DnrVTMFAMT rFP T?R'1P?ATTnMAT BAmv t-Px … · and flood fighting program must be included as an integral part of the plan-ning and imlementation of eembanlrmennt projects. The reDort

DnrVTMFAMT rFP T?R'1P?ATTnMAT BAmv t-Px PYrVJxTcrDTTTCrTIn AMnDT7I17T CED1k4Vfl.Jr

INTERNATIONAL DEVELOPMENT ASSOCIATION

Not For Public Use

PS-13VOL. 9

Report No. PS-13

LAN-D AND WATER RESO-u-KCES SECTOR STUDY

BANGLADESH

(in nine volumes)

VOLUME VIII

THE FLOOD PROBLEM

CONTAINING:

Technical Report No. 24 - Floods in BangladeshTechnical Report No. 25 - River System AnalysesTechnical Report No. 26 - Embankment Maintenance

December 1, 1972

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 theaccuracy or completeness of the report.

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Note

"T'Phe T-mind nnt W2te'r RPeniir-.A RSeentnr Studi -

Bangladesh" dated December 1 1972 was prepared betweenMay 1971 and the simrnnerof 1972 urnder the generalsupervision of the Bank, by staff members of the Bank,,,nA TiAC5 Ld 4-i oa,i +9rd- n1 hol rt

9wm onrcni1 +.avd-° rI1a

UNDP and the Bank shared the cost of the consultingserv,tices The stu,dy s A -.ae 4 1 ia on the+1- .d-ear.-d=

ing that it does not necessarily represent the officialposition of the Government of4' Bangladesh or of the Bank

T',h stud i base mns-lyr on dta co.-U' egv , a ct AUwvprior to March 1971. Although some of the informationcon tair.ned iLfln the4S + AJ 4.u is -u of U- theA essence of. 4i.t

is vralid and it should be useful to the Government ofOILACAi'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 SmTMVVUL2"JJ ±ulliJ VUII'Ji L IU.J~XI -I. TJ I 'JIVIL PIP.O IJB

TTrATTrnxrV TTTTT- mun' V~Tnr%-n D n~T 1'UIV VJ,UI'UL. V IiiL J111-i .LAAJILJ LLL tJU.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-uralproductivity, there is an increasing need for controlling floods.

ii. This Volume including Technical Reports 24, 25 and 26 is devotedprimarily to the river flood problems. It should be noted however, thatin the coastal regions the greatest danger is from flooding caused bycyclone storns. For instance in November 1970, after sufiering unusuailydestructive floods, Bangladesh was hit by an unprecedented cyclone and tidalwave which killed several hundred thousand people and destroyed the assetsof millions of farmers and fishermen in the coastal area. WA1hile somecontrol can be exercised over the river floods, there is as yet no measureto prevent the occurrence of floods due to cyclonic surges similar inmagnitude to that of November 1970. Destruction, especially of humanlives, can only be minimized by an effective early warning system and alarge number of shelter facilities.

iii. Technical Report No. 24 delineates the river flood problen, themagnitude of the damage and methods of flood prevention. Close to half cfthe country is vulnerable to flooding and on the average almost a third isflooded each year. Flood damages are estimated to average Tks 655 millic,nannually. Embankments and channel improvements constitute the onlypractical means of preventing inundation by the rivers. Pumping plantsand sluices wqould be necessary to evacuate local drainage and to provideirrigation water as a substitute for the flood waters which now are reliedupon. Proper design of em1banmanents must be based on consideration of thedeDth, 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 mechanicsand sediment transfer aspects of a river system and their relationship todesign of river training facilities. In Bangladesh, the only feasiblemethod of training the major rivers to prevent vast overland flooding duringpeak river discharge is by construction of embankments. Factors criticalfor 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 theflood stages for embanked river channels are presented. The embankmentswould cause an increased main channel discharge which usually results in

- ii -

increased depth and stage. The increase in stage and depth are dependenton the decrease in bed form roughness in snd bhed channels wh-ich usuanllyoccurs with increased discharge. A combination of bed degradation,channel widening and decreaed bed r - lUd result in decreasedstage for embanked reaches. In heterogeneous alluvial deposits all channelros-secti will not respond in the snme manner. ToH determine stage

response a careful analysis is required. The Report also deals with themovem.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 ofthe privirpJles otined, 11usincg +the nDacca 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-+n +A1 - Mmio rl Dv+; ormoron+^-rnnnV e..±Jr ..k. U a .L'. -V W at t4In . * ......a.j................J............ . . ................ 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 +ti4 nethe

major components of an embankment maintenance and flood fighting program.Because of t+h-1e variety of sz _ nd -x -iA of e.mbanr..ent projects ar.

attempt is made to develop a set of maintenance principles and a typicalorgan 4za 14 nal anA a A4 m mstra"1ve -arrage..nt +1-4 'ou 4-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. UntilU,lithe riVers arL[e stab UiLzU, a UU1coUnsLtnU V±m,.LL .mu.t Li U -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


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 .... 6........... .. .. ...... 1oEabankments *D......,*,..............- ..o.* ..... 17Design 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 Bangladeshis flooded. Alt Uough thile flaoods uen e-fit soirrne areas and thte people have daptedtheir lives and farming habits accordingly, the floods still damage crops andproperty, curbtail crop production and sometimes resuit in loss of life. Te.Uuncertainty of flooding in terms of area, depth, duration or time of recurrenceinhIbits development especially in agriculture. Most of the flood problemsresult from large flows in the major streams; Brahmaputra, Ganges and MeghnaRivers. However, flooding by smaller rivers, local rainfall, the high ocean tidesand cyclone also create significant problems. Flood studies by WIAPDA show thatduring the 10 year period since l954, the area flooded ranged from 9.9 to I".Othousand sq. miles. The "flood vulnerable area" comes to nearly 26.3 thousandsq. miles or close to half of the entire country. A -Flood Control Plan" preparedin 3eptember 1968 estimated the average annual flood damages to be .5 billionrupees. It is suggested that these estimates are too high and that a morerealistic value for direct damage may be in the order of 655 million rupeesanually.

ii To prevent flooding by the major rivers, only embankments and channelimprovement appear to have practical application. Storage reservoirs, to beeffective, would nave to be tremendously large and if suitable sites are available,they would be outside Bangladesh. Previous studies have indicated that floodwaysare not a practical solution to flooding by the major rivers. Pumping plants andsluices woulcd be necessary along with embankments to care for local drainage and toprovide irrigation water to areas isolated from the rivers by the embankments.Proper design of embankments must be based on consideration of depth and dirationof flooding (with design flood), foundation and construction materials, rights ofway conditions, construction and maintenance standards.

BAN4GLADESH - SECTOR STUDY

VOLUME VIII - THE FLOOD PROBLEM


FLOODS IN BANGLADESH

T Tntroduetion

1.01 At one time or another, close to half of the 55O000 sauare milearea of Bangladesh is flooded. Although the floods supply water for aman. andboro riGe crons in some areas and the npeonle have adanted their living andfarming habits accordingly, the floods still in other areas damage crops andproperty and curtail cron production and sometimes cause loss of life. Theimpact of flooding results not only from the actual flooding event but alsofrom. its uncePrtaintv whether in terms of area; depth- duration or time ofrecurrence. Because of its overriding impact, a better knowledge of floodsand nasciant.ed drainageP nrnohlems and of means to mTnnAe them is essential tothe long-run development of Bangladesh.

1.02 This Report descrioes the causes of flooding, the area, depth,duration and frermencv of' flonnrli na the benefits and damages resultingv fromsuch flooding, the available means of managing floods and the need for.q rii t i nri Ilf (i t nd s tudi-ies.

Can-se of Ploo5ding

streams such as the Brahmaputra, Ganges and Meghna Rivers. However, floodingby smller .streams, llocal rainfall, the hiJgh. ocean tiAS ar.d cyc.]oes zalso

are of major importance.

1.04 MaJor streams. The livelihood of the people of Bangladesh is

Padma and Mghna Rivers which flow into the Bay of Bengal. Over the centuries,>.ese h 4. ee riJ.vers hna,v buJl.tL. t he .la± rges' anud one of Ahle luu L. er Lle Ude1 tl.tas

in the worldl. Ranging generally from sea level to 100 feet in elevationtvuq thover ha 1- lower Cf.^r 50 -+ feet), -; A-+ cover rost- _ ngladsk,* V'4. A'4.~. A~J~. UA~4. .JJ ~ /, L.LL %A.LC 4UVVV DJ. £1100 V.L F3C..,LVLU,OL'W..

