detect tbis defect in the supply turn;;. it is ea'iy to ciscovtr it in closures. TABLE No.2 Sharma's Table of silt conductive po :ver of outlets.

....

~

o· Z....

_

Q.)o..

~E

,_::= .... ·U CO -

v

I-<

~

~~

Vo

o..-:_ mJ)

cd ....

co

i-·-jo----oo--- - - wti 1'00 '9S '96 '94 '9! '90 -S8 '86

92 93

-84

89 99 100 100 100

'82 '80

'78 '76

9~

95 96 97 9S t}S

100 100 100 100 109 100 100 100

lOll 100 100 100 100

111

llO 109

lOS 107 107

lOG 106

105 105 104 11)4 103

103

l~o

1,j~

114

t!4

lH

lh

124 122 120

130 123 125 123 121 119

112 111 llO

112

112 III 110 109

112

liS 116 114 112 111

110

109 lOS 107 107

117 115 114 113

112 III

110

109

lOS lOS 107 107 106 103 106 105 10:;

111 110 109

III

lOS

108

110 109 108

108

108

IUti

107 107

107

107 107

106 106 106

105 105

106 lOS

107 B6 lOS

106 105

lOS

1()"

10:';;

)U5

Note [iJ The silt conductive power of the outlets is expressed as percentage rtdat ve to the silt charge in the parent channel determinerl in Paper No. 168 read ia the Punja~ Engineering Congress 1933, Its variation with respect to the quality of the silt carried in th ~ channel wa~ noticed iu the ~xperi~ents described in paper No. 168 and was varified by analysing distn butanes knowo to be III regime,

3-18

"-'" ' . ' . ' [iiJ -\.P.l\L~Ailjustable Proportional Module.; I.B.=Irrigation Branch; S,S.O;O.=Sub_ merged Semimociul Orifice Outlet, J [iiij In the case of pipe outlets set at bed level the sil_!_ conductive power drops to ,

.'

about 90% with all valuf's

v __ , if vertex i$ formee upstream of the outlet in the rar n t Channel. V
16. The Author'; improved

A.P~M.

[Submergp.d Se'Tlimodule Orifice Outlets]. The author carried on very exhau,tive r,search work supplementing the work 'a\ready done hy crump fo' all width" and depths on crest hom 1'0 to 4'0 feet Tbe rt~s11lts were pUblished in papers No. 168 and No. 176. Punjah Engineering Congrpss, Lahore, The first paper gave the meaSUlements of the silt conductive

L. SEcnO"l" I:.

<j

PLAN

Fig. 8

.<.,

:.

power of the irrig"tion ()1]tlf,ts as given in table No 2 and the second one investigated the hydraulics of the A p, M.e outlp.ts. Whilp. discussing tbe paper No. 168 and 176 the following conclusiops were aect'ptfd unanimously hy a committee consistillg- of E. S.' Crump and fl. W. M. Jesson ~uperintendi[lg Engineers. and tbe author, pubhl ed in Appendix I o~ithe author's paper N'Q P. E, C, LahOJe , (i) The channel fitv,d wjth A. p, M. out Ids set at 6/ J Oth had It tendency to silt up because A. P. M. outlets as constructed did not take their due Sfl'lTe of silt. The propnrtional silt conduction wall not enough becau~e 10 to 11% water waR lost in absorption arid the due share of silt to be drawn by an outlet was considered to be 110 to 112 percent. The improvempnts made by the author in the approaches of the A. P. l\1, outlets as sho""n in Fig. 9 were sati;factory. (ii The rli~charge co·efficient C in the formula of an A P. M. Ip=CByJ-h) was· not" cnJ)stant. '·S, bllt showed considerable variation from 6'2 to 8.4. In the case of narrow outlets '2 It. wiilth With H=4 0 and ),=20, the co-efficint droPPt'd as low as '6'~, "·In Crump's outlet the CO-t;fPcient decreased with 1he dec"'ea,e in width 'and with the 'increase"in depth on crest:' . . [iIi> The Crump's A. P. M. r€:ised to be a submerged· semim'ojule .hen the hydraulic jump took place on the glacis b,yond the leve IfJ.oor of length H downstream of the roof block. In such cases, the co' efiicien t :is high as 8 4 was recorded, In this case the mere formation of jump dId not indicate modul:'rity.

.., I~0

¢I

~,

~

," t;

,:

~

~

II

,--'," >~

.~

,

.,

15

"

~; ~

"'l

::Q

..... :a:"' ...0 ....

,,

.~.

"~

.~

'"

lo. . ~

~

Q» PI c:;,

1"\

()

>: l:iI,

~

(;) ~

-,

t ..

-"'~

0

~~

." .'

-..,.'.

~i

~ i:;.~ ~

...

C'-

~J~

(\'

,:

-(:_"

!5

<:

-

~-"I,

~

>')

r.:

,~:"

)0.

c:

50

..,

(I)'

3

"0 "1 0

<

ell

~

------:--... _---,

>

.

'i:!

~

PI

It

:r

if)

'Jl

=:~

0

~:! ,. o ..

,......-

g

"," I .lI-

I

T ..

'.

• ...

~-4..

••

T~ ;.

;;-1

"t.

.A.

~

o.

N

(/)

n

P>

~

II -~

en

0

\ ., <: :

I

r

.....1

"'j

,

T I

.

~

~.-2$

~·.I,.

---+ . ., I..

~

-..o.....!--+-t

OJ

"'"

~

I

_J_

t',

iflciillllIf

-~-::.L.,;"

'¢\Ii"t

*f-

/'

/

II

~17

-1

~i~

+ t-:l

V)

II

ttl

II

"'I q;;1.Q ~I

. .

.

II II II II II II II

::r:: "'.Q Il (I)

0.

0-10 Cl- 0Ao -

[ivJ The minimum modular head required for the Cmmp's A. P. M. was founc1 to he considerably more than that given by him in paper No. 16. When the outles were narrower than 5 ft. and also when the depth on crest was more than 2'0' M. M. H. was r"ughly :-i3% of H. (b) Fur.ther exppriments Were carried out by the author to att::lifl perfecti m in thp, points Iii) to (iv) enumerated above nnder the supervjsion of E. S. Crump Superintending Engin'.er, Upper Jhelum Cana.l, at Shadiwala and the' results were published in Paper No. 237, Punjab Eng-ineering Congress, 1910 In the case of the A p. M. outlets to ensure modularity by visual examination of thp hydraulic jump, the following conditions must be fulfilled at the control section upstream of the jump: (it Depth not mo ethan 2/3 H (or allowing for frictionallGsses in the aproach not more than 2'3 KI total energy {iii Filaments bey"nd the c >ntrol section either convergent, :tdherant or rectilinear. (iii) let leaving the orifi ~p aciherant. chat is, in cont::lct "ith the bed. The first one W1S fulfillec1 in Cru ,jJ's design by limiting the valve of y not greater than 'SH and tho last two conditions were not attaimd as indicated by the low pres,ure pockets I eyonri the control st'ction under the roof bock at it" end. The jet leaving the orifice was therefor.. i I hIe to pressure inflations and capable of ::Ittaining a coefficient of 8'4 even beyond the theoretiral value of S'O The'ip. deftcts were rectifie,i in the author's improved A. P M as !'.hown in Fig. 9 ly making the following changes with a view to rpduce the coefficient variation and also to make it work as a perf~d submArged semi-m'ldllies. (i) The curve of the roof block (Bprnaulli's Lemniscate) was giTen a tilt of 1 in 7~­ greater than sbpe of the bed to ensure an adherant jet and to reduce the variation in C by giving a bell-mouth appro::lch upto the control section. fiiJ The level floor was removetl and a slope of 1 in 15 was given in hed to ensu e rpctilinear or convergent adheran~ filaments in the flow beyond the con trol section indicatmg pressure on the ben equal to y or slightly more than y and-in no case less than y. Ciii] The value of y sholllc1 be between 0'2H and O·SH. The upper limit of the value of y wa~ fixed by Crump to ensure that the outlet should run full bore with no vertical starvation of the control section and the lowpr limit of Y='3H was introduced by the author on the Lower Jhelum canal in 1930, because when y is less than this, the hypercutical jet becomes non-adherent and the discharge increases In the author's improved A. P. M. this limit is y=·2H. The defects as given in [i J and [iiJ were completelv removed. The co-efficient variation was very much reduced as given in plate No; XVI A. The variation of C dne to H has now totally disappeared and the co-efficien t now varies only with the. size of the orifice i. e. ratio B

Whatever be the position of the jump, the discha:-rge does not now vary so long as it ]s

Y formed

Coefficient Variation. B

'2

Y

·8

1

2

3

4

·5

6

8

10

7'0 7'28 7'43 7 54 7'6 7-76 7'82 7'86 7'87 7'S8 789 7 90 [cJ Ihe minimnm modular he~d is comprised of the followiug losses in the A. P. M.' outlets ;,. (al Loss in the approach upto the control section indicated by the coefficit nt C. (b) Losi! in the hydraulic j u m p . , . . (c) Loss in thQ outfall jn expansion. . .~ . (dl The frictonalloss from the COn trol s~ct ion to the water course. Crump simply stated that the math_ematical formula for the losses was very cumbersome. The author worked out the mathematics a<; published in the; I;'unjab Engineer; Th-e ,~, C2 :W(k)-2k;3' Mall, Lahore, January, 1940. It takes the form hm=h(l- -) +.054· - . kJ h t3.6 f} C

' .

~2~:

...

:

2g

F (k) . ( .)

.h+f2h where hm =M. M.'II.: C==Co efficient in the f{,rmula of discharge; k=v/h=Height -

~¥~2

350 of orifice/Depression of roof block; £1 =a factor for outfall losses=5 ; £2=factor of friction loss in outfall='15 tn ,25: F (k) = i Y i{iq:. :'::1>1'1 C"k - k) An approximate formula as sometimes suggested by mere guess work in the form hm = 75h is used in actual practice. The author analysed a lot of observations of M.M.A. as published in Paper No. 237 and found that the outfall losses were more than 50% of the total M.M.H. It was thought desirable to have a standard design of the outfall. The bed prof Ie has already heen fixed and tbe side walls were carried straight for 1.0 ft. length be~ ond the roof block and then expanded with a radius of 25 ft. on both sides to the width of the water course in all cases. M M.H. observations are not comparable unless the outhll design is the sa'1l~ anri <:tand"l.rdised This formula cannot be used III practice but actual observations Were plotted in Plate ~('. 4 of paper No. 237 and are noW drawn III plate No; xvn tAl for use of the students, M M.H. is roughly 20 to 25 per cent of H

(d) Though the M. M H. re~ults as given in Plate XVII (A) show improvement over the Crump's A. P. M. outlets, they are still very high. In some cas~s it is necessary to put an A. P.M. in cases of water courses with. poor c .mmand. It I.\'''S investigated in paper No: 2a7 tn r"duce the M.M.H. further by covering the outfall beynnd the straight sides with a flat roof with cluved edge in the begining as shown in i
and

calculate B = C?Vh A. P.

M

size. having width of the flume equal to

or just higher than B (:alculated) to suit the standard width. will give the required width of A' P. M. Then calculate. a= C~

yyl1 =a

i

"

'( . ,11

,,(.

CAl

')

1'1.

'.

<

"I; ;
d;.

:.j(;:" ;.{;

B the

.!

h+y=H (BI The solution for equation (A) and (B) is given by one setting of the side rule. This method is not only more accurate hut also quicker than the Nomogram method. Rule. "::)et the reversed slide to 'a' on the 0 scale. [he values of hand yare given under the cursor of the A and C scales respectively. Proportionality versus rigidity. . ,f) hoportionality in an A. P. M. is a great scientific achievement. and is an asset of incalcul&ble value in outlet, of regime channels. It is the considered opinion of Crump. who inventeri this outlet and the author. who developed it. tha.t proportionality shonld not bl'! s"crificed on regime channeis. which could be run -nonsiiting by suitablt grading and silt selection at distributary head regulators: (fhe author's paper No. 189 Punjdb Engineering Congress' 1936). If a channel cannot run in ree-ime, proportionality;n its outlets become, a disadvantage. Once it is discarded, there is no limit to tile lowering of the setting and to make outlets suh-proportional., i.e, rigid. The author's S.S.O O. may be set even below bed level, if the available working head permits. [he Uge of an S.S.O.O. approaching a rigid module is far superior to the known dev-ices of rigid modules with mo\oing parts such as Kent's, (g) Practilliof cultivators to foul the control Section. I he 4I1O·eificient of discharge Cd in the formula of the discharge of a submerged semimodule is , he product of Ca and Cv as in the case of Vena contracta of a free fall orifice. If the co-efficient of sectional area Ca and the co-efficient of velocity Cvare changed. there shaH

,~

351 be a correspon iing change in the discharge even if the jump be for n~d and the control section be convergent adherent Ca can he changed in two ways. Ca) Vertical starvation fhis means that the outlet does not run full bore. This happens in Crump's A P.M. when the depth on crest is more than 2 5'. The discharge can be increased by having a wider roof block or by adding a lip downstream of thp. roof block. In such outlets zamindars U5U'>Uy put in a wood an strip of metallic flap downstre-un of the roof block. Thev just make u? their shortage although the dischar~e cannot be Increased beyond the theoretical. Thp. chances of vertical starvation have been I:urecl by a fit in the lemniscate curve of the roof block in the author's improvement of the A P.M. (b) H)fi~on'al Starvation. It i~ either due to exesdv~ width of an approach resllting in back now or due to rough sid~s The Zamindars usually cure the former by putting a Iloriz >ntrl.l woorlen plate up3trea'11 of the roof !'hck and the latter by ruobing the sides approaching the A.P.M. bl )ck, similarly HlP, value of Cv can be varied by tWI) methods:(i' Excessive length of approach. The 10SS'H in fr:ction are increased before the control section resulting in draw down. It has been observed to be as much a'S three inches in some cases, Unsuitl,le apprr)acles The head hst in entry causes serious flrror in the discharge. We have Sf) h· explained the hvdraulic, of the Eagineers and the cultivatosr but the subord nates executing the construction of the outlets introduc~ sometimes changes to benefit the cultivators fne Engineer in-chuge should he c:l.refull to watch them These are practised in three ways resulting in 12 to 15% increas~ in di<;charg~. (i) Bac'{ tilt in the ro:>f block, resulting in concavity of stream lines with consequent increase in r1ischar~e (ii) Groove downstream of the ro')f block in bed causing partial aeration below the jet. (iii) Upward tilt in down<;tream level floor causing a low pre,sure pf)cket. All these factors have been effectively cured in the author's improvements of A P M It is enough to show that the hydraulics of the sublLerged semi- modules (A.P. \1: ) is much morE' complicated than it is u<;ually supposed to be. It does not mean that the control section of tl)ese types of outlets can only be affe;:ted but that other types a t outlets K.G.O. Harvey Stoddard or Jamrao, Bend outlets are worse still in this respect. 17.

crump's open flUme outlets.

The design of the open flume outlet is given in Fig. 10. The length of crest is 2H. It is eX3.ctly the same design as originally invented by Crum.) but the author's approaches and the sta ndaT d outfall design as accepted by Crump have been added. Open flume outlet with i s proportional setting of 9jlOD takes its due share of silt, that is, about 112%. Minimum Modular Head is 10 to 15% of the depth on crest. The coefficient of discharge is steady, 30 in the formula q =CBH3/2 for all values of H and Width from 0'3 to 1'0 foot so long as the length of crest is 2H. for TI!in ow open flume. 18. Author's narrow open flume outlets. (al Crum! did not investigate the behaviour of narrow "pen flume .outlets. In Crum p's - design the length of "lpproach is very long ann the length of crest is 2H. In the case of narrow open flume outlets, the coefficient drops very much due to very high frictional losses and M. M. H. rises. The author carried out detailf'd investigations on outlets wi th widths from 0'3 ft. to '05 ft. The experiments were dividfd into three secti~ns. (i) Length of crest 2'H. (ii) Length of crest 1·25H. (iii) Length of crest '5 ft. in all cases. . In the first two cases, the coefficient variation in the formula q_CBH3/2 as found out, is giveR in Plate XVIII (A) and the Modular minimum Rea is, as obsorved, were found to satisfy the relation h m =0'18 ( 3 ~9 . )2 R which can be obbPined from Plate XVIII (A). In the third case it was sl1ggestf'd by Crump to reduce the friction losses further when discussing the results of the first two cases and the ohs~rvations in this case were taken uader his suppervision and results were published in paper No. 237 Punjab Engineering Congress Lahore. The design of the outlets js given in F;g II and the results of the value of C and hm are given jn Plate No. XVl[f (B 2) and XVIII (B l ) respectivdy. Th I ngth of crest being constant and small. the control section shifts beyond the contracted section and under oertain conditions tho

852 co-~ffi~ient of disch~rge, increaSfS eVf n wore tha,n, 3'09 The visl,lal examin?-tion of the jump does not indicate modulanty 1U :-.11 case'> hut the provlSlon of the reqUlred h m as per Plate XV[ll " essential to en~ure modular condition. Is . (b: .Open flume outlets ?oth narrON and wi~e are ven' sensitive ~lltlets .becausq the discharge vanes as H3/2. The dIscharge of these slmple outlets can easIly be lllcreased by adopting undermentionerl devices fOIl ling the control se~tion Ii) 'he discharge is increased by heading up water in the small channels by cattle and men sitting accross the section rlown~tream of the outlet. \iil Then have been r."sp.s where two men sat the whole night in water with a cloth strp.tehed across near the tail rear.hes of distribut~ries. This deVIce passes water below while heading up 3 / / to 4/} and cannot be detected. (iii) The cultivators usually throw bricks and rubbish accross the channel downstream of the outlet which is usuallv known as Daft )Bund), (ivJ rh .. discharge of the open flume outlets can '>e increa'ied by inserting horizontal lamina as shown in fiig l2. The upper portion runs as a weir and the lower nne as orifi~"'. The sum total of these rlischarges is more than the weir formnla discharge The greater the nnmber of lamina the larger the increa,;e. By lUsertmg even one plate, increase of lO to 12% is Lkely, i v J The discharge of the open flume mit ;et can also be increased by simply putting a pumpkin nr a pla.te in front of it as shown in Fig. 13. Ihe control section Fig. 12 shifts from middle of crest at G to C i in a widf~.r section and more dischargd is passed even thougf-t ,t may act as a drowned weir [he increase is { bout 20%,. 19. Doabie moiule outlet, (Orifice cum A P. M. or Open Flume3). SECTIO~ The first known outlet of thiS was called· after the Scrachley'S name. It used to be a masonry orif.ce outlet discharging into a well and then followed by an orifice in the well. The modern practice {Paper No. 146 P. E. C. Lahore, '1931 .by K. R Sharma, is to conscruct a pIpe outlet a.t bed lev~l of the parent channel and then to take out an open flume or the fig. 13 A,P.M. frilm the well as shown in· Fig 14 ' " These typ~s of ouUets are e,~onorriical and ensur~ a good ~ilt entry and ::easy adjusta ':lility where Pipf'~Cllm F.

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353 they have to be constructed across wide patrol-roa.d banks in the case of Branch at.d main canals. The design presupposes that the available working head is enough and to spare for dJuble loss first on the drowned pipe outlet and then in the module outlet. The loss of hearl in the pipe or tn'lsonary may be kept 0'1 ft, in all cas~s and the rest of the available working head to be used to set O. F. or O. S. M. (A. P. M.) as low as possible. 20. Rigid modules. (A) Kent's module Its design was based On a pressure float device as originally used by Italians in the design of their modules. These outlets failed because the floats could be raised by inserting sticks through the air-vents and the discharge could be increased. (B) Gibb's module. (i) This outlet was invented by A.3. Gibb, Executive-Engineer, Punjab Irrigation ~LSpublished in Paper No: 12-A Class A.P.W.D Irrigation Branch Publications. The module is named after it" inventor and gives an almost constant discharge over a considerahle range of water levels upstream and downstnam. It is only a rigid module without any moving part. fhe. module consists of a chamber, semicircular m plan, called pLAN

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Fig. 15 the eddy chamber, round which the water flows. Water enters this chamber through an inlet pipe, which delivers weter to a 1800 rising pipe in which. a free vortex flow is developed. It then enters the eddy chamber-vide Fig. 15.

355 the range of a module of one Sl'rni·dccle. This was not borne out hy experiments. the range f one cusee spiral module with 3 s"mi·cirdes wa.. only 1.42 tim..s that of "a single semicircl;' module. (g) Maximum pennissible tlownsheam depth above the module flooT was found to be ()'Sl G agamst O.5t D accnrliof! t,) Gjbh. When a • 'n 10 diverging flume was added to the spout the maXilllllTl downstream water level increaSl'd to n·] [) This modification is. therefore desirabl' th)\Yhen the Jellgth of exit flume or -;poul: i~ =2D.the Tange is maximum. Gibo's ide: th at the length of spout shc.uld 00= B was incorrect. (C)Other ri~id mooufI;Js KIIANHlsRIC10 MDDUU OUTL£T

Rt{. )\ llan'l3 Assistant EJ);;inpu

Punjab Irrigation and ChafluT EXt'cu'iv~ ::; EngiDec~, Punjab 1!J.iga1ion, have brDu~ht ':1.: out deslgns of RJgJd l\irnlules without ,c', moving parts . The Junjts of their working l nl'ed to he deteJrninc? in actual practjc.. . ID bot h cases. fhe de'l]gns cue shown in Fig "","'~'f"I'7..,."~,,,";;;:~~~f6...!!~ 6 and 17 Jespectively. ,.j

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Toe tail ma50nTY work on a channel is caned tail duster. When the fhscharD'e of a di ... tri',utary or minoT TH'lllf:e3 bPIl)w 5 cu·ecs. it is desirable for p.quitable disrribUl~)n to construe: ;11 the 1a.i~ outlt:t, in the LHn of a cluster. The length of the water coone from the tail dus.t~r s'wull! 10 noca"e be mnr" HY'n 2 mile-., ,be most sujtable oUIlet for use on the tail cluster is an optm flum~ ..~il outlets at the t~ il aTt.~ open ilumes> with. CJests at the ~e ~evel.. Usually liJt' dep,h on crc'~t IS kept one foot. I fie type de:>lgns of tile tall clusters are gIVen In FIg. IS (0 FIg :-cO. Design of oemi-moduJe outrets ill ebanneis with varying eli c!larglb. FIg ,b

[.,;,

(il The supply avaihble in the Sutlej Valley canals is so short In t!"'e ~riti".al sowing and maturing penods that it has been found necesisary to nm the,e channels WIth wilat is call.d normal supply for c~ rtain important period,; in the agl'icu! tura! rotatioll. fhis normal sup::>lv is 55 per cent of the iull supply. The design of ontlets on these channels should, therdore. be sudl that they take their proper share of the discharge both at full supply anti at normal slJPplv. III other words,! t is necessary to rl~sign t he out lets on the e s y"tems as proportional nudets: (il) fhc following are tl.e three types of proportional outlets which are suitable for us, on these canab;tal An open flume outlet having its crest at 0,90 and having an available working head of nct le,;s than OAD wm draw a prop.>rtional disc:harse at both fun and norrna l. supply conditlons in a channel. ~b) An O.~ VI. with H,==t143D and an avaih.ble working head of not less than 0.4D win draw a pruportional diSCharge at both full supply ant:: normal supply conditions in a Channl I. provided G does not excet'd O.69D. tC) All. 0" M. wit h G = 0.7,.,.D and Y =H~ will draw its due share of discharge al full and normal supply levels. in the latttf case it works as an open flume. fhe workmg head reqUIred in thIS ca'le is also O.4D. ,iii) It will be seen that a working head of 0'4D i'i requiJ'Pd for the design of outlets with the reQllired conditions. An ex~minle working heaf\s of outlet~ On th~ Sutlej Valh'Y Canals shows that whereas connitinns vary consirltrablv, a substantial number of outlets does Dot pO.~SeS;' a working hean of 0.40. It will thus be recognized th.u w]ltreas it is possible to design a large numb"r of outlets such that they would work proporliona}]y under both lnll aul n)flUl.l s'lp;:Jly C )llditiollS ttl~ nu.noor 1)f those whici\ cannot he so designed IS OClsidpra:.>!e. {iv) For pnrpnses of design, therefore, the outlets on ti~ a)[} -llece:mia distril>utalY Oil the Sur lej V"l.lly canals may be classIfied as follows:(a) Outlets which can be designed to work pmp0nionaiJy under both full aud nonnal supply conditions·-Such outlets must have an available working head of not less than O.4D ,b, Outlets which cannot be designed as class A but have a sufficient werking head to IJt" modular at full supply conditions, Sue!:! olltJets are those Vlhicll bav~ a working head of 02D to O.4D. (e) Outlets other than tnose included in class A and B. Such outlets have a very poor com mand i.e. less than O'2D

354 The exit at the downstream end of the m"
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d,=Depth of water at inner cinnnfO'!renre. dn=!}poth of water at outer circumference: h ==Head ..au<:ing flow, v~rying from 110 to hI : h,,+ 0= Total diff(~rence of level measu.red fmm the minimum wati"f level in the parent channel 0(' dist-ributarv to til" lion, of the eddy chamber (i.e indu.ting hea.d lost in inlet pi.pe=h" ) m=rofry=Ratio of outer radius to inner radiu,,; Q=Dlscharge. B=Width of eddy chamber=ro-rt. ' . . _ The [<}rmula is based on free vortex fiow. in which the velocity at any pOint van~s mver<>elyas the ~adius and by BemouHli's theorem that the total energv nf'a.d of all filaments IS con!'tant : ,. t fatal energy 11ead due to velocity pbs static head measured fmm the same datum.) Gibo's formula held only f(lT his standard design in which . h m=rofrt =2, and =1/7 ._cA.

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(iii) Poona ExpeIiments of Gibb's Modules.

The resnlts of the pooua Experimet1t..~ on Gibo's modl~le have be(>n Published in Reoearch Publication No.3 by CC. Tnglis and Rao Sahib n. Y. Jo!!lekar of CeniT"l Irrigation and Hydroclynaruic Rc!<earch Station Po lOa. Bombav, 1940. The conclusions :lrrived therein ::Ife summarised :(a/ Of the 6. bamt>~ in the eddy charnbH of the standard 3 cusecs modulE" in wl1idl rad~us of outer ~c:ir('~umference of eod_y_."_h~_I11~':leT: =2-0 radIUS of inner drcumferenc· d eddy ctu.mlJer

Md the r~tio of llll-:_~~~~~sing 'I7«locj~_at_ °llt.er _ c~rcnl11fere~c~ = 1/7. the first . D=depth of water at outer ctrcumference+h o

4 baffles weremo'-" effective in killing the hea.d viz. 0'12 ft. in 3 cusecs module than b~ffies 5 ~nd 6 which increased tt",· range by only. 0 18 ft. (bi When a hell-mouth was added to the inlet pipe. conisdeTably less he ld was requirftd 1;l'~ a~tain modula.rity and the range was increased. (c) lhe range was a minimum with m=r,,!r1 =2 as adopted by Gibb; but he wa"· wrong ill assnming that the r31'lge of his moflule could be inCTl'ased hv increasing the ratio BID; and the values of BfD within which a high Tange is obtained are 0"8 to .'5. (d) [ncreasing the number of baffles in semicircular mocble had a negligibJe effect on range. though fluctuation.. of di~charge within the ran~e. werf'o sl!~htly n:ducedo (e) [he range was not increased by"increasing the I.. ngh of the arc of curvature through which water flows before entering the eddy ch:lmber. (fl The Tange of a module can be increased by incn
356

After the outlets of a distributary have been classified as above and before proceed' with the design of outlets, an attempt should be made as explained in paragraphs 10-25 to lDg if any of the outlets clas£ed D cannot be converted into cla~s A or those classed C to class B orse; For successful dj~t~ibution it is essential that the number of outlets of classes Band C shOUld reduced to the mInImum. (v) The type of outlets that should be adopted for each class is as follows:1. Class [AJ. Fer this class of outlets which can be designed to draw a correct discharg at both normal and full suppl V conditions, the following type should be adopted:e (a) An ollen flume outlet with crest set at 0.9D provided B t does not work out to less than 0.2'. (b) If in [aJ above B works out to less than 0.2' an O.S.M. Set at O.75D may be designed such that the value of Hs ranges from 0.375 to 0.43D. (c) If an O.S.M. outlet as above cannot be designed for a particular discharge, then O.S.M. set at 0'69D may be designed satisfying the conditiom Hs =0'43D I[ Class [BJ. For this class of outlet, it is not possible at present to arrange for proportional working at both full and normal supply conditions. The best type of outlet for this class would be either :" (a) An open flume with H equal to five times the working head availabe or. (b) An O.S.M. outlet ~et at 0'75D with Hs from 0'375D to 0.4SD. whichever of the two would give a lower setting. so as to enable the outlet to draw some discharge at low supplies. Ic) In case the width Bt of the open flume outlet works out to less than 0.2' or it is not possible to design on O.S.M. accordnig to [b] above for the parhcular discharge then the outlet should be designed as an O.S.M. with crest at O.69D, provided it could work modularly under full supply conditions. Ill. Class (C) For this class of outlet which'has a working hea.d of less than 0.2 D it is not possible to design an outlet of the semi-module type. The only outlet possible is of the pipe or orifice type and the best type is Scratchley outlet. The working head Hw to be adopted for purpose of design of the outlet should be the average of working heads observed during the time of keen de.nand (1st to 15th September) for a period of 10 days. A fair proportion of these working heads should be personally checked by the sub-Divisional Officer (hy surprise visits if possible). (vi) when water level in a distrbutary rises above the designed full supply level on account of chan~es in regime, the open flume outlet draws a high percentage of excess. To guard against this, all open flume outlets, whether of class A or B. should be fitted with roof blocks.

m;

23.

