DnrVTMFAMT rFP T?R'1P?ATTnMAT BAmv t-Px PYrVJxTcrDTTTCrTIn AMnDT7I17T CED1k4Vfl.Jr INTERNATIONAL DEVELOPMENT ASSOCIATION Public Disclosure Authorized Not For Public Use PS-13 VOL. 9 Report No. PS-13 LAN-D AND WATER RESO-u-KCES SECTOR STUDY Public Disclosure Authorized BANGLADESH (in nine volumes) VOLUME VIII THE FLOOD PROBLEM CONTAINING: Technical Report No. 24 - Floods in Bangladesh Public Disclosure Authorized Technical Report No. 25 - River System Analyses Technical Report No. 26 - Embankment Maintenance December 1, 1972 Public Disclosure Authorized Asia Projects Department I ..i.. Aeport was preparedU for offi-cmi-I ua. onlty by Ue Bank. G.oupj. IUttr.a notn be puUb':he, quote I or cited without Bank Group authorization. The Bank Group does not accept responsibility for the accuracy or completeness of the report. Note "T'Phe T-mind nnt W2te'r RPeniir-.A RSeentnr Studi - Bangladesh" dated December 1 1972 was prepared between May 1971 and the simrnnerof 1972 urnder the general supervision of the Bank, by staff members of the Bank, 9 ,,nA TiAC5 Ld 4-i oa,i +9rd- n1 hol rt wm onrcni1 +.avd-° rI1a UNDP and the Bank shared the cost of the consulting serv,tices The stu,dy s A ae -.4 ia 1 on the+1-.d-ear.-d= ing that it does not necessarily represent the official position of the Government of4' Bangladesh or of the Bank T',h stud i base mns-lyr on dta co.-U' egvct AUwv, a prior to March 1971. Although some of the information con tair.ned iLflnthe4S + AJ is4.u -u of U- theA essence of. 4i.t is vralid and it should be useful to the Government of OILACAi's iVs inUII± t,heALLLLUJ..LVOj of B4Ld.A institutions interested in the development of Bangladesh. T AITT) A1kT I.TArVlt' D1VC°TTDPrCT'O OEVCOTIRP VUL2"JJ±ulliJ VUII'JiL IU.J~XI-I. TJ I PIP.O'JIVIL SmTMV IJB TTrATTrnxrV TTTTT- mun' V~Tnr%-n n~TD 1'UI V VJ,UI'UL. V IiiL J111-i .LAAJILJ LLLtJU.UL:,I71 FOREWORD i. ~Floods constitute one of the most critical problems facing Ban.gla- desh. Each year the major rivers flood close to a third of the country. With the increase in population and a greater demand for high agricult-ural productivity, there is an increasing need for controlling floods. ii. This Volume including Technical Reports 24, 25 and 26 is devoted primarily to the river flood problems. It should be noted however, that in the coastal regions the greatest danger is from flooding caused by cyclone storns. For instance in November 1970, after sufiering unusuaily destructive floods, Bangladesh was hit by an unprecedented cyclone and tidal wave which killed several hundred thousand people and destroyed the assets of millions of farmers and fishermen in the coastal area. WA1hile some control can be exercised over the river floods, there is as yet no measure to prevent the occurrence of floods due to cyclonic surges similar in magnitude to that of November 1970. Destruction, especially of human lives, can only be minimized by an effective early warning system and a large number of shelter facilities. iii. Technical Report No. 24 delineates the river flood problen, the magnitude of the damage and methods of flood prevention. Close to half cf the country is vulnerable to flooding and on the average almost a third is flooded each year. Flood damages are estimated to average Tks 655 millic,n annually. Embankments and channel improvements constitute the only practical means of preventing inundation by the rivers. Pumping plants and sluices wqould be necessary to evacuate local drainage and to provide irrigation water as a substitute for the flood waters which now are relied upon. Proper design of em1banmanents must be based on consideration of the deDth, and dulration of flooding (with design flood), stability of the rivers, and foundation and construction materials, rights of way conditions, con- struction and maintenance procedures and past experience in Bangladesh. iv. Technical Report No. 25 discusses the geomorphic, flood mechanics and sediment transfer aspects of a river system and their relationship to design of river training facilities. In Bangladesh, the only feasible method of training the major rivers to prevent vast overland flooding during peak river discharge is by construction of embankments. Factors critical for a successful embankment system are embankment height, embankment loca- tion and the maintaining of an adequate embankment cross-section. A method- ology for de-termining embankment heights and factors which determine the flood stages for embanked river channels are presented. The embankments would cause an increased main channel discharge which usually results in - ii - increased depth and stage. The increase in stage and depth are dependent on the decrease in bed form roughness in snd bhed channels wh-ich usuanlly occurs with increased discharge. A combination of bed degradation, channel widening and decreaed bed r - lUd result in decreased stage for embanked reaches. In heterogeneous alluvial deposits all channel ros-secti will not respond in the snme manner. ToHdetermine stage response a careful analysis is required. The Report also deals with the movem.ents of the low flow charLnels and how these movements affect-a-iiln'hilit-i of water for pumping plants. It concludes with a concrete application of the privirpJles otined, 11usincg +thenDacca Sotht Prniar-+. 