1.05 These rivers have a total draire ~ area of ~ 600,wOsquare

with only 7.5% lying within Bangladesh. Diring peak flow these rivers4sck---- -. , 4to e mi"ior. c-asecs%Cs(2.5 Vt-.ls Uthe al_l.-"'Wi I-tcord- UX '-he

Mississippi River) and carry an enormous sediment load of about 2.4 billionton anually, greater thai ar,y other river system in the world. Tne conidinedrivers flowi.ng into the Bay of Bengal are exceeded in size possibly only by4.U A _1 _V _ 3 I ._ L1.. -.4 _.^... L_t _e . . I.

Le IAiUCzon TVur- in aeourLs±h 1W1tuI±Ua d.UU ulCu Lungo niver in Airica. -ne estimatedfrequency of recurrence of peak flood flows on the Ganges, Brahmaputra andrPa^ma Rn.Lers are pr-esented In Plate 'L. Tne flood peaks oI the Megnna amountto less than 10% of the combined peak flows of the Ganges and BrahmaputraRivers.

- 2 -

1.06 The runoff of the Ganges and Brahmaputra Rivers is derived fromsnowmelt of the Himalayas and monsoon rains from the lower elevations.The snowmelt flood peak on the Brahmaputra occurs usually in June and canbe the highest peak flow of the year. However, the peak annual floodgenerally is due to runoff from the monsoon rains combined with snowmelt.High flows can be expected any time between about June 1 on through Octoberalthough they are more likely to occur during July, August, and the earlypart of September. Even during this period in any year the river levelmight fluctuate up to about 10 feet. The flow of the Ganges generallyreaches high stages near the end of July and remains high through Augustand September. In some years, the stage declines rapidly during September.

1.07 By mid-July, the flow of the Padma at Goalundo downstream fromthe juncture of the Ganges and Brahmaputra Rivers reaches bankful stageswhich are maintained until the end of September. This is a period whenboth the Ganges and Brahmaputra Rivers are at high stage. The yearly peakflow stage, which generally occurs between late July and early September,fluctuates within a range of about 4 feet -- in other words the highestpeak stage is about 4 feet higher than the lower peak stage. However, duringthe high flood period (for any particular date) the high flow stage couldbe about 7 feet higher in one year than the corresponding flow in another(See Plates 2 and 3). These fluctuations in stages are an importantconsideration in connection with the area.depth and time of flooding andresulting effect upon crop product-ion. Fluctuations in the flow of theMeghna River at Bhairab Bazar appear to be about the same as the Padmaat Goalundo although the flow is onlv about one-tenth as large.

1.08 Table 1 compares the Deak levels recorded at Hardinge Bridge.Bahadurabad and Goalundo for the periods 1954 to 1956 and 1962 to 1970(these are the years for which damage data are available), and gives theflooded areas for the corresponding years. According to Table 1, in termsof flooded areas, the most severe floods have been in 19q4- 1955. and 1962.which is in accordance with the water level recorded at Goalundo andRphadiirhai (Thi s idaitEa e-nrr& ates- wi th t+he u tpr I evel reod natrr ttHardinge Bridge except for 1956). The Goalundo peak flood occurs generallyhitmwen the enfi of .Tnlv anti the hbieinningy nf Spntpmnhpr_ except itt onceoccurred on the 21st of September. The same regularity is observed forthe Ganges River - peak flood between AugUst 19 and Septem.ber 21. TheBrahmaputra River, however, is much more irregular. There has been oneflood in June, SiLr in JTuly, five in August, one in October. As pointed outpreviously, these facts may have a great effect on crop damages.

1.09 Smaller Streams. Many smaller streams throughout Bangladeshcause severe flood problems. Ea-les are the Ti sta A-t-.a -ar Vr--

tributary to the Brahmaputra River, the Kushiyara, Suma ,Manu, Khowai,

River, tributary to the Ganges River and the Little Feni, Feni, Karnafuli,SAnu an Manhar RiverA A_AI_s trib.suta _vry to th Ba of BngalX. _ _ off fromL -As 171vMU sUAL n^L v s X ;zI vs uL Li ws ,y-M wu vii L)C. Dd,r lus W I 1 d . U LX -Vill

these streams is directly related to the monsoon rains. Accordingly theflo-ws arnd stages fluctuate greatly over short per-ods of ti,me durnlg themonsoon season. These flash floods can occur any time from June 1 throughSeptember.

-3-

1.10 Rainfall. Mean annual rainfavl in Bangladesh varies from 6Oinches in the west to 200 inches in the northeast, with most of the countryreceiving 70 to 100 inches. About 80% of the rainfall occurs during the5-month monsoon season, May through September and about 5% during the5-month period, November through March. During the monsoon period extremerainfall often occurs but there are large variations from year to year asindicated in the following tabulation of monthly rainfall during theperiod 1934-69:

Dacca Comilla CtLttagcr- ------------ Inches-------------------

June

Minimum 0 8.72 8.24Mean 13.54 19.44 21.07Maximum 30.28 41.30 37.76

July

Minimum 4.57 5.13 7.28Mean 12.90 17.54 23.54M4aximum 26.50 41.22 52.66

August

Minimum 4.09 5.34 0.11Mlean 13.33 14.59 22.93Maximum 27.75 27.25 42.78

September

Minimum 3.28 2.99 3.33Mean 8.82 ini)In 12.22Maximum 28.12 29.12 29.88

October

Minimum .03 1.06 1.77Mean hL 7 7.89 8.81Maximum 16.70 25.29 22.79

1.11 An indication of the frequency of occurrence of extreme rainfallfor one andl 15-day neriods is nresented in the fnllnwina tabulatinn:

Average interval of occuri-nce (years) 25 25 5 5

Days of rainfall 1 15 1 15

Station Rainfall -- inches

Dacca 6.2 18.2 3.8 13.7

Comilla 5.8 17.7 4.4 13.9

Chittagong 10.2 30.0 6.5 22.5

1.12 Ocean Tides. water levels rise and fall with the ocean tidesthroughout southern Bangladesh. During winter months when river flowsare low, tidal effect extends up the Padma River to Goalundo in the westand as far as Sylhet in the northeast. River flows dampen these effectsduring periods of heavy runoff. Tides are semi-diurnal with a normalperiod of 12 hours 25 minutes. Two high tides and two low tides occurevery 24 hours 50 minutes with a pronounced diurnal variation betweenthe heights of two consecutive high tides. The tides approach Bangladeshfrom the southwest and occur along the westerly side of the south coastabout three hours earlier than in the east near Chittagong.

1.13 In the northeast portion of the Bay of Bengal below NoakhaliDistrict, the phenomenon known as a tidal "borelt takes place. It occursimmediately after low water at rising tide, but does not exist under alltidal circumstances. It is most common and of grentest magnitude duringspring tides, especially in March, April, September, and October.Distortion of the normal deep-water tidal wJave as it crosses the shallowBay of Bengal creates a condition which, from a hydraulic concept, maybe considered a moving hydraulic jiwp. The vertical-appearing wall ofwater, usually less than two feet but occasionally as much as 10 feetin height, moves across the Bay and upstream into the river channels.The bores generally do not damage embankments but do cause localizederosion and present a hazard to small craft.

1.14 Normal tide-water levels are subject to influence by meteoro-logical effects such as wind, variations in barometric pressure, andrainfall. The increase in water level due to cyclonic storms is describedbelow. River flood flows also increase tidal heights, particularly thelow tides. The normal tide range (difference between the mean high andmean low tides) varies from only a few feet at inland stations to over 13feet at Sandwip Island.

Cyclonic Storms

1.15 Cyclonic storms are an important feature of Bangladesh'snlimna+e and have caused great suffering and damnge +t the people and thestructures in the cyclone path. The storms usually form in the southeastportion of' the Bay of Bengal, move ina northerly or nor+-hs+erlydirection and often turn northeasterly or easterly toward the east coastof BnTgladesh * here Ae o ata -f nkno .' re-ia1bility on theoccurrence of cyclones in Bangladesh that date from 1870, and definitely

incomplete information that dates as far back as 1584. Severe cyclonistorms are defined as circulating winds with surface velocities about 54 mph.Approximately 34 damaging cyclones have been reported in the Bangladeshcoastal area in the 100-year period from 1868 through 1967. Thus cyclonefrequency during this time has averaged about once in every three years.However, there have been seven severe cyclones recorded in the period 196othrough 1967.

