Study Of River System And Flow Routing Of North East Region Of Bangladesh_mohammad Ali

STUDY OF RIVER SYSTEM AND FLOW ROUTING OF NORTH EAST REGION OF BANGLADESH A thesis By MOHAMMAD ALI Reg no.:0097310228 Reg. no :0097310228 MD. MAKSUDUL AMIN Reg. No. :0097310230

Bachelor of Science in Civil and Environmental Engineering

Department D t t off Civil Ci il and d Environmental E i t lE Engineering i i (CEE) Shah Jalal University of Science & Technology (SUST), Sylhet, Bangladesh

INTRODUCTION Floods are more or less a recurring g p phenomenon in Bangladesh and often have been within tolerable limits. But occasionally they become devastating. Each year in g about 26,000 sq q km, 18% of the countryy is Bangladesh flooded. During severe floods, the affected area may exceed 55% of the total area of the country. In an g yyear,, 844,000 , million cubic metre of water flows average into the country during the humid period (May to October) through the three main rivers the Ganges, the Brahmaputra-Jamuna p and the Meghna. g This volume is 95% of the total annual inflow. By comparison only about 187,000 million cu m of stream flow is generated by g the same p period. rainfall inside the countryy during

INTRODUCTION Types of floods Fl d in Floods i Bangladesh B l d h can be b divided into three categories: • Monsoon flood - seasonal, y and increases slowly decreases slowly, inundates vast areas and causes huge losses to life and property; Flash flood water • increases and decreases suddenly, generally happens in the valleys of the hilly areas; and • Tidal flood - short duration, height is generally 3m to 6m, blocks inland flood drainage.

INTRODUCTION

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The factors for causing floods in Bangladesh ¾ general low topography of the country with major rivers draining through Bangladesh including a congested river network system, ¾ rainfall in the upstream country or in the mainland, ¾ snow-melt snow melt in the Himalayas and glacial displacement (natural), ¾ river siltation/lateral river contraction/landslides,, ¾ synchronisation of major river peaks and influences of one river on the other, ¾ human intervention of the environment,

INTRODUCTION • The factors for causing g floods in Bangladesh g ¾ tidal and wind effects on slowing down the river outflow (backwater effect), ¾ construction of barrages and protective works along the banks of the river - some are very close to both the banks - in the upper reaches thus making the passage of water flow downstream increasingly narrower and resulting in greater acceleration of water flow downstream presently than before. before ¾ deforestation in the upper reaches of the rivers is not only leading acceleration of water flow downstream but also lead g in reduced deposition of loads in the river beds, resulting channel flow and consequent overland runoff water and ¾ tectonic anomalies (earthquake) those change in river flow/morphology.

INTRODUCTION

OVERVIEW OF BANGLADESH Geographical location • In South Asia, between 20°34' to 26°38' north latitude and 88°01' to 92°41' east longitude. g Maximum extension is about 440 km in E-W direction and 760 km in NNW-SSE direction. Area and boundaries • Area: 147,570 sq km. Boundaries: West Bengal (India) on the west; West B Bengal, l A Assam and dM Meghalaya h l (all the Indian states) on the north; Indian states of Assam, Tripura and Mizoram together with Myanmar on the east; and Bay Of Bengal on the south.

OVERVIEW OF BANGLADESH Physiography: • Configuration of a land surface including its relief and contours the distribution of mountains and valleys contours, valleys, the patterns of rivers, and all other features, natural and artificial, that produce the landscape. Although Bangladesh is a small country, it has considerable topographic diversity. It has three distinctive features: • a broad alluvial plain subject to frequent flooding, • a slightly elevated relatively older plain, and a small hill region drained by flashy rivers rivers. • • On the south, a highly irregular deltaic coastline of about 600 km fissured by many estuarine rivers and channels flowing into the Bay of Bengal. The alluvial plain is part of the larger plain of Bengal, which is sometimes called the Lower Gangetic Plain. Elevations of the plains are less than 10m above the Sea Level; elevation furthers decline to a near sea level in the coastal south. • Th hill The hilly areas off th the southeastern th t region i off Chitt Chittagong, the northeastern hills of Sylhet and highlands in the north and northwest are of low elevations. The Chittagong Hills constitute the only significant hill system in the country. It rises steeply to narrow ridgelines (average 36m wide), with elevation ranges between 600 and 900m above mean sea level. In between the hilly ridges lie the valleys that generally run north to south. West of the Chittagong hill iis a narrow, wett coastal hills t l plain l i llying i parallel ll l tto th the shoreline. Figure: 3.2 shows the physiography of Bangladesh.