Water course discharge observations, The discharge of water courses downstream of the outlets are observed by any of the following rr,ethods:(i) Float obstrvations (ii) Trapezoid.1 notch cip ,H.-tte Weir. It (iii) Wooden flumes or Portable Detachable dErAIl OF Tin flumes. 1--. -L. .. --t (i v) Calculations from the discharge formula , of the outlet L In the first case, the surface wirlth is measured say w feet and depth D in the mipdle is taken. The o j surface velocity is takfD by running a float or a cowl' 1 .5",_1' Ell . . dung piece for 20 feet length in a straight reach a~d ! 'l: liiliu-s " /:'-0 elf'• .,. 7i']iby taking the time by a stop-watch. Tile velocltYd i , ED D WA"1.1f etU/lf'SI. per second is then worked out say v ft. per sec?n -t. CU""'''GIDG£ The discharge= 06 wDv cusecs. This IS a faIrly approximate method. Fig,21 In the second case a trapezoidal sharp·crested notch is used as shown in Fig 21. It is called cipollette weir. Its us~ ~s desc~ibe? by A.S. Gibb, in pap~r No: 14,. Punjab P.W.~. Irrig:ttion Branch, PublICatIOn. It IS fixed across a water course WIthout headmg up w:ater 10 it or into a field by diverting the supply from the water course. The gauge readtng IS ta~en and the discharge can be got from tables published in the said publication. This method glves

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357 accurate results only when free fall conditions for the weir are available without headin water in the water course. The working head is required equal to the depth on crest Whi~h ui~ not generally available. 24. The Author's portable tin Hume fOT water course discharge. Experiments were carri;d out by the author to design suitable flumes for this purpose and the results were published in the Punjab Engineer, Lahore. February. 1940. A brief summary is given below for ready reference; (a) An accurate determination of watercourse discharges is a very essential factor for successful irri~ation and equitable distribution. Water is supplied to the cultivators from an outlet which is supposed to discharge the permissible discharge of the water course. The design of the outlet is based on certain coefficients which are liable to vary with different conditions of the design of the outlet and its imperfect construction. The public opinion is getting enlightened dav by day and the cultivators are now keen to get theu permissible discharge correct to the second !Jlace of decimal. (bl A cultivator is not satistied to know that the Irrigation figures are more thad the permissi bIe, (c) The discharge observations of water courses by means of floats generally result in great dissatisfaction among thfl cultivators. [he overseers and zilladars always report different discharg,~s taken by means of tloats, rhe discharge observations of a water course are, thus, very unreliable. The Use of the cippollette weir, as described in Irrigation Branch Paper No; 14, t::lass A by AS. Glbb, gives fairly accurate results. fhe free fall conditions for a cippollette weir are not generally available and the observations in the drowned conditions by an average subordinate generally give wrong results. It will, therefore. be a great improvement to observe the discharges by means of an open flume under modular, conditions, when the hydraulic jump is formed downstream of it. In practice, it \Vas observed that it needed special efforts to make the cippollette weir water-tight because water falling down the crest generallv scours the downstream bed and the weir is creeped out. Moreover, the velocity of approach under different conditions of the upstream water course section. affects the discharge considerably. (d) The idea of disci arge observations of water course by means of a portable flume, was introduced by Mr. Abdul Gafoor P.S.E (Sub Divisional Officer. TandalianwaJa) in his note dated 2-8-1926 circulated by the Chief Engineer. A coefficient of discharge 3'0 was adopted for the wooden flume for all readings which is not correct. A gauge of the flume was provided upstream in the return waH which is liable to be affected by the I )SS of head in entry and velocity of approach under different conditions of the water course upstream. Moreover, the design of the dume was not suitabl!'! as it required as much as 25 per cent of the head fat free fall conditions. The experiments were taken in hand by the writer in summer 1931 to improve the design of the flume and to ca.librate it for different heads and under different drowning ratios by means of actual discharge observations. The discharges were observed by melns of tank measurements. (e) The drawing for the type design of two sizes of portah le flume is given in Fig. 22. The flume No. 1 of one foot width is capable of measuring discharge upto 1'00 cusecs. The flume No. 2 of 1 5 feet width is capahle of measuring discharge upto 3'00 cusecs. The flumes were made of galvanisea iron sheet G.W.No. 22. They are quite light and can easily be carried by a beidar or on the carriflr of a motor car. One beidar can fix them in position in ten minutes. Each of the fluRles is in two parts. One part comprises the glacis and the other consists of the upstream approaches and the crests. One part can be folded on to the other. (f) The flumes are made according to the standard design of a meter flume described by the writer in his pader No. 154, Punjab Engimering Congress, 1932 and sketched in Plate No.2 of the said paper. They have a uniform width throughout their length. The length of the crest is 2H. The upstream approach curve in bed is laid with radius 2H. The gauge is providpd on one side in feet reading upto '01 foot and on the other side in cusecs at a distance of 3H from the beginniug 01 the crest. The flume is straight up to a length of 2H upstream of the gauge and is curved out with a radius 2H from the upstream return wall. The floor is kept level opposite the gauges. The dowDstream part consists of glacis 1 in 5. This design ensures a standing wave with a working head of 10 per cent of the depth on crest. The proper location of the gauges and the silt·free level flow opposite thl'm removes the error generally introduced by the velocity of approach, which would otherwise vary with the shape of the waC':L course upstream. (g) The graph for the discharges of both the flumes is given in Fig. 23 for different heads in modular conditions, so long as the hydraulic jump is formed on the glacis. It will not

358 Design of Portable Flu:nc>

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generally he neces ary to lun these (tumes in rlruwnec conditi,ms, bec::tuse in no case the requi:'e,f wNking Iwad is mf)re than 0·1 foot for modular condition; of the flume, Such a small ht)ad is generally available by pntting a flume in a hranch water course or in an open field. !11e discharge can De read if(,m the graph ')1' a cu~ecgauge may be provid~i in the flumt: itseH or by n~ing table NO,3, Tll!! main and thfl most impl)rtant precaution in obsPTvation d the dischar'gt' by means of a portable flume is th'lt its crest should be absolutely levd. This can ea"ily be arrang,'d hy means of a mason's spirit lev... t The spirit level may even be rigidly fixed with tne side walls and on the rigid cross bar across the ~re,t. fhls shoulrl 1ll practice be te~ted invariably by letting in a little water befoTE' the water course is cut on to the meter flume so that the depth on crest is 0'005 foot as read from the gauge. This should clearly show unevenUfSS in the cr(:~t. . The upstream ends should be well puddled aJJd the water course bflrm and bed should be s,haped upstream of the flume so that the entry is smooth There should be no leakagt' oolow the bed or on the sides. This can be very easily arranged on account of the ed f e provided upstream and the curved return walls, Care should be taken tha.t the tb')T opposite gauge is clear of any deposit at the time of observation, TABl,E No, 3 Sharm's Table for Portable Flume. Discbarge Oischarge Gauge Gauge Flume width 1'0' Flume width 1'5' Flume width 1'0' fiumfl widthl'S'

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~hl When th~ discharge is to be ()b~erved for ~n out>t whic 1, i.~ work:ng lr,'e [,jll cr ·,·jth a hydrauli~ jump, it noes nnt matter If water levd i~ sowlI.vhat he::tded np or depr -s,~d hy in<;ertion of the f}nme. The gauge of the m")ter wiilllecome steariy after a few minute.i ill such a c~"e. Bllt ",h<':n the discharge of an outlet is to be ob3erved when it is not working "dularly. it i" imDp.rativ> th'1.~ the ~....ater level In water course should not be changed lJy insprtiol1 of tlw flume in water-course or on the sides. rhe discharge of the watercourse is generally approvimatpl.y known from the conriitions of the wnrking of the Olltlet. fhe flume should be fiXld so th'lt the gange H',iding on the CllS c gilllge is in level with the wat'"r lwvel in the watercOllrsp. -\ pIg shoukl he fixp(l in the watercourse with its top Bush with the water level in watercourse befor(; \ .. , er is onen .. o into the flume. In case water ("vel in the watercourse overtops the ]wg or is dc, ressed tleio".v thf top of the p"g, the obsp.rv:ltion should he repp.ated by adjusting the crest a CCI [ding to appf'oximately )bserved gauge. rhe flume should he fixed neu the outlets as much as possible so that the loss in ()bser. vatlOn on the wat~reour~e nt 1 • hy the liHadar ann the Overse~r with thesfl flumes on compldints of shortage from t he cult; vat or, . ft is very difficult 10 satisfv the Zamindars afterwards when a wrong dIscharge is once inhmated to them by a Zilladar who generaIiy bases it on inaccurate float observations.

25.

01ltl"t. Chaks.

irrigatpd from one individual outlet is called cllak of the The 'lrea outlet. The discharge of the outlet is u aTken from the culturable commanded area in the s~j(l chak based en the permissihlp jnt~nsit y of tte irrigatir·ri and the water allow~nc'C. The maximum (-li,,~harge of an outlet is 7:75 cusecs ann thp minimum 1'0 cusec. The length of watncot1rse irrig'lt* ing a chak should not be more than 2'0 miles. The procedure to design f he watercourse and to fix the chaks and the method to work out the area, commanrl ann draw-off statement~ is explainE.d of this part 0'1 irrigation projects. I he A. P. M. outlet set helow 8i 10 D or even in ChaplH upto 12/1Of) or rigid modu les He suitablt' t:ipes of outlpts in the head reach of a channel so tha~ the increase of sup)ly at head is conveyed to the tail re::lches where it is most wanted. The proportion" 1 outlets slIch as O. F @)'jIOth, and A. P.M. @6/10th, ;ue suitable for the middle reach. The open flumps are suitahle for the tail reaches of channels an(l prefelable in the form ",f distributJrs and dusters. They are sensitive and can absorb the exce~s wt ich usually floods the tails ;n rains Or when the upper outlets arc closed by the cultivators for silt clearances of the watercourses.

xvn

Examination Que,tions. I. \Vhat do you kn')w about Kennedy's gauge outlet and explain the use of it. (T.C E. 1933) 2 Give the formu la us.d for calculating the discharge of three types of outlets used in the 1rrigation Branch. vVhat is the normal seUIl>.£( fo~ each type? 3. Give the formula for mea-snring the discharge of water-course with fair accuracy, exp!;.ining the ,arne (P I.B. 1141) and any co-efficient used. How would you mea~ure the discharge with great accuracy? 4. How would you calculate the minimum water level required at. an outlet from a contour plan of the outlet chak? \Vhat is the minimum size of outlt't chak you wruld normally permit on a canal in which the water allowance is 3'25 c"secs per 1000 acres? what are the objections to outlets of smaller s;ze? (P LB. 1940) 5. V\'hat difficulties. if anv, would ycu expect to find in the irr;gation of ... clzak which has an cutlet of 3'5 cusecs? ~ (P LB. 1940) 6. Make a dimensioned sketch of a clistributary tail cluster of two outlets, one 'Iront' and the other on the left s;de (at right angles), the paT1iculars for which are as fnllows:Full suppJy discharge front 20 cusecs, Left I'S cusecs Working hear! frant '5 ft. left ·75 ft, (P.I B. 1939 ) 7 The enclosed blue print plan shows the area which is proposeD 10 be ;Tngated from a channel m~rked 0:": it. Propose in it a suitable chak (without marking l1alws of watercomses, and design suitable outlets tor these. Each rectangle may be taken to contain 25 acre". Permissible annual intensity is 75 pc. Khanj Rabi ratio 1: l a.nd full supply factor at outlet head is 88 cusecs of I{/zal'ij permis'ible. !P.I.B. 1939) 8. Give the standard formula for calculating the discharge af e"ch of the following outlets. (a) A.P.M. outlet, (h) O.F outlet, (e) Pipe outlet and state the relative advantages and disadvantage of each of the~e types of outlets? (P I B 1938) 9. On the enc'osed blue print, mark the alignment of thp principal water couree from tne two tail outlets allowing one Naka to each square. (P.LB. 1938) 10. A certain minor distributary would he improved if the water level wen', lowered as much as practicable. A tail cluster for this minor has to be constructed for the firEt time. The R. L.'~. of wat .. r surface

360 n the water course at the site of the cluster are 512.40, 512.0 and 512.1. These levels are sufficient for command. The reduced level of the water surface in tbe minOT as nvw measured is 513.2. The discharge of the water courses are to be 1.3, 1.4 and 1.7 cusecs. The positions of the approaching water-courses are shown. Design the tail of cluster. (P.LB. 1938) 11. On the Blue Print supplied mark the alignment of the principal water-courses from the outlets. allowing one naka to each square. (P I.B. 1938) 12. Describe the two m@thods of measuring the discharge in a water-course. POlDt out what precautions are necessary and how the formulal are derived. (P-I. B. 1937) 13. Design the water-courses for 2L miaor on the enclosed blue print. Describe briefly the essential working principle of an A.P.M. How do you tell on inspection when an A.P.M. or an O.F. outlet is working properly? What are the respective advantages of an A.P.M. and an O.F. and in what situations would yon prefer one to the other? (P.LB. 1937) 14. Give a dimensioned sketch of a two-way tail cluster to distribute 5 cusecs supply at the tail of a minor. The front watpr-course is aligned on the same centre line as the minor. It is to be given 3 cusecs with a working head of 5 ft. The outlet on the right takeli vff at right angles and is to be given 2 cusecs with a working head of 1.5 ft. (P.I.B. lS36) 15. What governs the size of an uUet chak? What IS th .. optimum size for it? (P.I B. 1941) 16. Whatis the difference between a semimodule and a rigid outlet? WhaJ; is the main advantage and disa.dvantage of these types of outlets as compared with those of iron pipe outlets? (P I.B. 1936) 17. What is the maximum length suitable for a water-cour~e? (P,I.B. 1935) 18. Desctibe the hydraulic features of the following types of outlets and state under what conditions you would use each type. (1) A.P.M. and (2) O.F. 19. What are the hydraulic shortcomings in the working of:\ Crump's Adjustable Proportional Modul( ? How can they be remedied to make it work as a perfe"t submerged semimodule? (P. U. 1943)

PART II

CANAL IRRIGATION CHAPTER XVI

Irrigation Projects Introduction. Irrigation Projects usually fall in various categories such as :(i) Gravity system canals i rriglting the traci. hy flow. The rivers usually have a relatively steeper slope than the adjoining country due to their tortuou~ length. If the main canal bE' taken out from a suitable site in a river, it is designed with a relatively flattened slope. The main ca.nal at its tail with full supply abovJ the natural grouni surface is splct into distributin<: branch canals depending up,m the config ur ttion of lhe ground. Ii) Punlping system. In this ca,e the supply is pumped flOm the sub-soil reservoir or from a natural stream into the distributing channels (iii Drainage Scheme The drains rna" tJe surfac a, seepage-cumsurface orains seepage drains ano underground covered drains to remove! storm water or lower the water table. (iv) ... tOT;lgll reservoir schem s as de3cribed in P;trt II [ of thi~ book. lVj Reclan,ation Schemes. They are nece_isary to reclaim the thur and long~dlands. It is not c0nsider~d neces~ary to descri 'e all such schemes ;lnd projects in this book. In what foU()ws, the gravity system project is d'scribe at length. The principal req1lirements are generally the same; although the detail and design differ a lot ill other cases. 2. Preliminary Investig2iions. (a) Reconnai~sance Survey:- Before a p:oject is sel 'cted f)r detalled investigation, it is essential that the whole of the country in its n~ighbourhond shoulrl be pxamined by means of a reconnaissance. The principal obj .. cts of this prelimina y surve.\' are to b:} oota ned. at comparatively srr:all expense of time and mor'ey, gpneral information a.s to the nature of the tract examined. the facilities offered by it for irrigation, ::lnd the relative merits of all projects practicable in it. Such a reconnaissance en lDles a general plan to be drawn un sa as to utilize those facilities in t!1e best and the most comp ehensivd manner possible s() that each individual project prnposed will work in, and will not clash with other schemes feas~ble . To enable a proper comparison to be made of the relative advant"ges of competing schemfs, approximate geuel-al surveys of the 'Porks and irr:gable areas should be undertaken, and rough plans and esjmates of th~ pfl)p),ed work.; Should be rna Ie. fhe de3 i gns for these shoukl not be considered as final ones, nor the estimatf's for them as txact. bu t sutiicient care should be taken in th"'ir prepartion to obviate extensive a:terations thereafter, as those may greatly lesspn the value of the prelimin,lry work. C:lre ehollld also be t:lken to prepare the designs and estimates of competing pmjec s a'i far a; . pos'iible on the same general Lnes, so that a fair comparison as to tl1eir costs all(i advantages may be obtained. . (b) Hydrographic Survey. As soon as it has been a~certained that a favour a scheme is practicable III the area und r reconnaissnce, all hynrograph c investigations lltcessary should Le started, ano thty should be continued for as long as possible. Rainfall data must be studied. High mean annual rainfall does not pre:lude the necessity of canal irrigation of the rainfall is not available at the sowing time of the principal crops. (c) Soil· Survpy. Soil survey should be taken to know the alkalinity and aciditv of the soil and its ~uitability for the irrigated crops. Agricultural Depa.rtment shou~d be consulted about the crops which would be suitable for the tract. (d Com'l1unicati()n c • The Roads and Riilways departments should 1;e cor,sulted to extend mans of lommunications, to cheapen the cost of construction and to develop the rapid:ty. (e) Geological survey. The Geological Department shonld advise on the general geological conditions. and in licate what special precautions are necessuy to ensure the safdty and success of the works.

362 (f)

Drainage.

me draiage of lands should be invt'stigated and jJrovided for in the

schemes. Detailed Surveys. After the f~asjbilty of thf' project has ;hen established with (lue consideraton of the preliminary investigations, detailed survey;; are requ;r~d toinve~tigate the f lllowing aspect!; :d) The !rcation of Headworks. The dptaiJeo riVI'T ~urveys are required. The usual plane table or Techometer survey methods II.re not applicable in river beds of large riv!lTs special methods not usually dec;criced in survey book~ are required: The student is advised to study the book wr tten 1y Rai Rahadur A. N. I( hosla •. LeveIiing of Precision Across Rivers 19:4 (Disc. Method)" which deals with thi .. suhjectiQ detail di) Alignment of Canals and Distibutaries. Cant' ur surveys usually to a. scale of 2 inches to a mile are requind. These contours may be at 5 ft. intervals. They are generally available from the Survey of India Department, and if not, they h::lve to be preparen. (iii) Al"gnment of water-courses and Irrigation chaks. The contoured. survey plans showing contours at one foot intervals on a scale of M inches to a mile are required. The areas are divided into rectangles a nd Squares and levels every 500 ft. distance observed along long and cross lines. These i ~ not genprally availabe with the SlJrvey of· India Departm3nt and have to be prepared by a special staff of the Irrig::ltion Dep:trtment.

3.

4. Alignments. ~. ',Having determined the source of supply and its relation to irrigate lands, the third questio.a\i$tile alignment of the canal. This should be so made that the canal should reach the highest part of the irrigable lands with the least length of line and a minimum expAnse in construction. the line of the canal should follow the highest line of the irrigable lands, preferably, skirting the surrou T1 ding foot hills. and passing down the summit of the watershed 4i:viding the various streams. .: To get at the best alignment. preliminary surveys are necessary. On a large scale contour plan the C. L. (Centre line) of canal, may be marktd. The flnallocaiion may be made on the ground with the aid of a few trials. ()bstAcles to Alignment. (,;,,'.' (b) The best meJhod qf avoidiDg the cross drainage wodes should be considered. Estimates of ,cost of materials required for consbuction and subsequent maintenance should be made. . 'c '.,. " ! ):,

.'

I. Curvature • . ';;~l ;••. (c) ~ ,A dire(ft or straight course is the most economical, as gives the .gre~test f~edom of flow and CilU$CS tke least erosion of banks. The inst::rtion of sharp bends mevItably results in the destruction of the canal banks.

it

MINIMUM CURVES IN IRRIGATION CHANNtLS.'

.! [.;.

..-.:

'-.L.

,The minimum radii for curves are given below ;--Capacity 01 channel Minimum Radius of the curve Over 3,000 cusecs 5000 it. 3000 to 1000 ., 3000 ., 1000 to SOO •.. 2000 500 to 100 1000 106 to 10. " 500 " I_ess than 10 " 300 " As far aspOS~ible.longer radii should be given.

Bench Marks. • ...., [d] Permanent Bench Marks should be left at regula~ intervals •. These should gi~e ,inscribed redu,ced levels for cross reftrence purposes. 5. Slope and cross Section. ~ .. According to Lacey's silt theory, there;j~Lonly one section of· a channel and only one slope at whidlihe' canal carryhlg a given dis~harge will carry a particular grade of silt (silt factor). The wajer in. the, main ,canal carties. 9ilt with a high silt factor, . This is gradually reduced in Branch Canals and Minors. The channels section slope i1\ hence fixed by silt analy'i:!is. Any excess: in the slope of the country.. has to be destroyed by'suitable dT(;)ps (Falls). •. .:.;...,' , . r . . ('or

4:~

" The cross section of a canal may be so designed that the channel may ,be' wholly m excavation, wholly in embankment or partly in excavation and partly in embankment. The typical ross. sections are given in chapter VII of part II. , Fall and Drainage Works-L. Section. ,/ f . . , . As the natutal fall of the country through which a canal runs is usually greater tMn the slope of the canal, falls are provided. The location of these is usually fixed at thel site whete the canal come3 too high above the surface of the ground, while their distance apart is So arranged that they shall not have an excessive height or fall. If a canal can be so located and aligned that it will skirt the. slope of the country on a grade contour it becomes possibie to give it tile most desirable slope throughout its length without the introduction of falls, but where it runs down the slop~ of the country, compensation must be made for the difference between the excp.ssivo ground slope over that of the cand If the alignment of the caRal cuts the natural drainage lines, either the drainage should be diverted or cro.;sings provided. In no case are the drainage lines to be obstructed. 6. Location ot H€adworks. The aim of the canal Engineer is to supply water to the irrigable lands by rHrect flow from the distributing channels. Hence the headworks have to be so located that this condition is brought about. It may either result in tapping water upstream or rai;;ing the pond level of the river by aptificial obstructions. A headwork comprises the following :(1) Diversion weir or barrage; (2) Undersluices ; (3) Head regulator: (4) Silt Excluder; (5) Silt Ejector, (6) Escape. fhe desL;n of the fint three works has already been describ~d in Chapter IV of Part 11 and items Nos, "and 5 have beeD ex;>lained in Chapter X[ of Part II. Canal Escape. Escapell are int.,ded to escape surplus water from a canal into the nearest river or some other natural drainages such as river ereeks. They serve as safety "alves for the canals. Their function is three-f.,Id:(il The excesses upto ten percent of the authorized discharge can generally be utilized without endangering the canal or distributary banks. The abnormal excesses which sometime; enter a canal due to sudden changes in riv
~

~~"

:,--:

No direct o~tlets should be given from the Main Canal and Branche!. as th~ regUlation . of supplies is very dIfficult. All outlets should take off from Distributaries and Minors. . The water is drawn a.t proper intervals from the main line into moderate. sized branches "~ich ara so arranged a, to cOlllmand the greatesf area of land and to s~pply the laterals , (distributari•• and water courses) in the most direct manner ..

364 Location of Distributries. Distribution from a distributing canal is m0st economically effected when it runs along a ridge, so that it can supply water to its branches and to channds on either side. In ~he c~se of main canals this location can be made only in occasional instances, but the distnbutanes taken from these, mains should be made to conform to the dividing lines between water courses. The capa :ity of the distributries, which traverse the sepal ate dra.inage divides, are prop()rtional to the duties they have to perform, (the natural bounrling streams limiting the area they have to irrigate). '.'''--

Fig~ 1

.

'-_ ...... , ,

...

Fig. 2

Careful serveys should be marle and grea te3t care taken to h aJance cuts and fills and to so locate the distributries that the least loss of water shall occllr from P'1; alation.

Go.d

Fig. 3 Fig. 4 , The figures 1, 2 and 3 above show an ideal distributary system. Such an arrangement enables the least mileage of channels to command the greatest area of country by furnishing wat~r t~ both sides of its line, At the same time perfect drainage is obtained by the water fl? W1!lg In ?oth directions into the natural drains. Fig. 4 shows the faulty alignment of dlstnbutanes and drainage channels.. .

365 Design of Distributaries.

I

,? \

The capacity is proportional to the the duty performed and water surface kept at a level where flo N irrigation is possible. Th~ cross sectional area is diminished with steady drawoff from the outlets The capacity of the different parts of the system must. be based on the full supply capacity. . In order to avoid high banks and to ensure the surface of water being above that of t~e countr~, the slope of the disty : should be made as nearly parallel as possible to that of the land It traversps.

Hence alignment falls must be introduced.

Dimensions of Distributar:es . . The' greater the ,amount of water discharged by a distributary, the smaller will be the proportIOn of cost of malUtenance. Hence hrga sized distributaries are better than small ones. The minimum bed usually kept is 3'0 ft. i:' . .

8.

Intensity of Irdgation and water allowance.

The relation of water supply to the lanrl depends on the raiafall and the q 11ality of land, as the depth of each watering is fixed by the composition of soil. The soil survey should give both the chemical composition and the fea<;ible texture. The soil must contain chemical plant f?od and humous (decayed organic material). It should be free from Alkaline salt. The periodiclty of watering is fixed by the climate, the crop period and the number of "aterings required for the maturity of a crop. The losses in transport have also to be considercd. . Generally speaking the intensity of irrigation in the Punjab may be kept about 50% In the case of proprietary villages, where means of irrigation such as wells exist. In the case o~ ~ro'vn Waste land of the colony areas. the intensity of irrigation from 75 to 80% will do gl,:mg about 20% land for rest during the year. Near the Cities where the vegetable crops are raIsed, the intensity of irrigation shoull be cent percent. Generally speaking a water allowance of about 3 cusecs per thousand of the C. C. Area is enough in the Punjab and in the case of the sugar, rice and garden area, about double the quantity will do. 9.

Capacity 01 Channels.

The record of areas taken from the Settlement records of the villages to be irrigated by a distributary is used to work out the capacity of the channpl. The area is abstractl:.d in a statpment called the chak-bandi form given on page 366 in Form A. Usually chaM, salab, abi and banjar shamlat induding ghair mumkin areas are not allotted any water. The uncommanded area is excluded, The remaing area is called C. C. Area to which water allowance is applied and wari is allotterl. The command statement is worked out as shown in Form B to work out the levels required downstream of the outlet to command the chak served by it. It is a bad practice to include the uncommanded area in the C. C. Arpa, because it rasults in temptation to the cultivators to head up supply in tm. parent channel. This upsets the equitable distribution of supply and results in silting of the channel. Then the Capacity Statement of the distributaries and minors is worked out as per statement form C attached. The columns of the Capacity Statement are self-explanatory and need no comments as detailed information in designing the sections has already been given in Chapter V of this part.

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369

10 Watercourses aad 0 utlets. The watercourses are designed on contour phns, scale 4 inches to a mile, showing contours at one foot intervals. The watercourse usually follow3 the ridge to avoid embankments.

FigS

The length of watercourse is generally limited to 2 miles. The watercourse is usually branched to reduce the length and to gain command, lowering thfTeby the highest levrls nquired down .. stream of outlet when working a!> calculated in form (B) given in para 9 above. The usua watercourse slope is 1 in 5000 and the command at the fiel. 6 inches. The workin~ hearl fo 'he outlet is kept not less than 1'0 foot. A typical layout plan of a watercourse is given in Fig. o.

370 The desigl'l of the Qutlet is worked iIi a: statement called the Outlet ~tatement. A. copy of the usual form used is given in Form D. The columns are .$elf-e~planatory, anc;l, need no "luddation. The sl!b-proportional outlets are used in the head re:lches of' a Distributary, such as A. P. M. set b~low .6 D down,to 1. 2 D. Proportional outlets are desirable in the middle reaches : set at .6D up to .8 D because the setting )f the ~. pM .. to give due share of supply is ;8D~. In the tailreaches of a channel where the command IS poor. open flume outlets are desirable, as they neer! comparatively low WQT king heads and are sensitive to absorb the exees,> reaching the ta'l in the case of slack demand. Theory of ontlet design has been described in dptail in Chapter XV. 11 Rules governing the sUbmis'sion of Estimates for and the con",auction of IrrigatLn work" , ,l.

Ge~eral.