2S an. innmnla Finally, recommendations are made for future river system investigations. v. According to Technical Report No. 26, embankment projects are of Ve..±Jr ..k. U a.L'. +n --Vat t4InW- . * +A1 a.j................J............rl Dv+;...... ................ormoron+^-rnnnMmio s raA .... 'U and flood fighting program must be included as an integral part of the plan- ning and imlementation of eembanlrmennt projects. The reDort nethe +ti4 major components of an embankment maintenance and flood fighting program. Because of t+h-1evariety of sz_ -x -iAnd of e.mbanr..ent projects ar. attempt is made to develop a set of maintenance principles and a typical organ 4za 14 nal anA aA4 m mstra"1ve -arrage..nt +1-4 'ou4-e--l or-v U.., LLI0 UJ.L -J ~LU. d.UJLJ.L LL I..! U....VU r QI . aIA1r'~-11&L1 UILA1 U 'U-U.L-! UV...4vJJ 'U- U'J each individual embankment system and to the conditions of Bangladesh. Until U,lithe riVers arL[e stab UiLzU, a UU1coUnsLtnU V±m,.LL .mu.t LiU -intuinu u elocaue the embankments well in advance of direct attack by the river. RE,B.3ICTT7i INTERNATIONAL BANK FOR RECONSTRUCTION AND DEVELOPMENT INTERNATIONAL DEVELOPMENT ASSOCIATION BANGLADESH LAND AND WATER RESOURCES SECTOR STUDY VOLUME VIII THE FLOOD PROBLEM TECHNICAL REPORT NO. 24 FLOODS IN BANGLADESH December 1, 1972 Asia Projects Department BANGLADSH -SETOR S1UiDY VOLUME V111 - THE FLOOD PROBLEMijI TECHIICAL FREPURT jNO. 24 FLOODS III BAN-GLADE-SH{/ TABLE OF CONTENTS Page No. Suimary I. introduction * L Cause of Flooding ................. , .L Cyclonic Storms ...... @**-*v@@&*-*@ ;4 IIi, Area and I)epth of Flooding *....................Q.......... -, III4 Flood Daraage 0 0 0 0. .0 . 0 0 .¢e@@@¢@ Damage Estimates................................. WAPDA Estimates ....... *.*.*... .. .. *..... 00e 13 Roads and Highways Directorate ........................ 14 Relations Between Damages and Flood. Characteristics ... 14 Loss of Lives .................................. 1• IVe Flood Protection ..................... ,.......... ,.15 Frevention of Flooding .... .. .. ...... 1o6........... Eabankments *D......,*,..............- ..o.* ..... 17 Design of Embankments ...... ................... 13 List of Tables 1. Flood Characteristics 2. Losses to Crops and. Properties. 3. Shadow Price of Rice Imports Replacing Flood Losses 1X. Recapitulation of All Recorded Losses 5. Comparison of Rice Crop Losses ANIEX 1 - Drainage and Flood Control Costs 1/ This report was prepared by Mr. V. Hansen using material contributed by Mr. H. Auffret (Consultant). Annex 1 was preparAd hy R- Mn,-ROn Of Acres Internationa:L (Overseas) Limited (Consulting Engineers). BANGLADESH - SECTOR STUDY VOLUME VIII - THEI FLOOD PROBLEM TECHNICAL REPORT NO * 24 i Each year, close to a third of the 55,000 sq. mile area of Bangladesh is flooded. AltUough thile flaoods uene-fit soirrne areas and thte people have dapted their lives and farming habits accordingly, the floods still damage crops and property, curbtail crop production and sometimes resuit in loss of life. Te.U uncertainty of flooding in terms of area, depth, duration or time of recurrence inhIbits development especially in agriculture. Most of the flood problems result from large flows in the major streams; Brahmaputra, Ganges and Meghna Rivers. However, flooding by smaller rivers, local rainfall, the high ocean tides and cyclone also create significant problems. Flood studies by WIAPDA show that during the 10 year period since l954, the area flooded ranged from 9.9 to I".O thousand sq. miles. The "flood vulnerable area" comes to nearly 26.3 thousand sq. miles or close to half of the entire country. A Control -FloodPlan" prepared in 3eptember 1968 estimated the average annual flood damages to be .5 billion rupees. It is suggested that these estimates are too high and that a more realistic value for direct damage may be in the order of 655 million rupees anually. ii To prevent flooding by the major rivers, only embankments and channel improvement appear to have practical application. Storage reservoirs, to be effective, would nave to be tremendously large and if suitable sites are available, they would be outside Bangladesh. Previous studies have indicated that floodways are not a practical solution to flooding by the major rivers. Pumping plants and sluices woulcd be necessary along with embankments to care for local drainage and to provide irrigation water to areas isolated from the rivers by the embankments. Proper design of embankments must be based on consideration of depth and diration of flooding (with design flood), foundation and construction materials, rights of way conditions, construction and maintenance standards.