River Metamorphosis, Neyyar

RIVER METAMORPHOSIS DUE TO HUMAN INTERVENTION IN THE NEYYAR BASIN, KERALA

BY K.P. THRIVIKRAMAJI

TECHNICAL REPORT OF PROGRESS OF WORK SUBMITTED TO THE GOVERNMENT OF INDIA, DEPT. OF ENVIRONMENT, GRANT NO. 9(6) 83. ENV. 2/DTD. 15-3-83. REPRODUCTION IN WHOLE OR IN PART IS PERMITTED ONLY WITH THE SANCTION OF DEPARTMENT OF ENVIRONMENT, GOVERNMENT OF INDIA

DEPARTMENT OF GEOLOGY / UNIVERSITY OF KERALA / TRIVANDRUM 695 81 / INDIA

PREFACE

This annual report is divided into three parts, each part dealing with some or other facet of River Metamorphosis due to Human Intervention. Part I dwells at moderate length to present a perspective of the main theme. Part Ii describes the various components of the research programme designed for implementation in the Neyyar basin. A format field and laboratory procedures and methodologies for base-line data-capture, processing and analysis have also been discussed in the second part. The last part presents the investigators report for the first year of the study. Indeed the first year did not provide sufficient research time to be solely devoted for work, as several items of preparation for implementation of the research programme naturally formed part of the first year s activity. Lastly, I myself would concur that with a very modest number of diagrams and other data formats this report will make a monotonous reading even for the novice.

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ACKNOWLEDGEMENT Whatever contained in

this

anthology

of

the

Project

on River

Metamorphosis due to Human Intervention would not have been possible to achieve, had not the expert group assisting the DOEn, in selecting, and scrutinizing

proposals

for

research,

realized

and

recognized

the

significance of the problem and the need for research into it. Published works by Profs. Ian Douglas, Stan Schumm, Kenn Gregory and Chris Park had always spurred my thinking and approach in the intriguing field of fluvial geomorphology. However, I am solely responsible for the lapses, if any. Virtually the achievements reflected in this report are partly the result of a group of young dedicated staff assisting me in the field and in the laboratory. The University of kerala generously helped me in the implementation of the project, by adopting a maverick approach in respect of sponsored projects implemented in the departments of the University.

THRIVIKRAMAJI. K.P.

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CONTENTS

i.

Preface

ii.

Acknowledgements

Part

I.

River Metamorphosis due to Human Intervention

Part

II.

Goals set and procedures adopted in the study

Part

III.

Achievements in the year ending March, 1984

A Perspective

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Part I

RIVER METAMORPHOSIS DUE TO HUMAN INTERVENTION Introduction The fluvial systems are one the most dynamic environments of the earth s surface, where interaction of meteorological, pedologic and fluvial processes jointly act at varying scales to modify the physical aspects of the system. However, only in the time frame of the geological processes the changes undergone by the fluvial channels become perceptible. This end is achieved by study of landforms, from topographic maps, aerial photographs and similar bases. Such river channel changes have been traditionally designed as river metamorphosis, and the erosional processes that have been active in the basin and which modified the system are called geological erosion. According to Shumm such changes are caused by large scale alteration in sediment and water discharge, related to climatic accidents which lead to the changes of regimen of the system. River metamorphosis to some extent can also be the result of various types of human intervention, and then one could as well designate such changes as The River Metamorphosis due to Human Intervention . In that case, one has to consider the various types of Human activities in the river basin which may have varying degrees of influence in the modification of the system. Table 1. Types of Human actions modifying the fluvial system Sl.No. i. ii. iii. iv. v. vi. vii. viii.

Type of action Interbasin diversion of water Construction of dams Shift in landuse practices River Training works Borrowing of channel sand Channel dredging Borrowing of flood plan mud Drainage network changes

The consequences of such actions by the Human have not attracted the attention of the geoscientist at any length in our country. We are beginning to turn our attention to the problem only recently. However, the situation is entirely different in other parts of the world with the new awareness created by the environmentalists and ecologists. There has been good deal of work done in this aspect of earthsciences in countries like Malayasia, Australia, United Kingdom and also in the United States. Thus information is now emerging from different continents of the world on the modification of the behaviour of the fluvial system due to one or all of the above actions. Now we will take a detailed look at the various actions and responses.

i. Interbasin diversion of water From the point of view of an engineer, most of the time the rivers of the world are carrying excess water either seasonally or annually. His immediate concern was then to harness the excess water for purposes of irrigation, power generation, some times even interbasinal diversion of water to augment the supplies. It was realised only very late that the prime forces acting in the maintenance of the river channel network, are the sediment and water that are discharged through the network. The engineer s amendments of the river system had always been and still are related to the control, diversion or subtraction of water that was available in the network.