1.16 Storm winds move at speeds up to 150 miles per hour and causewidespread damage. However the most devastating element of the cyclonicstorm is the water surge. This is caused by a large mass of water atand around the storm center accumulating in a mound higher than ordinarysea level ancl progressing with the storm as a wind-driven storm surge.As the storm reaches the shallow water near the coast of the Bay ofBengal, the surge is intensified as it sweeps inland. Coincidence of thestorm's passage with high or low tides would tend to increase or moderatewater damage..

1.17 Historical data on surge heights vary considerably. Inundationcaused by the 31 Ocltober 1876 ttBakergani ec.lon&' has been variouslyreported at 10 to 45 feet above normal tide level. Storm surges for recentcyvlnnes have been noted to be snme In t+ 20 feet in height_ Thenreticalanalyses of surge heights were made using data on actual cyclones andconsidering the shape and configuration of the RAv of BPngl anrd theBangladesh coastline. It was determined that cyclonic storm surges of 15to 25 feet c-n behe,rnected. t.pr oanhing +he .shore tend to exYpendtheir energy by running up a slope beach and thereby cause inundationto heights even greater +.hn the +--u hei ght of t.. offshor sr.Cyclonic storm surges could thus inundate lands, or overtop embankments,up to elevations of 30 to 55 feet should the surge occur at the time ofhigh tide.

1.18 Reports of property damage and loss of life caused by recentcyclone- have been greatenr than those of ea-lier cyclones. a,-h n-m iS pr1O A

the result of increases in population density as well as the availabilityof more cormpLet repors on Tage- The +ime of occurrence of a cyclone asrelated to the stage of planting or growth of rice influences markedlyt-he amouint of crop damage. rrclone damnge in +he coastal areas ofBangladesh dLring the period 1960 through 1966 has been estimated to beovero . 70n million t-o property rnd mor - h--e than tE 00 ; -1ves ha- b-n

iWe I VV -. V W ==Vv Js.|- V - -_ V V

reported lost. The November 1970 cyclone took several hundred thousand

14. Area and Depth of 1 oo14v. ng0 n- -r--P~~1.. ft10 UA. J'} '4 141

2.01 Sources of imo,in Agnrlrp of the flooded a-reas fPorc VL. . l..JL4 ar 1.4 JLLL o.JL. ±1 0 U. A± Ai gen d. LAOj J L. IA1 .1. LO.L';% 0. 15 L4..

the entire country has been published by WAPDA each year since 1960. EachfieldU UJ-V±s.Lo±n senuds a small fo od ---- --- to 4he oice Wiere

they are assembled to produce a composite map. Much of the information isve-y rough and inaccurate since it is sent in frorm, the field on m,Laps witha scale of 1:1,000,000. These flood area maps do not give any indicationof the depth of flooding.

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2.02 For the purpose of this study, a review of the area and depth offlooding was made from relevant information in the Reports on ReconnaissanceSoil Surveys of Districts and. ubdivisions prepared and issued by the Directorateof Soil Survey, assisted by the UNDP and FAG. The delineation of areas subjectto various depths of flooding was made primarily on the basis of areas thatare or may be made suitable for optimum paddy production during the monsoonseason. This review is presented as Annex 1 and gives information regardingnormal flooding as observed by land classification personnel in the field..

2.03 WAPDA Flood Area Studies. During the 10 years, 1954 to 1956 and1962 to 1968, the area flooded has ranged from 9.9 thousand to 15.0 thousandsquare miles. (See Table 1). Analytical M1ap III delineates the areas floodedduring the 6-year period 1962 to 1967 and gives some indication of the frequencyof flooding. Studies of the above information as well as other fragmentarydata indicate that there is an area of about 5.9 million acres that is floodedevery year. This area is flooded almost entirely by the three major streams whichflood an increasingly larger area as the size of the flood flows increase.

2.014 Although the annual flood-affected area varies between about 5.9 millionto 9.6 million acres, the area subjected to floods over a period of years is muchlarger. This occurs because the localities affected from year to year are notthe same and different areas are inundated depending on the distribution of rain-fall, coincidence and, magnitude of river peaks and tides in some areas. The"flood vulnerable area", that which has been flooded in one year or another, comesto nearly 17 million acres, out of which about 114 million acres are cultivated.

2.05 The area flooded in addition to the 5.9 million acres flooded everyyear results from one or a combination of factors: (a) greater runoff and co-incidence of runoff from the 3 major rivers; (b) flash floods on smaller streamsdue to intensive short duration rainfall. (c) intensive rainfall directly on theflooded area; and (d) high groundwater table which in some places is above theground surface after heavy rainfall. Analytical MIap III shows the area floodedevery year and that flooded less frequently, based on the lJAPDA flood maps. Theabove areas do not include the coastal region where some 4,000 to 5.000 sauaremiles are flooded each year primarily at times of high tide.

2.06 Land Developmnent Unit Flood Estimates. As previously indicated theestimates of Annex 1 are based on observations and interpretations associatedwith the land classification surveys. This valuable contribution gives informationregarding deuth as well as area of flooding. The 39.000 square mile area con-sidered was found to include approximately 2{r highland, 36;6 medium highland, 15%medium lowland and 15 lowland. The highland constitutes land that generally isintermittently flooded by less than 1 foot of water during the monsoon. Themedium highland is flooded to denths of 1 to 3 feet- medium lowland 3 to 6 feetand lowland flooded to more than 6 feet of water. According to these estimatesan area of abolt 26-nnn squrare miles normally is flooded to a depth greater than1 foot. This does not include the flooding in the Chittagong Circle area. Thisis a ,mich larger area than that indicated bv the WAPDA mnaps. The prinrcipal aresof apparent discrepancy are:

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- along the district boundary between northern Mymensighand Sylhet, where the composite indicates greater flooding;

- in the Chalan Beel area where the composite map showslittle flood damage but

in the districts of Kushtia, Jessore and Ehulna where noflooding is shown on the composite map.

However, these differences are largely explained by the fact that theWAPDA surveys concentrate primarily on unusual and related damages.

2.07 As indicated above, data regarding the area normally floodedis difficult to ascertain from existing data. Even less is known aboutthe normal depth of flooding, the duration of flooding and the time ofoccurrenceof flooding. The frequency of flooding of various depths, atspecific timnes of the monsoon season and various areas is not available.However, from a cursory examination of available hydrologic data thevYri,qtnion in depth, duiration, and timnng of flooding in rmmrh of thearea is large. Some of the indications of the large variations which occurare as follows:

U- I Ti ah flemi'q -.̂f PsHmin :+. r^.nli,ntirn tn+. -nir Myna rf f'lnnvi

season varies about 7 feet from year to year. Therange is even greater +fi.er upstream on the 3 majorrivers.

(13) Flood peaks on Brahmaputra can occur any time from1.,,,, 1 to~ ^to,4--,a, 1, .an 4he, flcvu+o in 4,'U is4

more rapid and of greater depth than at Goalundo.

(c) Flood peaks of smaller streams can rise and fall 10+vo 1 feet t,4+hl a Let? days ard can 0cc,,, ar,. 4-42

from the middle of June to the end of September.

(d) Intense rainfall can occur during several months of theuonsoon season. Fr inst. . ace at tu rlJlJa, .i 4- a fre=quency of once in five years, there can occur a seven-dayr_44arfl'l _of rir.e inches_ ir. May, '11 inah_ in J.e, '1 4. aJ..J.J -.Li. J.J. &"414.1 _L%%jU &.I4.L 1i , AI.LI. .L.,AJtU, O .411 .J"LU4 , L~4

inches in July, 10 inches in August and nine inches inSkepteuber. These 4. Ii-atonrainaa.ll.1 cau.se severeinundation particularly in the lower areas.

-8-

III. Flood Damage

3.01 The "Flood Control Plan" prepared in September 1968 by the PlanningDepartment, presented the following estimated average annual flood damages:

Million Rs.

Damage to crops 1,200Damage to cities and towns 2,000Damage to roads and canals 300Indirect losses 1,000

Total Rs. 4,5oo

These are direct damages and do not take into consideration the losseswhich occur because of crops not planted due to the regular occurrenceof deep flooding or the threat of occurrence of such flooding.