The following rules define the proced'hre to be adopted in connection with irrigat fon projects. Throughout the rules. the term "Irrigation projects" or "Irrigation work" SllOUld be held to include the Navigation, Embankment Drainage, u ater-storage projects or work,. The expenditure on works only should be the criterion for determining the authority, whose sanction is necessary to an estimate (original or revlst'd). II Classification of Works. 2 Irrigation works for which capital accounts are kept are classified as either" Productive" or"unproductive". The criteria to be adopter! in deciding questions of classificattotl: are given in paragraph 12 of this Chapter. Rules regarding the prepar3tion of Irrigation Projeets. 3 ·T]ie. papel s to bP. suhmitted with the projPct for an irrigation work consist of a report, such pl"n~, measurements, quantities, rates and specific~tions as may be necessarv to enablp the suitability of the designs and the
" 371

which the work is to be divided and the' time likely to b
372 prudence would exercise fn respect of the exp~nditure of his own money. 11. fhe co:np\ete estimat~ for a project besides incluriing all anticipated direct charges .. houlrl furth~r in:lude a:; iniirect ch'lrges the amount required to cover the capltalizltion of abatement of land revenue on the area o:cup:ed by the works, cost of audit and accounts establishment and simple interest on Capital Outlay prior to the work being brought into operation. The direct charges should be classified. under the aopro .Jriate sll~-hea.rls of Account. the main headings being (1) Works, (2, E,talJli3hment. (3) fools a'1d Plan t and (4) Leave and Pensionary charges. The items incluied under the head "Work," should be cia,sifi.dd under the prescribed "head Service" and 'D~taileci heads' enu n~ratpd in F0rm l[ The c03t of surveys' including expenditure incurred prior to the ~u) nissil)n of the project, should also be included in the estimate An abstract framed on th~se line;, in the Form No. Il appended, m'lst acc')mpany every proje<;t submitted for sanct'on. In the cas~ of a large project the subNorks mlY, if de3ired, be further sub·divided sc> a<; tf) show individual large works. 12 If it is known that the project will constitute the sole charge of one Of more Superintending Engineers the estimate of th'! Cl)st of th} Sup~rint~ndin~ Engioeers and other establishment should be framed in d~tail, a suitalJle amount hein~ added to cover an ddequate shine of the cost of the Chief Engineer's ec:tahlishment. Even where a S'IDerintencJing Engineer's charge i'.ctu1.ls may be entered in the estimate. Unless Government directs ot'1erWlse the provision to be made br es~ablishment should include 25 per cent on the estimate of Works Outlay for dep'lrtnental establishment and 1 per cent for Audit and \ccOllnts, while the provision for Tooh and Plant will be I ~ percent on ~he Works Outlay Estin ates for large surveys for new irrigation projects should. hONever, provIde only for a charge of 5 por c"nt on the cost of sp':)ci~.l e,tablis'lrrv~nt to cwer th~ supervision charges thereon. In the case of irrigation project. hr which neith<>r Capital nor Revenue :\CCJunts are kept, it is unneces<;ary except in the case of large surveys for lieN irrigation projects, to enter provision for Established and fools and Plant in the estimate unless, for any reason, it may he deemed desirahle to do so in order to forecast the ultim(l.t~ fE.su1t of th" project. 13 Charges for capitalization of abatement of land revenue should be calculated. at twanty times the amount of land revenue remitted. while provision for Leave and PenslOn allowances should he at the rate of 21 per cent on the gross charges for Establishment. 14 Simple interest on Capital will be calculated at the rate sanctioned by Governments from time to time. on the probable annual outlay. 15- No provision should ordinarily be marie for the minor head "Suspense" as this head in the accounts represents services of a general character not necessari ly pertaining to a particular project. If howtver, one or more Divisions are expected to be maintained exclusively in connection with stock required for the proj(ct, provision for "suspense" may be inclurled, but only to the extent of the balances likely to be outstanding under Suspense on the date of closing the constructiln

IV. Storage Projeets. 16' The report should, in addition to the information specified in rules 3-15. give thearea of !ank and contents when full, the area to be irrigated per unit of storage the length of the dam, Its maximum height awl shape, materials proposed to be used in its construction and the mode in which the Wa ter is to be let off for irrigation, The questions. of the available water supply, number of times the reservoir will probably fill. rainfall and proportion flowing off the catchment, lo~s by evaporation and ahsorption etc: should De fully dealt with as well as the quantity of floodwater for which provision must be made. the flood absorption cap~chy of the reservoir, and the water~ way of the escap' weirs or sluices. The re~ults of any experiments bearing upon the strength flf the ml,terials proposed for use in the dam should be dea.lt with, as also the silt content of the water and the probable effective life of the reservoir. V. Projects Affecting any other Province or an Indian State. 17. Where any other province ot' an India State is also concerned, the report should detail the arrangements mutually agreed upon fOf financing the works, ihe terms upon which

373 the water is to be sharerl, the agency by which the work; will be con,tructed and wherl' an Indian State is conCflrned, the ag~ncy by whom th! aC~f)unts are to be audited on behalf of the Stat" . When a project or different projects are likely to brin a land into the market simultaneously in differen~ provinces or Indian States, and the sale-p~oceeds of such land form part of the estinnted revenue from the project, the report should state what arrangement the Governments concerned have made to meet the contingency. A draft of any formal agreement into which it. is propo ;ed to €ilter to regulate these and any other matters in respect of which agreement is deem"d is necessary should a :company the project. 18. In all projects wJ.ich may affect riparian or other interests in Indian States, Government will ascertain the views of the Durbar or Durbars through th~ political authorities concerned. VI E mba.nkment5. 19. In the case of new lines of ri ver embankmen ts, the report should show cl >arly the financial responsibilities of Government in connection there with, and the manner in whi0.h it is proposed that the outlay shall bp. recovered. vn Nature of sanction. 20 The sanction accorded by the Provincial Government to a project for an irrigation work shall be regarded as in th ~ na.ture ot an a·Lninlstrative approval to the project,and not as the final technical sanction to the detailed estimC1tes of the works. Such technical sanction will '0~ a~cordej by tbos:! officers of the Public Wurks Department. Irrigation Branch, to whom pJwers hav
YIlt. com.mencement of Works. 21. It is a fLlnd tmental rule that no work to which these rules apply shall be commence 1 upon an Irrigation project, until the folbwing conditions have been fultitled.(a) rh~ approval of Govarnm :nt to the project has been obtained. (b) There is a slnctLOned d~s;gil and djtailed e,tima.te for the portion to be commenced (cl Funds have been allotted for the work. When these c >nditioni have been fulfilled, Public Work's Department. Irrigation Branch. are co:npetent to authorise the commencement of construction. 22. Government in the Finance Dapartment. in consultation with their \udit Officers may prescribe rules to regulate expenditure de~itable to a sanctioned project upon such survey and preliminary operations as may be necessary in order to ena')le the detailed ejtimates to be drawn up. IX. Rules Governing the Accord of Technicll Sanction. 2~. When a project has been sanctioned by Government, an officer of the Public works Department, Irri~ation Jjranch, to whom power has hean ilelegated by GO'lernment, may sanction detailed, estimates for component parts of the project against the amount provided for the 'Sevice' or "Detailed" head in the abstract estimate (Form No. [I). 24. (a) Detailed estimates, subsidiary to a project estimate' may be for a single work such as a bridJe, a certalO num'Jer of miles of excavation, etc; or for a distributary in which a numb"'r of small works are incllHied. In the first case, the cost of the work should be specified by detailed heads in the abstract while in the second case the abstract should be prepared to show the component items and liabilities separately in detail under the various service heads of clas,ification But if a work of exceptional magnitude costing more than Rs. 10.000 becomes necessary, a separat p estimate shou'd be prepared for it. (hi A separate estimate should be prepared for eaeh distributary or, where thp.re are minor channtls, tWG estimates one for the main distributary and its important branches and one for the minor channel" but the whole e'ital account shoul d contain provision for these charge 0; except I per cent on account· of audit and accounts establishment, at the rate given in rule 12.

374 - 25. When it uecomes evident that 'the amount provided for a "Sub-work" or a • detailed" head in the project estimate will be exceeded, the following rules must be obsevred . (a) Subject to any orders which Government may pass in the matter, the officer-incharge of the project may transfer provision to meet such excess from another detailed head of the same sub-wor« on which a saving is anticipated. (b) Should it become evident that an excess over the amount pnvided in the abstract estimate for any sub-work will be exceeded, the officer-in-charge of the project must report the fact immediately to the Finance Department. He should, at the same time. intimate what savings, if any, are anticipated upon other sub works of the project. . (c) rhe Finance Department may -transfer provision from Ot,e sub· work; on which a: saving is anticipated, to meet a probable excess on other, or it may permit an excess over the provision made in the abstract estimate for any sub-work 11pto an amount to be stated by it. (Note.-The sub-works into which the minor head "Works" is divided are enumerated in J.or~n_No. II appended to these Rules. X. Modification after accord of Sanctions, 26. After the Government's approval of the Project for an irrigation work, the Chief, Engineer m'ly, if necessary, and suhject to the provisions of rule 25, modify the details of the works; providt'd that if any such morlitication is in the opinion of the Chief Engineer substantial. a report of such modificatIOn shollid he made to Governmpnt. Note.-Modification will include abandonment of iterns included in the original estimate or provision of items not included therein, and an increase or reduction in the area to be irrigated by ~ the Proj ect. XI. Rpports of Probable Excesses. 27, Whenever it is ascertained that the expenniture upon any project is likply to exceed the amount sanctioned by the Provincial Government by an amount' higher than that which the Public Works Department. Irrigation Btanch are empowered to pass, Finance Department should be immediately advised of the anticipated exess without waiting for a revised estimate. The revised estimate. if npcessary should he prepared in due course. and sudmitted to Government with a full explanation of the causes of the excess ann of the probable effect on the financial results of the work. The Finance Department should also be imrnediatly informed, _ ., if at any time during the course of construction, it b"comes probable that a work, sanctioned as .' -.' productive, will fa.il, in operation, to satisfy the criteria which must be satisfied before a. work can be regarded as productive. '. ~ . _~ '._ ~ ~ "i·;" _

X 11

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Supplementary and Revised Estimates.

28_ Any development of a prJject thought necessary while the work is in progress which is not fairly contingent on the pr,)p~r execution of th;! work at first sanctioned, must be covered by a supplementary project e,timate. accompanied by a full report of the circumstances" which render it necessary. The abstract mmt show the arnount of the original estimates and the total of the sanction required including the supplementary am')unt. 29. A revised estimate must be submitted when an original san~tionerl estimate is likely to be exceeded oy more thln 5 p ~r cent and a second revised estimatd when any excess is ~mticipat ... d over a sanctioned revisci estimlte. The revised e3t;mate should be accompanied by a comparative statement in Form No. ) Il.appende
XIV: Completion Reports. C

. 32. , The estima.te for const(~~tion aLan irrIgation work should be clo<;e~ a.c; s'o;~ ~c;. the project is praCtically in full oper form s~()uld. be..prpareci only in resp~ct of p£(')jects ianctio '! d by Government. For sm'l.ller proje~ts, and other open capital works which are sanctioned by top. Pu'llic Works Department, lrrigation Branch, co npleti ,n reports s.hGuld be prepared in 0 e of the forms p'''escribed. . ..'" . '" ." .... : Schedule A. A, statem mt showing by wor'~~; and sub-works, clas,>Hied ullder the relevent aetailed heads. the actua.l expenditure on works completed upto tile' da.te of the closing of the 'Construction estimate. . . .:' ~ . ' . ,. ,. Schedule B. A statement of works which are within tJ.. e scope 01 the sanctioned estimate, and of which detailed estimate~ h!lve been pre'paten ;"nd sanctioned by competent' authority, which were incomplete!ot had not been begun on the date of the closing of the construction e s t i m a t e . . ' . Schedule C. A staternE'nt 0.£ works, whether included in the construction estimate or riot, which have been sanctioned by competent authority, between the date of closing the construction estimate and the date of the submission of ·the completion report. • . Sehedule D. A statement of works for which no estimates have been sanctioned upto the date of the submission olthe completion report. but the probable exp~nditure on which can be foreseen and which is necessary to complete the Project. (. .'. Schedule E. A statement compiled as a combination of statements A,B,C & D. This. statemflnt should also show, for purposesof comparison, the sanctioned estimate by works an i sub-works, classified under the relevarlt tletailed heads of account. A repQrt, on' the works executed lipto. the time of the ,closing of the construction ~stimateand an index map or maps showing the Project as completed, will accompany the~e. documents, fhe report wilL discuss the - financial result already attained and expected in the fuiure and will be accompanied by' forecast fin:lncial statements in Form No. 1 based on Schedule E ,above 1. e. on the total antidpatell ultimate ~x:pendit\1re on the PrQj~ct. Part III of this form will be signed by the Chief Revenue Authority of the province. 34. l'he schedules A to E ,accotnp:J.nying completion reports should i!litially be signed by the ~ ?:ncer. in- ~har!2'A of the Project (who is particularly responsible _. f6i-.figures in co~u;m~~ 5-9 of '-'cnedule D and consequently column 10 of Schedule E.l and ,coumer-sIgned as "venfIed by the Accoun~ant Geaeral, in token of his verification of actuals and classification. 35. The finaIlcial statement submitted with (';)mpletion reports should similarly be SIgned and cQlmtersigned>c but 'in this case t4~ Audit Omcer sho.uld do so under the words "Actuals and calculations checked". , 36. These documfnts should ordinarily be prepared ani submitted to Government within '6 nonths of the closing oj the cons~ruction estimate, o:r 12 month~ in the case of.. an exceptionally large work. If this. is nat found possible within the . per~od specified, the Finance Department ·should be advised of the reasons for delay _and t,he probable date when the documents may be expected to he ready. . ' . . 37,. Schedule E.will be treated as a revised forecast of expenditure against the'sanctioned' Project .. All important works whi~h had not been commenced and which were within the scope 'of the sanctioned estimate should be included in schedules B, C or D as the case may be. 38. Subject to the restriction tha~t thetotal expenditure against thq project shall not exceed 'the amount sanctioned for the Project by ltn amQunt ,gr~ater ,th~n th'lt which t~e Departments are empowered to, pass, the Public. Works D(jpartment,. Irr.lga!ion Branch, 15,. competent ,to pass expenditure between the (late of closing the Gonstru~tIon estimate, and that of. tDe' approval' of the completion report by' c()mp~tent authority on- (a) 'Works entered in schedules B. & C. (b) Works, ~n~ered .in Schedule D, within the limits and subject to the .' . 'conditions 'specifif!d. 39. On receipt of approv,al of the Government to the completion yeport. works included in Schedules B. & C. ma.y be carried to completion by the Public Works Department, Irrigation

Branch, within their powers of sanctioning excess over estimated amounts, approval of Government being obtained to any higher exces<;, Public Works Department, Irrigation Branch may also. on receipt of such a )proval, sanction further outlay on other works aga inst the open capital account of the Project subject to the conditions usually laid down.

FINANCIAL STATEMENTS. FORM No. I. Part I. Summa.ryof the estimated direct charges to capital account. Years.

Works.

Establishment including leave salary and pension charges. 3

2

1

Tools and Plant.

Suspense. Total.

4

Less receipts on capital account.

6

5

Net total.

8

7

---------------------------------------------------------------------------* Form No, 1 Put [l Summary of the estimated indirect charges to Capital. Capitalized abatement of land revenue.

year.

Cbarges on account of audit and accounts establishment

2

I

Total 4

3

FORM No. I PART III. Estimate of growth of Irrigation and revenue receipts and charges. Revenue receipts and charges. Gross revenue due to work.

y

Irrigated area ear at end of year.

2

1

Net revenue due to work.

Charges Enhanced both land direct and Including Excluding Direct revenue or Total. indirect enhanced enhanced ~ receipts. indirect against land land :; E revenue. revenue revenue, revenue. QJ P::i account. 3

5

4

6

7

8

9

FORM No. I. PART IV. Estimate of net financial results of-years after the probable date of completion of the work. Simple interest at

% on capital outlay Direct capital Year outlay during the year. 1

2

Direct capital outlay to end Qf year.

3

to end of previous year plus half outlay during tbe year. 4

Net revenue includin~

Net enhanced Simple revenne land reVenue intere~t less less simple column 7 of net revenue. interest. part III. 567

377 Form 1I. Minor head. Works.

Establishment including leave saJary & J=ension charges. T. & p, Smren,e. De'luct receipts on Carj'al Account TotaLDirect charges. Capitalized abta.. . ment of land revenue. Audit ano. Accounts . . Total indirect charges Grand total.

Abstract Estimate of cost~_~-:-;-----;-___ Project. Sub-work. Detailed head. Amount. Direct charges 1. Headworks. A. Preliminary expenses. B. Land. C. Works. K. Buildings. O. Miscellaneous. p, Maintenance. Contingencies. 2. Main Canal. A. Preliminary expenses. B. Land. D. Regulators. E. Falls. F. River and Hill torrent works. F. (I) Other cross drainage works. G. Bridges. H. Escdpes. I. Navigation. .T. Mills . K. Buildings. L. Earthwork. M. Plantations. N. Tanks. and rivers.· • O. Miscellaneous. P. Maintenance. Con tingencies. 2. (a) Branch No. 1 As for main canal. Z. (b) 1?ranch N o.2 do .. i. 3, (a) Distributa,ries ~ . group No.1. A. Preliminary expe ses. B. Land. C. Works. ·K. Buildings. O. Miscellaneous. P. Maintenance. COBtingencies. 3: (5) Distys : gtoup As for group No I No.2. . 3. (c) Distys; gnlUp No.3. do 4. Drainage and pro. tective works, . 5. Watercourses. 6. Special Tools and plant. Unforeseen expenditure.

Indirect charg~.

FORM IlL REVISED ESTIMA TE. Comparison between original and revised estimate, Sub- Detailed work h ead .

Minor head.

o"

I Modifications flgtl~a sanctioned by es t1('om PI' t ent rna e. authority.

Total (/) sancrevised ' E ~ t'lOne d e~ t'Ima t e Sa.vmgs. xcess. ~8 estimate ~

FORM IV. CO:VIPLE nON REPORT. Schedule A. Schedule of works showing actual expenditure on works completed upto the date of the closure of the construction estimate, ( lassification. Serial No. of item

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Schedule B. Schedule of works of which detailed estimates had bp.en sanctioned prior to the date of the closure of the construction estimate but whIch were incomplete or had not been begun on that date. Outlay to date of the closure of the construction estimate.

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o

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379 FORM

COMPLETION REPORT. Schedule E, Comparison of expenditure by main and s'lb-head;; with the provision in the estimate sanctioned by Government. ~

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14

12. Classi!iCltinn of Irrigation. Navigation, Embankment and Drainage Works into "Productive" and "UnProductive". 1. Prnjects of Irrigation, Navigation, Embankment and Drainage, are of two classes :(I) Productive and (2' Unproductive. 2. To admit of a new work b~ing classed as Productive Public Work, the following conditions must be satisfied :(a) There must be good reas~:m to believe that the revenue deri 'len from it, will within ten years after the probable date of its completion. repay the annual interest on tile capital invested calculat~d at 6 per cent but in preparing a project: for sanction no deduction is to be made from the total capital outlay on account of. antiCipated excess of revpnue over simple interest. Note :-Capital invested includes (I) direct charges, (2) indirect charges and (3) all arrears of simple interest, if any i.e; balance of total interest over total net revenue. (1) It must be susceptible nf having clear Capifal and Revenue Accounts kept for it. (c) Its cllssification as a Productive Public Work must be authorized by competent authority. 3. The rules for determining (l) whether a work which has been classed as productive shall continue t~ be so classed, and (2) whether an unproductive work may be reclassed as prodtcctiV6 are as follows, the percentage rates referred to being those prescribed for the time being, and being subject to alteration at the discretion of the competent authority :I. Every irrigation, navigation. embankment or drainag, work for which capital accounts are k"pt ShOllld, until ten years after the date of the closure of it, construction estimate, be classed as productive, if the net revenue anticipated from it appears likely to repay, on the expiry of that period, the annual interest charges on the capital invested (including direct and indird charges and arrears of sirrple interest). calculated at 4 % in the case of works sanctionerl before the 1st April, 1919, at 5% in the case of those sanctionedbetween the 1st April 1919 and the 1st August 1921 and at 6 o/"in thecaSfl of those anctioned after ]st August 1921. Conversely, if it is not expected to yield tt e relevant return, it should be classed as unproductive. If moreover, at any time during the period of comtruction or within ten years of the date of the closure of its construction estimate, it b'!comes apParent that a wor:< originJIly classed as productive will not a~tUllly be remunerative according to tht cri tedon prescribed ahove, it shon ld be transferred from the productiv to the unproduct:ve works. and similarly if it becomes obvious, riming the same period, that a work sanctioned ::IS unproductive will actually prove remunerative, the ttansfer of the work from the unproductive to the productiv~ class may be effected. II. Every work c1C!ssified in accordance with clause 1 above will retain its classification unchanged during the eleventh, twelfth and thirteenth years after the closing of its construction estimate. . , III. If any irrigation, navigation. embankment or drainage work for which a capital account is kept and which is classed as productive fails, at any time after the expiry of itn years from the date of the closing of its construction estimate, in three 5uccessive years, to yield the

380 releva.nt return prescribed in dause 1 above, it should be transferred to the unproductive class. A work classed as unproductive which succeeds in yielding. in three succes,ive years, the relevant return prescribed for a productive work may. on the same principII', be transferred to the producti ve IV.class. If an existing irrigation. navigation, embankment or drainage work be extended or improved, the creterion of productivity prescribed in clauses I to 111 above or improvement, as whole system, including such extension or improvement had been executed simultaneously with the original work and· the date of sanction referred to in those clauses for the purpose of determining the percentage to be returnpd by the system as a whole. shall be that of the accord of sanction to the original project. As an exception to this rule, if any extension he, owing either to its nature or magnitude, such as may reasonably be considered to be a separate project and if it be susceptible of having clear capital and revenue accounts kept of it, as distinct from those of the project as ::l whole. it should be treated as a separate project and in that case the conriitions relating to original projPcts and not those relating to extensions and improvements shall be applicable. In all such cases separ ate capital and revenue accounts should be main tained for the extension in order to enable the productivity test to be periodically applied.I, III & IV are, however, subject to the proviso that V. Clauses the compet€nt authority may postpone the transfer of a work from one class to the other in cases in ~ hicl:l. it is satisfied that its success or failure is purely due to transitory causes. . 4. Forthe purpose of the determinin~ the productivity of an old work which has been developed by the Government only the capital expenditUle expended by that Governmer.t should be regarded as the r capital at charge on which. interest is chargeable. !:' ~ __.L...j.-I.-"__ 5 .. The traQsfer of a work from the productive to the un productive ~ ! ~ category, or vice versa, will affect the recording of all future transactions in :II ~ ;:. connection with it. No adjustment will be made in the general accounts in respect of past transactions, but the necessary transfers will be .effected by;; ~ .... o the Accountant General in the Pro Forma Accounts of the work in question. j o

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Plans. The fonowing list of plans comprises all those generally required;(a\ INDEX pLAN :-(Art. 58 (a) Usual scale 1 mile to 1 inch. This should be a tracing of foolscap size, or folded to it, so that it may be bound 'tYith the report: a duplicMe copy of the plan should be placed with other plans. (b) Storage reservoir :- (i) General Plan of the Catchment : Usual scale 1 mile to 1 inch. If topographical sheets exist, this plan should be prepared from the~, the boundi~g watershed line should be clearly marked, and the area 10 square mIles of the catchment printed on the plan. .

. plan of the reservoir;--Usual scale 660 feet to 1 inch (ii) Contoured connected WIth the reserVOIr partIcularly the tall channel of the waste weir and it outfall; a table of the areas and capacities of the main contours should b! printed on it. ... :'" ~.' .

T~e plan should .shOW ~ll the main c~ntours and also all the works

. (iii) prlepared

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381 should show all land to be acquired and the offsets from existing fields to where Its boundary changes in direction. They should show the roadcrossings and village boundaries. A typical land plan for a distributary is shown in Fig. 6 (iv) Dam :-Plan longitudinal and cross-sections; details of foundations and closure arrangements. (v) Waste Weir :-Plan, longitudinal and cross-sections details of sluices and temporary crt:s t. (vi) OutIe: --Plan, longitudinal and cross-sections details of tail and fore-bay:> approach bridge, valves. lifting Hlds and capstans. (c) Weir or Headworks:- (i) Contoured plan of the backwater :- As for restrvoir. (ii) L':llld plan :- As for reservoir (iii) Flood Embankments ;-Lmgitudioal aBd cross-sections. (iv) HeadwOJ'ks:-General plan showing all works longitudinal and cross-sections; details of all sluices. (d) Main Canal and Branches:·-(i) Longitudinal Sections:- To show canal bed and fnll supply line, ground line, and top of embankment; the location of all proposed works to be ;ndicated. Notes to be given of the bed fall, full supply discharge and the irrigated area under command of different sections of the canal. (ii) Cross-sections: -To be given of all typos and unusual sections. (iii) Cross -drainage and other Works:-Plan, elevation, and cross-section of each main work to be drawn. For minor works type designs to be prepared. (iv) Plan of frrigable Area :-On this to be shown all villages, roads, etc., the main, canal ani! its branches and sites of the principal works, drainage lines and channels and the boundaries of ir) igable and unirrigable land. 14. Examination Question. Mark a suitable alignment for extension of a channel for Irrigation of the area shown on the blue print plan supplied. Divide the area into suitable chaks and work out the minimum F. S. L. required in the. channel at each outlet head, discharge for each outlet and total discharge required in the channel at the beginning of the extension. Design an A. P. M. outlet for one chak and a standing wave flume outlet for another. Draw free-hand of dimensioned sketches for both. Intensity 70%. Full supply factor at outlet head 88 for Kha"lj permissible. Khanj Rabi ratio 1 : 2. . (P. I. B. 1941) 2. On the attached contoured plan, the alignment of a minor is marked. Discuss for the advantages and disadvantgaes of this alignment and propose a better one if you consider this feasible. (P. I. B. 1941) 3 On the attached contoured blue print plan mark the alignment of a minor taking off from the most suitable point on the distributary to.) irrigate the area inside the irrigation boundary of the proposed minor. Divide the area into suitable chaks keeping to the village boundaries as far as possible and mark these chaks in the plan finally showing the positio];l of outlets and water courses to irrigate each square in each chak (P. I. B. 1936). 4 Describe briefly what information you would collect and the survey you would conduct for the preparatIOn of a complete irrigation projoct. (Mysore 1939). 5 \\'hat are the main pOints to be kept in view, in aligning a canal for irrigation purposes? (b) \Vhat preliminary surveys would you conduct to enable you to fix up final alignment? Mention the important deta to be collected for properly designing the channel. 6 What data would you collect and what are the plans you would prepare for an irrigation proiect? 7 Work out the detailed flow irrigtion project for the Karol Tube Well Scheme area from the Lahore Branch. The following alternatives should be adopeted :(a) The eXisting Shalamar Distributary taking off from R. D. 218500 R. Lahore Branch to be enlarged and remodelled to irrigate this area. (b) A new channel to be designed taking off from R. D. 23000 R,crossing the Shalamar Distributary. ' (c) F. S. Facter=250 Rabi Kharif ratio 1:1. Intensity of irrigation 100%. .': . Complete draw off, Command and arta statements and alteration forms of outlets to be worked out The alignmellt should be marked on the attached contoured pIau and Longitudinal Sections to be prepared with cross sections at every thousand feet. The land plan should be prepared showlDg the detail of the hlnd to be acquired. The typical design of the fo~lowing works should be given:. , (i) Distributary Head Regulator (ii) Meter Flumes. (iii) Falls (iv) Crossing of the Shalaipar ,Pistributary. (,,)Outlets. (vi) Syphons over the drainage a'ld tail clustero. ' , '; . The cost of the scheme will be evaluated under the following sub head:',' . " (i) Preliminary surveys. (ii) Land. (iii) Earthwork. (iv) Service roads. (v) Masonry' works. (vi), Outlets etc. (0. Miscellaneous.) I' (~" U. 1942)

PART II

CANAL IRRIGATION CHAPTER XVIII

Remodelling Channels Introduction. In the lac;t chapter, the student was acquainted with the design of new channels and the preparation of their projects. This chapter deals with the troubles and the working vf the existing channels. It is intended to describe here briefly how to di<.tgnose the trouble and to apply the remedies. The object of all remodelling of the existing channels is to aim at equitable distribution of supplies with a reduced cost of maintfDance. As the holdings of the cultivators in the Punjab are generally small, the question of equ it able distribution of supplies is very important. In the colony areas, the educated cultivators clamour to have, the discharge of their outlets correct even to the second place of decimal. The work of remodelling channels requires a great experience of this type of work, because a good deal of complaints and dissatisfaction starts when on~e the outlets are changed. Really honest work alone can make a remodplJing successfui. A brief summary of the author's experience of this type of work is givpn here and the stud en t shou Id study the followi!!g paper, available in the proceedings of thll punjab Engineering ((lngress, Lahorc, for a detailed study. (a) The Author's paper No. 154. 1931, (b) S. L. Malhotra's Paper No. 172, 1934 describin
Necc'sity 01 remodelling channels. The channels having the following troubles need to be remodelled:1. Chronic shurtage at the tails 2. Widespread comlapints of individual outlP.ts. 3. Drowned bridges. 4. Excessive silting up and frequent silt clearances, 5. Excessive supply over the authorised full supply discharge at head necessary to feed the tail. 6. poor command at head of a distri butary or at heads of its minors. 3. Bench Mar:{s and HydraulIc Survey. 2.

When the necessity of remorlelrng has been deCided upnn, then just put reliable bench marks along the channP.! to he renodelled, by douhle levelling, along closed circuits. The masonry works are li:lble to be demolished, the bench marks should be fIxed on the R.D. (Rf>duced Distance) marks or by constructing masonry blocks 1.25' X 1·25' X 1'5' neer the land boundary limits at every mile with top one inch above ground level. An arrow head marked in cement plaster should indicate the point actually o1:served in levelling, A detailed hvdraul'c survey of the channel should then be carried out and the longitudinal s~ction and the cross-sections p}.)tterl. Typical remorlelling. L. section and Cross ~edions, are given in Plata XXII. D. II and Fig. 1 to 4 respectivel,!, Tre hydraulic survey should comprise all the information shown therein, When preparing a longitudinal section, the points to obsen'e a!'e :(a) The horizontal scale should te 2*=1 n,ile and Vf·rtic:lI !'cale 1/50. (b) Last designed and existing f' II supply and ted Jeyels shC'uld be shown in different colours on the paper section. (When a tracing is made, do not use blue colour, as it produces very faint lines on the print especially on glazed prints.) (c) Crest levels and working heads both existing and proposed, for all outlets and also the w::tter levels in the water courses should be shown. The water level in a water course should he that prevailing when a high field is being irrigatea. Record plans of all masonry works should be checked at site, while carrying out hydraulic survey to See that they are correct.

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384 4. History of a Channel. The history of a channel should be read if one is available. If not available, one should be prepared after reading the old files to give the following information. The reasons for aU changes in the original channel design with respect to slopes, sections, outlets, ialls, di;;:tribution miner head and distributary head regulator should be recorded as given, out by the engineers then. The record of all silt clearanees should also be traced if available.