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As pointed out the most important work-horse, as far as a drainage system is concerned, is the sediment and water that is put through the channel network. The depth width, velocity and other channel characteristics like the nature of sediment in the banks and the bed, the types of grass, brush, or other growth along the channel walls or bed and whether the channel is bedrock floored and walled, are very intimately related to the channel pattern, the shape of the channel crosssection and the long profile. The diversion of water (the socalled excess water) to an adjacent basin can cause many irrevocable changes in the donor basin as well as in the acceptor basin. As far as the donor basin is concerned the sediment and water discharged through it are considerably reduced and hence the channel network down stream of the point of diversion will be forced into sediment and water starvation, resulting in derangement and degradation. The master stream will become a misfit stream very soon. Generally the response of the master stream due to diversion of discharge is like the following. The channel bank failure is normally common along the river bends and even in sections with straight channels, the slumped blocks are normally removed by erosion and transportation during the subsequent floods or bankful discharge events. However, due to diversion, the stream will no longer be in a position to remove the sediment in the slumped blocks as it does not require the preslump channel capacity any more, nor has it at its disposal the required discharge. These slumped blocks therefore should become more or less fixed to the ground and added protection to it will be afforded by the riparian vegetation, brush or grass that will establish on it. After a while these blocks will appear as shoulders and benches in the channel cross profile. The sediment in the channel bed will authenticate the reduced discharge by several means. This sediment in the channel bed moves down stream mainly in the form of down-stream-migrating bedforms. One very commonly noticed change is the stabilization of ubiquitous sand bars in the channel bed by natural turf that establishes on it. This is taken as an important indication of reduced sediment movement as bedload in the stream bed. The turf that grows on the bars, not only stabilizes the bars covered with bedforms, but would also tend to increase the bed friction. Coarseing of bed sediment is also taken as an indicator of increase in the stream power. Diversion of water to elsewhere, naturally should tend to reduce the stream power, leading to fining of the bed sediment. However, this point is yet to be established by actual field data. Such modified reaches of stream bed have been noticed by this author in several channels in Kerala. But the point, that the changes undergone by the stream either along its banks or in its channel due to reduction in peak discharge or duration of peak discharge, does not extend or manifest all along the downstream side of the channel. The peak discharge and its duration if reduced affects the entire length of the channel, the way it would affect, may be by way of lowering the frequency of floods. Through the events like floods are capable of transforming the channel dramatically, the changed channel is maintained and established by the bankful discharge events that occur with more frequency. Therefore, we must conclude that the changes undergone by the stream whether it be along the channel bed or along the channel wall, the propagation of these changed downstream need not essentially manifest in the entire length of the stream channel.

ii. Construction of Dams Another category of diversion of flow in the channel network, is by construction of dams to create artificial reservoirs to store water for irrigation purposes within the basin or for generating electricity, in which case also the tailrace water will be used for irrigation or just let out along the main channel. Such diversion will result in the reduction of peak discharge and duration of peak discharge or both. For this reason one should expect channel bed and bank modifications considered in the previous section to manifest.

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A point related to reduction in discharge is the change in the water quality experienced through out the length of the stream. Lower water discharge will be inefficient in transporting the particulate waste and liquid refuse entering the network from time to time and from place to place. This modification of water quality sometimes attains very detrimental levels. When one examines the lower reaches of the stream, then again, due to the reduced flow, (less than normal baseflow in summer) the saltwater wedge advances very much upstream, creating problems of water portability. The concentration of particulate matter as well as salts in the water will have to be properly reckoned. People enjoying protect water supply are least concerned with the enormity of this aspect of the problem. The negative amendment of the water quality due to the above may be of considerable consequence. The substrate sediment in the channel bed is capable of absorbing in it some amount of dissolved salts, and particulate matters will tend to act as a buffer, especially during baseflow seasons; ie., in summer. The flood flow on the other hand causes some degree of scour of the channel bed, and thus be able to subtract a certain quantity of the substrate material, along with salts and particulates that were detained in summer during the baseflow stage. However, the role and efficacy of this buffer system is yet to be understood scientifically.

iii. Shift in Landuse practices Landuse has been changing continuously in every continet, and is progressing steadily from the forest landuse to others, like agricultural, industrial, residential and recreational landuses. The landuse has been indetified as one of the prime candidates that determines the quantity of sediment lost from the uplands and slopes in the the channels. There has been several tens of well documented studies that had demonstrated the choking of river channels by sediment, which then turned into braided channels by sediment, which then turned into braided channels, the result of excessive soil loss in the uplands. It has also been documented in some studies, that the present century is an example of reduction in the sediment output derived from farmlands and from the watersheds in the mountain ranges, where until now excessive erosion due to deforestation was the rule. This was the result of the new awareness among the people and governments leading to conservation practices, which resulted in reducing the sediment loss, by way of soil erosion. However what has been said is true only of the developed countries. But the story in developing countries is far from satisfactory. In the past say, before the onset of Industrial revolution, they type of landuse was mainly agricultural, and the population was also rural, nomadic or shifting. They felled trees, burnt forests and raised their living. However, the degree of destruction that was inflicted on the forests were nowhere comparable to what was done during the industrial revolution. It was due to the lower size of population that the earth has to support then. But during the industrial revolution, growth of industry went hand in hand with the growth of urban centers and increasing population. This naturally led to the destruction of forest for consumptive, constructive and settlement purposes and to further agricultural output. Large chunks of new areas were cleared of forests, to locate and to exploit new raw materials for input into the industry. All such growth-related activities led to shedding of new soil and sediment from the uplands into stream channels. The rivers were no longer allowed to flow on their own. Huge water storage reservoirs were built for irrigation and power generation, which affected the streams and modified many of them. Thus, this became the forerunner of accelerated erosion, which was identified as one of the banes of industrial revolution and population explosion. It has been demonstrated that denudation of soil by expanding population had achieved a higher order of magnitude in the thickly populated third world. Another consequence of population and industrial growth were the requirements of timber for various needs of population. The forest lands thus started shrinking in area in an ever-increasing and unprecedented rate resulting in

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the loss of precious forest cover. It has reached a point, where the optimal requirement of 1/3 of forest covered land, out of the total area of the nation could hardly be guaranteed in third world countries. One of the major consequences of this rate of forest denudation is the modification of sediment and water input into the river networks which led to the changes in the regimen of the river systems.