3.02 Simple consistency tests regarding the above estimates suggestthat they are too high and that a more realistic value for total damagemight average about Rs 675 million annually. 1:urthermore, it may be hotedthat the floods also serve a beneficial function - they provide waterutilized in crop production.

3.03 Three main sources of flood damage data are available: The Reliefand Rehabilitation Department, the Agricaltural Directorate and WAPDA.The basic data for preparing the estimates are collected by the Relief andRehabilitation DeDartment in order to deliver grants for emergency repairsand loans, and by the Agricultural Directorate for rehabilitation purposes.No detailed flood damage data are collected by WAPnA.

Tinmage Estimatps

3=XN Tvnpes of T)nmqrk The diirec,t. qrir-.iitiurq1 rdamcg rPecorded1 is-with respect to the Aus crop and the jute crop (due to early flooding in.Trne-Tiulv)- annei +.hp .imŽn crop (.Til-y to Sepn+ember floods. Tittle inor-mation on flood resistance of rice can be found in existing reports. Thefl.l growmy+th (a heig oh+f 2 9 feet) of Alic C! rea:hr in ir nd June Tf'

the depth of flood water is higher, damages appear after two or three daysof submergence an.d ncrease rapidly wher f+-- . 3-bmergence in still waterfor five days causes a crop loss of 40 to 50%. However, since the crop is

Cl. 4nS JtJC ripe i U IAlJ , floodingJS.L.l6

CIA.¼ .case Cltl dJJarae

3.05 ~ M" Asi o.w.avmrresistan+v to fo9n hntaslne

Aman, for which damlages seem to appear after 3 days' submergence in stillwater. MI . .e depth o.f -floodAing that causes subr.ergence 4. relative to 4the

height of the crop during the growing season:

1 foot (even less for seedlings) July-August1.5 feet August-September2.5 to 3 feet September-October

After 5 days of submergence, damages are almost complete during any ofthese periods. Broadcast Aman, however, is very resistant to flooding.Its growth rate may reach 6 to 12 inches per day, and continue up to adepth of flooding over 10 feet.

3.06 Indirect agricultural damage generally is not recorded. Forinstance, there may be lower yields induced by the delay in transplantin,the Aman crop, or due to the impossibility of growing transplanted Aman,when the flood recedes after mid-September. (Transplanted Aman may thenbe replaced by rabi crops.)

3.07 Apart from agricultural damage, other damages recorded aremainly to dwelling houses. Ten of the principal towns have flood problems:Dacca, Faridpur, Madaripur, Gopal Ganj, Tangail, Dinajpur, Bharab Bazar,Serajganj, Habinganj and Sanamganj. But, the urban population is ratherlow (4.6 millioni inhabitants out of a total population estimated at 72million) and damages to dwelling houses occur mostly to farms in smallvillages. Damages also are recorded for roads and bridges and otherfacilities. However, the agricultuiral damage far outweighs the damageto dwellings, roads, etc.

3.08 Table No. 2 shows the comparison of estimated crop losses (riceand jute) from 1962 to 1970 according to the two main sources of informa-tion. When the damazes are low, the Relief and Rehabilitation Departmentoverlooks them (1963, 1965, 1967). Eccept for 1964, when both estimatesare similar, great differences can be seen. In 1966, for instance, theRelief and Rehabilitation estimates are higher than the AgriculturalDirectorate. The latter's estimates were higher in 1962, 1968, and 1969.A large difference appears in 1969.

3.09 The Agricultural Directorate's estimates are more complete, andprobably more accurate. Therefore, the revised estimate of total losses wasobtained by- adding to Relief and Rehabilitation estimates of damages todwelling houses, cattle and losses on "other accounts". the agriculturaldamages estimates done by the Agricultural Directorate (See Table No. 2,Col. 6). As the damages stated are mainlv agricultural, the 'WholesalePrice Index (food) was used to get comparative annual values in constantprices. This is not quite satisfactorv (the Agricultural Directorate usedmarket prices a-t the grower's level), but the 'Wholesale Price Index is thelongest available series. This approximation is auite admissible; in viewof the inaccuracy of basic estimates.

3l10 n A sPonnda nne+rAntjn rmint. hp donp tc nomnlete nnuia l valneq. ASfar as the whole country's economy is concerned, the market values donot reflect the true losses. It is necessary to import rice to replace

- 10 -

the lost crops, and for all these imports the shadow price of foreigncurrency has to be taken into account. Table No. 3 compares the ricelosses and the corresponding imports for each year. (Admitted thatthe imports for the 1962-63 campaign were the consequence of the 1962losses that consumption follows production, with a six-month delay.)When the losses are more than the imports (1962, 1964, 1966, 1968), itis necessary to apply the shadow price (double the official rate -Rs 9.5 for one U.S. dollar instead of Rs 4.76 for one U.S. dollar)to imports that are the consequence of flooding. This means the stateddamages have to be raised by Rs 78 million, Rs 47 million, Rs 67 millionand Rs 44 million, respectively, for these four years (1969 prices). Forthe other years the portion of imports from abroad determined by floodingwas calculated and the shadow price was applied to his part. In fact,after converting the current prices in constant 1969 prices using theWholesale Price Index for food, the shadow price was applied directlyto the values of imports deducted from the statistics of foreign trade.(See "Economic Survey" - 1969-1970, pp. 25, 28).

3.11 Table No. 4 gives the total recorded losses with the correctionsmade. Because of the inaccuracy of the data-collecting process, thistable can give only rough estimates. Direct annual recorded losseswould be between 600 and 700 million rupees. (On the same table thecost of road repairs was added for 1968 and 1969 floods). Crop losseswould represent roughly 85% of this total. As shown in Table 5 themaximum recorded rice crop losses (1,105,571 tons in 1968 cleaned rice)represent one-tenth of the total rice crop production for the same year,and the recorded losses from 1962 to 1970 on an average 4.5% of the annualproduction. More than the absolute level of damages recorded in thistable, it is felt that the main interest of the table is to give a comparisonof annual damages,which have to be linked with the intensity of flooding.

3.12 It is quite probable that crop damages have been overestimatedparticularly when the flood was very severe. Two elements justify thisfeeling. One, because damage estimates bring relief and rehabilitation,it is probable that people not belonging to the damaged area are puttingpressure on the agricultural union officer to be considered as victims.Along the same line, it is certain that farmers try to overestimate theirlosses to get more relief. One example was stated by the Acres GeneralConsultant. After the 1968 floods in Karnafuli Valley, when officialswere revising the damage estimates, they found that the stated damagedarea was larger than the total cultivated area.

3.13 Dr. Fazlul Huq, WAPDA, Director Land and Water Use, has donerevised damage estimates for specific feasibilitv stdldies (2handniirproject, for instance) by comparing crop yields of affected and non-affented areas by samnle surveys. HTe has found that the nvernge v-ieldson which the union agricultural assistants apply the percentage of damagesnrp" uinyll overe.stimnt.Pod Thesa.me holds true for the percentage ofdamages. We can add that it is now impossible to separate flood losses

1- 1 -

and losses due to heavy rains during the monsoon season. In certainareas this second type of loss may be important. However, the totalsite losses stated as 4.5% of the total yields do not seem very high.We think that another element might counter-balance, at leastpartially, the overestimation done in badly affected areas. Possiblya lot of small losses are not recorded either because the farmers orthe union agricultural assistant are not aware of these losses, orbecause they think that they cannot get rehabilitation anyway.

3.14 For damages to houses, the total results given at the countrylevel are not homogeneous from one year to another. The annualaverage value of losses for damaged houses is proof of this fact:

NUMBER TOTAL VALUE ANNUAL AVERAGE VALUEYEAR OF OF OF LOSSES

nLAMAGFf T-nTHSES D5A nAMAGrE, PER nLMArFfn nT4TTE (RS).

1962 197,333 39,466,550 200

1964 222,729 26,545,724 110

1966 69,659 13,931,925 200

1968-Tin-Tllil -r IT 1C9 09)3 6 ARI 750 760

October 115,915 14,441,95o 125

1969 131,221 16,473,513 125

.r.JSPeat;mes da a is prepare F n a ccord-a. e *-44 te + a- c values t v V .the union level, which does not seem quite satisfactory. (For instance,

an average damage value is applied to the total number of damaged houses.Tn. -6an 1966 ave.age value of .00 Pw was uI sJ .4 19 .70EA foLte or

putations now in progress, an average value of 300 -is was used, for totallydmaged~~~~~t houes 1d10 s o partvi-alo damaed huse.