OVERVIEW OF BANGLADESH Rivers Total rivers including tributaries and distributaries are about 700 under three mighty river systems: Ganges-Padma River System, Brahmaputra-Jamuna River System and SurmaMeghna River System. System Rivers of the southeastern hilly region are considered as the Chittagong Region River y Principal p rivers are: System. Ganges, Padma, Brahmaputra, Jamuna, Surma, Kushiyara, Meghna, Karnafuli, Old Brahmaputra, Arial Khan, Buriganga Shitalakshya, Buriganga, Shitalakshya Tista, Tista Atrai, Gorai, Madhumati, Kobadak, Rupsa-Pashur, Feni.

OVERVIEW OF BANGLADESH

Definition of the seasons in Bangladesh In Bangladesh the water years is defined as beginning g g on 1st April p and ending g on 31st March,, and it is divided into four more or less distinct season: Source: Banglapedia Pre-monsoon Monsoon

April and May June through g September p

Post-monsoon Dry season

October and November December through March

OVERVIEW OF BANGLADESH Climate Bangladesh is located in the tropical monsoon region and its climate is characterized by high temperature heavy rainfall, temperature, rainfall often excessive humidity, and fairly marked seasonal variations. ¾ Atmospheric Pressure and Winds ¾ Temperature ¾ Humidity y ¾ Clouds ¾ Rainfall

OVERVIEW OF BANGLADESH ¾ •

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Rainfall The single most dominant element of the climate of Bangladesh is the rainfall rainfall. Because of the country country'ss location in the tropical monsoon region, the amount of rainfall is very high. However, there is a distinct seasonal pattern in the annual cycle of rainfall, which is much more pronounced than the annual cycle of temperature. The winter season is very dry, and accounts for only 2%-4% of the total annual rainfall. Rainfall during this season varies from less than 2 cm in the west and south to slightly over 4 cm in the northeast. The amount is slightly enhanced in the northeastern part due to the additional uplifting of moist air provided by the Meghalaya Plateau. As the winter season progresses into the pre-monsoon hot season, season rainfall increases due to intense surface heat and the influx of moisture from the Bay of Bengal. Rainfall during this season accounts for 10%-25% of the total annual rainfall which is caused by the thunderstorms or Nor'wester (locally called Kalbaishakhi [Kalbaishakhi]). The amount of rainfall in this season varies from about 20 cm in the west central part to slightly over 80 cm in the northeast. The additional uplifting (by the Meghalaya Plateau) of the moist air causes higher amount of rainfall in the northeast. Rainfall during the rainy i season iis caused db by th the ttropical i ld depressions i th thatt enter t th the country from the Bay of Bengal. These account for 70% of the annual total in the eastern part, 80% in the southwest, and slightly over 85% in the northwestern part of Bangladesh. The amount of rainfall in this season varies from 100 cm in the west central part to over 200 cm in the south and northeast. Average rainy days during the season vary from 60 in the west-central part to 95 days in the southeastern and over 100 days in the northeastern part. Geographic distribution of annual rainfall shows a variation from 150 cm in the west-central part off the th country t to t more than th 400 cm in i th the northeastern th t and d southeastern parts. The maximum amount of rainfall has been recorded in the northern part of Sylhet district and in the southeastern part of the country (Cox's Bazar and Bandarban districts).

Figure: 3.6 shows the mean annual rainfall of Bangladesh.

OVERVIEW OF BANGLADESH • River and Drainage System The system can be divided into four major networks: (1) Brahmaputra Brahmaputra-jamuna jamuna river system, system (2) Ganges-padma river system, (3) Surma-meghna river system, and (4) Chittagong region river system. The first three river systems together cover a drainage basin of about 1.72 million sq km, although only 7% of this vast basin lies within Bangladesh. The combined annual discharge passing through the system into the Bay of Bengal reaches up to 1,174 billion cu m. Most of the rivers are characterised by fine sandy bottoms, flat slopes, substantial meandering, banks susceptible to erosion erosion, and channel shifting.

OVERVIEW OF BANGLADESH •

Brahmaputra-Jamuna System The Brahmaputra-Jamuna river is about 280 km long and extends from northern Bangladesh to its confluence with the Ganges. Before entering Bangladesh, the Brahmaputra has a length of 2,850 km and a catchment area of about 583,000 sq km. The river originates in Tibet as the Yarlung Zangbo g Jiang g and p passes through g Arunachal Pradesh of India as Brahmaputra (son of Brahma). Along this route, the river receives water from five major tributaries, of which Dihang and Luhit are prominent.