iv. River Training Works General types of flood protection, bank protection and sediment reduction procedures adopted in the river channels will have its own deleterious consequences. Such protective structures often tend to reduce the contribution of sediment to the channel from such reaches and had in several occasions led to the scouring of the channel leading to undermining of the structures resulting in their collapse.

v. Borrowing of channel sand The adverse effects or otherwise of excessive borrowing of channel sediment for construction and similar uses from the river channels are yet to be documented scientifically. However, according to me, one prime consequence of this practice can lead to is overdeepening of the channel in the sand borrowed sections. The deepening not only makes the stream unsuitable for crossing by wading even during the baseflow seasons, but also might lead to adverse alteration and loss of riparian aquatic fauna. The borrowing process leads to the reduction in mean size of the sediments and shifts it to the fine sand or silt size; As a result the life that depended on the sand substrate for sustenance would perish. The exact damage and the degree of damage is outside the purview of this study. The damage caused to the physical system of the river by the streaming process is rather in alarming proportions; at least as far as the riparian land owners were concerned. The over deepening of the channel in non-rocky sections tends to undermine the channelwall-slopes and has led to the slump of the channelwalls all along the streamed sections. The over deepening has led to the increase in height of free face which is no longer in equilibrium with the excess height. The deepening must also logically lead to the erosion of sections of channel bed that were not streamed for sand.

vi. Channel Dredging Thus the streaming process should lead to the speedy failure of the channel walls and narrowing of the channel that was active before the streaming process started. A common practice related to navigational modification of the channels is dredging of the channel to maintain a specific draft. However, such dredged sections are continuously maintained by repeated dredging and the cross sectional parameters of the dredged section are designed ones. Therefore one could conclude that the dredging and its consequences are more of a problem from the ecological point of view than from the physical system point.

vii. Borrowing of Flood Plan Mud Another important form of misuse or excessive use of the river basin is the borrowing of flood plain mud for brick and tile making. As the flood plain mud contains most of the time an ideal proportion of clay and silt, this mud is extensively exploited by tile, pottery and brick making industry routinely as a source of raw material. This borrowing activity has made many large scars of considerable extent in the flood plain on either side of the channel. The mid is excavated in such a way, that only a considerably thin partition alone is left between the channel and the mud borrow pits, in the form of a dike. Instances of breaches of this dike are not uncommon, which had let in flood waters into these pits. Farmer s claim that the new surface and the soil contained in it after removal of the top layer of flood plain sediment, has very improved fertility. How such ditching of the flood plain affects the hydrology or the hydraulics of the stream has to be examined in detail. This may be a serious type of intervention in the river basin; out what is not certain is the type or degree of the modification of the physical system. Nonetheless, it is an

8

eyesore and mars the aesthetic appeal of the scene. Moreover, at times of flood, these ditches would serve as stilling basins for retaining flood waters, leading to the reduction of flood crest. Thus one could conclude that the various actions in the river basin, including those in the channel network, would lead to some or other type of modifications of the physical system of the river. Some of the changes are irreversible, others with some careful planning could be made milder in their intensity, and still others can be avoided if careful thought were given before implementation. Truly, and attempt is made to formally identify the various categories of human activity to which the stream network would attest with various types of responses. The moral of this discussion is that the stream network and the basin are dynamic systems which on some or other type of provocation would respond may be with a lag of time and the response may not always be in the interest of the human.

vii. Drainage network changes By drainage network changes, what is mean here is the modification of the first order (finger tip) streams in the basin. While embarking on a study of River Metamorphosis, the investigator should pay appropriate attention to the changes and modifications of aerial and linear parameters of the basins of the lower order streams too. Many approaches are available to the investigator, to examine the aerial and linear changes. The main base materials in addition to field checks for data capture are the aerial photographs, and topographic maps. Normally several sets of serially flown air photos will be available for most of the regions and same is the case with the totpomaps. These maps are the best source available to the analyst for recognising, identifying and modeling of the network changes, including that of the master stream through time. Further results of field surveys, mapping of land forms of depositional origin and identification of erosional and depositional features in the area are also taken into account while proposing a model for the evolution of the landforms. When it is the case of finger tip streams, generally the changes and modifications expected in them are extension by gullying. Generally the mapping scale usually adopted, tends not to depict such extension of gulleys due to the small dimensions involved. Another way of estimating the network enlargement or reduction is to estimate stream frequency from maps of specific dates to compare the results. Yet another approach is to study samples of selected first order streams and compare their lengths along with field checks wherever possible. Fluvial geomorphologists have noted that the enlargement of stream network to consume the upland area is in the normal progression of fluvial cycle. However, in certain cases, due to very intense shift from forest landuse to agricultural landuse, highly sophisticated land management programmes will be designed and implemented, like for example, contour bunding, rehabilitation of gulleys into lined channels, plugging of channels, construction of tow walls, terracing etc. These practices may load to conservation of soil and regulation of flow through restricted channels. Such practices will easily lead to the inability to trace the true extent of finger tip streams out of airphotos due to the extensive foliage cover of plantations. Landmanagement measure usually tend to reduce the extent of finger tip streams, on the one hand and to curtain erosional loss of soil on the other, in spite of the Human intervention. Therefore, while looking for a retrogression of channel length of the finger tip streams in areas of plantation type landuse, the consequent reduction in soil loss needs to be appreciated. For the same reason, while comparing maps of areas that had evolved in the above fashion, it is not unreasonable, to expect a reduction in the length of the first order streams, despite the fact that such reduction of channel length is against the accepted norm of channel network evolution. This facet of human action should therefore be considered as an exception rather than the rule.