3.i1 .s..~ it WLs .J'.j 1968LJj Lies reprsn a 6 Lcent of ltiheA total.

recorded damages from 1962 to 1970 (constant prices), these damages havea greai 4nirtnnaan u

1h, -,-l an,.-,, awe. a n.. acco.Lt fo r

a J.C . AU.&JJ L-UCL t~IL% .JLL UVO&~ U64" J. 0. C.LV *LS, ULLjSCJ 0.L VLJLL i J.J J.%J 1 U.A6A"LJ L4V

million Rs out of an annual average of 60 million. It is, however, impossibleto Ute.LJl W. Lu U.L -e val-ue4. o 0.4. e I oLsse sUD W.LUhUUU roreIZ detai.LedU st-uiLUs. * L '1fly

case, the magnitude of these losses is not at all the same as 2,000 milli'LonRs per year, the aUmaduages two ci-:ties and tow:ns as stuated in "iLoodU blnrOl r.Lanl

- 1968", page III - 2. Even if we understand that these 2,000 million Rs4- ke int+ accont wide nanan, no (tra.spo.r.+t s e, srtior fa; no

commercial activities, factories and buildings) this figure is difficultto uUderstUnd.

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WAPDA Estimates

3.16 Data compiled by WAPDA are published in "Annual Reports on Floods.'The data published, by the Agricultural Directorate and by WHAPDA on the 1962flood were compared in detail. Although the basic data are supplied by theAgricultural Directorate, WAPDA estimates are quite incomplete for Aman andjute crops, and losses to sugar cane, Kharif vegetables and banana are noteven stated.

flata stated bv: Azricultural Directorate wAPDA--- (Millions Rs)-----------

Aus 152 .85 152 .85

Amnan 391.227 254.71

Jute 56.87 56.85

S3xgar Cane 16.Oo49

Iharif vegetables 3.714)

Banana 39.396

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3.17 As far as Aman crops are concerned, the following estimates bydistrict are available:

Agricultural Directorate WAPDA DataDistrict Data (Millions Rs) (Millions Rs)

Mymensingh 76-808 55.52rlhet 88.666 36.75

Ranmpur 25.525 3.25Bogra 43-419 19.58Pabna 13.283 63.69Dacca 47.797 60.42Raishahi - h.89Faridpur 65.729 10.61

Total 391.227 254.71

3.18 Tn. 1961L. it is ouite the same!

Agyricultural Ralief &Directorate WAPDA Rehabilitation

nata nata fData(Rs) (Rs) (Rs)

Rice & Jute croplosses 1).r0 Al85 Air) 10 15 7,1 6 7,940 158 I 0.

Total crop losses 158,355,120 198,381,000

In 1968, dataStated are:

T.Potval losses of cleanedrice

Acr i ml l +i. IJA DPfA

Directorate Data

tons tons

Aus 515,852 515,852iILd.I1 I , L4-L.L5 46J, 8 0.

Boro 2,304 2,305

Total 1,105,571 98h,960

Ju losse iU,it InDU JLt- ).1U Lcu'Ltu± vuraL iL reUc torabe VVIA

nRo^ Z oR n nRo! An

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3.19 WAPDA is stating only very partial information for a few years; forother years, no damage data is recorded. Perhaps by centralization of allrecorded damage data and close coordination with the other agencies involvedWAPDA couldpresent a more complete estimate of losses.

Roads and HigEhways Directorate

3.20 The following evaluations have been made for fiscal years 1969and 1970:

Year Repairs* (Rs) Necessary Improvements (Rs)

1958-1969 26,134,718 36,728,0721969-1970 29,136,648 11,797,896

* Including emergency repairs.

Although the granted funds are comparatively low, this does not mean that thenecessary repairs are overestimated. The normal budget for maintenance,including repair of flood damages, is an average of Rs 20 million per year whilethe annual funds allowed for improvement of existina roads and construction ofnew projects are about 10 million. These estimates for repair of road damagesare as satisfactory as possible.

Relations Between Damages and Flood Characteristics

3.12 Comparing the annual damages stated (see Tables 4 and 5) to the floodcharacteristics gives useful ideas about the type of flood frequency analysisthat may be done. Those flood characteristics having the main influence onflood damages are:

a) The deDth of flooding. This may be represented by the peaklevels at certain key stations, mainly Bahadurabad. One cansee that, of the most severe floods according to the extentof damages (1954, 1955, 1956,1962, 1966, 1968 and 1970),five correspond to the highest recorded neak levels atBahadurabad (1954, 1955, 1956, 1962 and 1970). The 1966 floodwas certainly far less severe than the 1954, 1955- and 1956floods because it was mainly localized in the Mymensingh andcvlhet tditrint-q The damage data stat-ed, however, is notcomparable since more data has been recorded within the lastfew years. (thJ JS true for the 1968 and 1970 floods as well.)

It appears that for anry flooding season, damages are alwayssevere when the Brahmaputra peak level at Bahadurabad exceeds65.nn .DTm (two feet above danger level).

b) 1he season- of flooding. .h.e season e -lams why the 1968 d-mages,due mainly to two Brahmaputra floods, have been so severe,

alQhouth uhe peak llevel1s recorded at Baladurabadd w-eree lower by1 to 1.7 feet than the peaks of the other big floods. A difference4n water l eve-l of one to VwLJ feet. expa V a Uins thLbe d-Lf ferences of

aamages from one season w anoiuner. mLis is in acCorualIcUwith the resistance of the rice crops as described earlier.The explanation for the 1956 damages is exactly the same; itwas a very early Brahmaputra flood.

c) The duration of flooding. The duration itself may explaincertain crop damages even if the depth of flooding is nothigh. It may have an indirect effect--the postponement ofcrops giving lower yields or even the impossibility of growingcertain crops. The duration of flooding, however, is notindependent of the peak level. Along the main rivers for whichwe analyzed these water levels, the peak levels caused asubmergence of riverine lands, generally longer than five day3and exceeding a depth of two to three feet. These characteris-tics are very dangerous for rice cultivations. The depth-durat;Lon frequency analysis will also be necessary to explainthe damages occurring around the fringe flooded areas of largeand small basins.

Loss of Lives

3.22 Loss of lives is stated by the Relief and Rehabilitation Department.They have been the following for the period 1962 to 1969.

Year Loss of Lives

1962 1771964 101966 391968 2211969 77

The magnitude of these losses is very small in relation to those stated forcyclones.

IV. Flood Protection

4.01 Until now the people of Bangladesh have adapted to flood conditionswith very little modification of their environment. Cities, villages and home-sites have been located in higher areas or on built-up mounds so that they areinfrequently or never flooded. Rice varieties are planted which take advantage:of the normal flood conditions at dif'ferent periods of the monsoon season.By exercising more control over flood conditions it is possible to reduceflood damages. Besides direct damage to crops, floods hamper rice productionin a more fuudamental way. In deeply flooded lands (over 15 feet in the.Mezhna Valley) farmers cannot grow rice. On lands that are flooded from 3 to12 feet they can grow only low-yielding broadcast Aman rice. Where floodingis from 1 to 3 feet. farmers grow hizher-vieldinq Aus and transnlanted Amanrice but they must accept risks from occasional higher flood or from droughtand they do not generally use fertilizers or improved seed effectively. Trtmany instances, because of the risk involved, farmers plant both B. Aus andR. Aman to insure some production in case one of the crops is lost due toflood or drought -- a form of insurance which carries a substantial cost.

- -I6 -

4. U iLUJI J-. LUUUo pIrkt: UI1 5 benefits ab W-l.l as cU6s'. IU Ls

essential for these benefits and costs to be clearly identified in specificcircumsta-ces before de'ucisions to invest in flood protectrion re made. Inparticular, in providing flood protection for agriculture consideration must begiven to all phases of water management, inciuding irrigation and drainage.Fbr instance, if embankments are constructed to keep flood water out provisionfor drainage also must be made to prevent internal flooding due to high rain-fall. Farthermore, it must be recognized that elimination of flooding alsoeliminates irrigation water so that a replacement supply must be provided.The impact of flood protection on fisheries must also be analyzed. If completecontrol of the water is afforded, the incremental costs of providing winterirrigation also are generally small. Flood protection projects designed inorder to be effective must involve many disciplines including engineers, economists,agriculturists, fishing biologists and many others working closely with thelocal officials and farmers. In addition to the ordinary engineering, economicand social aspects the considerations relating to the possibility of loss oflife due to flooding are primary importance.

