STUDY OF RIVER SYSTEM AND FLOW ROUTING OF NORTH EAST REGION OF BANGLADESH_Mohammad Ali

STUDY OF RIVER SYSTEM AND FLOW ROUTING OF STUDY OF RIVER SYSTEM AND FLOW ROUTING OF NORTH EAST REGION OFNORTH EAST REGION OF BANGLADESHBANGLADESHNORTH EAST REGION OF NORTH EAST REGION OF BANGLADESHBANGLADESH

A thesisByBy

MOHAMMAD ALIReg no :0097310228Reg. no.:0097310228

MD. MAKSUDUL AMINReg. No. :0097310230

Bachelor of Science in Civil and Environmental Engineering

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

INTRODUCTIONINTRODUCTION

Floods are more or less a recurring phenomenon ing pBangladesh and often have been within tolerable limits.But occasionally they become devastating. Each year inBangladesh about 26,000 sq km, 18% of the country isg q yflooded. During severe floods, the affected area mayexceed 55% of the total area of the country. In anaverage year, 844,000 million cubic metre of water flowsg y , ,into the country during the humid period (May toOctober) through the three main rivers the Ganges, theBrahmaputra-Jamuna and the Meghna. This volume isp g95% of the total annual inflow. By comparison only about187,000 million cu m of stream flow is generated byrainfall inside the country during the same period.y g p


Types of floodsFl d i B l d h bFloods in Bangladesh can be

divided into three categories:• Monsoon flood - seasonal,

increases slowly andydecreases slowly, inundatesvast areas and causes hugelosses to life and property;

• Flash flood - waterFlash flood waterincreases and decreasessuddenly, generally happensin the valleys of the hillyareas; andareas; and

• Tidal flood - short duration,height is generally 3m to 6m,blocks inland flood drainage.


• The factors for causing floods in BangladeshThe factors for causing floods in Bangladeshgeneral low topography of the country with major riversdraining through Bangladesh including a congested rivernetwork system,rainfall in the upstream country or in the mainland,snow melt in the Himalayas and glacial displacementsnow-melt in the Himalayas and glacial displacement(natural),river siltation/lateral river contraction/landslides,,synchronisation of major river peaks and influences ofone river on the other,human intervention of the environment,


• The factors for causing floods in Bangladeshg gtidal and wind effects on slowing down the river outflow(backwater effect),construction of barrages and protective works along the banks ofthe river - some are very close to both the banks - in the upperreaches thus making the passage of water flow downstreamincreasingly narrower and resulting in greater acceleration ofwater flow downstream presently than beforewater flow downstream presently than before.deforestation in the upper reaches of the rivers is not onlyleading acceleration of water flow downstream but also leaddeposition of loads in the river beds, resulting in reducedgchannel flow and consequent overland runoff water andtectonic anomalies (earthquake) those change in riverflow/morphology.

OVERVIEW OF BANGLADESHOVERVIEW OF BANGLADESHGeographical location• In South Asia, between 20°34'

to 26°38' north latitude and 88°01' to 92°41' east longitude. gMaximum 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 l A d M h lBengal, Assam and Meghalaya (all the Indian states) on the north; Indian states of Assam, Tripura and Mizoram together with Myanmar on the east; andwith Myanmar on the east; and Bay Of Bengal on the south.

OVERVIEW OF BANGLADESHOVERVIEW OF BANGLADESH

Physiography:• Configuration of a land surface including its relief and

contours the distribution of mountains and valleys the


contours, the distribution of mountains and 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 riversa small hill region drained by flashy 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 f th th t i f Chitt• The hilly areas of the southeastern region of 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 i t t l l i l i ll l t thhills is a narrow, wet coastal plain lying parallel to the shoreline. Figure: 3.2 shows the physiography of Bangladesh.