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Landuse related changes Due to large scale conversion of forest land into agricultural, industrial, habitational and recreational categories, it is common place to expect, accelerated erosion and soil (sediment) loss. This premise may not hold good for the entire land area in question for the following reasons. Where holding are large and are under plantation crops, the land management practices are executed reasonably well. This is expected to lead to reduction of the usual quantum of soil loss in plantations, though there are no turn or brush cover on the ground. The barren ground in the plantations must normally lead one to the misconclusion that there is bound to be large scale erosion of soil. Such a contention, however, needs to be buttressed by supporting field data. Shed same is true in the case of other types of plantations like coconut etc. But the story is entirely different when one considers, annual dry crops like tapioca whish is raised in all kinds of terrains and slopes. Being an annual crop, and one needing at least two or three raking of the bed before harvest, and further with the generous input of water by two seasonal rains, like in Kerala, the tapioca cultivation raises serious doubts about even the continuation of this crop without any proper land management practice. Generally speaking, annual crops like tapioca needing special types of crop and soil management, should tend to result in a more than average soil/sediment loss from such fields, which obviously will be transported downslope into higher order streams and finally into the master streams. However, one should not overlook the fact that there are many temporary and local sinks for the new sediment shed from such land areas.

PART II Introduction In this part of the report a brief outline of the objectives of the project on river Metamorphosis due to Human Intervention will be presented along with the discussion of the field and laboratory methodologies to capture appropriate baseline data and the methods of analysis that will ultimately lead to the understanding of the extent to which the Neyyar River basin and its channel network were modified. In Kerala, due to the intense pressure on land resources, time and again, people have been encouraged to clear forests, so as to add now areas for raising more food crops as well as to accommodate various other developmental programmes of the Government. Such unprecedented conversion of forest land into non-forest type landuse, should have tended to initiate accelerated erosion of the river basins or even accelerated the pace of accelerated erosion. While preparing a programme of research for consideration of funding by the DOEn, Govt. of India, this author was overwhelmed by the above awareness, and hence, the research proposal centering around the investigation of the accelerated erosion leading to River Metamorphosis due to human intervention. For this purpose, the Neyyar basin of the Trivandrum District of Kerala was chosen for the study.

The Neyyar Basin The Neyyar basin is not one of the larger river basins in Kerala, and it has only an area of about 492km2. The cumulative length of all the streams in he basin stands at 605 Km., and the state irrigation Department has estimated the surface water potential of the basin at 229 Mm3. At Kallikkad, there is a major masonary dam (and a reservoir) constructed for the irrigation purposes in the basin. The Reservoir was completed in the secondfive year plan. However the distribution network is still being expanded. Physiographically, the major divisions of the basin are the highland (600 m), the mid-land (600-200 m), the lowland (200-5 m) and the coastal land (5m). Large part of the river basin is composed of crystalline rocks like Charcockite, Gneisses of different categories and their altered products, like the ubiquitous laterite and the soils derived there from.

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Like most parts of the state of Kerala, the population density of the region is very high and the people are agricultural labourers, small business men and some large planters, Industrially, this area can be classed as backward area due to lack of any large industrial undertakings. One could conclude that, most of the people depend on the land and agricultural resources for their livelihood. Holdings of land with the majority of families are relatively small.

Objectives of the present study Many study components have been identified for pursuing in the field and the laboratory to answer the basic question of the modification of any or some or all aspects of the physical system of the Neyyar river, due to what is called Human Intervention in the basin. The study components are: (i)

Estimation of the present area under forest cover and estimation of the area redovered for non-forest land use out of the forest area.

(ii)

Documentation of landuse practices and landuse classification of the study tract.

(iii)

Through field observations and surveys in specific areas, estimation of the soil erosion rates, in various geomorphic domains, ie., with the various types of soils profiles (catenae), and slopes.

(iv)

Estimation of the rate and extent of aggradation and degradation in selected valleys and stream channels.

(v)

Identification of a model for evolution of slopes of different categories in the sub-basins subjected to accelerated erosion.

(vi)

Formulation of a model of river metamorphosis in sub-basins subjected to accelerated erosion.

(vii)

Documentation of features of aggradation or degradation of channels in the upstream and downstream section of the reservoir.

(viii) Estimation of sediment discharge rates through several channel reaches in the basin. (ix)

Study of load through-put by the Neyyar River into the adjoining sea.

The expectations set in the objectives are reasonably very tall and efforts will be made as detailed below to realize the objectives. The methodology for examining the study components are listed below: (i)

Study of airphotos, topomaps, landsat imageries, forest maps (f available) and other derivative maps in order to achieve a reasonably reliable estimate of the original extent of forest area and the present extent of forest cover in the basin.

(ii)

A survey has been carried out by the Soil survey department, in the basin and the maps published by that agency will be used as a base for selection of study areas for landuse practices. It is envisaged to carryout the study in 6 to 9 sub-basins in such a way to cover, areas upstream and downstream of the reservoir, the landuse categories will be identified in the subbasins.

(iii)

The next step is the identification of catanae, and slopes for monitoring the soil loss-rate, and quantity. A range guage, sediment traps and stakes will be established in each of the selected slopes of the sub-basins to monitor the degradation or otherwise of soil material at different reaches in the slope. This monitoring will continue for one year, as to cover the NE and SW monsoons. The analysis of data collected will help to decipher the short-term slope morphodynamics. This investigation will also help us to understand the decay of soil profiles in various slope morphotypes.

(iv)

Filed mapping, pitting, augering and related activities will be carried out, in the flood plain of selected valleys in the subbasins, in order to identify and

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estimate the aggradation and degradation due to accelerated of erosion of the upland. (vi)

Total dissolved load and suspended load discharged by the stream for various types of flow conditions will be estimated by systematic sampling temporally and spatially and further analyzing the samples in the laboratory subsequently.