OVERVIEW OF BANGLADESH •

Ganges-Padma System This system is part of the greater G Ganges system. t Th Ganges The G h has a total length of about 2,600 km and a catchment area of approximately 907,000 sq km. Within Bangladesh, Ganges is divided into two sections fi t the first, th Ganges, G 258 km k long, l starting t ti from the western border with India to its confluence with Jamuna at Goalandaghat, some 72 km west of Dhaka. The second is the Padma, 126 k long, km l running i f from G l d h t Goalandaghat confluence to Chandpur where it joins the Meghna. The Padma-Ganges is the central part of the deltaic river system with hundreds of rivers. The t t l drainage total d i area off Ganges G i about is b t 990,400 sq km of which only 38,880 sq km lie in Bangladesh.

OVERVIEW OF BANGLADESH • •

The Surma-Meghna system The Meghna is the longest (669 km) river in Bangladesh. It drains one of the heaviest rainfall areas (eg, about 1,000 cm at Cherapunji in Meghalaya) of the world world. The river originates in the hills of Shillong and Meghalaya of India. The main source is the Barak river, which has a considerable catchment area in the ridge and valley terrain of the Naga-Manipur hills bordering Myanmar. The BarakMeghna has a length of 950 km of which 340 km lie within Bangladesh. On reaching the border with B Bangladesh l d h att A Amalshid l hid iin S Sylhet lh t di district, t i t th the B Barak k bifurcates to form the steep and highly flashy rivers surma and kushiyara. The Surma, flowing on the north of the Sylhet basin, receives tributaries from the Khasia and Jaintia hills of Shillong. Some of the important tributaries of these two rivers are Luba, Kulia,, shari-goyain, g y , Chalti-nadi,, Chengar-khal, g , piyain, Bogapani, Jadhukata, Someshwari and kangsa. The Surma meets the Meghna at Kuliarchar upazila of Kishoreganj district. The Kushiyara receives left bank tributaries from the tripura hills, the principal one being the manu. Unlike the Surma, the tributaries of the Kushiyara are less violent violent, although prone to producing flash floods, due in part to the lesser elevations and rainfall of Tripura hills.

OVERVIEW OF BANGLADESH •

The Chittagong Region System The rivers of Chittagong and Chittagong hill tracts are not connected to the other river systems of the country. The main river of this region is Karnafuli. It flows through the region of Chittagong and the Chittagong Hill It cuts Hills. t across the th hills hill and d runs rapidly downhill to the west and southwest and finally to the Bay of Bengal. Chittagong port is located on the bank of Karnafuli. Karnafuli The river has been dammed upstream at Kaptai to create a water reservoir for hydroelectric power generation. Other important rivers of the region are the Feni, Muhuri, Sangu, Matamuri, Bakkhali, and Naf.

OVERVIEW OF BANGLADESH

• Floodplain

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Relatively y smooth valleyy floors adjacent j to and formed by y alleviating g rivers which are subject to overflow. In the context of physiographic, Bangladesh may be classified into three distinct regions, viz (A) Floodplain, (B) Terrace, and (C) Hill areas, Floodplains of Bangladesh have been divided into 18 sub-units: (i) Old Himalayan Piedmont Plain; (ii) Tista Floodplain; (iii) Old Brahmaputra Floodplain; (iv) Jamuna (Young Brahmaputra) Fl d l i ((v)) H Floodplain; Haor B Basin; i ((vi) i) S Surma-Kushiyara K hi Fl Floodplain; d l i ((vii) ii) Meghna Floodplain: (a) Middle Meghna Floodplain, (b) Lower Meghna Floodplain, (c) Old Meghna Estuarine Floodplain, and (d) g Meghna g Estuarine Floodplain; p ; ((viii)) Ganges g River Floodplain; p ; Young (ix) Ganges Tidal Floodplain; (x) the Sundarbans; (xi) Lower Atrai Basin; (xii) Arial Beel; (xiii) Gopalganj-Khulna Peat Basin; (xiv) Chittagong Coastal Plain; and (xv) Northern and Eastern Piedmont Plain

STUDY SITE

The North-East Region The northeast region is defined as the area east of the old Brahmaputra or Lakhya river channel, and north of the upper Meghna river channel and the Titas river basin (Fig: 1 1.3). 3) It comprises an area of 24,265 km2, and constitutes 17% of the country and 20% of its deltaic sector. t It can be b divided di id d conveniently into two distinct sub regions, the larger Meghna sub region in the east comprising 4,004 km2 or 16.5% of the region.