RiversTotal rivers including tributariesand distributaries are about700 under three mighty riversystems: Ganges-Padma RiverSystem, Brahmaputra-JamunaRiver System and Surma-Meghna River System RiversMeghna River System. Riversof the southeastern hilly regionare considered as theChittagong Region RiverSystem. Principal rivers are:y pGanges, Padma, Brahmaputra,Jamuna, Surma, Kushiyara,Meghna, Karnafuli, OldBrahmaputra, Arial Khan,Buriganga Shitalakshya TistaBuriganga, Shitalakshya, Tista,Atrai, Gorai, Madhumati,Kobadak, Rupsa-Pashur, Feni.


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

Pre-monsoon April and May Monsoon June through September g p

Post-monsoon October and November Dry season December through MarchDry season December through March


ClimateBangladesh is located in thetropical monsoon region and itsclimate is characterized by hightemperature heavy rainfall oftentemperature, heavy rainfall, oftenexcessive humidity, and fairlymarked seasonal variations.

Atmospheric Pressure andAtmospheric Pressure andWindsTemperatureHumidityyCloudsRainfall


Rainfall• The single most dominant element of the climate of Bangladesh is

the rainfall Because of the country's location in the tropical monsoonthe rainfall. Because of the country s 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 rainfall increases dueprogresses into the pre-monsoon hot 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

i i d b th t i l d i th t t thrainy season is caused by the tropical depressions that enter 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 f th t t th 400 i th th t dof the country to more than 400 cm in the northeastern and

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 BANGLADESHOVERVIEW OF BANGLADESH• River and Drainage SystemThe system can be divided into four major

networks: (1) Brahmaputra jamuna river system(1) Brahmaputra-jamuna river system, (2) Ganges-padma river system,(3) Surma-meghna river system, and (4) Chittagong region river system.

The first three river systems togetherThe 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 ofthrough 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 and channelsusceptible to erosion, and channel shifting.


• Brahmaputra-Jamuna System

The Brahmaputra-Jamuna river isabout 280 km long and extendsfrom northern Bangladesh to itsconfluence with the Ganges.Before entering Bangladesh, theBrahmaputra has a length ofBrahmaputra has a length of2,850 km and a catchment area ofabout 583,000 sq km. The riveroriginates in Tibet as the YarlungZangbo Jiang and passes throughg g p gArunachal Pradesh of India asBrahmaputra (son of Brahma).Along this route, the river receiveswater from five major tributaries,of which Dihang and Luhit areof which Dihang and Luhit areprominent.


• Ganges-Padma System

This system is part of the greaterG t Th G hGanges system. The Ganges has atotal length of about 2,600 km and acatchment area of approximately907,000 sq km. Within Bangladesh,Ganges is divided into two sections -fi t th G 258 k l t tifirst, the Ganges, 258 km long, startingfrom the western border with India toits confluence with Jamuna atGoalandaghat, some 72 km west ofDhaka. The second is the Padma, 126k l i f G l d h tkm long, running from Goalandaghatconfluence to Chandpur where it joinsthe Meghna. The Padma-Ganges isthe central part of the deltaic riversystem with hundreds of rivers. Thet t l d i f G i b ttotal drainage area of Ganges is about990,400 sq km of which only 38,880sq km lie in 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 The river originates in theMeghalaya) of the 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 Barak-Meghna has a length of 950 km of which 340 km lie within Bangladesh. On reaching the border with B l d h t A l hid i S lh t di t i t th B kBangladesh at Amalshid in Sylhet district, the Barak 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, Chalti-nadi, Chengar-khal, , g y , , 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 although prone to producing flashare less violent, although prone to producing flash floods, due in part to the lesser elevations and rainfall of Tripura hills.