5. Diagnosis of the trouble. In the existing. channels, the supply levels of the parent channel cannot be chal1ged appreciable and the supply levels of tails are also fixed irom considerations of the command of the area to be irrigated fhere is usually little scope of steepening the slopes. The channel has to be run with the available slope. It can generally be run non-silting with the available slope by controlling the silt conditions and the bt'd width depth ratio (Para 6 Chapter VI Part II). A reference- to appendix 1 of Author's Papar No. !54 P. E. C. 1932, will show that the channels do often suffer from excess slopes steeper th:tn the regime slopes. The excess sl~De cause silting up of the channels by eroding· sides and widening, by meandering and shoalmg aad above all by sweeping velocities killing. the silt carrying vertical and rolling eddies. The causes of trouble should be investigdted under thd following su~·heads;la) Defective slopes (b) Wide Channel sections (cl Defectivij outlets (d) Defective Head rlJgulator (e) Drowned bridges (f) Lack of control points and distributors. 6. Channel Seetions. The channl'll sections should be within 20% of those obtained from L::Icey's formula P .. 267 Ql '2,or Wood's bed-width depth ratio If channel is too wide, as is usually the case, the remodelling should provide its contra~ti()n to the designed sections. Very wide channel sBCtions are general! attained in course of time by cattle tress pass, and collapsing ef berILs a.d pedastrian crossings. A relatively wide section silts up more than a narrower section on account of the decrease of the vertical silt lifting and rolling eddies (para 15 C Chapter VI). The contraction should be attained by hanging spurs if sCQuriug is also to be attained along with the herm formation which is, a slow proce~s. rf it is desired to form berms quickly and also not to disturb the equitable distri1ution of the supplies to the outlets, the channel should be silt·cleard to the designed bed tavels with bed width equal to designed bed width plus depth and- then to construct longitudinal bushing. Both processes are explained in detail in the author's paper No. 154 and are giveR in paragraph No 9 Chapter Vll of Part rr. Grass should Qe sown on new oorm formation. If bU'lhing be not available the contra~tion is attained by silt filling on sides protected by gachi pitching (berm clods) or by compacetd earth protected by dry brick pitching. 7. Outlets. The outlets should be, designed to take their due share of silt, to give the' corred discharges based on correct coefficients and to work modularly under full supply conditions in the parent channel. [n t he head reach of a: chimnel, A. P. M. outlets should be set as, low as p()ssible 'f'ven '%D lower than the bed ) according to available working head, as permitted by the reqnired M.M.H. Tn the middle reaches they should at least take there due share of silt which is about H2 per cent. the author's A, P.M. with '80 setting permits this much silt conductive power and in the tail reaches there should be open flumes set at .90 or bed level. The author's modifications in approaches increases the silt conductive power of these outlets by about 6 to 8 pereent. . 8. Head Itegulator. The -rrobable defects 'n head regulators of different types have already been given in Chapter XlV Part II. Blind silt exclusion by constructing skimming platforms should be avoided. as it is likely to give 1rouk.le in the parent channel. With the known C. V. R. in the parent channel and that which can be permitted in the off-take with the available slope. the required silt conductive power of the head can be calculated and a silt selective distribntary head regttlator can be designed with this silt conductive power. (Para~raph 8 Chapter XIV. Part II.) 9. Drowned bridges. The drowned bridges cause unnecessary headirtg up and upset the regime. The heading up results in siting up of the reach upstream of this. They should be raised with 1'5 ft. clearance by R.C.

385

Slab or T. Ream bridges in the distributaries and with 2 ft. clearance in the case of Branch and Main Canals. 10.

Chakbandi, Command and Draw off.

Having decided upon the causes of trouble, the next thing should be the preparation of correct chakbandis and the area statements. Tne classification has been given and the preparation of the area statements is explained in Chapter No. XVII Paragraph No.9. Similarly Command and Drawott statements should Le prepared a$ explamed in pargraph No.9. Chapter No. XVII. Part 1[. 11. Lowering of channels. No outlet should have a working head less than 1'0 ft. If the working heads are high or if there is no irrigation from a reach, it should be lowered as much as' economically possible. From consideration of seepage losses. it is desirable to keep the water levels in the channels as low as pessible. 12. Control pOints and mete! s. (a) There should te control points at about every 5 miles with a minimum working head of 9". [he suitable design of control point is shown in Fig. 29. The outlets should be groupl d to take off from upstream of the control points and combined win in the form of distrIbutors. <\ 111f~ter flume at about R. D. 1,000 of the channel should be provided so that th: supp y passing the distrbutary is correctly gauged, if correct metering is not possible in the head design. Two control points in a major distributary are absolutely essential, one about 2 miles upstream of thq tai~, say wlJere the dIscharge is 15 to 20 cusecs, so that the silting and b(;rming up of tail, reach does not spoil the regime ot the whole channel, and the other about 2 miles downstream of the head regulator to localise the effect of any mistakp. in the design of the head regillator or in selection of silt factor or C. V. R. in the beginning. These should be provided even at a risk of slightly flattening the slope. The middle reaches shall then remain immune from silt trouble even with relatively flat slopes. (b) DL;tributors There should be distrihutors at the heads of all minors in the form as given in Fig. 8. aed Fig. 9. 13. Raising and Strengthening Banks. Wh
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where F=height of de~igllE(l bed above ~o. S. D=designed full supply Depth: B=designed bed width. Height of bank above full supplv lev61 up to 10 cusecs discharge=I'O' 11 to 25 cusecs clischarge = 125'; 26 to 1Of) cusecs discbaTge=l 5'; 101 to 250 cusecs discharge = 1'75' ; above 250 cusecs discharge = 2'0' Berm width at full supplv level up to 10 cusecs discharge=2'+d/2' 11 to 25 cusecs dis:;harge=I'S'+d/2 ; :'6 to 50 cusecs c1ischar ge=2'0'+d/2; 51 to 100 cusecs discharge=2'S' +d l ~; 101 to ::!SO cusecs discharge =3'0' +dj2 ; above 25U cusecs discharge =3 5/+d/~. The formulae ~ivcn above provide strong banks and liberal berms. If funds are scarce a lighter section may be adopted. 14. Remodelling operations. In the case of small channel,:lll Works Tf'quired, such as silt clearances, remodelling outlets, raising bridge-, constructing meter flumes and control points and COl traction of channel sections should be done in one and the same closure. fhe stregthening and raising banks should follow as soon as possible. In the case of major distributories the reaches 3 to 4 miles, starting from the tail reach sid~ should be tackled. All works required as mentioned above, should be finshed in the reach in one and the same closure. It is preferable to take reaches as defined by control points at the ends. Some engi neers are in favour of taking up remodelliug reaches in major distriburaries, starting from the head. This may be possible only when the distributaries are not taking ~xcess

386 a' haad and only outIes to and masonry works are to be remodelled to the modern designs In the case of channels drawing excess at the head, the remodelling reaches must be selected bl'ginning from the tail. . All remodelliJllg of outlets must ne~cssarily be carried out in the beginning of a crop. kharij or rabi, say in April or October so that the changes in outlets do not adversely affect the crops when they have been sown to avoid discontent among the cultivators cr.d excessive remissions. ] 5. Silt clearance and berm cutting of a Remodelled channel. After a channel ba!' been contracted to the designed sections, the protruding bra:rtches of bushing should te cut off and chanllf~l should be fina;ly cleared to the designed bed levels. The tail reaches need annual berm cutting in the month of 5eptember generally, due '0 berm growth throughout summer caused tv very fine silt in the wa.ter near tail reach which fertilises tht berm growth especially lD the rainy season. Ihe belm growth heads up supply with the consequent rise in the bed levels. It may be that in the remodelling, the channels ClDnot be designed with regime sections due to the existing fiat slopes in certain reaches. Such reaches should be given sections as limited by the wetted pt::rim~ter discharge rtlation or hy the hed width ~epth ratio as far as possible and should he declared that they shall nped silt clearances say every 2 or 3 years as the experience will show. (Page ?56 'of this book). The remOdelled channels with correct values of X. Sand p in Kennedy's designs and with regime slopes, correct values of p,~ and silt factor in LacE'y's theory, with discharges over about LO cusecs, do run nonsilting and no not need silt clearances However, this does not mean that they could be neglected for all times to come. The damage caused to them by cattle trt'sspass bv way ~f widening should be repaired by hushing the berimir,g up s~ould be straIghtened by cuttmg and the bed interference by the cultivators by way of dajJs, bed Clods and branches sticking in bed shoul.1 be removed by bed clearanre whenever the necessity arises preferably before the month:> of keen demand in the Punjan (June and October). 16. Watching cnannels after remodelling. The remooellen chann ... ls need to ba specially watched for at least a few years. The following observations should be taken ;_ (a) H. Re~isters (Modularity Register) The H. Registers are now maintained as normal routines glvmg observations by the subordinates once a months of depth on crest of all outlets and the actual working head. The cloumns of the register may ct' as per specimen below ;~ ,

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I (olmn 9 shall show the fluctuations of the VI ater above the designeds water levels and column No. 10 shall gi ve the indication of non-moduL r outlets where actual working hea4 is les-.; than hm requirr;d for the modular working of tha outlet as got from plate X VIII (A.&.B) column 8. (b) SpecIal gauge slips. Special gauge slip should be introduced for at least 3 years after remodelliBg upstream mettr gauge and downstream channel gauges at all a channel giving control points including the hp.ad of the dlstrihutary and the heads of the minors daily. All tail gauges should be read daily. After the channel has stabilized. it will be necessary to have just the head gauges of distributaries and minors and the tail gauges. The overseers, the zilladars and the S.D.O. inspecting a tail ptrsonally should report the actual gauge reading. This serves a useful check on the work of gauge readers. Ic) "Characteristic curves," 01 distrIbutaries. (i) There has been a progressive development in recent years in the m· thods of "

387

distribution of supplies form the remodelled Distributarie". With the universal :lpplication " modules for outlets and Minor heads, the distribntion of supplie~ has now become automatics and interference by the Gauge Readers has almsot ceased, The sy"tC'm has yet by no means attained perfection and freqlltnts silting of channels introduce conditions, which are inmical to the proper working of the nAwly evolved automatic distribution of remodelled channels Moreover Distributaries are being required to run with different suppliRS in Summer and Winter to meet the require nents of land reclamation, and of additional land given out for temporary cultivation. All th.is senously upsets the distribut;on to various outlets and minors. Alttlough the minor heads c:oulrl be adjusted every crop to make them take their authorised supply and no more, it is neither practicable nor Hesirable to adjust outJets in th!' same way It WOUld, therefore, happen that when pxcess supplies are run at the head. the intervening outlets wonlj also take a certain share of this excess It is of utmost importance tn be able to calculate readily, evtn though approximately, the excess discharge that would be needed at the head of any channel to deliver specific suppl as at different points of a channel (ii) To meet this requiYerrent. charactHistic curves have been evolved by R.B. Hakim Rai, Superintending Engineer. These curves afforn a f'ady means of finding l'ln anSWf'r to variou, questions. which otherwh~ would need lengthy cal ;ulations each time it is desired to carry out such investigations. SOITJe of the problems for which a ready solution could be obtained by the applicat.on of these curves are:(1) Excess di!Oharge requirerl at head to give say 1-0 cusecs at different points of a Distri butary. (2) The effect on tail discharge of lowering the Full Suppl Y' Level by silt clearance in a certain reach of the Distributary. (3) The effect of tatiling vf outlets in a paiticular reach on tail suppl:e<;. (4) If any minor is over drawing the effect of redudng the supply in the Minnor without reducing the supply downstream of it on the head discharge of the dis ·ributary. There would be many other problems for which these cnrves WQul·i prove useful. (iii) For the present the follwing characteristic curves have been drawn ;(1) a-Curve. This gives the excess discharge reqUired at e;J.ch point of toe channel to give one cusec extra oischarge at the tail. This is the basic curve. as other curves are derived from it. (2) fi-Curve. This gives the exce3S discharges at head required to give out CllSPC extr a discharge at any point of the chane!. (3) 'Y-Curve. This gives the percentage of the extra discharge at any point that would reach the tail (4) A -Curve. This gives the increase in depth in 1 he variou;; reaches when excess supply to give one cusec extra at tail is running. This also gives the e:iect of stlt clearance of certain reach, s on the taj I supplies. (5) ::;g -Curve. Below the A Curve is)given the excess withdra·val by all the outlets in a reach when extra sllp:)iy tf) give One cusec at tail is running in the channel. No~e : -For disci1arge other than that for whkh the curves are drawn. values can be obtained by direct propflrtion (except in the case of 'Y curve which remains unchanged). (iv) Method of plotting the characteristic curves;a Curve is called the basic curve, as calculations are made to determine values for plotting this and other curves, are then derived from this. The tabular form used for this, purposd is S1nwn in' tlble l. The channel is divided into small rear.hes beginning from the tail uowar is The discharge at the taU is to be one cusec in excess of that sancti lued This results in inCfj~ase in the depth of the channel, which is found by using the formula Q=QD5/3; Percentage increase in depth can easily be .d~termined as it is approximately 60% of the percentage increase in discharge. After h;lvir,1Z det~rmined the increase in depth in the reach, the excess di!Ochargp. drawn by eac 1 outlet is worked out and the total withdrawal plus the extr::1 supply reaching the tail plus the absorption lossps give the proposed discharge at the tail end of the next reach. The same process is repealed till the discharge originally required at the head. and that now detemined is worked out. For purpolles of th6slt caiculations. it is a"sumed that all the Minor heads would not draw any share of excess 2.<; it would be Dossible tn adjust them for the increased depth. Figures tbu, obtained are then plotted as ordinates and reduced distances of the channel as abcissa to get a curve. Calculations for elC~ Minor are also made separately from which and

388

......

o

(7Q

~.

3S9 with the help of these curves figures can be easily worked OLlt, if the min'lr h3ad.; are not adjusted. The excess discharge drawn by each Minor per hissa rise in depth is worked out and the .. xcess discharge required at thf'l head to give this much excess in the Minor is aloo determmed as would be clear hom the exarr.ples worked out. .. The figures for the f3 curves are obt::lined by dividmg the ordinate at the head as ppr a curve by the ordinate at the haad of the reach. The points thllS obtained when plotted give the f3 curve. The figures of the y curves are obtained by aividing WO by the ordinate at the head of the reach as per a curve. The figures for A curves are obtained from column 6 of table No. 1 of this Chapter. The ~ figures are obtained from column 14. These curves are shown for Maduana Distributary of Lower Chenab Canal in fig. 5 (v)Examples of the use of curves. (i) What extra discharge is needed at the hea i of Maduana Distributary to give I.S cusecs at tail and 0'75 Cusecs at 350'00 if. (al Outlets are not adjusted. and minors not allowed to take excess. (bl Both outlets and minors are not adjusted. (ii) If one cusec is saved as a result of silt clearance in the reach, head to 35,000 how much of it whould reach the tail? (a) From a curve excess required at head to give 1'0 at tail =2'4 Cs. at R. D. :~50()O=I'4 Cs: do do do :. Excess required at head to give 1 5 Cs. at tail = I'S x 2 4:.:3·6Cs, do do do 0 75 at R. D. 35000=0'75 x 1'4= 1'0 Total 4'5 Cs. (b) If Minors also draw excess, addition for this fo be made as follows:Rewazabad minor:-for 1'5 at tail, rise in depth at, head of minor=1'5xO'1=O'15 (sees curve); From the curve for every hissa rise in depth @ head of Rewazabad minor, the excess discharge neede.l at Maduana head = 1'2 Cs .', Excess discharge nef'ded at head if Rewazabad minor is allowed to take excess='lSj'l X 1'2= l'SCs (A); Similarly for Karimpur minor, Rise in depth='09; Exc~ss discharge needed at Maduana head = 09/0'1 X 1'5x'S9-'S CS (R) and in th~ same way for ::iehtewala minor cxcess discharge required at head would be= '051'IX I'Sx 1'9='14 cs For supplying 0 75 Cs at R.D. 35000 eXCess required at head =0'75 X 1'19 (From a (C) curve', = 1'4 Cs This is p.quivalent to sending= 1'4/2'4=0'0 Cs at tail. The excess discharge needed at head in c:onsequence of the two minors above 35'000 i.a Qaimpur and Sehtewala. drawing excess is worked out below:For Karimpur='09j'l X 0'6X ·59=0·32 ............... (D). For "ehtewala ='05/'1 xO'o . :: J·J=0·57 ............ (E) Tota I excess required at the head on account of minor heads not being adjusted = (A +(B)+(C) +lD) -T-(E)=l'S+ SO+I'4+'32+'57-4'89 lotal excess at head in the case of 1{b)=4·6+4·89=9·49Cs. (III) If one cusee is saved in the reach, head to R.D. 35,000, 60% as &een from curve, will reach the tail. Thus if Rewazabad Millor in the way does not draw a[;,y e.hess discharge reachin§1 the tail=0'60 ;'<1=0'6 If the minor also draw excess, decuct for this as follows. 0'0 cusecs at tail would raise supply at Minor head by '1 X 6 ='06 and the millor will get the discharge of '6 X '65='39 Cs, and thus tail would get '6-'39=21Cs

390

TABLE 1 Calculations for increase in discharge at he~d of Madduana Distributary for an increase of one cusecs at tail. ._

.; +0>

..... (IS

I-<

..c::

0

0

(IS

s::

~ (!j~ ..c::u u (IS '" .v. Q

(IS

'"0..

v

i:it


~

..c::

0..

+0>

...

"0

0

q,)

..c:: .....

..c:: u

I~

v

0

v

b.O

....

(IS

..c:: u

i:5'"

10. ua;>..d

"1;

Ig

\~

0

I, ,::C

0

0

1-0

"0

q,)

"CI

::s

a;>0

"0"0

OV

v "0 .iii

0..

q,)

"'C...;

I!.)

= ....

..c:: .... 0

c:

Size of ou tIet.

+0>

.0.

ttl

.~"O
..c

I.> • <'a

..... Q.;

e:!

"0

,

....

.S v

I!.)

I"::~

~~

s::

~

I-< U

':g

s::

s::
A

I-

V

'Cl !

'"v (1;

"0

r

H

B

Y

.8 ....

h

u

s::

:<j

'" '" (IS

q,)

I-<

._

c:

Iq,)

q,)

I~

CI)

..d

Ii

'"s::

+0>

Ig

....

.:a.....

01

'!i (.)

(IS

rlJ

'"

V

u

(IS

i:it

ill

(d U

15

IH

1'0 I I 5-77 '45 ['15, '89: '94 '051 '3311'27 '68: '73 '05 '49;1'11151'1-62 'Il

577 3'29

01

101

IX !~

Z

~--- -~---- --~--~--~.-~---------~----

2

3

63
to

I

4

5 1

1-4

,

1'57

9'97

'

49000! 16'24

i

I To 17-76

_~:J13

11

14

I

i

tal

3-08 329

1'90

i 20

I (SO ON AND SO FORTH)

'tal

\ti'I1'

I

19'97

i

7'U8 l--:W, 1776

I~S994R 12

'25[

1

708 '71

I

I

1-'061--i I

'1 46982L, 2'0 i '9 , '55 1-45 1 94 2 '00 455, 42R 24 '4 '43 1'97 1, 76 ,1'81 '051 1 40()77L 228 '32 I -51 1'77 I-59 \1'62 7l.J /36!Z'35 1,ozI1'031 '01

I

'33 "58

9'97

'21

I

34625

16.

10

FALLl'lOl 'I 49465L \I-41 '32 '58 1'82,1'231-30 '07 1'0 149425L ,Rewazab:ld minor_ 4'32.4-82 i 49100R' 1'4 032 0'68' 072: I' ~R 1'46: '10

I, to

9

,Excess! '17 61043L, 1'6 i '25 57548R 1'6' '25 55936L i 1'6! '4

I To

49500: 8 64

!

8

7

1

4950°1 to 1 49000\

6

17'76 6'46 I '65 1

031

1

6'3)

Total

6'46

'IS

24'S7

, Examination QUestions, .. '.' 1. An existing distributary of 100 cusecs capacity designed f~~ an ~Ilnual inten
ratio of 1: 1 is to he remodelle
PART II

CANAL IRRIGATION 1.

Introduct.lon

..

CHAPTER XVIII

Inundation Canals

The canals which usually flow only in summer, when the rivers are high, are called They have no permanent headworks and no weirs across the rivers. Owmg to the changes in the river cou~se the off-takes. of the ca.nals have often to be changed and fresh channels dug or creek~ cleared mIt. The supplies of tnese canals aTe not laways as desired. In most of the districts in which inundoltion canals ex.ist, tlle rainfall is very scanty, and the crops chiefly depend on canals, flver inundation 'lnd wel!~. In order that the water of a. can~l may ~e m::tde to flow on to the surface of the country, the canal must generally have a dIrectIOn maktng an acute angle with that of the river aUfl a general slope flatter than that of the river. but when the country falls away from the river, a c::tnal may off-take at right angles to the river. Sometimas a canal. after crnssing the river valley, runs nearly parallel to the river along the slope of the watershed and irrigates land many feet higher than the flood level at a point immediately opposite. The bed of a canal is below the surface of the ground, hut th., water level is generally above it, and the irrigation is by" flo N ". The land near the head of a c~nal is generally too high to recei,:,e flow i.lri~ati Jll except in floods: It J?ay be irrigated. by lift eIther from the canal or from the flver. Owmg to the smaller lift thIS IS much eaSIer than irrigating form wells, and the water contains ;fertilizing' silt. Land irrigateri by canals yields two crops, the KhariJ or summer crop and the Rabi or winter crop. The land for the latter is soaked with water in August or September and afterwards ploughed. The. Rabi crop is sown in November and December, and is generally matured by water railled from wells The principal summer crops are rice, indigo, cotton and millet, but the largest of all crops is the winter crop of wheat and barley. The inundation canals of the Punjab used to irrigate about Ff4 millions of acres yearly They were more then fifty number. Nearly half of them have been converted into perennial canals by the construction of the Sutlej Valley and the Haveli Canals. The Dera Ghazi Khan and Muzaffargarh Divisions have inundation' canals even DOW. There are private and Government inUladation canals in the Shahp,ur district. ... ." 'In~ndation Canals'.

General Description of Canals. The bed level at the head is generally about the same as the winter sub-soil water level, and thisis about the same as the low water level of the river. The depth of ~atftr in the canal at any time is thus about the same as the height of the river above its low water level. Iri most canals it averages about S feet, but it may sometimes be 10 to 12 feet A large canal usually gives off branches or distributaries. These again give off water-courses which are. maintained by the people and not by Government. The bed slope of a canal is se Idem steeper then 1 in 4,000 or flatter then I in 10.000. The side-slopes generally become, by silting, about half to one. The canals were in most cases dug originally by the c1lltivator without any Engineering knowledge and are sinuous. The width are also somewhat irregular. The banks of the canals are often somewhat weak arid liable to breach. In such ca5es the banks are patrolled and watched. The strengthening of canal bamks. \\here liable to breaches. is a work which should constantly be seen to, A canal generally has a masonry flood regUlator, a few miles from the off-take, to enable excessive supplies to be shut off. The ragulator cannot be placed near the off-take because this is often chang eo and there would also be the fear of its destruction by the river erosion. At the flood reguhtor there is generally the off-take of an escape leading back to the river and there is often also the off-take of a branch or distributary. . If the canal crOS5es a flood embankment the flood regulator is at the point of the crossling. Further down the canal there are other regulators generally at the off-takes of branches IDI' distributaries, but sometimes at other places in order to head up the water during low supplies

2.

392 The Head Reach (often called, for shortness, the "Head" , while the actual point where the canal begins is called the "off-take" )is the uppermost five miles or so of the canal, and this often corresponds roughly with the reach upstream of the flood regulator. The banks of the canals generally have trees and jungle growing on them. Fresh trees are also planted in lines on the banks and slopes, bnt- not generally near the channel because they are somewhat apt to fall into it. A canal generally has a bridl~ road, and often a proper road fit for wheeled traffic, along one or both banks. The road on one bank is genera' Iy called the Insl'ection Road an i i5 reserved for the use of the Canal Officers The other bank is open to the public. Where watercourses take off, rough bringes made of branches of tree3, grass and earth are constructed across them. For the purpose of fixing the dates of opening the canals they are divided into three classes. An "ordinary" canal is opened about the 6th May. An "eady" canal is one which serves that tract of a country where certain crops whic!! require early watering. are grown in sufficient quantities to renner an early open in!? necessary. Such a canal is opeiled about the 26th April. A "Late" canal is one where there are no considerable areas requiring watn till about 15th May or (sometimes) 1st June. All the ahove dates are averages and approximations. The actual dates depend upon demand for water The height to which the river has risen, the tendency of silt to dfposit in the canal and the probability of damage occurring from breaches. The canals generally go dry a bout ::50th September and thus the period of flow is generally about 5 months. 3.

Silting of C:lr..als.

The slope in the canal is usually flatter than that in the river. The velocity in a canal being less than that in the river a deposit of silt generally takes place in the canal. fhe silt consists of saRd and clay. The sand, with a little clay, is deposited in the head reach of the canaL At the close of irrigating season. the deposLt at the off-take is gpnerally from 1 to 5 feet deep and it extends downstream. gT'adually decreas'ng in depth, for a di"tance whkh may be lfss than a mile or may be 6 miles. The deposit is generally the greatest when the canal takes off from the main stream, pspecially if erosion of the river edge upstream of the off· take of the canal is going on, and If.ast when it takes off from a creek There may be some oepo!':its, due to berming up, near the tail of the canal. There is generally no deposit in thp mirldle portion. There is nearly always a silt deposit at the insirie of a bfnd, but there is a corrfspontiing hollow at thp outSIde, so that the gpneral level of bed is about the same as it is just above or bel;;w the bend. Large sums of money have been wasted by removing the silt deposits which are known as 'side-silt'. Their removal makes the cross section greater th'l.n elsewhere and they quickly form again on bends. A grea~ amount of silt is deposited in the water-courses. The silt when removed from the canal is gpnerally placed equally on both sides behind the banks and levelled down to the height of the banks. The deposit of silt in the head reach of a canal is the greatest evil with which the Canal Engineer has to dea1. Deposit in reaches further down the canal, if it occurs; IS not of Sl) much consequence. In many cases a Su',siniary Head is provided :lnd kept clo"p.d. Deposit in the head reach not only reciuces the supply below the demand, eXl"ept in high floods, but it also cuts off the supph when the river finally falls and causes damage to, or failure of, ' >:tal'lding crops. The subsidiary head is then opened. Erosion of banks may occur, especially in large canals and at hends. It is likely to be very serious in sandy soil, and this is most cornu on in the l,ead reaches. The upst ann most common method of ~topping it is "Bushing" The various methods of bmhing have already been described in the case of perennial canals. Sometimes fascines and mattresses have also been tried where river action is high. 4. Canal Head Reach.

(a)i The general lavout of the head reach of a canal is as shown in Fig. 1 The main problems of inundation canals is to secure adequate supplies for these canals in the middle of April or very early in May, so that the cultivators can sow valuable crops such as Indigo, sugarcane and cotton instead of cheap ones as rice, fodder crops. hajra and chari.

393 If flood waoor breaks into a canal, it freque:tlly breaks out again on the opposite

Fig. 1

side and it may form a deep hole in the bed of the canal. This hole may flnlarge in all directions, fOIming a pond whose diameter may be much gre:l.ter than the width of the canal. When the banks an~ made up they are carried round the pond forming 'ring banks'. In course of time the pond silts up and the banks can then be brought into proper linc. H the damaged place is in higa eround, little harm may result, except the expense of repairs, but if the gronnd is low, the canal supply will continu@ to escape and be wasted even aftert he subsidence of the flood and the closure of the breach may be difficult. The rush and distrubaance may also cal1se falling in of the banks for a considerable distance upstream and a short distance downstream of the breach. It the water merely breaks into the canal head, and does not breaks out again, the heading up, at the point of afflux, is likely to be consideraple. It may be dP!'irahle to cut the other bank if the ground is not low. It is nearly alway:> diffic1Ilt, and generally almost impossihle to close bad breaches (i e. breaches not in high grount) in head reaches until the river finally falls and money should never be spent in attempts b9 close them unless there is a real hope of succe;5 awl also something appreciable to be gained by success. (a) ii Anything which reduces the silt duposit in the head reach of a eanal is of the utmost value, anrl a small change may make all the difference. Any sharp bends should be removed and loops cut off so as to shorten the channel and increase the gradient. The width, supposing the gradient and discharge) to be the same, should nnt be greater than that of the next reach downstream of regulator It may with advantage be slightly less so as to give a "draw". Anything which causes heading up of the water, such as the continued use of the flood regulator or an influx of water into the head reach at a point downstream of the actual offtake is a source of danger and may cause serious deposit of silt. The in-flowing water may be simply flood water or escapage from another canal or flood water impounded in a "pocket" For the reasons just given, a flood regulator should newr be built within, say three miles of the off-take of a canal if the gradient is steep and six miles if it is flat. The actual site is generally so fixed that the regulator can be combined with a bridge for a main road or so that it may suit the off-take of a branch or distributary. It may be many miles from the canal off· take. Unless it is so, it should not be used more than is absolutely necessary to reduce supply and cause the escape to work. If there is a flood embankment which has to croSs the canal it shoud be altered, if necessary, so as to bring the regulator site lower down. (b) Escape in a head reach.

At a flood regulator there should always be an escape, and it should be large enough to carryall the surplus water. Otherwise there will be heading up in the head reach of the canal. The size of the escape con be calculated by taking the difference of the discharge of the reaches ab and be (Fig. 2). Escapes, usually lead back. to the r.iver, .but .occasi~nally an escape In thIS cast} the JunctIOn wlth lower canal leads into the canal next below, is probably not far from off-take of the latter and the heading up caused by the inflow is likely to be detrimental. Such an arrangment should not be permitted unless

394 the escapllge is likely to be slight or unless the water can again be let out of the lower canal ose to where it enters.