(vii)

Channel and slope modification (bank modification) due to controlled discharge and reduced peak flow in the river will be examined by analysis of suitable data collected from the stream net work.

To summarise, it is hoped that by proceeding along the lines of investigation and methodologies listed above, we will be in a position to characterize the present status of the River system, including the river basin.

Geomorphology of the Neyyar Basin The Neyyar system is the southern most of the drainage basins in the state of Kerala and about three fourths of the basin falls in the district of Trivandrum, while the rest of it is in the adjoining Kanyakumari District of Tamil Nadu. The basin lies between 77000 and 77020 E of Greenwich and also between the North Lats of 8040 . The river takes a southwesterly course from the Agasthyamala. This 6th order stream (?) has an overall dendritic network. But tributaries like Chitar show a rectangular network, due to structural control of the underlying rocks. In total, the basin covers an area of 469Km2. The Neyyar rises from Agastyamala in the Western ghats at an altitude of 5500 ft., and after flowing down through a distance of 44.5 Mi., (73 km) it enters the Laccadive sea at Poovar, where during the summer months, the connection between the stream and the sea is cut off by a river mouth bar. A straight gravity Masonary dam was commissioned in 1959 at Kallikkad in the Neyyar master stream mainly for the purpose of irrigation.

Morphometric analysis After thorough study of the morphometry of the basin, using the topographic sheets of SOI published in 1914 and 1969 (scale 1 : 63360 and 1 : 50000 respectively), it was felt convenient to divide the basin into two parts, one falling on the upstream side of the dam site at Kallikkad, and the other on the down stream of it. The dam Kallikkad has affected various attributes of the drainage network more on the downstream side of it than on the upstream side. So a study of the morphometric parameters out of the two sets of SOI maps antedating and postdating the construction of the dam became inescapable. Parameters like total stream length and stream frequency have been examined in detail, which demonstrate wide variations between 1914 and 1969. The changes showed by these parameters may perhaps be due to the construction of the dam in the river at Kallikkad and may be more so, due to the unique changes that occurred in the landuse pattern of the basin, viz., shift from a forest landuse to non-forest landuse.

Shrinkage of stream length In the sector downstream of the dam site (Kallikkad), in the basin, eleven major tributaries exist on the left bank and eight on the right bank. When the two sets of map data were compared these tributaries clearly demonstrated that presently there has been considerable reduction in the stream length and stream frequency. For example, as per the SOI 1914 toposheet, in the sector downstream of Kallikkad, the streams had a cumulative length of 735.7 km(457 Mi.). But as of 1969, for the same area the stream length has reduced to 505.7 KM. Perhaps such a drastic decrease in stream length owes itself mainly to human actions in the basin and field studies are in progress to collect ground truth to support or oppose the above conjecture. Our preliminary search reveals that many first order streams have been plugged for one reason or other.

Long profile

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The thalweg profile of the Neyyar system from the source area to its mouth presents the ubiquitous concave upward shape. A steep to vertical profile is noticed in the highland area in the headwater reaches; say over 750 ft. above MSL, and a gradually sloping profile excurs between 750 ft. and 100 ft. The river further traverses a distance of about 12 miles to descend from 50 ft. elevation to reach the MSL at Poovar. A knick point noticed in the filed at Aruvipuram as a cascade, coincides with 50 contour and is controlled by lighology. 0

0

Latitudinal profiles in the basin have been generated at N.8 20 ; N8 25 ; N8 30 and 8035 transects. These profiles bring out the well marked coastal land, lowland, midland and highland sectors recognized in many other river basins, in other parts of the state. 0

The Catchment area The geomorphic aspects of the catchment of the Neyyar reservoir, were also examined carefully and critically with the help of the SOI toposheets published in 1914 and 1969. The straight gravity masonry dam at Kallikkad has a water spread of 6.92 km2. The map data on stream order indicates that the Neyyar basin th th was a 7 order basin as per the 1914 topo sheet, whereas it reverted to a 6 order basin in the 1969 map. This retrogression of the stream order, is perhaps a compound effect of the construction of the dam and filling in of the lake and the dynamic shifts that occurred in the landuse pattern of the area. The region that was under a tropical forest, had been changed perforce to one with lot of plantations and other agricultural crops, which are the direct consequences of the unprecedented human encroachment in the basin. More and more first order stream channels have been plugged when forest land was converted to agricultural and plantation fields. The reservoir had drowned several lower order streams and several new but minor marshes have developed in the tributary valleys bordering the lake. The influence of the marshes on the physical system of Neyyar is not of direct concern to the present investigation. As per the 1914 SOI toposheets, the total number of streams (all orders included) was 2259 with a cumulatitive length of 675.9 Km. But the 1969 toposheets of SOI, showed a dramatic reduction in both the stream number and stream length viz., 678 and 421 Km. respectively. Field verification of this aspect is in progress. The comparative study of stream lengths and the numbers reveals that this drainage system had a total stream length of 1250.3 KM in 1914 with 4469 individual streams. After a long span of time in 1969, the total stream length reduced to 650.8 Km with 1019 streams in the basin.