OVERVIEW OF BANGLADESHOVERVIEW OF BANGLADESH• The Chittagong Region System

The rivers of Chittagong andChittagong hill tracts are notconnected to the other riverconnected to the other riversystems of the country. The mainriver of this region is Karnafuli. Itflows through the region ofChittagong and the ChittagongHill It t th hill dHills. It cuts across the hills andruns rapidly downhill to the westand southwest and finally to theBay of Bengal. Chittagong port islocated on the bank of Karnafulilocated on the bank of Karnafuli.The river has been dammedupstream at Kaptai to create awater reservoir for hydroelectricpower generation. Other importantrivers of the region are the Feni,Muhuri, Sangu, Matamuri,Bakkhali, and Naf.


•• FloodplainFloodplainRelatively smooth valley floors adjacent to and formed by alleviating y y j y grivers 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 ( ) H B i ( i) S K hi Fl d l i ( ii)Floodplain; (v) Haor Basin; (vi) Surma-Kushiyara Floodplain; (vii) Meghna Floodplain: (a) Middle Meghna Floodplain, (b) Lower Meghna Floodplain, (c) Old Meghna Estuarine Floodplain, and (d) Young Meghna Estuarine Floodplain; (viii) Ganges River Floodplain; g g p ; ( ) g p ;(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 PlainPlain

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 3) ItTitas river basin (Fig: 1.3). It comprises an area of 24,265 km2, and constitutes 17% of the country and 20% of its deltaic

t It b di id dsector. It can be divided conveniently into two distinct sub regions, the larger Meghna sub region in the eastsub region in the east comprising 4,004 km2 or 16.5% of the region.

• Topography of the Northeast Region and Adjacent Tributary AreasAreas

• 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 dh T t l i t th th t f th th t• the Madhapur Tract lying to the southwest of the north-east region;

• the north-east region plain comprised of the north-east region itself, except for its Tripura border area., p p

• Indo-Burman rangesIndo Burman ranges• Shillong plateau

T• Tura range • Madhapur Tract

• ClimateThe MonsoonSouth-West Monsoon (wet season)North East Monsoon (dry season)North-East Monsoon (dry season)Inter Monsoon Transitions (pre-and post-monsoon seasons)

•• RegionalRegional River SystemRiver SystemBarak system Kushiyara systemKangsha-BaulaieystemMeghna systemMeghna systemOld Brahmaputra- Lakhya systemSurma system

SurmaLubhaSarigowainPiyainUmiumUmiumDhalaiJhalukhaliJadukata

Flood RoutingFlood Routing

• Lumped System RoutingLumped System Routing• Level Pool Routing

Di t ib t d Fl R ti• Distributed Flow Routing• Dynamic Wave Routing

SaintSaint--Venant Equationsassumptions Venant Equationsassumptions

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 axislongitudinal 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 b tt l f th h l i ll d th h l b d i fi d th t4. The bottom slope of the channel is small and the channel bed is fixed: that

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 effectsresistance effects.

6. The fluid is incompressible and of constant density throughout the flow.

Computer Programme and A li iApplication

IntroductionI hi h d l d b Vi l B iIn this step we have developed a programme by Visual Basic, 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

i tiapproximation.Initial input

Known water level (h) and discharge (Q) of two station of same timetime.Distance (d) of the two stations.

OutputDischarge and water level of unknown distance.gRate of change of discharge and water level.

Compute lead time.

Computer Programme and A li iApplication

Case studyCase study

Conclusion and RecommendationConclusion and Recommendation • 7.1 Recommendation• Need more station for the effectively prediction of flood and specially flash flood in• 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 riverFrequently check the cross section of the flashy 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 regionLack of available data of river characteristic of north east region.• Lack of hydrological data in short duration gap.• It is not possible to collect the upstream (Indian Catchment) data.

Conclusion and RecommendationConclusion and RecommendationConcluding Remark

Initially our aim was to calculate the lead time of flash flood which is the majorInitially 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 Which is notparameter of the regional area but also depend on the global 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 part of the forecasting of flash flood which occur in pre-monsoon season p g p(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.

STUDY OF RIVER SYSTEM AND FLOW ROUTING OF NORTH EAST REGION OF BANGLADESH_Mohammad Ali

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