Fig. 2

An escape, of course, extends only as far as the nearest creek of the river. It should be inclined downstream at, say, 45° to the general direction of the river. Sometimes, in order to get a short line, it is run out at right anF!les. Such a channel is likely to hwe a poor gradient. It is almost peculiarly liable to have its banks breached in floods. This may not matter, much while the floods last, but the breac0.es have to be repaired afterwards. In the absence of an escape. cuts are sometimes made in that bank of the head reach which is nearest the river, at points where the ground is high and the escaping water finds its way to the river. Such cuts close of themselves when the floods suhside. (c) Changes in Bead reaches. Owing to the changes which take place in the rivers. it is frequently necessary to dig new heads. If the heads could be dug rapidly, and at any time of the years, matters would be greatly simplified, but the excavation requires time and it can only be carned on in the winter and the spring when sub-soil water level is low. Moreover, labour can only be obtained in sufficient quantities in the winter and the early spring. As soon as one irrigation sea"on is over, the heads for the next seaSOR must be arranged for. The old head may be retained or a new one may be necessary. In arranging for heads regard must be had chiefly to the state of the river as it is at the time. Some little idea may be formed of the changes which will take place in the immediate future, but beyond that all is mere conjecture. A canal head, whether new or old. may begin to work badly soon after being opened. When serious erosion of the river edge takes place just upstream of a canal head the latter may become heavily silted in a few weeks. or the creek supplying the head may silt up. or the stream may move away and the watpr level be in consequence lowered. Subsidiary heads are also dug as shown in Fig. No.1 which are opened if the main head has silted up. (d) Selection ot off-take. TbP' foU-owing are general rules for off-takes :ta} A site where erosion is occuring, or is likely to occur, is a bad cme. Sites in the main stream., or close to it He thus objectionable. (h) A site in a small or silted creek is open to the risk of filting up of the creek. (c) A site in a large creek is generally goods. The site should not be at a bend which erosion. seems liable (d) to A site near the tail of a creek, but not so low down as to be close to the main stream, is generall)' an excellent one. If the head of the creek silts up, the supply will be drawn in from the tail. (e) A back water, such as that marked in Fig. 1 is also a good site. The principle of placing the off take as far upstream as possible is . followed when other considerations do not interfere with it. This ensures a long feeding cbannel which is desirable. A good site lor an off-take can generally be found by going far enough, but both funds and labour are limited and practically the length of a new head seldom exceeds two or three miles. A head (Haad reach) should not run for a long distance near the river edge. Such a head offers facilitits for new off-takes in case they are needed, but it is open to the danger of being cut in half if erosion occurs. If an off-take is carried too far upstream, it may result in the supply becoming so great in floods as to be unmanageable.

395 (e) Subsidiary heads. (i) When a canal has two heads, the one first opened is called the Main Head and the other the Subsidiary Head. The following points may be kept in view in deciding which is to be the Main Head:(a) The main head should be the one which seems likely to give the better imm~diate supply. It is not much me having a good supply for maturing crops if thete is not a good supply for sowing them. (b) The main head should be the longer of the two, because there is then less chance of the silt extending down below the junction and so ob3tructing the flow of the subsidiary head when opened. (c) The subsidiary head should have good banks so that, being closed by dams at both ends, it may be completely' boxed up," and no flood water allowed to break into it. A channel to which flood water has a access is quite unsuitable as a sllbsidiary head. Generally. the longest head, i e. the head whose off-take is farthest upstream, will give the best supply unJess erosion seems likely to occur at the off-take. The main head usually giv!1s sufficient supply for the greater part of the season. At first, the deposit of silt in the canal or in the feeding creek is small. By the time it has become considerable, the river has risen high and the silt has little effect. It is when the hig\:l floods are over and the river is falling, that the silt begins to have a serious effect, and this is the time for opening the subsid;ary head. A Slliable date generally for the Indus is, about 10th or 12th of August, and for the other rivers a)out the ~Oth of August. Premature opening of a subsidiary head may be disastrous, causing e«cessive supplies or silting one of the heans if it has a flat surface slope. (ii) When the subsidiary head is opened it is sometimes de"ireable tQ close the main head. It may happen, however, that both heads bring in appreciable supplies (this is likely to occur if both heads are long ones or even if the upper one alone is a long one, and is the more silted of the two) and both should remain open. No doubt some additional silting is caused. In one head or the other owing to both being open, but there is also an additional supply, The question whether the additional supply is worth the additional silting (the C(Jst and difficulty of closing a flowing stream being also considered) is one of judgement. The quetion whether it is desire able to close a head, is also affected by the information received from station higher up the river. Possibly the river may be falling so fast that the head will soon close of itself. (iii) Special cases may now and then arise and give rise to special measures. For instance, if erosion occurs near the off-take of the main hea.d and it begins to silt up, and the erosion seems likely to go on, it may be desireable to close the Main Head, even quite early in the season and to open the subsidiary head It may even: happen that what was intended to be the main head is not opened and the subsidiary hea<'l is opened instead. Sometimes if there is spill water sufficient, cuts may be made in the banks to feed the canal thereby. In large number of cases the subsidiary head is not used. Either the main head continues to give a good supply all the season or erosion sets in at the subsidiary head or its feeding creek fails or the ri ver recedes from it. 5. Bunds (Dams) for callal heads in winter. The canals having gone dry in September or Octorber, earthen d~ms are constructed at th.e off-takes in November. The object is to prevent the rainy river water from accidentally entering the canals, before they are ready for opening. Any such accident may cause immense trouble. Contractor's earthwork may be unfinished or unmeasured or mat~rials' for masonry works nay be lying about. The danger may occur during winter freshets or in ApriL or May when the river rises permanently. In order to allow for a slight falling in of the river edge, the dam in the ma,in head must be set back, say 20 to 50 feet, from the actual off-take. To prevent this space from silting up when the river risesl a minor dam is necessary at the actual off-take or as near it as possible. Setting bank the main dam several chains is most objectionahle. The whole lengt4';, may silt up if the minor dam is carried away. , , The dams must be parallel to the river edge. If made square to the canal Wq.~ the :off-take is skew, a space is left for the collection of fine tenacious silt. Such silt has at 'tilnes ,

396 absolutely prevented a subsidiary head being opened aBd has interfered with the opening of a main head. The dimeosions of the dam may be :Top width Height above water level on 15th N 0vember 10 ft. 8 ft. Main Dam Minor Dam M ft. 5 ft. If the off-take is from a dry creek, the height can be mea<;ured from its bed. The material should be got, if possible. from the bed of the canal Sand does very wen. The side slop"s of the dams should be protected by fascining Long twigs are made into bundles .and tied up so as to form fascines. and these are laid on the slopes and secured by pegs driven mto the slopes. at short intervals, between the fascines. . If a creek is to be cleared, the dam will be ~t the off-take of the creek (from the flver or from a~l.Other creek-which is n<:.t to be cleared) and not at that of the canal from the creek, unless the dam at th~ creek off-take is considered to be insufficient If there is any creek or channel or depression which is not to be cleared bu! by yv~ich water can enter the canal or can enter a creak which is to be clund it must be closed In a SImIlar manner, but the material need not be taken from its bed and there need not be a minor dam. On the top of the smaU dam a grass hut should be made and a watch-man should live in it. For a subsidiary head the dam should, unless erosion seem likely, be close to the off-take with 15 feet top width, height 3 fept above H. F. L. and sides protected by fascining. If prosion seems likely, the dam may be silghtly set back, and if erosion actually sets in a second dam (No.2) should be constructed. say 200 feet downstream. A dam can be built on the top of sandy deposi t, but it should never be built on the top of tenacious silt or on grass or dibh growth. The silt should be dug out to bed Ipvel and then the dam made. In opening a canal it is impossible to remove the whole dam. Some of it must necessarily be left and be allowed to be swept away by the water. If time and labour are short, the whole dam may be left to be swept away a mere cut being made in it. It is better to do this than to delay the opening of the canal. The material in the dam when spread over a great length of canal, causes no appreciable raising of the bed. 6. Miscellanous Works. (a) Bank erosioll, Erosion of the banks may oc:ur espeiaUy in large cal'l.als and at bends. It is likely to be very serious in sandy soil, and this is most common in the head reaches The btst and the most common method of stopping it is "Bushing." The various methods of bushing have already bpen rlescribbed in the case )f perennial canals. Sometimes fascines and mattresses have also been tried where river action is high. (b) Bridges and water course crossings. In the tracts served by Inundation Canals, roads fit for wheeled traffic :Ire somewhat scarce. Masonry bridges are somewhat few. Many bridges suitable for c;une!s, horses and foot passengers are made of rough tree trunk;, placed on end to act as piers, with rough branches 1aid across them and cnvered with coarse grass are earth. Such bridges require repair, or reconstruction yearly and not infrequenty portions of them fall iato the channels. They are gradually being replaced by masonry structures. Bride-es of sawn tim')er are cheap, but do not last. There are very numerous ghats or places where the banks are sloped off so that animals or men can get water from the stream or wade across it, ~ . • . . In \vinter the people put up numerom temporary acqueducts, rough wooden troughs . supportEid on stakes, in order to rarry Nater raised from wells on one side of a canal to fields on tre other,side. The canal banks, being generally above the level of the fields, have to be cut .through at such places. Before the canal are openen in the spring, the people remove the acquedeucts and repair the banks. This procedure is troublesome and objectionable, and is only permitted at places fixed by usage. 1£ a crossing for water becomes necessary at a new place'

a maso.nry syphon has to be constructed or a new well sunk, the cost being borne by Government, If a new Government channel has severed the connection bet'veen well and field, otherwise by the people concerned. (c) Drainage Crossings. , In the Dera Ghazi Khan district there are numerous streams which issue from th~ Suleman mountains (these lie twenty or thir ty miles to the west of the Indus and flow towards the Indus). The channels are generally dry, but after rain streams come down and break into the canals at numerous points, generally toward~ the tails or into the western branches and break out again on the opposite bank. Much damage is done to the banks and some silt is brollght into the channels, but the water brought in is, on the whole, useful in supplementing the regular supplies which are not generally very good tow~rds the tails of the canals or in the western branches, as these have necessarily somewhat flat gradients owing to the land rising towards the mountains., (d) Duty of Inundation Canals. The "Duty" of water on inudation canal is low, being generally about 70 acres per cubic foot of discharge per second, (measured at the canal head) as against 200 or 300 acres on perennial canals. The duty is low because the canals flow only for about five months of the year, because the soil is sanciy porous and because the rainfall is very light. Long water courses also, to some extent, cause low duty. In matters sucn as the observations of discharges, the keeping up of Irrigation Registers, tbe Distribution of the Supply, the fixing of the sizes and sites of outlets for water courses, the remodelling of water' courses and the maintenance and extension of plantations, the principle and practice are the same as for perennial canals, except that trees are not planted where they are likely to be cut away by the river. The chainage of an Inundation Canal usually starts from the flood regulator and runs in both directions. The mile posts, etc" in the upstream reach should be of a kind which can be shifted. The same remark applies for the whole canal until all necessary straightenings have been effected. (a) River Behaviour. (7) P. Claxton produced on this subject paper No. 119 the Punjab Engineering Congress 1938. His practice is shown in Figs. 3 & 4. In this paper the writer deals with the Iaundation Cl\nal practice in all its bearings. He t~kes as an example the whole of the Dera Ghazi Khan Division in which he had served for many years, from 1910, off and on, till 1927. He has been able to watch problems as they has arisen and developed. "It is well known that alluvail rivers, be'lring large loads of silt, carry them on, not in one sustained effort, but by a series of jumps, or by saltation. The loads have not travelled down continuously from the hills, but are removed along by the processes of SCOl1r and erosion. Of these tWI), erosion, the action at banks, in contradiction to scour, that is over the ceci, is the more important. It gives the heavy excess loads at various points and causes the river to meand.. r. In doing so it presents the problems with which the inundation canal practice has to deal". One of the first principles lays down that silt eroded from a bank very soon deposits as a shoal on that side. Many engineers argue that it may be, and is, carried over to the other side. The argument is based on experiments on very narrow streams in which the whole surface slope is affected; This brings about a cross current which has the power of laterally deflecting particles. This is due to the surface slope and in rivers is confined b the bank. The silt for the remaining width is entirely controlled by the strong forward current, across whicn nothing may pass. The writer does not appeal to laboratory experiments for his proofs, but has shown by a few examples in other papers that the principle is supported by large dver movements, sometimes involving square miles of shoal. These shoals appear and melt away in step with erosions above them, and have the power of deflecting even the main stream. They all obey the same law which the writer has enunciated, He has, therefore, considered it fully established. The theory is illustrated in Fig. 3 which is believed to be drawn strictly to principle.

398 . In this diagram there is erosion from A to B on the right side. At A the stream comes Into the bank, ba.ving deposited its load of silt on that side in the shoal above. The water A

e.

"LgM

£MIIAH!!I1I!IIT

CI

r;: .

Fig 3 is, therefore, clear. From A te B erosion is active. and the loan of silt is consequent Iv increasing. At B it has grown so great that the river is no longer able to carry it forward, and a shoal begins to form, 'diverting the stream a.cross to C. From C the process. as at A, is repeated, only this time on the left side. The erosion from A to B is responsible for t1e shoal BCDE and the erosion from C to D for the next shoal on the left. It will now be shown how, on this theory the favourable points for inundation canal heads are d.eter-mined. The favourable n()n-silting points are these just above A,e ann E. The canal off-takes may be placed a little higher up in the creek which forms the out fall above one of these points. Creeks are favoured since they are usually more constant than the main stream. being subject to milder attacks. They al"o allow of the building of groynes or dams and thereby the off-take may be carried higher up towards the head of the creek itself. Inundation canals invariably work upstream for better comm::md and such canalizing of creeks is very useful, (b) River Control. In controlling rivers for inundation canals, there being no stone available, u~e of the still-water pock~t principle must be adopted to the greatest extent. The principle is illustrated at every Bell's Bund built for protection and training at important works of the province. It need not, therefore, be described here. Water to be held by earth embankments mrlst be brought to a complete stand still, and this is effectf'd by the iormatinn 01 the stilI-waterpocket. Such a plcket is formed when a creek is completely closed by a dam. ThiQ, however, is not always, possible, and a compromise is got hy means of a groyne. The groyne is a dam which has the canal bank or the high main land for one flank while the other flank Is in the o~n river bed. Whenever possible. the nose of the floating fl:lnk is placed on an island, or is carried up to a high shoal. across the main cr€'ek, w()rking upstream at the same time so as to create a pocket. Some times it cannot be carrieci across the stream but is finished off to from ::t pocket on onC side of it. T.he nose is protected by stakes and Prush-wood, and spurs may he added to throw off longitudinal flow along the groyne. These groynes are not only helpfnl in securiug the early supplies. bl1t are strong factors in keeping the canal heads clear of silt. With experience they may often be maintained even through the floods. Whether or not throughout the season, they form undoubtedly a feature of inundation canals which should be recognized. A head with some sort of groyne may nearly always ce fDund and by it much silt clearance may be avoided. Another very important advantage is the control of the river which groynes afford. Developments of down side creeks are prevented, and the main stream is kept away. Tbese are some of the leading features of control. Ic) Policy Combining river behaViour and control. The usual form of river is shown by the meandering course A, B, C, D, E, G, within the normal flood embankments which, of course, will not be so regular, out will be more Of less comtant, marking the limits within which the river may wander. Beyond these limits the flood emLankment and main lines of canal should be bnilt as at a e and c g. One of the features of the policy was the combination of the canal and flood embankment by 'iligning the

399 canal along t~e borrowpits of the embankment on the river sirle, Thus the cost would be that of the emban~m"11t only. lhe,canal wo~ld have on river bank but will spill over the whole river front, and Itself, would remam clear, slnc~ It wonld be the deepest channel which would form naturally along ,the emb~nkfl,en~. eve!! wIthout the help of borrowpits, On the river eage it wou,ld have a h.lgh marg1n of sI?lll which would keep it from returning to the river. The cross sectIOn,at the t11;'1e of constr~ctlOn would be as ~hown by the diagram Fig. 4 and in time with succeSSIve deposIts of sIlt, th1S would tend to grow into that shown by the dotted line. ~" This trunk canal would run the waole t :, lengt~ of the district, more or less constant in ~ capacIty. It would feod other branches off taking f .:::...,. at the points A, E, C, G, etc. rhe trnnk canal , ;t~ ~ " itself would he ltd by Inks, run in from each .., ----." of the favourable points A. C. E. as describeri above. They would be at angle so as to form ,. pockets with the trunk canal, at the junction w:th which regulators and escapes would be built. These points would also be the heads of the branches. Each link would be under entire Fig. 4 control at the junctions A, E. C & G, a regulator into the next compartment, and a head of a branch canal, being built at each point. By means of any of these regulators, the flow in the compartment above a link would be brought under entire control, even to the extent of causing the link to work back to the river by heading up. This control would regulate silt deposits in the upper compartment to some extent. These compartments bv arresting silt, would grow veluable for Rabi Irrigation, while behind the embankment, kharif crops would be sown, The system would be unique in making all the heads on the river available for service. The trunk canal also would be impregnable, i. e. it would be impossible for ri Ilef erosion to sever it, Such action frequently ruins an inundation canal. Hear, however, should erosion threaten to eat into the canal, it would also threaten the embankment; and as this must at all times be maintained for the preservation of the district, it would have to be built further back as a loop, and th6 canal would automatioally follow it. Not only would existing favourable point::; of the river be made available, but short cuts to others, might at any time be made along with other links, The canal, as a trunk canal, could make up shortage at one off-take wi eh excess at another, thus makivg the supply mQre ewn. The large com;:H.rtments w·.)uld also act as dampers ani!. would neutralize temporary shortage. Thus, this plan provides for every difficulty with whien an inundation canal is faced. It aims at affording a steady, even ann assured summer supply. It may) be noted that one of the objects of a trunk canal, such as that decribed above, is to olDtain, jf possible, not only 8. summer supply, but also a smail winter one. Tbis is" often possible even with the present system of canals which are not in a position to tap all the availaMe hads. By having a. continuous trunk canal, all the availa~le heads will be greatly enhanced.

f :.J

8.

Examination Questions. 1. Define Inundation Canals. Describe the function. location and the working of subsidiary heads in Inundation Canals. 2. Describe briefiy the Layout and the points you will keep in view fOr determininig the suitable main head for the head reach of an inundation canal. 3, Why are escapes neessary at the end of a head reach of a canal? \Vhy canno they be done away with by heading up supply at the regulator to top excess supply? 4. Describe Claxton's systm of aligning head reach of an Inundetion Canal.

PART II

CANAL IRRIGATION Chapter XIX

Discharge Observations and Regulation 1.

IntHdl1ctIon. Discharge denotes the volume of water passing a section of a stream in a unit of time, It is measured in cubic feet per scond, commonly cated Cllsecs in India. For successful irrigation operations the correct knowledge of the discharge in the rivers feeding the canals is very eSSf'ntial. The supplies available will be distributed into the canals taking off from the river, The discharge sites along the great rivers of the Punjab are fi xed, where daily discharges are taken. Similarly carred discharge observations arC necessary along the canals and tranc~.. to ensure equitable distribution of supplies in the distributing cbannels called distributaries and minors, The methods commonly adopted for the river and the canal discharge observations are described in this cbapter. 2. Objects and applications of discharge observations. The objects of discharge observations and uses to which the data 50 called are pllt, are as below:(i) Stati:stical. By collecting daily discharge data for a sufficient numbu of years and scrutinizing it,it is possi91e to forecast the normal supplies for basing the irrigation projects on and also the highest supplies for fixing the magnitude of works and storage projects. Accuracy in observation of discharges at all stages is therefore needed. The Sind-Punjab dispute shows the importance of collecting discharge data for inter-provincial distribution of river supptes. The importa(lce of collecting, in the first instance, correct data for highest discharges is illustraed by the subsequent adrlitions at a comp:lfatively higher cost required at the Panjnad Headworks and Kalabagh Railway Bridge, , (ii) RegUlation and. distribution. Accurate measurement of river supplies for distrbuti(ln among partners of an irrigaion s~ stem and of canals, branches distributaries and outlets fur equitable distribution' is an essential feature of the sucessful running of callal system.

(iii) Scientific and Hydraulic. investigations. For this. accurate observations of discharges both in the fied and laboratory are necessary, Of the numerous invesigations in connections with the advance of hydraulic and irrigation engineering some are' estimation of absorption losses in channels, determination of co-efficients of roughness or various types of channels both lined and unlined, sluice gate co-efikient studies of the conditions of flow in streams and ,investigations of hydraulic laws.

·3

(a) River Gaaging

Site in Plains.

The site chosen must so far as possible comply with the following specifications:-

It must not be located where the river is too wide and shallow, nor too tight and during high floods it may result in excessive and dangerous velocities. (ii) Widths may vary from a few hundred feet or even'less during the Winter season, to several thousand fe~t in the SUmmfT months, but the site is to be such that at all times the section is reasonably uniform. A site where the sectbn is very deep on one side and very shallow on the other, or shows some such deparature from normality at .different times of the year must be avoided. (i)

~eep. In the former case it results in shoals and slack water, while in the latter

401

(iiiJ The discharge section line as for as possible is to be located in a straight reach of the river. [ivJ It is preferable to locate thp. site for obviom; reasons where ,the rive,r is flowing in one channel. But if this cannot be avoided, it means that the multIple sectlon line will require observations to be taken on each arm of the river in flow, On the other hand, a very large rivpr may more conveniently be treated at more than one arm of flow when in all probabiIi ty each arm would b') treaterl. as an independent si te wi th its own seperate a tlservational staff and equipment. . [v] The section line must be so orientated as to be as nearly as possible at a ngh t angle to the direction of flow. [VI] A site mu,t never be located upstream of a confluence and sufficiently near to it, as to be affected by heading up at the discharge site due to increased flow in the channel into which the flow through the disch:uge site falls resulting in higher and false levels. Similarly, a discharge site should never be located above a Weir or Barrage, within the effect of the Pond formed there by the heading up of the river. [b] River Gauging Site in Hills. In this case the same arguments apply as for phins gauging sites, but generally speaking, silts in the hills are more difficult to select ann all the desirahle features cannot be found; but it is es,ential n~verthele ss, to select a site which is:fi] Free from proj ections from ei ther the bed or, the side~. [iil The site should not be too close to any bridge or fall, Any incoming torrent upstream or dONnstream of the discharge section should be as for away as possible and not nearer than 600 feet, [iii] Straight for at least 500 feet, above the section line. [iv] Accessible ~n all se~sons. [c} Artificial channels(Canals). Such sites gonerally are easy of selection, but nevertheless must be :[i] In a straight re'lch of length not less than 10 times the mean width of the channel. [Ii] Not in close proximity to any fall, bridge or work of any kino likely to cause obstruction to smooth flow anrl cosequent eddy action. [iii] If the channel is not pitched, the existing channel must be kept to a clean section f~ep fom fallen berm~. For a perm'lnent discharge SIte, Hie side slopes and preferably the bed also should be pitched over a length equal to at least 200 fcet. 1

~.

"

4. Permanent and temporary gauges. [a] permanent ganges may take the form of:[i] Graduations directly engravpd into rock or masonry. Ii] F. 1. gau;es fixed to an angle iron, old rail, or masonry-pillar and g'ven secu:e foundations. LiiiJ E. I. Gauges fixed to masonry structure such as Railway Bridge, Piers etc,

rt is most important that the zero R. L. of a permanent gauge. when once-fixed is on no account changed, [b] A temporary gauge does not reqt1ifl~ such secure foundations and may be used as an extention gauge to a permanent gauge which has been temporaril~ left high and dry or in connection with a disch'lrge site the section line of which is not in itself a permanent fixture. When temporary gauges are required to be fixed not les,; than 500 feet upstream and 500 feet downstream of a discharge site section line. for the purpose of recording water surface slope a.t that discharge section line, they, must be graduated to read to 0'01 foot in order that surface slope and ultimately Kutter's constant may be sufficiently accurately determined, [c] All gauges, whether perman~nt or tempora y. mmt have their zeros fixed relative to a permanent bench mark which, if not existing near enough to the gauge or gauges to be set from it, must separately be located and provided. S. Methods of stream gauging. The measurement of discharge is made by thc following methods: ~

/

402 [iJ Velocity area method [ii] Gauge discharge curve method [discharge tableJ Weir method [Meters chapter X.] The above three methods are the most {'onmonly employed for discharge observations and s~all be described in detail hereafter. In addition, the following methods are also used, thougn they ;.vill, intp.rest engineers only :. [ivJ Pilot tubes. This method is based on the the principle that the dynamic or Impa~t pressure of a current moving with velocity v, and striking a r,lass tube with a nozzle, pomtIng upstream, makes the water rise inside the tube by an amount 'h' above the sllrface and that the velocity is represented by the equation v=Gy 2gh. The value of the co-efficient G can be determined by calibration of the tube. [v] By chemical means. This method is based en the principle that if a w~ight w 10 of a chemical is added each 5e~ond to a stream discharging Q cusecs and after a thoraugh [iii]

mixture if a lb of the chemical i:: contained in nIbs of water thp.n _W_ = _1 6~'5

Q

orQ=--~.

62'5 The J?etbod reqaires special apparatus and arrangements and is not easily applicable under conditions prevailing in the field. [vi]. By venturime!er. This is a?plicable only to discharges c::lpable of being passed through a pipe and its theory is described in all te· t books on hydraulics. . [vii] Bya travelling screen. In this method a light varnishp.d canvas screp.n fixed J~ a. rigid frame is hung from a wheel-ed carriage and is made ~o move with the water in a spe.mlly prepared rectangular channel. The velocity with which it moves. after being corrected for leakages from sides is takpn as the mean velocity of the stream. 6. Velocity area method. This method involves measurements of area and velocity.- It being impossible to detfrmine ~he mean velocity for the entire section of a channel in one single measurement, the area IS divided into vertical strips of suitable size and mean velocity for each compo~ent strip is observed, the total of the discharges for all strips bein.g the dIscharge of the channel. In other words the cross section of a river IS observed by soundings and the mean local velocity perpendicular to the cross-section is observed at as many points as::possible. The discharges at tl:.ese points are denoted by the p~oduct of the mean velocity and depth. If now a curve is plotted with the water surface wldt~ as the base and the discharge at each point represented by product of depth ~nd veluclty as the ordinate. The total discharge is represented by the area of the enclosmg polygon. The area of the polygon may be determined eitoher by taking straight averages or by Weddles and ~impson's Rules. raJ Measurement of area. The area of cross section of a stream involves twe elements viz, the horizontal width and vertical depth which are both measured as below :[iJ Width. If thp. discharge site is located at a bridge or other masonry work, the measurement of width is a simple affair. In the case of an open channel of width upto about 1,000' a wire is stretched accross the channel and segments are marked on it tw means of pendants. At Rupar on the Sutlej a weir has been stretched at a width of 1,700 fe:t of the river. The necessary precaution in such cases is to make a suitable allowance for the sag. Alternatively, the pendants snould be fixed by a theodolite. In bigger channels accross which wires cannot be stretched, the segments are marked by pivot-pomt method which is baised on the principle of similar triangles to be described hereafter. [iiJ Depth. The points where depths have to be measured are located as above and in deep and fast stream in which wading is not possible, boats have to te employed for reaching such sounding poin ts. Depth is measured either by direct reading on a sounding rod or log line or by indirect methods. raj Direct Method. (i) A sounding rod consists of an oval wooden rod with E. I. gauge on it, flat iron of 2"x t" size or bamboos of 2" to 3" diameter all graduateo in tenthS of feet and with iron .discs of 4" to 6" diameter at bottom to prevent sinking in bed. Bamboo rods have been used even up to 30 feet depths in low velocities. The depths are measurer! at downstream ends thus omitting effects of afflux due to velocity. n

403 (ii) Lead Line. In higher velocities and depths, observations are made with a weighted log line. Log lines consist generally of copper cores covered over with hemp. Such a line does not shrink"" hen. wet. nor stretches u~der weight and remains free from knots. Alternatively, when such metallIC lInES are not avaIlable as IS the case at present due to war, weighted manilla rope can be used, tut with due precautions regarding stretching and wetting it before lIse. Constant checking during use is essential. The lead or sounding weight is generally of the shape of frustum of a cone. The weigth varies from 10 lbs to 56 lbs depending upon depth ann velocity encountered. At Kalabagh even a weight of 56 lhs has to be used with care and experience to measure depths accurately. It requires an experienced hand to observe depths properly with a logline. The depth of water surface below a reference point is first measured and marked on the line. The weight is then swung and released a little upstream of the observer. After tCJuching the bed it trails down and the rope or line is pulled, till the weight is vertically under the observer when the length of the rope is marked against the reference point. The dist:tnce hetween the two points gives the depth at the point A dif ere:1ce of 6" between two consecutive readings is ignored. for large differences observations have to be repeated (b) Indirect method. In deep and rapid rivers the observations of depth with log Haigh's Depth Meter. Scale 3/8"=1"

C(1a STIMW it/Nil ~~V~~~~-;--I--- 8'10~£0 TO

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404 line requires skill, experience and prf'EeVerancc and thp accurar)' of results can to some extent be questioned. The problem of measuring depths with ease, rapidity ::Ind accuracy has not yet been satisfacturily solved and attempts are being made to apply some indirect type of sounders for the purpose of which the following ale worth mentioning. Ii) Haigh Depth meter. This is an ingeniouc, device recen tly invented by F. F. Haigh C.LE., Chief Engineer, Punj'lb Irrigation and is based on. Boyle's law viz. PV is constant and thp, observations so far m'loe give remakably consistent rcsults. It con~ists of a tube coil in a cylinder containel', in which watfr under pressure is entrapped by compressing the volume of air in it. The volume of water entrapped is proportional to the depth upto which the meter is immersed :lnd the dppth is read from a calibration curve Fig. 2 prepared by actnal obf,ervations tefore it is brought into use. The details of the meter are as shown in Fig. 1. The ir1stru·nen~ b~sid ,s b~in~ U3ed i.\ rlischarg \ o·)servatio 1~ wJl be oi immense value in observing scour depths at salient points of Headworks, training works and railway bridgf's. (ii) Kalvin tUbes. These have been tried in Sind have lind not proved to give consistent and accurate results. . .c.: (iii) Echoe Sound9r. Sugge;tion has beer} mvie by Montagll, to explore the possibility of using sllr:h sounders as are used on ships hr ob3erving ciepths. This needs further investigation.

general characteristics.. Attempts at V , determining location and magnitude of /' one single value for mean velOCity for the entire cross-: ection of a channel have so III ~ far not been successful and therefore, for I'M c: rlischarge measurement mean velocities 1/ 80 for component strips of area of crosssedioTls ale observed. The vertical lOa velf'city curve showing velocities at I various depths is accepted to be a parabola 44 with a horizontal axis. Actual observations by various investigators in America and India have shown that the p')sition of '"-. 4 IZ. to I!.... a- t I1ID .4() ... ... mean Vflocity in a vertical occurs, under normal conditions of flow, at 6/IOD. It Depth in feet Fig. '2 has been proved mathematically also by Lindell from the paraboLc stape of the vertical velocity curve that the mean veIccity occyrs at 0'6D and the maximum velocity a.t 0·15D. Further, it can be proved that the mean velocity equals the average of the velocities at 2' 21 D and 0 79D generally accepted as velocities at 2jlOth and S/lOth depeh which is the basis nf the "two and eight tenths method". When measurements of velocities at known depth are not possible, Surface in segments or even central surface velocities in a cross-section are measured and corrected into mean velocities by application of a "reduction co-efflcient," Velocities are measured by the following meth@ds :_ (1) Surfa!le float!':. The,e consist generally of wooden discs from 3" to 6/1 in diameter. Observations with such floats are liaLle to be influenced by wind, ripples and eddies on the surface of water and bE-nds in the stream. The shape and weight shOUld, therefore, be Such as to mnimise the effect of the disturbing forces. To be safe against effects of wind, globular floats are better than flat discs. Simpler floats consisting of corked bottles, oranges, blocks of WOod, or even floating debris are used when improved types are not available.