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Topography of the Northeast Region and Adjacent Tributary Areas The north-east region and its adjacent tributary areas constitute the river basin of the upper Meghna river. Within this river basin are five topographically and geologically very distinct areas the northern Indo-Burma ranges lying to the southeast of the north-east region but including the region’s Tripura border area- a strip of land some 30 km wide along the region’s southeastern border;; the southern slopes of the Shillong plateau lying north of the north-east region, but towards the northeast; the Tura range lying of the north-east region, but northwest; th M the Madhapur dh T Tractt lying l i tto th the southwest th t off the th north-east th t region; the north-east region plain comprised of the north-east region p for its Tripura p border area. itself,, except

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Indo Burman ranges Indo-Burman Shillong plateau T Tura range Madhapur Tract

• Climate ¾ ¾ ¾ ¾

The Monsoon South-West Monsoon (wet season) North East Monsoon (dry season) North-East Inter Monsoon Transitions (pre-and post-monsoon seasons)

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Regional River System Barak system Kushiyara system Kangsha-Baulaieystem Meghna system Old Brahmaputra- Lakhya system Surma system 9 Surma 9 Lubha 9 Sarigowain 9 Piyain 9 Umium 9 Dhalai 9 Jhalukhali 9 Jadukata

Flood Routing • • • •

Lumped System Routing Level Pool Routing Di t ib t d Fl Distributed Flow R Routing ti Dynamic Wave Routing

Saint--Venant Equationsassumptions Saint 1. The flow is one-dimensional: depth and velocity vary only in the longitudinal direction of the channel. This implies that the velocity is constant and the water surface is horizontal across any section perpendicular to the longitudinal axis axis. 2. Flow is assumed to vary gradually along the channel so that hydrostatic pressure prevails and vertical accelerations can be neglected (Chow. 1959). 3. The longitudinal axis of the channel is approximated as a straight line. 4 Th 4. The b bottom tt slope l off the th channel h l iis smallll and d th the channel h lb bed d iis fifixed: d th thatt is. the effects of scour and deposition are negligible. 5. Resistance coefficients for steady uniform turbulent flow are applicable so that relationships such as Manning's equation can be used to describe resistance effects effects. 6. The fluid is incompressible and of constant density throughout the flow.

Computer Programme and A li i Application Introduction I this In hi step we h have d developed l d a programme b by Vi Visuall B Basic, i which is user friendly to calculate time and space derivative of flow rate and water stage (,,,) for solving Saint Venent equation based on weighted four point implicit finite difference approximation. i ti Initial input ¾ Known water level (h) and discharge (Q) of two station of same time. time ¾ Distance (d) of the two stations. Output ¾ Discharge g and water level of unknown distance. ¾ Rate of change of discharge and water level. ¾

Compute lead time.

Computer Programme and A li i Application Case study

Conclusion and Recommendation • • • • • • • • • • •

7.1 Recommendation Need more station for the effectively prediction of flood and specially flash flood in north East region. Need to use modern technology for updating the water level and rainfall data. To develop our program for the forecast of flash flood and lead time. Frequently check the cross section of the flashy river river. Need easy access of global hydrological data. 7.2 Limitation Lack of literature and research on flash flood. Lack of available data of river characteristic of north east region region. Lack of hydrological data in short duration gap. It is not possible to collect the upstream (Indian Catchment) data.

Conclusion and Recommendation Concluding Remark Initially our aim was to calculate the lead time of flash flood which is the major portion of forecasting of flash flood, which is destractive for the Robi crops in the north east region. As there is no suitable system to forecast flash flood in the present world and we feel that it is a long term supervision work with more analytical job. The forecasting system depends on not only hydrological, geological and topographical parameter of the regional area but also depend on the global parameter parameter. Which is not possible to collect the relative data from other neighbor country, for the lack of government collaboration and legislation. As the initial p part of the forecasting g of flash flood which occur in p pre-monsoon season (March to May) in the north east region of Bangladesh, we have study the hydrological, topographical, and river system of the north east region as well as Bangladesh. Our analysis part is highly related with flood routing, which is helpful to the further study of the forecasting of flash flood. Our study is comprise with a computer programme which calculate the rate of change water level and discharge and water level of any distance of the down stream, which is a major portion to find out the lead time of flash flood. And finally we hope that it is possible to go ahead from this point to reach the goal that is forecasting of flash flood.