Comparative study of topographic sheets for network changes Although the ideal procedure for understanding of the network changes, including those of the finger tip streams, is to verify such aspects in the field. Nevertheless analyst can always get a feel of it by a comparative study of topographic sheets published serially. Equally useful are the airphotos of the area again taken on a serial basis. This investigator has so far not been successful in accessing the airphotos of the study area, though efforts are being persistently made. In order to check this aspect of channel change and modification of network, an intense verification of the topographic sheets published in 1914 and 1965 were under taken. Our efforts have indicated changes of course of the master stream and that of the fingertip streams of the basin. There had been changes in the coastal land area in a very conspicuous manner mainly brought in by the littoral sand movement and deposition by the monsoonal wave activity. However, in the present context we address ourself to the changes due to modification of the discharge through the master stream as well as those changes of the finger tip streams due to the result of human activity in the basin, like the construction of the dam or forcing of changes in landuse practices. One aspect we noticed was the shift of tributary junction toward downstream reaches (ie., in the lowland area) where the flood plain has

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considerable width. Topographic expression of the shift of the tributary downstream can be recognised in the filed. With the exception of this change in a left bank tributary in the lowland area no other appreciable change has been identified. Nonetheless, I am not in a position yet to attribute this shifting of junction to accelerated erosion, but data collection and field observations are in progress to establish the reasons for such shifts. The story is slightly different when we take up the subbasins in the Neyyar system. The observational data from topographic sheet indicate large scale reduction of the number of first order streams in the subbasins of the midland and lowland regions. Field checks for confirming the observation is currently in progress. The apparent reduction in the first order finger tip-streams in the basin can be rejected simply as an artifact, resulting from the inaccuracy of data collection for the preparation of maps, or due to the larger scale of mapping in 1965, or due to the use of airphotos for generating the data with limited field checks. However, our own field checks are bound to throw light on this aspect. The apparent reduction in the number of first order streams of the subbasins may be due to the following. Generally the upper end of the fingertip streams is bound to end up in gulleys. The concerned farmer of landmanager will tend to rectify this manifestation by appropriate management practices while launching any serious cultivation. Further, the contour bunding, transverse rubble walling in the valley and lining of the channel with rubble would tend to restrict the channel along its width and length or the foliage in the crown may also lead to camouflaging the spatial pattern of the channel resulting in data that ultimately will tend to eliminate the finger tip streams from the maps. Another category of shift of streams also have been noticed, in the subbasins. The major valleys of the subbasins are present paddy fields, and the lower order stream that once occupied the valley, has been trained to occupy a course other than its own. This modification is achieved by the combined work of the farmer and the Minor Irrigation Dept. personnel and funding. In fat one has to look at these streams and adjoining paddy fields as temporary sinks for the sediment that is shed down by the adjacent cultivated slopes. At times of heavy rain storms, the streams will overtop the banks or dikes on either side flooding the paddy fields with sediment and water. The paddy fields thus function as moderately efficient temporary traps for coarse sediment. However, the overtopping phenomenon is the result of not only the flood waters but also due to the fact that the channel capacity is maintained most of the time without any change all along its course, going against the natural law of the stream capacity. Sediment accumulation in the channel bed due to accelerated erosion also may tend to reduce the channel capacity.

STUDY OF HYDROLOGY Method of measurement of channel capacity Generally speaking, the discharge at any channel cross section vs. precipitation in the basin upstream of that point, estimated for several channel cross sections in the basin and the interrelationship of these parameters expressed as a power function, serves as a useful measure to characterize the hydrological aspect of the basin in question. The slope estimate of the power function equation has been used to specify the altered streams from the natural ones on an empirical basis by several workers. More often than not, when one makes an attempt to study a drainage basin, one faces the problem of not having suitable number of gauging stations to estimate the discharge parameter. This has turned out to be true, even in the case of many instrumented watersheds. At times of need, it has been felt by many that there may not be available, suitable data to undertake an analysis. For this reason most of the time the analyst is forced to capture his own data by setting up gauging stations. Another way of overcoming the problem is to

14

measure the channel capacity at suitable sections and use it as a surrogate of discharge. Instead of precipitation, the drainage area has been made use of. In fluvial channels the discharge of water along with the sediment it carries, is considered as the cardinal factor in modifying or maintaining the fluvial channel and hence the discharge has been considered as an independent variable by the analysts. Once we concur that the channel is cut or built and maintained by the available discharge, then it follows that the cross sectional area at the bankful (also called the channel capacity) is a suitable substitute for discharge. Therefore, in the case of non-instrumented water sheds like the Neyyar basin, the channel capacity at bankful, estimated by field survey can be used for the analysis of hydrological aspect of the network. Such an assumption will ease the burden of not having many gauging stations in the watershed. In the Neyyar basin there is only one gauging station at Ottasekharamangalam, set up in 1977.

Procedure The easiest way of measuring cross sectional area of the stream at bankful, is with an Engineers level or Transit and Levelling staff and tape. Wooden pegs or stakes are driven on the banks as local but permanent markers of the survey points to be made use of in subsequent visit. With these tools, the surveyor can easily measure the cross section and the filed data can be plotted in section paper (in 1 : 1 scale for distance and height) and with the use of a polar planimeter the cross sectional area or capacity at that cross section can be estimated. Following this procedure, 16 cross sections were measured in the channel of the Master stream in the Neyyar basin. Yet another 16 cross sections were also measured in 16 major tributaries, above their confluence with the master stream. In the master stream, the cross sections were first established, by walking in the stream, and then selecting a fairly straight reach of channel of atleast 100 m length. This exercise was performed to avoid the channel bends.

Estimation of bankful stage Estimation of bankful stage from the cross sections or in the field is not very easy. One has to very carefully scan for the geomorphic expressions of bankful stage in the channel walls like the dirt marks on tree trunks, lichen growth on rocky channel walls, if available, and other features like shoulders or benches on the channel walls. Queries with the local prople also will be of help. Once this level is inferred in the field it can be placed in the cross section. Further it is a matter of measuring the area of the channel cross section below that level with a polar planimeter.