1....

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.,

405 The floats register the surface vd )city and a reduction coefficient has to be applied to get the mean vdocity. The exact value of this co-effir,ient is still a controversial rr:atter. The value IS i!>tated to be greater for sandy bed rivers and minimum in bedo; of gravel. Experiments on different rivers have shown the value to be between 079 to 0'91. In Holland the value has been found to be 0'87 in s:lndy beds. In the Punjab Goodman collected a large number of olservations and found the value to be 0'89, which is alreildy in use. The method i" not of an unquestioned accuracy and is applled in high floods only when o~servatiom hy more definite and accuraie methods are physically limpo~siblp. , Sometimes subsurface or double floats, consisting of metallic hollow, cylinflrical weighted subme~ed floats attached by means of a thin cord to surface floats were used. They have, however, become obsolete with the development of better methods. (ii) Rod or tube Boats. A rod float con<;ists of a wooden rorl, square or round, in section of width or d'ilmeter from I" to 2" proportional to length for strength against rough field use. It is weightt'd at bottom by means of a lead weight for immersion to required depth. Hollow tubes of tin r galvan:sed iron were also used but have been discarded being unsuitable due to cracking and developing leaks. That a rod float extending from -;-urface to bottom of a channel shall represent very closely the mean velocity in the vertical, is an obvious inference. Cunningham in his Roorkee exper:ments has, bv assuming that the force acting on the rod at any point is proportion&.l to the square of the diffprence between the velocities of the rod and water in contact with it and that th'l vertical velocity curve is a parabola, mathematically shown that Vr the velocity of the rod is equal to Vm the mean vf>locity when the immersed length of the rod is from 0'95 to 0'97 the depth of water, the exad value oCJending upcm p:>sition of maximum veloc Iy in the vertical. He takes mean value when length of immersion is 0'94;). Parker found that Vr equals Vrn if length of immersion is 0'9520 with maximum. and minimum valu'ls of '97D and 0'91 ). In the Punjab Irrigation Department, rods with length of immersion of 0'940 are used and they are mace of full length and weighted so as to have '06 of length out of water. Parker is of opinion that rod flgat give too high a result as compared with weir or current mater. The method of rod-floats is applied only for caMI observations and is rarely, it ever, applied to rivers, The rods form a simple inexpensive and direct method of measuring velocity easily followed by untrained men and are not afJected by the nearness of boundaTies of channel. section. They have, howevpr, defects like requiring a la'l'gf'r party for observation, difficulty to control their course, motion along a pulsation without neutralising effects of changes in velocity observation of more than one cross section and poc,sibilityof fouling bed by '94D rods and a consequent tendency for uoe of smaller roeg leading to over-measurement of discharge. This over~estiomation of observed discharges by the rod-floats is an admitted fact and in order to solve this difficulty the rods described below have been introduced as alternatives (iii\ Lacey Tabular rods. This type of rod consists of a hollow closed tube working in another hollow tube, closed and weighted at the bottom so as to float in water with only the top sticking out about two inches in length. The length can be adjusted by pulling out the inner tube and the depth of immersion remains upto the same point from top. the increased length of the outer hollow tube getting filled up with water. These rods are avaiable in sets which can serve for depths from 101 to 10.0'. Lacey has mathematically proved the relation Vrn =2v 2- Vi whf're Vrn ~ =the mean velocity or velocity at O'6D and v 2 for a rod of O.8D immersion and Vi = the velocity for a rod of AD immersion. He has, th, refore, reommended the sinlUltaneou$ use of two rods immersed to depth .40 and .8D and observations and comparison with current meter velocities at '6D has proved this method to be quite accurate. [t, however, in-volves too elaborate a system and excessive time and suggestions to substitute a single '80 rod have been made as described hereafter. (iv) Current meters:- Current meters are of two kinds viz. Cup meters, consisting of a wheel with conical cups revolving on a vertical axis a.nd screw or propeller meters, consisting of vanes revolving on a horizontal axis. To the first kind belong the price (Fig. 3) Ellis and Watt meters and to the second, Fteley and Stearns. Haskell. Amsler (Fig. 4) Stobroni. Kichard and Ott Price meters known as Gurley meters after the manufactureres, Wand L.E,

406 Gurley, are now almost universally employed in America, Egypt and India.

7. Price or Gurley meter :-The equipment consists of the following five principal parts fig. 33 (1) The head- As shown in the sketch the h~ad is yokeshaped, earring a wheel of of 5/1 dIaI?eter with six conical cups '2' attached to a honz.ontal frame. This wheel revoh'es in a counter clock-wise dirtction on a shaft '4' resting on a pivot point '5, 6' at the lowEr end, and pas~iDg into cUmml tatoT box 'II' at the upper end in wll.ich arrangements' 0 indicate electrically the numl:er of revol11tions hy single or penta strokes are provided. In Gllrlp.y No. 622 single and penta arrangements are provided in the sa.me box and in mder No. 623 separate boxes are pre video. Meter No. 623 is in use in the Pnnjab generally. (21 The tail : - The tail· 8~ consists of a . , stem on which there are two vanes, one bf'ing rigidly fixed and the other capable c f being plllIed out by sliding in a groove. Art adjustable weight in a slot is provided on one of the vanes. The functions of the tail are to balance the head and keep the meter parallel to the current. (:3) Ths hanger:-The hanger '23' consist of a thin steel bar, passing through the frame of the meter with torpedo-shaped weight at the bottom, the function of which is to keep the meter in pItimb when hung by a cable. (4) The recording or indicating devise-This consists of a telephone recieved '27' with necessary battary '26' equipment and ticks are conveyed to the observer, on closing of circuit after the " i~~~~~!!!~~!!i[iijtll single or penta number of revolutions according It to the commutator box in u£e. (~) Suspending device- This consists of a rod, cable or rack-and-pinion and provides for lowering the meter and weight (when used) in water. The rod is used in shallow str~ams of wadeable depth. The cable is used from boats and bridg<~s, but it has the defect of bowing an@! bdng deflpcted from the point of obseroation ill h;gh velocities. In order to enSUlf the location of the meter being truly at the point and
407

and

In using a meter revolutions are recorded and the relation between the revolutions the velocity is determined by rating the meter. The process of rdting

-AH5UR CURRENT ME7£R WITH 511SPENDING ARRANGEMENT.

Fig. 4

consists in towing a meter through still wat-'r at known uniform speeds and noting time, number RACK-AND· pr~ION Suspension Arrangement for current meter.

Fig. 5

408 of revolutions and distance. Revolution .. per srcond and velocity in feet per second are calculated. For each meter under rating. eight such observations are taken at different sPeeds, and the relation between velo:ity and revolutions per second is determined by either plotting the curve or by the method of least squares. The relation ha<; a str;li>:ht line equation of the form v=aN +/3 where v is velocity in feet per secono, N is revobltions per second and /3 is the intercept of the straight line on vehcity axis representing minimum velocity at which the wheel sta.rts revolving. A rating ta',le for each meter in use is prepared form this. For Gurley meters in use in the Punjab, a lies between 2'18 b 'l'38 and f3 between O'(J to 0'05. An up-to date arrangemtnt for ra ting meters consisting of a masonry tank 400 ft. long. 8' width and 7' deep with :ln electric trolly fitted with distance, time and revolutions-recording devices, exists at Lahore. Rating is carried out in still water and at the temrature of the season and will not it be out of place to mention briefly the effect of turbulent flow ano chanEU's in temperature on the perfor;nance of meter. Tnrbulance p )stulates variations in both magnitude and direction of velocity in pulsations, durations of which depend upon degree of turbul::Jnce. Investigation in America have shown that cup meters over-register and screw-meters under-register velocitifs and some authorities have recommended the mean of observations by b(;th kinds of rreters to .be taken as the correct discharge. Regarding effect of temperature, Blench found by analysing the discharge data at the head of the L.J. Canal that a Price lY,eter over-re!!isters by I per cent for every 6° C fall in temprllture. This may be attrihuted to changes in velocity observatir'ns.

The mean velocity in a vt:rtical is obserVEd by a current meter in one of the io]]owjng waY3:(i) Six tenths method. The meter is held at 6/iOth depth from surface and the oJserved velocity is taken as the mean velocity: This method is inv:lriably employed in the Pnnjab, except in conditions of turbulent flow. . (ii) Vertical velocity curve method. This consists in measuring velocities at a point O'S ft. below surfa.ce every tenth of depth and a point nearest possible to bed and plotting a curve with velocities as aJscissat: and corresponding nepths as ordinates. The area of this curve divided by the depth gives the m'2an velocity. This method is employed whtre, dne to turbulance, the position of mean veiocity does not occur at 0'6 D as can be the case in sume hill sits only. (iiil Surface velocity metind. The velocity is measured at 0'5' or I'Of below surf::tce depending upon velocity and turbulance at the surface. M"an velocity is obtained by applying a. reduction factor. This method is employed only when Ii) and (ii) are rhysically impossible to apply, say in floods in hill torHmts. (iv) Two point or tN;~and-eighi tenth mei'lOd. Velocities are obtained at two tenth and eight-tenth dpeth and average of the two gives the mean velocity of the verdcal. (V) Stlmmllti ~n lnt- gr:>Uon method. In this method the meter is lowered to the bed add then raised to surface at a uniform rate. The readin~ of the meter, which represents the mechanical av:::rage of the r:ltes at which it turns during its journeys up and down IS assumed to correspond to the m~an velocity. Cup type meters are not suited for this method which is never used in the Punjab. 8. Precautions for upkeep of eUtrent meter.;. (a Although the current me'er will stand considerably hani u<;age, it needs care full handling and atetntion to ensure its proper working. In this connection the following instructions shoukl be carefully o~'servcd:1. Be. sure that the set screws are all tightened up nefore putting the meter An the water otherwise some of the parts may be lost. 2. Before beginig a measurement loosen the raising nut snd see that the meter runs freely. Spin the meter cups occasionally during a measurement to see that they are running freely only by blowing and nnt by hand. 3. See that the meter is swivelling fully and frt'p.ly on the suspension ror. or rack. Tf cable suspens:on is used see that the weights are free to follow the direction of the current. 4. If any apparent inconststencv in th~ results of an observation throws doubt on its accuracy, investigate the cause at once. - Grass may be wound round the cup shaft; the cups may he tilted by tension the moter contact wire the channel may be o'Jstructed immediately above the meter may be in a hole; or the cups may be b2nt so as to come in contact With the yoke.

409 S. After a measurem~nt, it is absolutely necesslry to pour out any water that m:l.y have collEcted in the commutator box, to clean and oil th'" bearing (in order to prevent rust) and to inspect the pivot-point. The overseer must do this personally, using only the oil supplied with the meter by the Dhcharge Division. 6. When the meter is not in use, the cups must never be permitted to ride on the pivot-point. 7. Always see that the Lock Nut, on the Pivot-point is screwed firmly against the Frame Nut, so that it will stay in place and carry the cups prop~rly. 8 In measuring hw velocities, be sure that the meter is in a horizontal position. If it has a ter.dency to tip. the Balance Weight on the Tail is to be moved forward or backward as necessary to give a hOTizontal balance. 9. Avoid tak:ng measuremmts in velocities of less than (l'S foot per second, because the accuracy ofth~ meter diminishes as zero velocity is approached. 10 Should it be necessary to take measurements in high velocit;es by cable s1:lspension inste:l.d of rack-and-pinion suspension, it is essential to use sufficient weight and aho a stay-line in very high velocities, so that the rn ~ttr is vertically suspended below the water surface as nearly as possible. 11. When the meter is not in use, disconnect the meter line from the battery, so that it will not become exhausted, 12. Do not strike the telephr.ne receiver, as a heavy jar will injure the receiver. 13. Care must be taken not to short-circuit the dry battery when the meter is not in use. To avoid this, the poles may be wound Nith insulating tape. tb) Current Mete L Out:lt. 1. Meter itself, with its rating table. 2. Telephone ccnnected up with insulated wire in circuit, with dry c:!ll an j r;onnEcting plugs. 3. Oil--can filled with spindle oil. 4. Small screw-driver. S. Cable for supporting the meter. 6. Hanger. 7. Hangp.r screw. 8. Small tin-box containing 2 spare set-screws. 9. Lead weight pin· screw. 10. Commutator box screw-driver. 11. Penta Commutator box (Model 6~3 only). 12. Cotton sqaare for cleaning. When sending meters for re-rating all the equipmeat listed above must be sent along with it. 9. River disehargcs. The following procedure is adopted for observation of river disch:l.Tges :, (a) Selection of discharge site. The essential feature for the accurate measurement of a discharge at a site is that the flow should be streamline and regular, devoid of errors caused by irregularities in the motion of water. This postulates the following deciderata in selecting the site :(i) It should be in a straight reach of the river with regular streamline flow, undisturbed by bends leading to unequal distribution of velocities, cross flow and eddies, which affect accuracy of measurement. Iii) The section should be regular and deep with least tendency for wide spills even at high discharges. (iii) The section should have a reasonably sta ble bed and sides and be amenable to a regular disLharge relationship as far as pos!'ible. (iv) It should be far removed from confluences and structures causing vitiation br backwater heading up. . (v) fhe site should be easily accessible and free from cracks.

410 (vi) In case of hill sites, the stream should be straight at least for 500', site should be kee from projections in bed
(b,

Segmentation or spacing of sounding pvints.

The dist"nce between sounding points depends upon the width of the stream, profile of the bed and the accuracy desired. In short, the greater the numher of sounding points, the more accurate the area measured and discharge 0bserved, as there are greater chances of fluctuations in velocities being evened out. The following rules are used in practice for segmentation 0f river discharge section lines:Ii) The number of spgments should Lot ce less than fiite"n • (ii) For ri'ler width in excess of 2500 ft. seglnentation is to ce fixed -by the ~xecutive Engineer. keeping in view the pr~vailing cross ~ection, distribution of dIscharge across the cross section, equipment availahle and time involved in completing an observation. . (iii, For river width fran 1500' to 2500' segments shonld be 100' apart over the portIon of section passsing 75 per cent of total discharge and 200 I apart for the remainder. (iv) For river widths 7S0' to lSOO/segments are to be 50' :lpart. (v) For smaller widths segments to be 40',30',20' or le53 subject to condition Ii). . The principle to be followea is that in the portion of the section where the discharge IS concentrated. the segments mU5t be nearer and farther apart in the slack portion so as to have segments of more or less equal discharges.

(c)

Pro::edure and equipImnt.

At each discharge site the following equipment is requirpd : (i) Boat-This is required for reaching the points for observation of depths and velocities. A 3S' long Sukkar type boat is in use in the Punj abo (ii) Suitahle anc bar with about 250/ long 1" diamether manilla ro pe. (iii} Sounding rods of line and weight according to condition~ of site. (iv) Current meter with accessories comphte in all respects inclulling a swivel. At eaoh site a check meter is also kept and the local meter in us~ is checked with this once a foctnight to make sure that it works s"ltisfactorily under conditions in the field. A bracket for handing check meter is also provicled. (v) Rack-and-pinion suspension arrangement, described above. (vi) Stop-watch for use with meter. An extra-check stop-watch is also kept at each site. (vii) A torpedo float with cotton cQrd for indicating direction of current. (viii) Pocket sextant, with which the angle made by the current with the section line as indicated bv the float is read. In order to work out the component of the velocity. normal tll) tlae seetion -line. the obsevefl velocities are multiplied by the sine of this angle and a table for such corrections is provided at each site. (ix) A levelling instrument for checking reouced levels of gauges and a 1heodolite for reading angles. (x) The cross section line is marked hy three flags, ?OD I apart on fach bank. In case pf swift currents, the boat drifts down and drift flags apart are fixed for a requisite distance ~ .. dowDstream of the X section line. ,( (xi) Tn case of narrow strpams. say upto a width of 1000' as is the case with all the Punjab rivers in winter, the sectie>n line is marked across the stream by a wire on which

Fig. 6

pendants are hung at sounding points Fig 6. _ ~he boat is held by another wire. stretched a little upstream so as to have the ta'(;k, and-pu:uon under the pendant.

411

(xi]) When streams are too wide

for stretching a wire rope, the sounding points arb

Fig 7

DI$CH,fRtOl! :SECTION LINE.

located by pivot methnd which is illustrated in Fig 7. From point A on the cross section line on the bank, a line AP at ri~ht angles is drwn and from a point D on it, a line parallel to the section line is drawn. The ratio pn:PA is ~enerally kept 1:5 and the length (If AP is 1000 1 or upto .half the ~idth of t~e river. On line DD, point say 20' apart are marked ~nd rays jr~m ~ passlDg through. tl;ese POII~ts.intersect the section line at B1 B2 B a etc., each. 100 apart as IS eVlde.nt from the pnnc~p.le of sImIlar triangles. The point p is called the pIvot pomt For accurate dally work the posItIon of the flags along the section line, piYot point and direction lines are marked by cement concrete blocks with holes for flags and the arrangement is thus marked semi-permanently. The layout can be checkPd by the theodolite, as angles subtended by B1 P.B 2P etc. with AP should have tangents increasing in

rat, io of segments 2

e. g. with IOO' sf'gment and 500' length of Ap; tangent,(j=l~

200

500 '

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tangent 8 =-50 For rivers wider than 2,000' pivot point o ' tangent (ja=---etc. 500

layou~3

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Fig. 8

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Fig. 9

In slack velocities and Jow de,Pths the boat is kept in position by a boatman standing in water and in high vehcities or greater depths thi! boat is kept in position by an anchor. Upto about 5' pp.r second velocities, the b )at can be rowed up, from station to station. In higher velocities while pulling out the anchor it loses headway and has to be brought to bank or in slacker wa ter for being rowed up. This detouring involves a lot of time. To reduce the . number of detours the anchor IS th· own about 300' upstrFam of the section line by means of a subsidiary flag line or pivot-point arrangement, and at every station a little headway is lost, enabling about 3 or 4 stations to be done at a time without detour III velocities as high as 8 to 10 ft. per second. The difficulty and risk involved in pulling out the anchor under such conditions are appreciable, and the latest method of securing the anc'lOr shown in Fig. 9 is the safest, though it involves introduction of some drift. Trained crew can, however, c"pe with even the most difficult conditions met with at some sites during floods. Undet extreme conditions met with at some sites provision of power launches may be necessary which shall facilitate the procfss of observat on.

(xiii) Having divided the section into segments, the first procedure of discharge observations consists in taking the boat tn a station by wire rope or pivot-point method as is in use, at site and observing the depth. The current meter is then lowered, by rack-and-pinion to 0.6 depth and velocity is recorded. The angle of the current with the section line is then read by means of the torpedo float and pocket sextent. These obsHvations are Jloted in a discharge note-book, a specimen copv of which is shown in Ap pendix 1 which shows full procedure for calculating the discharge. The velocity at each station i; modified for it, angle ani! the product d X Vrn gives the ordinate of the discharge curve at each station. The total discharge is fQund by straight averaging. Further, the wetted perimeter is also calculated and the slope ob!ierved for working out the value of Kutter's N. This is taken as the mean of the slopes on the tW(} banks. Details of meters and other equipment u~ed, along with calculations for discharge and Kutter's N as prepared by observers at each site daily are shown in the form, ~­ a specimen of which is given in Apperlrlix 1. The metho i of recording is clear, self evident and foolproof and the data collected can be used to check the accuracy of field-work from day to day. In the absence of boats, improvised arrangements consisting of bull skims and charpoys, called khatnaus are prepared for discharge observation in hills. Another approximlte method of estimating a floo 1 discharge in the absence of suitable equipment, is to observe the slope and flood level at the time. A cross section is observed at lower supplies and from it the CrQ,s Section 3. t the highest flood derluced. Having determined the slopes and hydraulic mean depth R, the mean velocity is determined by one of the following emoerical formulae:{a\ Chezy's formula v =Gy'RS where the value of G is det{;rmined either by Kutter's or Bazin's formula given in all books on hydraulics.

413

(b) Manning's formula v= 1'4858

,

N

(c) Lacey's formula 10.

R2/3

v=1.3~~8 R 3 14

51 / 2

S1/2

River Di<;ebarge with Current Meter from a Bridge.

. When there is a hridge near or at a disc.harge site, that bridge m:ty be made use of if necessity accol'dingly dictates, either hy holding a current meter directly from the bridge, or, anr! preferably. by holding a discharge boat at a sufficient distnnce downstream nf the bridge by. mearJs of a rope traversed along the bridge. The distance marks hr segments should be pa.lI~ted on the up;tream and downstream railing or parapet. One flag should be fixed on each raIling and the boat brought in line with the section line and these flags. the sp.ction line being marked by three large pole3 on each bank. The section line must be far enough from the bridge so that the effect of the piers on the flow of water is reduced to a minimum. A distance of 500 feet should, how;}ver, be ~uffi?ient. From a bridge where there are railings, the hanclling of a boat by means of a rope IS fairly easy, but from large 'N' Truss Railway Bridges the handling of a boat is difficult. The :ope used is in thrpe pieces jointed in the form of the letter '!Y", the tail piece should be 400' 10 length and t~e two arms about 160 feet each. and all three jointpd to a ~teel flng of about 2" diameter. In the Fig: 10 when the boat is below point A, and an observation is in progress, the postion of the three ropes will be as shown by the firm lines. When the observation is over, the Flagman on the bridge is given a signal from the boat by means of a green flag, to move to the next station. The two sets of boatmen holding the two ropes at A and D, so that the final position of the ropes becomes as i3 shown by the dotted lines. When the boat has finally reached the new position and the r ope DE has fully taken the strain, the boatman holding the rope at A which is now entirely slack and free of any load, now travel to the third statio.n G, crossing the rope over the rope DE at E, so that it takes up the position GE. By HHS method which is repeated for each succeeding station, the boat is securely held all the time and automatically comes to each succeeding station.

1/(,

•

«10

•

Fig. 10

------------- -- ---- -'~----

..

I

--- -----.-

R_

•• 0..

- - __ -

~

(

.

In cases where a discharge is observed by directly lowering a current meter from a bridge; each bay should be divided into a suitable number of segments, so that on obs.ervation point comes too near a pier or within the zone of disturbed water. The meter IS to be held just below water surface so that the surface velocities only are recorded; if attempts to hold the meter at 0'6D are made there will be no guarantee that the mater is really at O'6D owing to excessive deflections of tbe supporting cable, Great care must be taken in measuring depths which in this case will be observed by means of a log liua held from the bridge, and since the point of suspension

414 of the log line will be so:ne distance from the water .surface, excessive de~ection from the vertical will result due to the pressure of the water 10 flow, and there IS. therefore. the possibility of a considerable error being inrtoduced in the observation of depth .. in this manner. 11. Canal Discharge Observation. • (a) The observations are divided in three classes of accuracy. Class 1. Dppths measured at the upper and lower ends of the float run and at the centre section line and meaned, (lass II. Depths measured at the upper and h1)wer ends of the float run only and meaned. Class II [. Depths measured at the central section only. For all the three classes of oJservations. three satisfactory observation .. through each velocity station over the whole float run are to be taken, divergence not being permitted to exceen-half a segment width. The boat holding wire for velocity rod o~servation is to be s;hifted irnmedi.ately above the upper float run.-wit:e, so that veloc:ty roes may be let into w~ter exactly oppsite the desired pendants. Placing a velocity rod in water is a job requiring previous practice as it is essential that it is released in suc'l a way that it does not bob and spin. The best way to do this is to hold it tightly by the upper end between the fore-finger and thumb and lower if gently so that it is in its floating position tending to trail downstream; then the rod should be ,relea sed with a slight fonnml push so that it immediatt-ly gets into the vertical and floats along steadily before it passes under the upDe~ float run wire_ fhe tim -: taken for the run is t hen to be timed by an observer on the ha"k. He times the rod over the whole run, using a stop watch, watching it carefully aU the \\-hile becau>e if it suddenly fods the bed or proceeds in jerks the observation has to be r"j~cted even if the roj passes perfectly below all the desired pendants. If after Tecording thre~ results one of them differs by more than 5% from the mean of the other two. it is to be rejected and the run rt~peater1. (b) The standard velccity rod is I.High e 1 10 float at 0'94 of the depth i. e., if the depth of water is 3'0 feet the rod \0 be use" will be 3'0 feet long and it will float with 30 X O· 4=2'82 feet suhmerged and the balance of 0 18 it above water !Ourface. As, however, a velocity rod can only record the mean velocity between water surface and the bottom of the rod. it follows that no velocity rod can possibly reAd the mean velocity b~twepn water surface and the bed of the channel, and it is that mean velocity which is rc quired. It may al~o be found that even if f Jr example a 3'0 feet rod is used submerged by '282 feet, it will foul the bed at some point or other when the use of a shorter rod cannot be avoided. The application ef a corr@ction factor, therefore, becomes essential and correction may be made from the Francis relationship:-

!-5=r

Vrr,ean= Vrod (1'012-'1l6v'--~)

; where

l=length of the submerged portion of the

rod used. For different ratios of velocity rod length to the mean depth (If water along the path of a velocity rod, the correction factors to be applied in order to correct a rod velocity to mean velocity. by the above formula are as follows:-

~

=0'75, O·SO. 0'85. 0'90, 0'93, 0'95, 0'96, 0'97, 0'98, & 099

V y rnean=0'954, 0'961, 0'968, 0975, 0981, 0'986, 0'989, 0'992. 0'996 & 1'00 rod

In the example given above if it was necessary to use a 2 5 feet rod submerged to 2'5 X 094=2'35 feet while D remained as 3'0 feet then_l_='783 and the corr(ction would be D =~·957. meaning, the error?y u~ing the s~aller rod and not correcting for it would be 4'5%. ThIS error would be on the tIght SIde, meanmg that there was really 4'5% less water flowing in that particular segment than the observation showed. The fundamental differp1'lse between a current meter observations at O'6D and a

415

velocity rod observations is that the current meter measures milan velocity between water surfacE' and the b~d over a period of time at a fixed point, while a velocity rod measures the mean velocity between water surface and the bottom of the rod only, not over a period of time but over a distan~A, and as the latter introduces two errors, a current meter is preferably to be used when the highest degree of accuracy is required, and necessarily to be used with the greatest df'gree of care when observation for the calibration of a meter flume or for the preparation of a discharge table are to be made. Ic) Segmentation. The cross-section will he divided into 5 main segments, as foUows:1 Central segment, wa; 2 Side segments, W 2 & W4; 2 Slope segments, WI & w5 • The width of the central segments 6w 3 , shoulrl be taken approximately at the full surface width, less 3 or 4 times the general depth, and should, if possible, be made a multiple of 6, S0 that W3 may be a whole number. If this cannot be arranged, it should be a multiple of 3. Th~ widths of the side segments w2 and W 4 should be equal tf) each other, exten<1ing as near as possible to the foot of the slapes. The balance of full surface width to be divided equally bdween the slope iegments WI amI w5 • The typical section given bela v will show the general arrangement, the notation to be adopted, and the pnin' s at which velocities and soundings are to be taken:\Vidths of segmpnts W1 W2 6w 3 · ..... • •• • .............. w 4 Ws Distances between WI 1'12 Wa Wa Wa Wa Wa Wa W 4 Ws velocity station. · I nterme d late

and

(Vl

soun d'mgs ....... rI ~ d f< f1" '

"

d 5 rI" 5

"d 6 d' 6

,{ d 7 d" 7

"d 8 d" 8

9

Soundings ("1 and d ll ) should be taken in the c entre of the slope segments and velocltl6 observed when practicable. When velocitips VI and vi! cannot be taken they may

Vll)

be assumed at~ and

2

respectively.

Vlo

2

Streamers will be atta~hed to the section ropes at all the points of the principal soundings which are also velocity stations. Intermediate soundings will be taken only )il .he central segment. at intervals of ~va.

•• ~I,~ ~ I,...I. I,....

U,

(1/1 ~ ~.C-

[tJ,a= 1#8 ,--1.-.. "+ GJs

(8

.

,~

..

'i~, .;~

.

'Ii

'" ~ ~~

q ;,~

't ,..

-

"i ''''II::

i\

i V

~

~

V

.... r...

"r-

~

•

.'i

4-

$

I

,\ 3

18

III

~.

Streamers are not necessary at these points.

,

..

...