Prevention of Flooding

4.03 Physical plans for protection from floods fall into five generalcategories: (1) embankments for containing flood flows; (2) floodways forthe passage of excess flows past critical reaches of a stream; (3) channelimprovement and stabilization for improving the alignment and stablizingthe channel, thereby increasing the flood-carrying capacity of the main riverfor navigation, and for protection of the embankments; (4) storage reservoirsupstream and on tributaries; and (5) pumping plants and sluices to evacuatelocal drainage. Any one or a combination of these methods could be employedin providing flood protection. T[ prevent flooding by the major rivers(Brahmaputra, Ganges, and Meghna) only embankments and channel improvement(items 1 and 3 above) appear to have practical application. Storage reservoirs,to be helpful, would have to be tremendously large and if suitable sites areavailable they would be outside Bangladesh. There is little likelihood ofdeveloping surface storage which would be of significance in curtailing flood flowsalthough this possibility should not be completely eliminated, especially on theBrahmaputra River. (On the other hand there is a good possibility that storagereservoirs would be the best method of augmenting dry season flows if necessary.)

The rposqsihilJ.y of utilizing vast underdeveloped groundwater resources inIndia to reduce flood flows also has been suggested and should be explored further.

Preus s+-tiide hqverA i nrli r.t.Pef that. flootways are not a nractical solution.particularly forflooding by the major streams; however, it probably would notbe desirable to confine +he flood flows of the Rrnhmanputra/Padlma ri vers to asingle channel throughout their length. Of course, pumping plants and sluices

-ul ben r.ec~nessary nI^ri(7 xAnh embahnhem..e+t +x%onnar fo%r loc-al tirinagea

1. oi, Aq A4 .:s.,A Y%- crr- iiQl7r 1 ernl rni r I 1nf l o n i I I trsn:mc ri;c no,&+ vq %S5S:r-. ZL l ocamainly within Bangladesh result in severe flooding in many areas. All of

LtheU J..LVtA f Ulood ctro U..J.eIIho U o-'d b applicable. v preen '' Vh the

ocean tides embankments and associated works will be needed.

- 17 -

4.o5 Existing Flood Control Facilities. To date, 15 major floodcontrol scnemes nave been undertaken, of which the following ha-ve beencompleted:

1. Improvement of Gazaria Ichamati River.2. Re-excavation of Ghungur-Saida and Burinadi in

Comilla District.3. Comprehensive Drainage Scheme for Faridpur District.4. Improvement of Old Dakatia and Little Feni River in

Comilla and Noakali.5. Prevention of Flood in Feni Sub-division in Noakali

District.6. Dredging the River Gumpti.7. Dacca-Narayanganj-Demra Project.8. Brahmaputra Right Flood Embankment.

4.o6 Of the above, the first six are primarily drainage projects involvingthe dredging of the river bed, river training works and loop-cutting. Theseprojects together have benefited about 627,000 acres of land. Schemes 7 and 8involved embankments along the river banks to prevent flood water from damagingthe Aus crops. These schemes have prevented flooding on a total of 631,000acres.

4.07 In addi-tion, seven major flood control projects are currently underexecution, including Chandpur Project, Coastal Embankment Project, Gumpti FloodControl Project and a Comprehensive Drainage Project in Noakali Sadar. Theseschemes will prevent flooding on about 4,200,000 acres, of which about 3,000,000acres will be protected from inundation by saline water. In addition to theforegoing a large number of minor irrigation and drainage schemes were executedunder the Irrigation Department and the Works Program. Furthermore, individualfarmers and groups of farmers have constructed low embankments and other minorworks in some areas, especially in the coastal country to prevent inundationof tidal waters.

Embankment1/

h.o8 As previously mentioned, for the major schemes embankments afford theonly practical means to control flooding. This is true also on many tributariesand distributaries of the major streams as well as other smaller streams. Ofcourse, along with the embankments in most instances there is a need for pimpingplants and drainage sluices to evacuate local rainfall from the embanked areaand irrigation works to provide a water supply for the crops, good management ofthe irrigation-flood control-drainage system, and adequate maintenance so failuresof the system are minimized.

4.09 on major streams such as the Ganges, Brahmaputra, Padma and MeghaaRivers, the embankments must be set back from the river banks so that they arenot vulnerable to direct attack by the river current. The establishment of

1/ See T.R. 25 for a more detailed discussion of consideration affectingembankment design and location.

- 18 -

se-bac~k 3-i t+.nnP.s nof the- filoroi .nmhan1rimPnt.P f-roTn +.he -v-iur hank is- affpet-'+ri

by many interrelated variables and requires careful consideration. Finallocati+on must give consideration +t foundation and rights-of-way conditionsas well as vulnerability to attach by the river. If the river flood plain,bet-een the ver cha-nel and the p oexbanivent, consists of essentiallycohesive silt-clay soils to depths below the river bed it may be feasible tomocve the e+1Aanmhan-a.ent t-o ud-r +hi-n onefI,urth m-'le of sr.allera rivers cihw" as theDoleswasi and Kaliganga, and within one-half mile of the Brahmaputra, Padmaand Meghna R-ivers, w1,he7n moren rosni ra cnd soils Cn7 +for rver rbank and

6- 8h _ - ,. ,,,,.e _ siie| _ _% ''V|||^;.- - - - - -. - -,

the flood plain, these distances should be doubled.

4.10 Observations of the major rivers in the area show that their banksarue Subject al=-,ly tno -hea,vr eros onrA a -n ,storically r,,o 4 r shl-f+s Ihavrn

occurred in the location of their channels. Shifting of the BrahmaputraRiver '-.e- has b- +^. be II to. thc-4-.-44e s.ou4 UiAiaeSt-. At thc

confluence with the Ganges it is thought the Brahmaputra has generallya L, uLLL.e1 UA.L A.I±LIJIe. 1±1)1ULI I A.4..L ±,.L1 4. ~ Li4-U lVd ".L ±IL-LgraO ULVIIJ. ±i1istablJli_zeUd, b'utu f-u>hier north it _ w-l.l. continue itUs Wes=.ardc r,gr-_ in4 Th

location of the Padma appears to be governed by two node points at Ancraan" Bayah-u1l wIere te riv is ret r.LcLeUd LJy dee pLLU siut L a .Lay dLpJosiLO

which resist further bank erosion. Barring the recurrence of t"catastrophic"eventis suchll as severe eartUhqu 1.akes, eIL.Jan11Iunt a.long- U £.J4- are considered

secure from annual river attack if they are located with the proper set-backdi4stances J-.di-ted above.%ALa Ll.Iu A LL" 0.1 LI0.L -4ULI

4. Xi J4sto4-- iclly,-ca 7,--, 4-- --.- s4ome sectlonsofL4-4e-, - -1-, --. 4 -a anAL4 IiJ.. VAJA. .L L.-01.J , LJ.Lf. A 'O_.V0lYJ -LIi DJ IL V. l .LL'.J.i J..A ii UlIA ;J.V i .L- LU .J1- .il C. Uiir

Padma Rivers of as much as 2,800 feet have occurred in one year, in vulnerableareas di'scussedu above. A set-back ofI 1 MILle `Ln suchil reachiles would a'L'lowsufficient time to provide for any threatened attack as well as provide lowervelocities nextu to the eIlle If * locadL erosion dUue utou lat.eral movemCen'tof' the rivers should recur there would be, with the set-backs, ample time forrepair Or even f__or Ofn_ne…_&.'I-.-- r-_ t'_ __: ___A_ r_ 1 1

X tSUdlI UL tS Cl 1 U t; J:I VUUt;IJi±Ull UII IICW ;: U.L IALlltf 0 1 C1IlUl1ull-itll IJ A

1/Design[ of i_i2UanoLnenUts

14.12 IriiLiankments shE0ouLdU be dUesiCgn7eud so 'Uh--t -withri des'Lvpn flood conditions±they will not be overtopped or fail. Proper design must be based on conesideration of dephn and duration Ol floouTng (wihn uesign flood), founuaLionand construction materials, rights of way conditions, construction andmaintenance procedures and past experience in Bangladesh.