Estimation of bankful velocity Manning flow equation is used for predicting the average flow velocity R 0.66 S 0.5 through the channel. V = 1.00 n 1 where, v = the average velocity in m sec R = Hydraulic radius of channel (bankful) in m S = Slope of the energy grade line (stream bed slope) in meter per meter and n = a roughness factor created by frictional forces of perimeter and water turbulence. The slope of the energy grade line is taken as the slope of the channel from the survey of India toposheets as well as by surveying the slope of water surface in the channel in a straight section. The product of bankful cross section and the average velocity estimated from the Manning flow equation will then give an estimate of Bankful discharge for that cross section.

Direct Measurement of Velocity Stream flow velocity at lower stages can be directly measured to estimate the discharge. This was done as below, using a propeller type magnetic current meter in the channel wherever the water depth was suitable for the measurement of velocity. In the surveyed sections, the flow velocity was measured using the

15

current meter at the middle of every two meter wide subsections, by holding the instrument at half depth (then deducting 5% of the observed velocity) by wading or by suspending the instrument from a canoe along with a 10 kg. fish weight. When velocities were below it 0.9 m sec 1 velocity was read off in an analog display. Back in the office to estimate the discharge, the product of velocity and the cross sectional area of the subsection was estimated. Cumulated value of subsectional discharges was then calculated to arrive at the total discharge at the specific cross section. Thus it was possible to estimate the bankful discharge as well as the discharge through the cross section during lower stages.

Discharge measurement at the tributaries Bankful discharge was estimate in the tributaries too, before their confluence with the main stream. As the flow was very low, the velocity could not be directly measured with the help of current meter. Therefore the bankful velocity had to be indirectly estimated using the Manning flow equation. The bankful cross section was surveyed in the field along with the channel bed slope in a straight section of the channel. By plotting the cross section at bankful, in cross section paper, the hydraulic radius was estimated along with the channel capacity at bankful. Average velocity at bankful was derived using the Manning equation using the suitable friction factor. The product of velocity and the bankful capacity was derived as an estimate of bankful discharge. This was done for all 16 cross sections surveyed in the tributaries The relation between the discharge, drainage areas for the several combinations of tributaries and tributaries and master stream are being analysed. Tables show the summary of data whose anlaysis is in progress.

Sampling of Sediment Stream sediment samples are considered by anlysts as the voice recorder s of stream behavior and variations in the stream behaviour either due to natural or due to anthropic causes. The data from sediment analysis is used to estimate the pattern of variation of sediment parameters along the direction of transport. Secondly the preferential coarsening of fining of sediment or changes in mineralogy are attributed to the change in stream power or variability of source available for exploitation by the stream. The channel bank sediment and its composition ie., the proportion of mud and sand in it is taken to characterize the streams as bed load streams or suspended load streams. The metamorphosis of a bed load stream into a suspended load stream or vice versa are considered to be due to large scale changes in the source area climate, landuse practice changes etc. In the present study, it was decided to examine the stream bed sediment variation to decipher the influence of sand streaming on its composition, the response of the bed sediment to excessive stream bank caving leading to supply of large amounts of finer sediment to the bed material and how the sediment could reflect and to what extent, the reduced flood frequency, after construction of the Dam at Kallikad. Bed and Bank sediment samples from either banks have been collected at points immediately below the 16 tributary junctions. It is pointed out that the analysis of sediment samples are in progress in the laboratory.

Linear changes in channel width Geomorphologists agree that the channel capacity of a fluvial system is a function of the sediment and water it has to carry, ie., the channel capacity is directly related to the discharge it has to handle. In other words, the stream maintains a channel capacity attuned to the available discharge. In that case, one should expect a relation between the channel width, its capacity, and some linear measure of its position within the network.

16

In order to examine this, the ideal starting place is to measure the channel width in the field at several sites for further analysis. In the Neyyar in addition to field measurements, notwithstanding the scarcity of ideal boxlike cross sections where the width could be easily measured, channel width measurements were taken out of Survey of India topographic sheets of 1914 (1:63360 scale) and of 1969 (1:50000 scale). It was assumed that the 1969 toposheets supposedly reflect the channel width modification after large scale interference in the basin and construction of the Dam at Kallikkad. The Surveyed width also will be used as third data set.

Measurement procedure After accepting the accuracy available for the topographic sheets, the width of the blue line (the channel) in the map was measured with the help of a polarizing microscope and a graduated eye piece. Before measurement, the specific eyepiece objective combinations were standardized with the help of a stage-micrometer. About 120 cross sections were measured in all, from the two sets of topo-sheets. The distance down stream of the observation points from Kallikkad was also estimated using a Rotameter, The data for 1914 and 1965 were plotted separately in logarithmic paper for comparison. The plots definitely showed positive increase in width of the stream from the upstream to the down stream end. However, there should be some subtle difference between the slopes of best fir line in the two plots. In order to assess this power function will be fitted and the slopes of the lines of best fir will be compared. The expected difference in the slope is due to the fact that construction of the dam decreased the quantum and frequency of discharge through the stream rendering the channel to maintain a reduced width. This reduction in width can also arise partly out of the sand streaming activity that has been going on and was perhaps rising exponentially.

17

18

19

20

21

22

TABLE: HYDROLOGIC DATA FOR MASTER STREAM (PREDICTED AND ACTUAL) FEB- 1984 Sl. No

Place Name

Drainage Area Km2

Channel capacity m2

Actual width w.m.

Effective width w.m.