1
/ .'"."-

I

The method of recording observations and working out discharges is shown in Fig. 11 and appendix If. 12. Preparation of Disoharge Tables. [Gauge Discharge Methed] [aJ A series of discharges are to be observed at round about steady full supply, three quarters, half and one quarter full supply, against a permanently fixed gauge. For each series of observations one meaned value I!)f 'Q' the Gauge reading 'G', I\nd the Area of waterway 'A' is to be taken out bv rejecting any obviously erroneous observation. 'D' or mean water depth as area divided by Mean Width is then evaluated, and from the four values of 'Q' and '0' so arrived at, the connection between 'Q' and 'D' is determined by evaluating for 'K' and 'n' in the equation Q=K.Dn uiing the method of least squares. The £il'lal stage consists of preparing the discharge table for values of rD' corresponding to gauge reading a<; read from

416

a plotting of 'D' against 'G' in order to determine intermediate value of 'D' cornsponding to intermediate values of 'G'. (b) For a channel section. When framing a discharge ta ble using the relation for a chanr.el secti Q=K.Dn .it is insufficient to assume n=5/3 ~~ a.r.tually It must vary for each individual SIte; on the other hand, where the highest it is degree of arcuracy is not required, sufficient to evaluate 'K' and 'n', graphically by plotting 10gQ against log D as shown in fig. 12 As Q=K.Dn expressed in the form 'TAN c( .. n of :A.N71 LOG )'= #( LogQ =n 10gD + 10gK is the equation. of a straig~t line, the four points i at representu,g the senes of observations, round about steady full supply, thrp.e quarters, LOG D. half and one quarter supply, will fall in Fig. 12 such all'ay that :1. The tangent of the angle, the line through the poini'> makes with the log D axis=n. 2. The ordinate. the line through the point makes with the log Q axis=log K. The solution to the values of' K' and 'n' is thus completed, but this graphical method depends on the corr~ct visual appreciat.iJU of th~ divEfge~ce o~ the points from ~he straight line and the fitting 1D of the appropnately fittmg straIght hne; the mathematIcal mathod appreciates the minutest diver~ence and pro,;,ides a solution which mathematically fits the entire range of supply over whIch the observatIOns have been taken. 13. Special precautions for Calibration Discharges. The followit,g precautions are to be taken before and during a calibration class of observation :1. The guage, whether in a guage-well or outside, against which the discharges are to be correlated mu:;t be absolutely firm and secure. To frame a discharl1" table againit a guage attached to a loose and shaking post is a complete waste of time. and in amy case no such guage should ever be used in connection with any recording of discharge. 2. The guage well, if any, must be functioning properly and it should be seen that it is not choked with silt, and that the holes or silts are perfectly clear. 3. Each observation of dbcharge should be in duplicate>, using two newly re-ratd check meters on the same suspension rod or rack-and-pinion, and operated by two independent observers. 1his serves as a check on the work during its prcgress as, if one observer gets at a stlltion an entirely different velncity from an other 01 server's, the o' servation can immediately be repeated after checking over both the meters. Finally the two results, if differing by not more than 1% may be accf'pted and meamd. 4. A complete observation must take the form of a double traverse, 1 hat is, one set of observations will te from left to right and immediately followed by another set from right to left; with two Observers there will in this way be four sets of results and it is essential that they are all worked out finally at site awl cross-cheked. 5. A regular program aLe for taking the whole series of observations of suitable suppLes is to be prepared in consultation with the local raguiating officers so that the series may not drag on indefinitely and yet cover as much as pos~ibR> of the whole range of supply from full supply down to not less than 40'/'0 of full supply. 6. Special efforts must be made by the 1<egulatiu~ 6[afl to kEep the supply steady and if the variation in gauge during a caiibration discharge observation is greater than 0'01 ft. the ob~ervathn is to bf' rEjf'cted. 7.. The discharge site mmt be as near the gauge of the flume under calculation as possible in order to avoid the effect of time-lag. If the distance, however, is unavoidablv appreciable then time-lag between the discharge site and the gauge or flume, has to be allowed tal. If an

"

APPENDIX 1

FORM D 1.

DAIL Y DISCHARGE DATA. River

Sutlej

Site

Harike

Meter No. and make Gurley No. 171-22,304-S

Date 7/30 hrs.

Time from

Equation of Meter 6-4 -1944-

--

__Zero_ ~.L~I

Description of surface floats . Length of float run

Beginning.

Float run marked- with

j, ; 9' Ip

Sounding ROd,$

Method of suspending meter

Rack and Pinion

Timf'piece used

Stop Watch

Weather Clear Wind driction

Weight used

Ibs.

and strength

I

of water~

i Temporary I R R. L.B.

-----~

,

~.erysligh:' ~slight.

_"'strong. __"""eT)' strona,

Yes

Ordinarily Silty

Current

I

"

SURFACE SLOPE ObSERVED. V = Mean Velocity= (? =3'05 Right Bank. Back

__

-

~ - I ~i~~r l'ore. , ellce. -_ . . -- ----

7'25

500' D./S. -

_e

_______

~c

I F- -.-

k

r Differ-

. ·ure.· ence.

yRS=O 040

1_--____ i"

.------

j

~I_~~

C= - "'_ =76'25 yRS

o --~--

500'

A

Left Bank.

B

'O./S.

..-------- -:").•~

i

i

,

..

X=41

I

~,

1)0281 5

6+~---=56

.

40

y= CX . =1,463

I'":_"~,,"

.

6'58 I

Fall 1,000 ft.

YH.

018

Z=C-X=Ht'90

Mt'an=O'185

N"", y(Z~+7;-244Y)-=~_ =0'028 2Y Character of river bl'd

Sandy

Class of roughness under which it falls . ~_ it j ; ' .~~---

1~_~9_~_

- .

Fairly Clear

l Intensely

8'9S

~::~F~~- ~:~ ~~:.

Pivot Points

Sounqing taken ",ith

Condition

-

__~~_~6_1670·56 j 670'56

Section line marked with

r

To 12/0 hrs. Permanent.

Gauges.

Date of last rating

10-9-1944

II Passed for check by Initials S.D.O. Check~ d by Collator R(" ugh-volumed by Collator

II daten ......... .. dated .......... .. dated .......... . Compared & recorded by Head Collator dated ........... . ON HIS MAJESTY'S SERVICE. THE SUB-DIVISIONAL OFFICER, DISCHARGE SliB·DIVISION. STAMP

'p;uoq:>uV

-------------~---------------

08·9'" 09·6f:=Zr..l X Z/09(~J) OZ·l =SI.OXZ/08 (!} pa:mpaa

·

--

- -

.

00

'"

0'0

UU

,:,

-'"rj,

Ib C':)

o

-""

;...

-----------~------_------_

--

iC':)

UN UN

--- -'" o

,~

----~-:__:_-'--'-----':':_---

------

--

------------------ ---------

-

'?

-

~

o


------------------------~---------

o

0)

o ~-------

------

----

--

--_.__ --_

----

- - ""8

00

-.to

o

--------_----------

-

o

o

(0

b

~

t1)

.L~ ---~--

o

.

c_> ._

'" u 't:..9

~~

o

o

~

§~

.0

~'';::

u

.~

~(/)

o

o

'" ~

o o

~

--- o

CD

g

o

CD

o oC"I

-~

Note :-1. Col. 16=(common width of segments-!the sum of segments on either side of the R. D.) X Col. 15 2. When floats are used, or more than one meter observations are taken at the same section, each obsarvaticn of time and revolutions must be rocorded in a separate line in Cols. 5 and 6 respectively. In Cols. 1 and 2 all the lines relating to one station will be bracketed and R. D. on section and water depth will be recorded once. 3. Co-efficient employed converting surface velocity into mean velocity should be noted in the remarlts column. Unless specially directed it is to be taken as 0'89. 4. If DO drift occurs. the same is to be shown as nil; the column is never to be left blank.

411 observation, for example. is from 10.0 A. M. to It.30 n. M. and the distance is 5000 ft. a.nd

the mean velocit ... is 2'S feet per secood the lag will be = J

5000

2·S.l( 60

=33 rr.inutes, when the com-

parable gange, if it is upstream of the iite, will be that prevailing from 9-27 to 10-57 A. M. 8. W)Jen observi:sg velocities, times must be recorded to the nearest IJSth second and the products of "D xv" mtlst be taken out to three places of decimal, and when finany prepe.ring the equation not less than seven accepted series of observations a.re to be taken mto mat:R.omatical analysis. 14. RegttlatioD. (a) Use of Discharge 'fa.ble. The discharge tables are calculated to give the discharges for every hissa, that is, up to first decimal place of a foot. The discharges for t1
Every Sub-Di visional Officer works out the requirements of 5uP9ly for the subdivision by adding authorised. Full Supply discharges of all off-taking Jistributaries and the seepage losses in the main or branch canal in the !lub-division which are usually sanctioneci by the Superintending Engineer in the Capacity Statement of the eanal. In the case of rain-fa.1l or slack demand in certail'l portions of the sub-divi"ion, he focestalls fhe reqUirement!! of the distributaries ann then adds up the required discharges to work out the indp.nts. The 'fail S. D. O. wires to the Upper S. D.O. and so on to S. D. O. Head works of the Canal. The rndents should specify both the Gauge and the discharge at the indenting gauge. Twenty four hours notice is usually required to meet the indent. The sub- divisional officers on the tail Peaches of a canal should calculate the time whelil the effeet will reach considering velocities in Main Canals 3 miles an hOUT and in Branch Canals 2 miles an hour. Regulation is a very important part: of the duties of an Irrigation Engineer. 'fhere are usually printed instructioJas hung up at the important regulators on the main and ocanches, 'canals sperifying the duties of the regulation staff. The regulation staff is on duty tor 24 hour on the important reg,Ilators. They atonce attend tG the orders issued by the officer-in-ch
1. Paper No. 272, Punjab Engineering Congress, 1945 "Methods of Discharge ObservatioI'ls" by S. L. Malhotra 1. S. E. Executive Engineer, Punjab Irriga.tion; 2. Discharge Observat i on5 by Hayat and Grover. 3. Lewett's Wydraulics. 15. ExaminatioB questions. (al De9cTibe different methods of measuring the discharges oJ fiVers and canal~. (b) Describe a -'discharge rod." What is the best ratio of the length of the discharge rod to .edeptho!water? (T.C.E.19B) 1.

418 2, Describe in detail how you would proceed to measare the discharge of a river about 400 yards wide, Max: depth about 20 ft, max: sud9.ce v~locity about 2 ft. per seeoud. (T. C. E, 1935) 3, The observed discharge of a canal with 7'5' gauge was 600 cusecz and with 6'5' £t gaur:e 450 €usecs, Frame a diseharge table showing discharges with 6'0' gauge and 8'0' gauge. (P.1. B. 1941) 4. Descpibe the mellhod for taking a first class discharge of a call.al with, current meter. A branch canal has a discharge of 1500 cusecs with gauge 9'5' ft. at site and 1000 cusecs with gaugCi 8'5' a4: site. How wiil you pr(')ceed t·) frame a discharge table for this site? What will be the discharge with a gauge of 6'5' ft. ? (P. I B. 1939) 5, FrQm your experience describe an accurate method of measurj,ng the actual disQharge of a channel having 10 to 15 Clasecs capacity, you have a stop watch, tape, measuring rod, Give specifications of the measuring rod, 6, Deseribe the method of observing the discharge:(a) of a nver where it is not possible to stretch a rope across it; (b) of a canal with 1st class observations; "J. (a) Describe anyone type of Current Meters used for discharge observations; (P.U.1942) (b) Give briefly the percauti~ns you will take for proper upkeep of Current Meters. 8. (a) W:ow wtll you work out the indent of supplies in the canal for your Sub-Division? (b) Explain the process of segmentation in a first class canal discharge. 9, (a) How are \Veddle's and Simpson's rules used for working out canal di-schrges ? (b) How will you make correction in the dischariJ€ observed by velocity rods. when a stroog wind is blowing ? 10. (a) How are the velocity observations eorrected I:ry' velocity rods to get the correct mean velocity? (b) \Vhat points will you keep in view while selecting discharge si te in an artifieial channel? II, What are the different methods adopted for measuring the velocity of flow of water in a stream? Mention the eondition~ to be satisfied in selecting the site for aocur I1te gauging of flow in a stream, (Mysore 1>941) 12. How would YOll observe the discharge of a channel using; (a) velocity rods. (b) Current meter? Deseribe any type of current meter with which you are best acquainted, {F.Sc .. 1941)

,

t,

,~...

419

Appendix II.

FiM Cla!!ls Observations. Discharge taken on ........................ at R. D. tO,Oeo Main Line Between 10 A. M and 1-0 P. M, By Executive Engi·neer... : ............................... .. Assistated by Assis.tant Engineer, Reading of gauge at R. D. 1,000 below ff·gulator-.

Before observation

60

}

Mean 605 Aft< r ,f i 1 Surfac-e slope-R. L. 500 f~et above centre of run ... 83470 R. L 500 feet bel~w ditto ... 83t 52 Bifference or fall in 1,000 feet O'IS Fall in 1,000 feet 0 18, or S = 0'OW1S Slight br€eze > Strong bref'Z6 > Much Wind - ~'-~ > Direction > Le14gtk iif r1tn-l 00 feet Timing doni-with chronograph. Floats used-loaded tin tUbes Surface width= 126. C6ntraZ segment= 108 w1 =ws=4o'.0. wa=w 4 =5'.G. w.-=IS'. TABLE OF SOUMDIMGS.

Diiltance I frorM

right bank.

i

Nota· tiol1.

o -dl-~ 2

4 3~

.; X

.; X

5:" X

~'

X,

~

Middle.1 Lower.

I

2'0 3'5 4'7 5'1 5'0 5'4

1--;3 I !

4'2

5'1

Total.

I'

4'0 48 59 (50 81

11'7 14'6 16'3 HN 17'1

6'4

17'8 18'1

8'90 4'87 "1 543 >5'47 g'70 5'93

t

5'5 5'6

45

60

6'_'

51 57

81

63

6~ 60

64 56

6'5 6'4 6'2 60 5'7

60

5'8

5'S

173

66 6'2 6'0 5'9 5·7

6'0 65 62

5'3 5'2 5'2

J7'9

6'3

54

6'6

5'6

179' 17'4 176 17'9

105

5'7 56

6'5 6'0


8 59

18'0 175

6'00

J 11 122

5'5 4'0

5'7 49

5'4 4'3

16'6

5'53 4'40

12(

22

~3

69 75 81

87 93 ~9

III

126

Average.

}J'ota. t40n,

I I -1·-2'~1- -~6-'4-- ~~-·13-1--2-·1-3-

27 33 39

I

I

Mean.

5'3 5'4 5'6 5'9 6'0

15 21

x

I(j"pp".i

18'8 18'6

IS () 17'3

13'2 ,},'S'

6'03 6'2,)

l"90 524

t tlI

5'8S

,I

5'91

6'20 ' 600 i 77 I 5:77 6'91 j 5'97 5 SO >-1

'17

~'g~ ~>-!.I i'83

250

ti

:

D II '73

I

4'40

I

250

JI

420 VELOCITY OBSEIRW A TrONi),

d

0

:;l

;g

Distance from right bank,

Length of rod used.

2

2'0

0

Time rf passing first rope.

Z

Timeo.! ~ndiDg

Seconds.

run,

Total.

Mean.

Veloc-ity per sellOnd.

208

69-8

I 44

193

64-3

1'.'16

59'7

1'67

!55

45'0

2'22

112

37'"

2'GS

42'0

2'38

124

41'3

2'42

204

40'8

245

~

VI V-2

4 9

Va

v4 Vo;

V6

V7

3-75 4'5

'1.7

.

1'03 2'31 4'02 700 8'15 930 12',,0 13'17 14'40 20-05 21'10 2 '30 :.15-02 28'10 0'14 1'20 2'31 5') Z 640 8'60 9'10 10'50 13'0 I 14'00 14'5-9

5-25

45

5.75

68

5'5

81

5'0

~

0''08

Vs

99

1'12 2'15 3'02 4'12 6'00 7'00 8'16 10'49 1208 15'00 18'00 19'30 21'12

5'5

V9

117

V10

122

5'25

I

I

Vn

124

3'75 2'0

2'15 3'40 5'09 8'04 9-20 10'34 12'59 14'15 15'42 2050 2['52 23'!7 2548 28'55 054 1'56 3'07 5'54 7'21 844 953 II 30 13'45 1441 15'38 . 037 I-52 2'55 S't5 456 6'49 752 9'08 11'42 13·11 16'1)4 19'10 20'42 22'25

72 "1 (;9 07 64 "1 65 -{ 64 )

J

~9

"1

58 ~ 62 ) 45 42 47 ) 46 I 45 ) 40 "1 36 I-

1

1

3(!l

42

I

I

I

1

41 4A I43 I 40 ) 44 I 41 ~ 39 ) 3'7'

II

)

40 40 43 44 49 52 52 62 63 64 70 72 73

179

210

i

I

"1

I }-

I

) "1

r

J

153

"1

I

51'0

}-

189

63'0

"1 }-

215

71 7

)

J

)'96

I

1'59 1'39

I

CALCULA [roN OF DISCHARGE, ,

Va =

524X!'67=' 8i'S

Q)

'3 ...

5D4 v4=5x5'70x!'22=

63'27

6DG v6 =6 X 5'S5x 2'38= 83'54 D7 v7 =

5'91 x 2'42= .

.......

5Ds vB =5x5'~~X2'45=

D9 v9 =

5'73 x 1'96=

.! J: titl 'n)

t=O· ..

\J

\)3 ~U

·.i

Discharge=3w3_or 5'4 X 1~

...

14'30

:f=..1..;

__;j 270'52

I

1,460'81

421

CALCULA nON OF DISCHARGE.-(c0ntiJ'lUed) D 2v 2 =3'9xl'S6 D3V3 =as above D9V9 =as above D10v lO =4',Ox l'~O

==

8 75

."

i

i

11'23 7'00

...

-

I

6 08

."

I

--33-061

82'65

I

"'_'..

ffi~ S ~ ~I::

i

12'27

4D 1 v 1 =4x2'13xl'44= D 2v 2 =as above = D1QV10 =as above _ 4D ll V l1=4X2'5x 1'39 =

~

~~

o'ns

7'00 13'90

,., ,,'

Dis€harge=~or O'67x

...

39'35

i

26'30 . _ __

__.__~_ _ _ _ _ _ _ _ _ _ 6 _ _ _ _ _ ! . . - -_ _-

D=1,5GS'76

Total Discharge OTHER CALClTLA TIONS. AREAS.

Wetted Perimeter. Central SegmQnt.

...

Da

5'24

.. ...

5D4

...

... ... ...

5Ds

Dg Total

'

..

X 3w 3 =

35'1

DIO

5'91

29'75 5'73 1

...

..

Du

5'24 5'73 4'40 19'27 1'95

... ...

WIX

W 2 +W4

=48'17

2'13

...

'

."

... 1

100

\

iI

1080

Total =17'56 64'73

8'78

628'5$

..,I

60

~-,

I

Area of central segment .. other segments

1296

'"

I

j 628'56 6.5 73

, A=Total area .1

5'6

· .. 1

V(ws,2+lD 1O )2

2'50

'"

6wa

.

I

... I

I

2'20 ~

!

-yI~Wl)2+(D2)2

3'90

, .., ..,

i W2x ... t D2 Dl ". t D,o ...

116'40

5'4

10

Area=

6'17

D2 D3 Dg

28'50

,

D5 6D s D7

Slope and Side 5egments,

;~.,

,

P=Wetted perimeter Hydraulic mean depth=~ P

=R

=

A-ylR'5 =694'29-y1S'31 xU'~0018

==

21'558

Co-efficient=

==

73-S

D AySR

1569'76

21'888

PAR r II

-'"

i'

CANAL IRRIGATION Chapter XX

Water Power from Canal Falls Introduction. The necessit y of creating canal falls (drops) has Ceen explained in Chapter X of this part. When the slope of the country is steeper than the permissible (regime)' slopes all(")wed for thft irrigation channel, th~ additional head available in a canal is given the form of a canal fall. Such falls ca.ft be utilized fur the development of motive power asd for other useful purpOies as under:(1) Generation of Hydro·Electrie power which can be utilized for lighting, heating and various inclustrial purposes. (2) Dirt'ct drives, lIuch as flour mills and lift wheels The latter can be used fe,r llfting water to commanc! the high ~djoi.nin!! areas. ~31 :,Hydromats (Saction or compressisn type). (Already described in chapter XIII of tms part). (4) AutosucNon weirs. (Dc£cribed in Chapter IX of tBis part). 2. Power available from canal falls. An approximate idea of the energy available from 8. canal fall can be obtained "(11m the foltl,,)wiJII€ calculation.s : Let Q = fhe ql1antity of water in cubic feet-per SfMnd flowing throug. the canal. H=Head in fed through which the water drops at the canal fall. w=Weight of water in Ib~ per Cubic foot=624 lb. The theoretical water power

62' 4 ~. H. horE9 power. The actual useful available fr om the canal f
1he ccmrr.cn unit of electrical power is a

/--

=

Expressed in kilowatts tke available electrical energy=_2!!__x _1__ QH_Kilowatts . 12 1'34] 16 (approximately). Taking an aetual example, suppose the quantity of water flowing through a canol i~ flO CUS€Cs and the height of the canal fall at a given point is 10 ft. Then the f leotriGa 1 el\ergy available from this fall would be : -.t

5001~ 10 =312'5 killowathl

/'

423

Placing 500 Ton Rotor in one of the 82,500 Killovatt amperesigenerating units Boulder Dam, U.S.A. / .

__/ /

424

Installation of four 82.500 Kilowatt ampere generators, Boulder Dam Power Plant, U.S.A.

us , To have ltD approximate Mea as to what this energy is clp~~)h~ of doing. the normal consumptions of various electric~l appliances are given below: ;: HIt. ~,il', [il Ordinary electri~ lamp=40 watts. ' +:'!i'F [iiJ Electric table fan. =40 to 50 watts. ", l',L'lI riii] Electric ceiling fan =60 to 80 watts. .... [Iv} Electric heater for room=500 watts. <::'1 "r di~lt'N ft, • [v] Flour mill 2£ ft. dia: stone=lO Kilowatts. " /; [vi] Tube-well with a discharge of 1'5 Cusecs and lift of 20 ft.= 12 Kilo Natts. ," '!~ ,-",J n , One Kilol'latt=1000 Watts. Hydro-electri, Installa.tions on canal falls. A Hydro-electric installation on a canal fall will consist mainly of the folloNing parts:[a] Headworks for diverting and confrolling the flow of water from the main canal to the head race or intake channel leading to tho power house. [bJ Headrace or intake channel. ~~:;~·:~/~.'~~+'·'.,,{.r~-r~""y~ttft 1)?£ 31 [cl Water turbines together with the control apparatus. Cd] Electric generators together with switch gear and control appartu~. [e] Housing for the dydraulic and electrical apparatus, items [c] and [dJ above. \r~\~; if] Tail race leading the water back into the main canal. 4. Design 01 Hydro·electrie Installation, In nesigning the various parts of a hydro-electric installation the engineer 'bas' consider \'ery carefully the most suitablp. velocities of water at each part so as to determine the cross section and design. High velocities mean the sacrifiCing of a large percentage of the total head available for developing power at the turbines. On the other hand, low velocities require a largtlr section of intake and out· flow channels tkereby involving a higher capital cost. The engineer has to determine the economical mean I etween the two. In low head platns it is m~st important that the head lost in friction and eddies be as small as possible and, therefort>, velocities should be as low as possible. Suitable veloclties in various paTh of a hydro-electric install~tion are given below :[iJ Headrace or intake channel The maximum velocity in open flumes should Qot exceerl about three feet pAr second as a higher velocity is likely to cause whirlpools ano. eddies which will enter the runner and cause cjisturbances ill the smooth flow of water. In steel pipes used on hiE!'h head installations higher vehcities can be userl. Usual velocities for heads up to 200 ft. are 8 to ]0 ft per second ann for higher heads the economical limits for velocities are still higner. To maintain a constant head and constant supply of water to the intake channp.I art overflow weir is necessa:-y which in modprn practice is designed as a spillway syphon. ,See chapter VIII of this part) The intake channel should be designed non silting. [Chapter VI, part II}. ':1;: '.,;;" . .[ii] Turbine pit. .. , ,

3.

..'

H

,

.iJ

'

to

In open flume plants, the intake channel leads direct into the turbine pit. The velocity of watfT on entrance to the runner on this type of installation should b~ about 2 ft. per seCClnd to avoid eddies in the runner, Wh~n turbines are prOVided with spiral casings so as to guide the water in smooth passages, higher velocities can be used. When spiral casings are of concrete, velocities of 5 to 6ft. per sec. are recommended. F()r plate sted spiral casings velocities as high as about 20 ft. per sec. can be used. [iii] Draft tube or suction pipe. The velocity at the exit end of the draft tube should bel about the same a~ in the tail race. In ION head plants this shOUld be about 3 ft. per sec. [iv} Tail-r:l.ce. In low head plants the velocity of water in tail-race should not exceed about 3 ft. per· sec So that the out-going water leaves the turbines with as little kinetic energy left in it as pos ible. Besides, higher velocities cause eddies and d~stroy the suction action in the draft

4~

.'

tube which leads to lower efficiencies. Slightly hil!'her velocities upto' 5 or 6 ft. per sec. m~y be allowed as the head incre;}.ses. In the case of Pelton wheel instiallations the tail water has no effect on the turbirle and its velocity is determined by such conditions as the available area of channel with respect to station foundations etc, " . (v) Inlet bend to Pelton wheel nozzles. :t ~";i';~; ~,hl'j'7f]: 'i:

=..

. The velocity in the inlet pipe sp~uttng velocity of wa.ter i. e. 10 Yo of whIch the turbines operate. For he
of a Pelton. wheel is generally kept at 18% of the Y2gH where H is the effective head of water und~r exceeding about 600 ft. it is preferable to reduce ~t very high heads of the order of 'l000 ft. and above, thIS to about 5%. The velocity should In no case exceed , ;'l.'." . '

....

,

. Hydraulic turlilines may be classified unuer two main headings:(i) Reaction turbines which work by me;}.ns ofthe p"tentia-l and pressure energies of he, wate:. Francis turbine runner is the chief example of this type in the present day use. It lS a IJll>.'_ed flow tuabine being partly inwarn flow and partly axial flow. , (11) Impulse turbine work unner the kinetic energy of water, and the POWlilf IS abstract.ed from the water by allowing the jet of water to act on a number of buckets fixed to the nm of a disc O£ whe~l. The principal example of this type is a Pelton wheel. . . The c~aracteristics of thesQ. two types of turbine runners are described in deta~l .lD a !ater part of thiS Chapter. Hydro-electric pJ.ants usieg reaction turbines are further subdivided lllto tll.e following principal categories:(a) ·Open flume turbines. (b) Concrete spiral cased turbines . .(e) Plate steel spiral cased turbines. (d) Cast iron or cast steel s~iral cased turines. ~a, Open Hump. turbine. "_,

.".

, In this type cif construction the intake water channel leads direct into the tnrl~ine runner. FOT low heads not exceeding about 30 ft. this is the simplest and most economIcal c?nstruction as it eliminates altogether the necessity of pipe lines, valves, turbine casi~g~ etc. Stngle runner vertical shaft type construction is usually adopted as this gives better effiCIency. The w~ter after doing' it~.work in the rnoner discharges through a suction tube into a tail water c~nal J116t beneath the' fo'o~ of the turbine pit. Ihe turbines should be so arrang?d that the distance from the .snrface of. the incoming water to the highest pomt of the turbine runner, or gui<;le vanes when these are provided. is at least equal to the diame~er of ~he ;l,lnner, as otherwise ai,r IS likely to enter through eddie5, thereby reducing the suchon actIon m the draft tube and din'iiilishing the output of th~ turbine. When rocky foundations are available, this type of construction may be economical even fOT heads upto SO ft. (b) Concrete spiral cased turbines. These are wled 'prIncipally for capacities above 400 H.P. at 10 feet head and above above 100ft. due to the necessity of remforcement in the cO'llcrete which makes them more expensive and less reliable. . They are almost invariably constructed in the single runner vertical shaft type. (c) Plate steel spiral caood turbines. Above this head a These turbines are used for heads exceeding 40 ft. upto 375 ft. <>ast type casing is used, These turbines are usually constructed in vertical shaft single runner . type as this ha!, a greater efficiency~ 50f)O. H.P. at 100 ft. head. They are seldom used for heads

Cd] Cast iron and cast steel spl'ial cased turbines. Cast iron casings are used only for moderate size units working tinder medium heads as cast iron is not a reliable material for .high stresse5. For large units and higa headg upt_o 1000. ft. cast steel castngs are used. When the head exceeds 1000 ft. the Francis type of fl:lDDer S ives too high aspeed. a~d implllse turbines are used.

(e) Impulse turbines. These are generally used for heads above 850 ft. They are alsO 'used in smaller uIl'its dowJli to 2f1l0 H.P. at 100 ft. head. These turbines are usually of the horizontal shaft type either one or two sets of buckets being used to drive each generator. Turbines of this type, are in use for heads upto 5000 ft. in Switzerland and for heads varying from '2000 to 3000 ft. in other parts of the world. . 6.

Suction pipe or draft tube.

>. The suction pipe or draft tube is simply an air-tight tube fitted to all reaction type turbines on the dlscharge,side It extends from the discharge end of the turbine runner to about 18 inches below the surface of the tail water level. The suction action of the water in this tube has the Eame efi( ct on the runner as an equivalent head so that the turbine developes the same power as if it were placed at the surface of thl!) tail water. The action is similar to that of a syphon, the water exerting a suction proportional to the height of the column. Theoreti~ cally the centre of the turbine shaft can be placed about 34 ft. (height of the water barometer) above tl1fl tail water at sea level, but full advantage of this cannot be taken owing to the dissolved air in water and due to srr.all air leaks. In practice the maximum head that should be used in suction is about 25 ft. at sea lev@t and less according to the altitude of the site. Straight draft tubes have generally a flare of from 4 to H degrees, depending on the length, so as to rec uce gra(Jually the velocity of water, which then discharges quietly into the tail water and with as little energy left in it as possible due to residual velocity. The draft tube should be supported securely otherwise severe vibrations are set up which may disturb the whole station. Large draft tubes are usually moulded iIi concrete as it is easier to obtain grandua curves in concrete than in steel plate. At sites subject to high floods the electrical equipment has to be placed above the high flooa level and in such cases the maximum length of the draft tube has to be used so as t9 avail of the total head upto tail water level. SueQ contingencies should be carefully studied from the data of rainfall and flood levels extending over a period of 40 years or over before designiog the installation. If data ava~lable js_ for alesser period, a safe margin should be added. lU.i

'jf~_"I,"::;''''''''''''''

IV.......