4.13 Design Flood. Rarely in low-lying areas subject to fiooding is itpractical to provide protection against the largest flood which would occur.Generally some risk-must be accepted in the selection of a design flood.The degree of protection afforded is dependent on a number of factors includingpopulation density and possibility of loss of life, value of property subjectto damage, the cost of providing flood protection and intangibles such asgeneral security and well-being of the people.

1/ See T.R. 25.

= ~19 -

life in the event of embankment failure is of utmost importance especiallyin suchI a LLL-,k-po 'ateJ-...Ld. U-. ara1 as 4ci. Special csetn

this possibility must be given for each embankment project being proposed..

Lac_ Where loss of life is not likely to occur the ontimal design canbe determined.by comparing the total annual cost of embankments and theannual losses nrevented by them.. However; in areas sub-iect to deen floodingand, where values are high the practice often is to provide protection beyondthat which ran he justified. on a strintlv economic basis. Tn the TJnited.States the decision regarding the degree of protection is based onconsitiprntion of a qst.andard nrnipet. floocL The design floodi for a narticiLlarproject may be either greater or less than the standard, project flood.denending on economini faetors and other nractieal considerations includingintangible benefits. The standard. project flood.is a hypothetical flood.devploped from a detailed t-.udV of Tnst meteortn1nPiA1 n nd fflood conditions,and,combining of events in a way considered. plausible from a meteorologicalviPwinni nt. whirch Would hnvp a resonable nrobhnhility of nornilrrPn Ce.

To develop a standard.project flood.for the three major rivers would requirea com.nplete .hyidrol.ogic ne+work th-m1cPhnii+. t.he nqs_ r to collect rainfallIsnow pack, and stream-flow data.

4.16 Flood Frequency Analysis. For the major streams of Bangladeshthe desigrt. flood. in thne Upast MBrahmnrmnt Pi.lit P_n-n1 andeJ 0.JA r1A P-ro

has been based. on a flood discharge with an average frequency of occurrenceof once i100 years. p Tstream on the BrTh.aputra in India the largestflood of record. has been considered. to be the design flood.. In Bangladeshthe0 0 est.JLhfl J. .¼lOC!=year..AlJA 5. .foodS.~l.0SJ is 0osierl greate thar.f the±4 î m.fl ood.ItAj*.. t..

of record., probably due mainly to the short period. of record.. The use of agreater safety factor may be justified in view of the great mnPnitude of t.herivers-and the dense population. Hiomever, this calls for detailed studiesas suggestedi 1 TR. 25f

4.17 In developing the design flood. on a frequency basis the lengthof discharge records is of great importance. Since marn of the records inBangladesh are Of short duration, efforts should be made to develop thebasic frequency curve for the groups of rivers that have similar flood-producing characteristics. For example, the Hardinge Bridge flow recordson the Ganges River are of sufficient length to define a good flood.-frequency curve; records on the Branmaputra are not. If the Ganges andBrahmaputra River basins are homogeneous with respect to flood-producingcharacteristics, the two rivers wi-l have similar frequency curves ofabout equal slope or steepness. Although these two streams are nothomogeneous in all flood-producing cnaracteristics, a regional statisticalapproach tied into long-term records may be a better alternative thanextrapolating short-term flood records.

- 20 -

4.18 In developing the design flood, consideration must be given tothe increase in flood, depth due to construction of edbankments. Studiesfor the Dacca Southwest study indicated that this is not of greatsignificance when smali polders are constructed. but it can be significantif double embankments are placed. along many miles of a stream. (SeeTechnical Report No. 25).

4.19 Embankment Design. The crest of the embankment should be set ata level equal to the design flood level plus freeboard. The freeboardshould provide for wave runup and imponderables. The wave runup should bedetermined from a study of wind fetch, wind velocities and wind directionexpected at the time of maximum flooding. The lxmponderables would providefor possible errors in basic hydrologic data and in hydraulic calculations.

4.20 The crown width of the embankmnent would depend primarily on road.requirements with consideration to maintenance as well as general publicuse. The side slopes should be selected after a study of foundationmaterials and materials available for the embankments, depth and durationof flooding and expected construction and maintenance procedures. In thepast, because of organizational difficulties involved with head-basketlabor, it has not been possible to follow procedures for compaction called.for in specifications. However, the General Consultants to WAPDA as wellas project consultants with long experience with embankment construction inBangladesh (Coastal Embankments, Brahmaputra Right Embankment and Chandpur)agree that adequate construction quality can be achieved by "semi-compaction"--spreading and breaking of clods, without use of sheepsfoot rollers.wnere mne new construction can undergo natural compaction through severalflood seasons before it is put to use. Semi-compaction would provide anadditional factor of safety over the good compaction experienced in thepast due to natural causes such as the heavy rainfall and flooding on bothsides of a period before final embankment closures are made. The soilsappear to be well-suited for emfbankment construction. Allthough more than2,000 miles of embankment have been constructed, there have been no failuresdue to seepage or poor foundation conditions. Experience indicates thatembankments along streams (no direct ocean exposure) with 3:1 side slopesgenerally are adequate. Hlowever, as previously mentioned, adeauate testingof construction and foundation materials and proper design must be made forall embankments.

4.21 Drainage* The principal benefits of embankments during themonsoon season will result from conversion of existing low-yielding floatingrice or no rice to high-yielding transplanted varieties which cannot with-P+nA iinrinM±ion for more than a few days. The embankments would prevent

inundation from the surrounding river, but rainfall still would. causeflooding of a large area w. ithin the Dolder if water is not evacuated bypumping or tidal sluices where appropriate. The area of improved ricedamaged wonild vary frnm year to year depending on the intensity, durationand time of occurrence of rainfall and the evacuation or drainage capacityprov"c. m, -A r-nngA mnnnirit.v nrovide.d must be determined on the basisP~~~M _ Vf V .. A _ g -a

of a comparison of the incremental cost of evacuation and the increasedvalue of crp productio-n as a resunlt of the evacuation.

4.22 There is adequate rainfall data to permit such an evaluation.However, in many cases there is not adequate information regarding depthversus area of flmOding. Gno to.nnnaprnnhic mnns are needed to Dermitdevelopment of such information.

FiloodI Characteristics

GANGES -HARDINGE BRIDG:E BRILHMAPUTRA - BAHADURABAD PADMA - GOALUNDO

Year Peak above or Peak above or I Peak above or Flood areabelow danger Date below danger Date below danger Date (square miles)

level level level

4W7T~~ 1 1 63.0 PWI) t 27.0 FWD _(feet) (.feet) (feet)

954__ 4-4 __30-31/8_ 2i _ /7 / 2.3 __ 4 _ 1X.200

1955_ 4.2 2_19/8 2.9 _ /8 4.0 19 18l.000 *

1956 3.3 2,/9 2,2 24/6 1.0 21,9 13.700

1962 3.0 28 _ 28.6 _ 23/'8 3.0 28-29/819 1 =l_

1963 2.7 9-lL/9 04 _ 16/7 2.1 _13.600

1964 2.7 hL/9 1.,4 4-5/8 2.8 _ 8: 12 .0 01965 0.5 15/9- 1 _ r L6/'8 1.4 17-18/8 lL. 000

1966 2.3 31/8-I9 1,,2 26/8 2J 4 _ 2-3/9 1iL20D

1967 _ 2.9 _16-17/9 - 1024 _ -3 9..6 24-25 'P.900

1968 11. 2 !9/83 _ 7/'lo 2.1 __ 31/8 7 h40 (two f:Loods)

1969 3.6 28_/8__ 1.6 23/7 1.9 30/8 not stated _

1970 1.2 2 2.2 28/7 2.4_ 31,/7-1/8 not stated

* -7.00in 196 annual report p. 'F -:1

Source - WAPDA Annual Reports o;n Flood in Bangladesh.