Depth D.m

Mean Velocity m.sec 1

Discharge Q 3 m sec 1

Bankful capacity m2

1

2

3

4

5

6

7

8

9

10

1

ULATHANKARA

434.85

25.60

32.5

28.0

0.76

0.48

11.89

199.60

2

PAZHAYAKADA

407.02

23.60

30.0

26.0

1.23

0.84

32.99

128.80

3

OLATHANNI

395.67

29.00

28.5

24.0

1.19

0.13

4.76

118.40

4

AMARAVILA

369.15

21.00

21.0

18.0

1.06

0.32

6.68

153.40

5

ARUVIPPURAM (S)

349.65

21.20

24.5

20.0

0.97

0.19

3.81

173.60

6

ARUVIPPURAM (N)

336.72

15.80

16.0

14.0

1.01

0.40

7.22

172.60

7

PERUMKADAVILA

287.22

39.00

31.0

24.0

1.44

0.06

2.18

160.40

8

ARUVIKARA

272.75

5.80

23.0

20.0

0.26

0.45

2.28

195.00

9

PARACHAL

270.32

29.00

16.50

16.5

1.76

0.05

1.88

161.20

10

KIZHAROOR (N)

257.87

16.80

16.00

16.0

0.99

0.12

2.07

170.60

11

KIZHAROOR

255.80

11.00

14.00

14.0

0.76

0.09

0.94

148.00

12

ARIYANKOD

253.32

5.40

9.50

9.5

0.44

0.24

1.37

184.00

13

OTTASEKHARA MANGALAM

248.62

8.20

12.00

12.0

0.57

0.16

2.08

170.80

14

MANDAPATHIN KADAVU

241.40

6.60

10.00

10.0

0.52

0.43

2.46

79,00

15

PUZHANAD

214.65

5.60

10.00

10.0

0.54

0.24

1.29

164.00

16

VIRANAKAVU (E)

210.75

5.20

8.00

8.0

0.64

0.43

1.66

206.00

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TABLE: HYDROLOGIC DATA FOR MASTER STREAM (PREDICTED AND ACTUAL) FEB- 1984 Sl.No

Tributary Number

Place Name

Drainage area Km2

Channel capacity m2

Bankful capacity m2

Sub Basin number

1

2

3

4

5

6

7

1

2

VLATHANKARA

22.10

1.2

14.00

L.B.2

2

4

PAZHAYAKADA

11.00

0.4

15.00

R.B.1

3

6

OLATHANNI

20.68

1.2

25.60

R.B.2

4

7

OLATHANNI

20.68

1.2

36.20

R.B.2

5

9

AMARAVILA

16.20

1.0

18.00

L.B.4

6

12

ARUVIPPURAM

13.40

0.8

15.40

R.B.3

7

13

ARUVIPPURAM

48.00

2.2

28.40

L.B.5

8

15

PERUMKADAVILA

7.65

1.4

33.20

L.B.6

9

17

ARUVIKKARA

1.80

0.15

4.65

R.B.4

10

19

PARACHAL

9.90

1.0

23.20

R,B.5

11

21

KIZHAROOR

2.50

0.2

4.50

L.B.7

12

24

KIZHAROOR

1.53

0.6

11.10

R.B.6A

13

26

ARIYANKOD

5.30

0.4

16.20

L.B.8

14

28

CHITTAR

49.20

2.2

63.20

L.B.9

15

30

AMACHAL

18.92

2.2

28.60

R.B.6

16

32

PUDUVITTUMURI

1.50

0.2

9.60

L.B.11

17

34

KALLIKKAD

4.90

0.8

14.00

R.B.7

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DISTRIBUTION LIST 1. Director, Centre for Earth Science Studies, P.B. 2235, Trivandrum Pin 695 010

14. Dean, School of environmental Sciences, Jawahar Lal University, New Delhi

2. Director, Geological Survey of India Kerala Circle, Thampanoor Trivandrum

15. Prof. B.K. Sahu, Dept of Geology, IIT, Powai, Bombay, 400 076

3. Librarian Legislature Library, Secretariat, Trivandrum

16. Prof. Dipankar Niyogi, Dept of Geology, IIT, Kharagpur, Midnapore Dist, W.Bengal

4. Director Centre for Water Resources Devlopment and Management, Kunnamangalam, Kozhikode 5. Director Kerala Engineering Research Institute, Peechi 6. Prof Stanely Schumm, Colarado State University, Fort Collins, Colarado 80523 7. Prof. Ian Douglas, School of Geography University of Manchester, Manchester, U.K. M13 9PL 8. Dr. Chris Park, Dept. of Geography, Lancaster University, Bailrigg, Lancaster, U.K. LA1 4YR 9. Prof. K.J. Gregory, Professor of Geography University of Southampton. U.K., SO9 5NH

17. Dr.S.K. Chanda, Department of Geology, Jadavpur University Calcutta. 18. Head of the Dept. of Geology Banares Hindu University, Banaras 19. Head of the Dept of Geography Madura Kamaraj University Madurai 20. Librarian , Central Library Geological Survey of India Calcutta 700 016 21. Librarian , Kerala University Library, Trivandrum 22. Dr. Indra Bir Singh, Dept of Geology, Lucknow University Lucknow. 23. Officer in charge Data Processing Centre, GSI, Hyderabad 500 001

10. Prof. S.M. Casshyap Dept. of Geology, Aligarh Muslim University, Aligarh, 2 UP. 11. Prof. Ramesh Prof of geography Madras University Presidency College, Madras 12. Prof. K. Vaidyanathan Dept of Geography Andhra University Waltair 13. Prof.V.k. Varma Dept of Geology, Delhi University, New Delhi

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