'

7. Specific speed. The specific speed of a turbine may be defined as the r.P.M. at which the runDer would run if it were so reduced in size, without in any wa.y changing the design, that it would develop one hon;e power under one meter head. Meter has been selected as the unit of head as the perRunners having the formance of hydraulic turbines is more often expressed in metric unNs. SQme specific speed have similar characteristics of performance, so t?at specific speed is a very ccr..venient term indicating the type of a turbine runner. High speCific speEd runners are suitable .. for low heads and low specific speed runners are suitable for high heads. The specific speed is a ocmplete measure of the possible performance of a given ruDner under any head, both as regards power and speed, and thus it gives an indication of the suitability of.a given design of runner for any given set of conditions of head, speed and power. When considermg a turbine which bas more than one runnp.r OIl its shaft, the specific speed is based on the capacity or. out put of one runner; hence the total capacity of the turbine must be divided by the number of runners on the shaft for embodying in the specific speed formula given hereafter. Let D=Dia : 01 runner in meters. Q=quanityof water passing through the ruoner in cub. meters per minute; N = B.H. P. developed; n=Speed in revolutions per minute; and H=net or effective head on the runner in rr.eters. Then :-(i) ncq/fI (ii) Qocv'H; (iii) NocH3/2 for a given; design of runner; (iv) NocD2; [v] QOCD2; [vi] nocl/D [vii] Doc VN-. The formula for specific speed is n

vN

ns=-~-

H514

powtr

\\ hen invesitigating any givEh scheme the head; quahtity of w{lter, and the total output are readily available and the first problem is to find a suitable type

428 soo

••, .!ND/ClTes TURBINES BU/~T AND IN SUCCESSrUJ. OprffIJTION, ,(ND INDICATES TilE f)EPAR"I/I1f£,~R(JM VAL IItS INOICA.,'&J 8" THE. 'CURV", WilleN MAY 8£ MAllE WrrNSAr£r,(.

j

f-

t\.r

300

::a:· \ tri 1\ I

)I(

~

\ \~

~

§ fO()

.

~

I

~ ~

;.

.......

..........

--._ •

II)

--

II

.&:: SO

100

Z()O

HEAD IN M£iRES

_ n

YN~..

_ n,

X

H 51 4 _ 360x

n - - - - -, .. n----=, H5/4 yN

Fig. 1

-

lOS!
---.-~-

• /S40()

v =79·2 r. P.M. This is not a suitable speed for the altprnatoJ, hence we will try two runner~ on one shaft. The output per runner will then be 3200 B H.P. and sub~titutiIlg this in the above equation. we get :360 X 105/4 blIwN n= ~.J-HOO =112 r.P."'. !Uj

;)

iu,;

of turbine and its speed. The curve in Fig. I shows the maximum specific speed suitable fnr various heads, and enables the maximum specific speed being dt:1ermined at a glance. This curve has been obtained by collecting the data of a number of existing plants, and -is not based on any theoretical calculat ions. The application of the specific speed will now be demonstrated by the following example. Example 1. Suppose it IS desired to devflop 6400 H. P. at IO meter head by a single machine. The electric ~ellerator is to generate alternating current at frequency of 50 cycles. To detetmine the speed and the type of turbine suitable for this development. It will be noticed that the head is 5uitdblp for an open flume turbine and this should be adopted. From the curve in Fig. I it will be served that the maximum specific !'peed for 10 meters head is 360. Assuming one runner, the actual spfed of the turbine may be determined from the specific speed formula as below :-

h.

'1f;:~'i;;'rhe nearest speed mitabJe for an alternating current at 50 cycies is 125 r.P.M. and this 125.,< y3200

will Le adop. ted. The specific speed corresponding to this speed will be ns =-'---,-----=401. . lU5~ This is higher than the maximum specific speed derived from the curve, r.ut as the head is very low, some deviation from the curVP is possible. This spEed "ill, therefore, be adoptHt Example 2. A turbint' is requireo to develop 3000 B.H.l'. at 80 meters hEao. Tbe generator is to gener:lte altnnating current at 50 cycles frequency. To determine the suitable type and speed of turbine. Froln the notes given under selpction of I'quipment it "ill l::e noticed that plate-steel spiral cased turbine will be suitable for this head. From the curve in Fig 1 the maximum specific speed corresponding to 80 meters head )S 150. Hence the speed of the turbine will be:-

n= n, x H6/4

yN'

150 X 8051~_ =654 r P II,f \,,3000

•.

The nearest synchronous speeds of the generator corresponning to 50 cycle fJequency are either 600 RP.M. or 750 r P.M. If we adopt 750 r.P.M. the generator no doubt will be less costly, as the higher the speed, the less bulky will be the machine. and hence the cost will be comparatively less. The specific speed corresronding to 750 r. P. M is:;",,: ;"-"'

n = 750 X y__]_Q_~ = 172, which is J5% higher than the maximum specific speed obtained s 80514

429 ~';!Ofi ~d 1~;<Jl !l.Z :~H ni flwoila ' ," <.rtt to'll i from the curvl'. This deviation is not desirable for a head of this magnitude, hence the next lower speed of 60l) LP.NI. will be arJopted. The specific speed corresponding to this spet:d is 138 and turbine runner of this specif,c "peed will be selected. 1,). ! II " :') 1'1. 'l 'J;; l ~ !, .

8. General Principles of Hydraulle t ubines.

.: ,~~j ~.:)~1:1j

..

r~'~,. ';:"'P ~ ;~,.~;:v:,

·. }i:~_~Hb·I' ecLt v~-! . ~f""';\ r': i J'\:i'J'l ~,;o It has been stated under para 5 that hydraulic turbines are of two principal types ta) Reaction turbines of the Francis type and (b) Impulse turbines of the Pelton wheel type. Below are given a general descripti .n and the principles of working of each type. "

t

:)~~ rc!n'~

[a] Franch turbines, The runner of Francis turbine consists of a number of vanes spaced round the circumference of a wheel which revolves on a shaft. The water is guided into the wheel by means of guide vanes, and n.e reaction of the water on the vanes of the runner proouces a torque causing motion of the turbine. The guide vanes also regulate the' flow of water into the runnp.r, being mOl1nted on a shaft about which they ca"! turn through the governor action. thereby reducing or increasing the water input according to load. In Fig 2 two circles ~' represent the inner and outer periphery of the runner , and one vane. is shown with tips Band C; LetCl ~_ _~.. represent the velocity of the jet before entering the runner. _ U1=periplwral speed of outer casing. U2 =peripherel speed of inner casing. Ul and U II are tangential at B C

I

,

L: VA,,! Til' P/tDPue~D

n where nand r are t h e radii of the . Vl =-respecbvely;-2 U2 r 2 outer and innl'r casings respectively. The triangle BOP is the entrance velocity triangle. in which BP is the velocity of jet at entrance and BO is the peripheral speed. aDd OP repftsents the relative

Fig. 2

......

.' ~

-....... '.

-' ~

~.

velocity between the jet and the casing. < The wattr should enter the runner smoothly without sho('k and for th:s end OP should be parallel to AH,i.e. the direction of the vane tip at entrance ..\ similar triangle can bp. constructed for the discharge end of the vane tip. such as CMK, in which CM represents the peripherHI velocity. Ck is the discharge velocity and Mk is the relative velocity between the jet and the vane at discharge. The m'lgnitude of Ck, it will be noticed,' will depend on thp. vane tip angle and this velocity should in practice be as small as po,sible. When the water enters the wheel, it sets up a pressure tangential to the periphery equal to ~-Q_ X CI cos. a in which "w"is the weight of water pp.r unn volum~ a~d HQ"is the g

.'

quantity of water entering the vane in unit time. Similarly. if the discharge velocity CK be, denoted by Cllthe pressure set up at discharge end is ~g X C~ cos f3 These two pressures set ;; t leverage of

f1

and

T2

respectivly. where r 1 and r 2 represt>nt the ou ter and inr.er
-g-

. I T ' t te h outer vane en d 15_r1 . runnpr rp,spectIve y. hus. the turnmg momen t a X wQ X C1 Cos a,' and that at the discharge end is r 2 x

~gg

X

C% Cos

f3.

The effective turning

moment on the

shaft is the differenre bp.tween the above two moments, and if we muhiply each moment by the linear velocity of the whelll at the respective 'points, the difference wilt give the work dOlle or the horse power of the mnner.

430 A typical efficiency curve of a Frand; Turbine is shown in Fig. 3. It will be noticed that the cune droops rapidly on both sides of the mlximum efficiency point and it is, therefore, necessary to run it at or near the load of maximum efficiency. . It, Pelton wheel. As previously stated, a Pelto~ wheel consists (lEa number of buckets fixed to the rim of a wheel and a water jet issuing from a nozzle under the pressure head of water impinge3 en these buckets, thereby setting the wheel in motion. The el1letgy is imparted to the whep.l solely by the kinetic energy of thp. jet of water. The speed of the Pelton wheel. has a definite relation to the theoretical velocity of water issuing from the jet and these relations are given below:'-~_"''''''''''''''!'''T'''T"'T''''''''''''''I'''T-r-:-rTlT1''''t.Q

Let H=the effective head of water in meters, then the theoretical velocity ~'D ~ t:±:q:t:tittjj"~,iGIf~,~t;~-~-~~~ of water, usually called the spouting "~;' ~ L!tlr.~(GU#RA~f;iot~ 80 .. velocity; will be V2gH ~ ... ~ 7D.)ba f-++-+-+-t.H~p~'-fl,I!:;CTtr-r-H-++-f-l-+.:l+H 10 ~ (i) The velocity of jet v=0.97V ~H ~ '" .tI ~ lie' meters per iDecond. iD ~ ~ 1"-1>' ~ Iii) Wheel velocity in meters per second ~ 50 200 ~ 1-+-+-:iFt--H-+-1H-rt....,.._'",.~~r'<.:~-4-iI-+-+4-150)... is usually taken between 0'43V 2.gH ..... S f~r.~~ ~~ l'f!,pvF++-+-{4D~ and o 47XV2gH. This gives the best ~.,fO 'a ",,, °.k1._1 ~,.t:~~i-+-+-+-l-I-l ~ efticiency. The lower figure should 're ~ ,~) I-Qu~"'('Xl.l "J,"I!"'_;:;"~4-H-+++HJII ~ used for high specific speed and the higher l:) 'AO"';/ /-::: ~ "LfI"I!E-~~+i++++-!+H-H ... <;). I,., '" 1D ~ figure for low specific spe@ds. ,~20.... " T h e term wheel velocity for a Pelton ~l '(J wheel means the velocity of a point on ~·o " "" 8 , 0 11 I t " an imaginary circle, to which the cenhe o I , S. H P IN iHOUSANIn }ina of the jet forms a t ang.en t. The diameter of a Pelton wbeel is the Fig. 3 diameter of this imaginary circle. lliii} The diameter of the Pelton wheel is det1trmined as follows :-

~+-1H-H+t+.J-+~~l.H-+-t-1I,+t-t-H'+i 9b

I

1

let wheel v~locity =v=0'45vZgh--meter per sec. readily be worked out.

Knowing the value of H this can

let n=r.P.M. of the wheel; then v=7\"D n/60 ; or 0= vx_60. . 7\"'n (vi) Jet diameter. To work out the jet dimeter the total quantity of wate r required by the Pelton wheel must firi>t be determined. The effiCiency of a Pelton wheel is usually about 90 Per cent and the friction losses in pipes, etc, must be taken another 5 to 10 percent Knowing the ov~raH efficiency, the quantity of water required for a given capac·ity can easily. bp. worked out. Let this be "Q" cub, meters per second' thus:d==d a of jet==

V

/

Q -=-meters.

VX\)'7854

where velocity v=velocity of jet in meters per sec. The ratio Old varies from 8'5 to about 15 . or higher effiCiencies. (v)

Number of buckets.

The number of buckets has a pronounced effect on the efficiency of a Pelton whee 1. The efficiency increases as the number of buckets increases upto a certain poin t anf, it then drops if the number of buckets 15 further increased. The graph shown in Fig. 4 is based on the data collected from a number of existing Pelton wheels giving good efficiency. The number of buckets is plotted against the ratio Djd of wheel to jet diamp.ter. This graph will give an a.pproximate idea of the !uitable number of buckets for the design of a Pelton wheel. (vi)

Size of ltuckets.

The width of buckets is usually frotn 3'7 to 4 times the jet diameter; height of buckets from 0'7 to 0'8 time the bucket width, and depth of bucket is 0'3 to 0'4 time bucket width.

4.31 .v, CIJRV£-IIE.PRE.S£N18 T1I£

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It is quite evident from the above relations that if the number of jets is increas~d, the bucket dimension will becOiTle smal!er, and as buckets form a very expensive part of the turbme, the cost of the turbfine will be less. On the otber hand, high~r stresses in tbe revolving parts due to higher 8peeu of the turbme produced thereby will involve higher construction cost and these two factors have to be balanced against each other to arrive at a suitable arrangement. The c_urve in Fig. 5 is a typical efficiency curve of a Pelton wheel. It wlll be noticed t}lat the Pelton wheel gives practicaUy the same efficiency at part loads as at full load, and in this respect it has a considerable advantage over a Francis Turbine,

9.

_I

"

Number ., units.

The greater the number of units in a Hydro-electric plant the more ealiiily can they be run at their maximum efficieRcy, and this has thus an advantage from the operation point of view. On ~-the other hand, the cost of foundations and installation increases o S .:II' as the number of units increases. Usually in an independent "'IO~~£~J installation, four to six units should be installed depending fln .IS" Fig. 4 the capacity of the installation. Six units is an ideal installation, four units being designed to take the maximum load, the fifth being kept as a stand bye for emergencies, and the sixth unit can always be opened for overhauls by turn. As each unit can take about 25 per cent overload, there are in fact two units available 10

'TYP1CA.1. E~F"'C'E.NCV CURVE OF'A

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as standbyes for emergencies and the factor of security of supply is, tnerefore, very great. Five units may be installed for slightly less security, and in installations of less importance, four units may be installed. Less than four units are Dot desirable unless the in!tallation is inter-connected with another so as to depend for inter-change of load in emergencies.

10.

Inter-linked canal Hydro-electrie Developments.

The main disadvantage 'Of Hydro-electric developments on canal falls iii the d'iscontinuity of supply as the canals have to be closed periodically :- (a) For repairs (b) When water is )1ot needed for cr'OPs, and (c) f'Or rotational running of inter-linked canals due to insufficif:nt supplies in the rivers t'O feed all canals simultaneously. It is necessary to have steam or Gil stand bye plants to run during canal closures to have continuous supply of electri .. ;city Such stand bye plant involves large additional capital cost, besides high running expenses.

Si{]gle vertical Hydro-Electric uuit in simple fll'lffie for low head;; up to 20' head PL ... N

[====-__

ope.u

SEcrrON

"i,~ ~;~};~T ~~: ~I

"l~~~~~~Z?2~~~~~L_

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Fi 6 Fortunately most of the adjoining canals in the l>un1al, ar~ illterlinked and if one is closed, an adja€ent one will be running. It is, therefore, possible to havtl interlink~d hydro~lectric developments on adjoining canals connected. with the same net-work of electric supply system, plan H(H..IJI-. ;.. '-I..... Section

,f

,

•• I ,, I

I

I

I 'f

•

f

r

I

Fig 7

1

433 and this will eliminate the necessity of providing and l:laintaining the standbyt' fuel plants. In the present canal systems in the Punjab there ar~ at soma places several small falls withm a f~w miles length of the canal. From the hydro-electric-development point of view, falls with bIgger drops are preferable, and it is an important point to be kept in view in the future design vf canal systems. Typical layouts of low-head plants with open Burne and spiral cased turbines are shown in Fig 6 and 7. . 11. The foregoing notes give a general idea of hydroelectric installations and their eqUIpment. The ilesign and selection of hydro-electric turbine and their equipment is a specialized subject on which the advice of hydraulic firms manufacturing such equipment must always be oDtained. Names of a ft''H important firms are given btlow:1. Boving & Co Hydraulic Engineers, Kingsway W.C.2. ":1\ E f!t}t)wbG 2. AILs Chalmers Manufacturing Co. Milwankee, Wis, U. S.A. 3. Escher Wyss and Co., Zur.ch (Switzerland). The electrical part of a hydroelectric installation falls withm the province of an Electrical Engineer and is not vealt with in this t.>ook. ; :;:)Jh\r; I1b'" I.r.l 12. Flour Mills run by turbines. ~ In the Punjab. the water power at the 'canal falls has been extensively used to run flour mills. They have been commonly run by the use of country made wooden gird wheel carrying a pair of stones described fully in the succeeding paragraphs. In a few cases the low head Francis turbines (suitable for falls. from 4 to 10 feet) have also been used. Two instances of this type are on the Lower Jhelum Canal at R.D. 25,500 and 64,000 of Northern Branch. Turbine shaft is coupled to a cam shaft rotating two to four pairs of stones. Generally speaking turbines flour mills are expensive in the initial outlay and expensive to maintain as compared with the gird wheel flour mills, ., 13. Gird wheel or tlour mills of t!te old Indian PattUB. ". The Flour Mills in the Punjab Canals bringiiB a considerable revenue to the Government. The income from Mills in the Upper Bari Doab Circle for the year 1944 and 45 is given below :~!,;:,

Name of the Mill.

H

lld

Number of stones.

.

., ./

'1,

1 Aliwal 1 & 2. 2 Aliwal No.3 3 Ahwa14 & 5 4 Parowal. 5 RaneVYaJi. 6 Kohali. 7 Kotla. 8 Pakhoki. 9 Jaura. 10 Athwal. II Raya. 12 Nagoki. 13 Alladinpur. 14 SUjanpur. 15 Sarna. 16 Tugial. 17 Nanunangal. 18 Dhariwal. 19 Bhuchar. 20 Bedian. 21 Lulliani. 22 Bhanba. 23 Bhanba.

·,·jl

(!

Daily Income Rupees. 64 /31/75[- .

9

5 12

11 6 8 i S

5 , I

'12

5 fi

5 6 6 5 12 6 6 8 6 3

. '1/.1 '.

' ):i.tlt/"": ~ i .

. iI_no:

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37f-

35/6616

Amount.

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•

;."

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·r t ...,_

'1:1

4,7/8 331

'51

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- '29311,,, .,

tI.O A

1:11

!. 0 ." et

x ;;;-

36/8 36/8

C
Sl/6 33/16/10

t'\I

0

1033/2 156 Total The above fi~UHS give the inc.ome for one cana.l syste.m. There are fifteen such systems in the Punjab. and vee" nearlv similar figures are obtained on other canals as we~l. The quan tity of the flour proluced T@r pair va.fies. from 20 .to .30 maunds per diem and approximately the num ter of pairs of stones workmg m the PUlllab IS about 2000.

434

, The niill wheel or "gird" varies very little in form or dimensions on the Bari Doab a.nd Sirhind Canals. being universally made about 2 feet in diameter, on the Western Jumna Canal 2 feet :1 inches is the size adopted, while on the Swat Canal wheels 3 feet 6 inches in dIameter are used. . The mill stones vary In di~meter from 2t to 3 feet and al'e about 6 inches thick, when new, and 2t inches thick when rejected as worn out. They are made of Agra sandstone, Ifxcept on the Swat Canal, where a very hard conglomerate stone obtained from near Michni Fort is employed. The "head" under which the mills work varies fr.om 22 feet to 6 feet, being generally between 3 feet and 5 feet, qut in few cases qpto 9.0 ft. 14. Desgin of Gird wheel. ' . . ~. ., .., I.

. The water is applied to the vanes of the "gird" through an inclined shoot of a rectangular section, the sides of which converge towards its lower end or mouth. The angle at which the shoots are inclined to the horizontal varies from 30 to 60, an inclination of.35 being a common practice as shown in Fig. 8. The dimensions of the mouth of the shoot very considerably, according to no apparent rule with reference to the height of f~ll or size of ~tones (a common size is SO to 90 square inches, that is 7 to 9 inches wide, and 9 to 12 Incbes 'deeP). ' . . On the Sirhinu Canal It bas been found that, with working falls of about 5 feet. the dlscharge rtecessary for a pair of 3 feet stones ( the size in common use) is given by the formula Q=

_4~_, '\'t>he!-e

Q=the discharge in cubic feet per second and h=the working fall in feet so

tha\. a 5 feet fall would require 9 cubic feet per second per pair of stones, and a 4 feet fall about 11 cubic feet per second, It has been pointed out by Higham, that Qh is not necessarily constant for all falls, and he, bas q~oted experiments on the Sirhind Canal showing that a t

discharge of

•

!~_

cubic' fe~~

•.

.

'

~uffices: to give

.

•

good results on a 4 feet fall in ,the case of some new

~i~is ~;-~~~~;~:·~"h~~~;·~:;';h~~~~~ at Kh:;~r the discharge c

was

~the working fall varyh

ing from 5 to 8 feet, but in the latter case more water was probably being admitted than the mills could utilize. It will suffice, however, for purposes of roughly investigating the subject, to assume that Qh has a constant value=45 for all heights of fall considered. It may also be assumed that the co-efficient of discharge at the mouth of the shoot is 0'81 and that the axis of the shoot is incli ned to the horizontal at an angle of 30°. Let AB represent the velocity and direction of motion 0 fa particle of water issuing from the shoot and striking the vane pq, and let the velocity and direction of motion of the vane at the time of impact be represented by the line CB then the velocity and direction of impact of the praticle relatively to the vane is represented by AC. The particle of water will do work in driving the vane, provided that the velocity of the vane is less.than;C}B ; where AC 1 is parallel to the vane pq. If the velocIty of the F' vane=CB 1 the particle of water will merely slide down the vane Ig. 8 , with a ve10city relatively to, it.:__AC] and do no work, and if the velocity of the vane exceeds C}B the particle of water will strike the back of the vane, and will tend to retard the wheel. Let AB=v and C1B=U. We may assume the plane of the face of the vane pq to be inclined at an angle of 60 0 with the horizontal, that being in accordance with parctice. Then C1B=ABsec. 300 :.U=V=1·l5v

.

,",

.-~

_.

"'.

, ,I:'" ., , .:',{

But v=O'Sl X l'1lv'2gh =7'48 v' h . ' . ", The table shows the values of U for verying heads from 3 feet to 10 feet:-'-

435 Head in feet U in ft. per sc.

3

4

12'9

15'0

5

6

7

8

9

IS'3

19'5

21'1

22'5

10

a.nd evidently no portion of the wheel should have a greater velocity than that as,signed to lJ in the above table. Th~ usual number of revolutions made by the native mills when working effi.ciently is 150 revolutions per m i n u t e . ' ~ The f0110wing table shows the circumferential velocity in feet per second of a point at 8. distance R inches from the axis of a wheel making 150 revolutions per minute:Velocity in ft. per sc

R ~-

..

5'2 6'S

4

5

: 6,

,

7 8 9 ]0 11

R

Velocity in ft, per sc,

---~----

.,

:,.,)

.,,,,,_,

12 13

14

78 91 10'5 118 13'1 14'3 15'7 17'1 18'4

15

197 21'0

16

2~'3

17 18 19 20

236 249 262 27'5

21

'22 23

!

bns

~"

l't·J

28'S

30'1

24

31'4" r

.f '1,( ~,:,,'

'1' <'

j 1 :~ ~\., :.'

It will be seen from these tables tbat with a 5 feet fall (a cornman working fall in the canals) the limitins distance from the axis at which a particle of water striki.ng ,a vane does any work in driving the wheel at 150 revolutions times per minute is about 12t inches so that any addition made to the size of the wheel beyond a diameter of 2' 1" will at only be of no use but any water striking near the ends of the vanes would in such a case actually retard the wheel. It is a noticeable fact that 2' 0" to 21 1" is exactly the size which the native millers have universally adopted on the Bari Doab and Sirhinrl Canals. , Similarly it follows that the following diameters should not be exceeded for the falls named below:Dia: of wheel in inches

Height of fall in feet

ii,

19

5

2~ 25

6

28

''4

height of fall

~ 9

10

,.

Dia: of wheel in inches

30

-'J;}t'

32 -;..

34 36

The work is done in these principally by the impact of water, and it is therefore probable that they work most efficiently when the vanes are moving at about half the velocity with which the water over takes them, 'This being true of other water motors which are propelled by impact. ,. The component of the velocity of ineffluent water resolved in the direction of motion of r,;

I

1-

the vane is v cos

300='\1';

/~

v and the best velocity for the vane would be, therefore, be vV-T

and the shO'lt showed be so placed that its center is situated as nearly as possible in the position where this would occur. The following table shows the distance in inches from the axis of a wheel making 150 revolutions per minute at which the velocity is vi and, therefore, the distance from the axis at w}:ijch the centre o~ the. sh~otshould. if pO!tSible, be placed,

Fl

436. Head in feet.

Vy!

in feet per second,

3 4 S 6 7 8 9

Distance from axis in isches.

6'0 7'0 7'8 8'5 9'2 98 10'4 11'0

10

Dimensions of the shoot:The shoot is to give a discharge Q=

:5

cubic feet per second. The values of Q and v

and the necessary areas of cross section of the shoot in square inches are given below : Working fall in feet

4

3.

5

6

9

5'6

5'0 19'5

4'5 20'S

37

31

Q=Dis : required in cubic ft. per second.... 15·0 v=0·8 I y2gh ............ ll·2 Area of shoot in square

11'2 13'0

9'0

7'5

14'6

IS'9

6'4 17'2

18'4

. hes -Q- X 144 ...... 191 Inc

124

88

68

53

44

v

10

8

7

The results obtained are summarized in a tabular form below:Working head in feet

3

Dia : of wheel in inches which should not be exceeded 19, Distance in inches from the axis at which the water does most work. 4'~ Area of ori gce of shoot necessary in square inches. 1911 Data assumed :-

4

5

6

7

8

9

10

22

25

28

30

32

34

36

5'3

6'0

6'S

7'0

7'5

8'0

8'5

124

88

68

53

44

37

31

Number of revolutions made by the wheel= 150 p~r minute. In~lination of shoot to horizontal 30°. Indination of vanes to the horizontal 60°. Velocity of vanes when the water impinging on them·a maximum amount of work in driving the wheel=half the horizontal· cemponent of the velocity of effluent water. Co-~fficient of disc:harge of the ilhoot=0·81. Now if we attempt to design a suitable arran~e nent for pairs of stones for various falls from 3 to 10 feet in accordance with the ab)ve results. we shall notice the following. First with 3 feet of fall. the wheel should be only 19 inches in diameter, and the best place for the water to impiJilge is 4f' from the axis, but the boss in 8 inches diameter, and the shoot ough.t to measure 191 square inches alld we find it quite imp:>5sible to bring anythi.ng like enough w:tter on to the shoot vanes which ara oaly 5! iaches in length, anrl scarcely :tny of what reaches them and strikes them near enough to the axis to work in the m')st ecnomical manner. Witll a 4 feet fall we meet with the same difficnlties, aTld the best point to appJy the water is 51 inches from the axis or 11 inches from tne rl) It of the vanes, which are 7 inche; long, and as the orfice need only measure 124: sqllare inches, we can apply a large prop)rtion of the discharge from a shoot say 7 inches wide and 14 inches high.

431

plan Fig. 9

Section

SECTION

/ of

c. L.-

Shoot

orWater Wheel .

PLAN' Fig. 10

438

With 5 feet or more of fall we have no diff!culty but when we have to deal with a

high fall of say 10 feet, we find that the shoot need only measure about Si inches square and

that the best point of application is 8t inches from the axis. There is no objection to the wheel being as much as 3 feet in diameter, but with such a small shoot having its centre only Ri inches from the axis nothing is gained by making the dia: of the wheel greater than (say) 2i feet diameter, as we can apply all the water necessary to a wheel of that size in the most advantageous way. The tails of shoots are shown in Figs 9 and 10. 15 Efficiency

or

Girdwheels

.

Light stones do not give such good results as full sized ones, as well as the quality of the out. turn -falls off when the stones are driven too slow. With the ordinary pattern of mill now in use both these causes evidently operate in reducing the efficiency of mills working on falls of less than (say) , feet, and it would appear that at sites where the fall is as low as this, and the supply of water abundant, better re,;ults would be obtained by designing a shoot which should deliver the water on to a larger two segment of the Wheel, or substituting two shoot for one. Also the sUbstitution of a )Vheel with a thinner spindle, 'perhaps a metal wheel, would apparently allow of more watf'f being arplii>'d at a part of the wheel where it would work economically. On the other band, at sites where the fall is considerable and the supply limited, it would be worth whi~e to make experiments with a view to find out whether the :;hoots in use are not extravagently large for the stones. It may also be noticed that where there is a high fall it would be quite feasible to use much heavier stones. In England stones 4 feet in diameter are commonly used and these are run at 140 revolutions per minute, and grind 5 bnshels [about 3 maunds] of wheat per hour. It does not seem customary in the Punjab to attempt to run such large stones. but one reason may be that the mill houses are so bnilt they could not be set up. In the Peshawar DIstrict, however, large stones are preferred, and are said to produce better floor than smaller ones. References. l' "Hydro-Electric Handbook" by William P. Creager and Joel D. Justin. 2. "Water Power Engineerng" by Danien W. Mead. Rushmore" and Lof• 3. "Hydro-Electric power Developments" by • , "Funnamental Princinples of water Power Engineering" by F. F. Ferque.:"son. 5. teN ote o~ Gird Wb.eel Flour Mills" by A. Reid, Under Secretary, Irrigation. Punjab, (1895)

ERllATA" 67 Line 21 45 74 80 3 From Bottom 87 8 II

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