LOSSES TO CROPS AND PRO]PERTIES

Value of Losses - Million Rs

(1) - (7) : Current Prices - (8) : 1L969 prices

Relief and Rehabilitation Agricultural DirectorateDeprtmen,t DEata _ Da ta - 77 _ r

Year Crop Losses Other Tota:L Crop iLosseas Total Crop Corrected Whole Sale Price Total Value of(Rice & Jlute) Losses (Rice & Jute) Losses Total Value Index for Losses

(2) + (5) Bangladesh (Food) 1969 PricesBase 1959-60 -lO0

1962 43 554_ 648 707 750_ . 106.5 1020

1.963 not .stated 60 60 60 10L44 _ 8;3

1964 159 214 183 146 158 182 106.9 2 2h6

1965 _ _ not stated 34 36 36 117.0

1966 5 _ 61 16 - 577 - 463 480 496 132.15 5LL4

1.967 _ not stated. 84 84 4 _ 13.6 _ 510

1.968 81 35:3 1164 - 1176 1186 _ 39_ 135L_4_ 16.

1.969 23 82 226 307 330 14W4.8 __30

1-970 _ 1307 73 .1380 not stated 1380 _ 1380

Total 5383

Annual. Average 6C)o

* Not yet pubLished

SHAI)OW PRICE OF RICE IMPCRTS REPLACINIG FU)OD LOSSES

(LDDEI) COST)

|EstLmated Rice Crop Total Imports from Value of Imports ValLue of Imports from Adied Cost Withi Added CostYEAR Losses Abroad and West from West Pakistan Abroad w:Lth the Official Shadow Price of 1969 Prices

Cleaned Ricet (tons) Pakistan (tons)** (Millions Rs) *-* Rate of IEcchange Imports Replacirg (Millions Rs)(Millions Rfs) Flood Losses

.- _…… _ _ __ _Ly 11 i-ions Rs) _

1962 7'!4.0Z)o 54,? 5 18 8. 73.3 _ _ 78-_ .~~~~~~~~~ 542OOC) :L18 .,_ ___-8.3 7 8

1963 8{3.5oo 3 .7_ 48__ _- - 34h6.OO3 ) 99.8 _ __. 44-t --

196 18J1.0.o)O 36.2 ___47_

196', 34.647 131362 17.4 11-~~ 36.o 147.12__~~:h6L... 3603.OOC) :_Lh7.7_____3_t _ 6

.1966 0' tO- 69?.2 67_966 -9 - - 1 432.000) :L39.8_ 69.2' _

1967 3 9 .2 __ _39-3013.O000 89,5; 44h.3

1968 .19'71 _-°__ - ._______ _- 236.00() 97. 7 4_ ( 4,0 44196 21L7.3160 95 _ 5

_, _ _ _ 5013~~~~~~.00()__,

* Assuming the same proportion of imports between West Pakistan aLnd foreign t:rade as iLn 1968-1969, and the same import price.

** Fiscal years 1962-1963, 1963-1964, etc.

3

CD0

Table h

PPvCADTqTMTTAq'TrOT OFY ATT RECOP3DTVn TrKSES

1969 Prices

Year Losses to Crops & Properties Added.Cost for Crop Losses Total Cost of(Without Sha (lu,ri Shadow Prices) Pd. Repairs

1962 1020 78 1098

1963 83 48 131

1964 246 47 293

1965 45 21 66

1966 544 67 611

1967 90 39 129

1968 1645 44 1689

1969 330 95 425 26 (1968-69)

1970 1380 ? 1380+ 29 (1969-70)

Total 5383 439 5822 +

AnnualAverage 600 55 655

Table 5

COMPARISON OF RICE CROP LOSSES

Year Estimated. Rice Crop Losses(cleaned rice - Tons

91' 443' °°°).7. 00 (1

-I orz'A Rnn rnrn (1 '9ff41 474,1.ooro (1)

L7vc- ~~~~~~~~~~~~~~~~cI _cL4, --

95 800 1° (- )L6u4 k82,) oov

9, 3

1969 459, 40 ,)U k)- ,Af 0 1 n MA. r71,

.LyO YvVv {l )

1970 1,190,000 (2)

Source

(1) - Krug mission:s report

(2) - Relief and Rehabilitation Department - Dacca

(3) - Agricultural Directorate - Dacca

I , I---- .----.-. - -- .-- ---- o

- I 1 I FW 1---1 --l- ---- -- I

- --- 1---- - i-- -t ,-.i-t --A---n 9|9 w ti

L~~~~~~~~~~~r _ htiQ 'A T i L .I_ i| -_I~ wa s s

I~~r _ _ _ I : ;1i :I !I I I I i I

I _1 At1 -Lr

C2XtLLiiVI 1LL 21SL___!I ___I LI I W b -

I .II I L

I ~ I Ii lil

I I _ . _ I .,

1- - -~- I __ I --1 Sv I tC5W'- frIo _Dlalt/- J''lD;A hS

~~~~as F''s1T 1' __________ ______ __

I SdLl~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PADMA RIVE=R AT GOALUNMDO

VARIArTION.l IN' Fl-oOD STAGES 195 4-1968

. ;-IGHEST STAiF.S -

Ull-_ . _ _ I _ --_

' 1 '~~~~~~- X A / '- _ ;

IL ~~~~~~~~~~ - ( V"%": T A G E S

~~~~~_ _ ___ ___ __ __ ____ __ _ __ _

4il'5!E tIt)L Y jAl)GUST SEPTEMBE.R OCTOBER'

t N tj U Ly W', US T S E PT E MBER OCTOBER~~~~~~~~~~~~~~~~I

°PPAHMAPurRA RIVER AT F'AHADURARAD

VARIATIOINI IN FLOOD STAGES 19 5 4-668

7 n

_--HlIC(HEST STAGE-S

" ~~ _- I_ __ _ _ S_ . - = __

C !_ - _ _ -_- _ ~ __ -__

(<.$Ra ___- - -_ _~ __ L _ ---------__----t- ' J, t!!.JUY A(JG,tJST SE TFMPBER OCTOBE R

TECH-NICAL REPORT NO. 24

ANNEX 1

DRAINAGE AND FLOOD CONTROL COSTS

Table of Contents

Pae

1. Introduction .. ............ 1

2 . Land and Flooding . . 2

3. Categories of Drainage and Flood Control 3

4. Potential Works ........................ . 5

- Northwest Region .. 5- Central Region ..... 8- Southwest Region ..... ......... ....... 11- Eastern Region . ....- Summary of Potential Development Areas ..... 18

5. Basis of Cost Estimates . .............. .... 19

- Introduction .. .......... 19- Estimating Procedure. 19- Estimating Data . .. 21

6. Potential Development Costs ..................... 31

- Regional Analysis by Land Development Unit . 31- Analysis by Category of Development . 32

7. Conclusion ....... . 34

Note: The material for this Annex was prepared by Mr. R. Morton ofAcres International (Consulting Engineers).

- ii -

LIST OF TABLES

Page No.

1. Broad Land Development Units (B.L.D.U.) ........................ 362. B.L.D.U. Areas in Relation to Flood-Depth Classes .......... 373. ,iummary of Flooding Conditions on Gross Agricultural Area ..... 384. B.L.D.U. Areas - Flood-Depth Classes in Northwest Region ...... 395. B.L.D.U. Areas - Flood-Depth Classes in Central Region ........ 406. B.L.D.U. Areas - Flood-Depth Classes in ,outhwest Region ...... 417. B.L.D.U. Areas - Flood-Depth Classes in Eastern Region 428. Analysis of Northwest Region h.0 439. Potential Development Areas by Work Category - N.W. Region .... 44

10. Analysis of Central Region ......... ...... .. ..... .... . 4511. Potential Development Areas by lWork Category - Centreal Region. 612. Analysis of ',outhwest Region ........................ ...... 713. Potential Development Areas by Work Category - iS.W. Region ..... 814. Analysis of Eastern Region ...... .. ....................... 4915. Potential Development Areas by Work Category - Eastern Region 5016. Flooded, and Potential Development Areas - Summary by Region 5117. Flooded and Potential Development Areas - Summary by

Works Category .......... ........... 5...... 5218. Categories and Costs by L.D.U. - Northwest Region ............. 5319. Categories and Costs by L.D.U. - Central Region ...... ......... 5520. Categories and Costs by L.D.U. - Southwest Region .. 0.00"00090 5721. Categories and Costs by L.D.U. - Eastern Region 58

- iii -

LIST OF PLATES

1. Broad Land Development Units (B.L.D.U.)

2. Distribution of Moderately Deep and Deeply Flooded Land

3. Distribution of Deeply Flooded Land

4. Pot;ential Drainage W-forks by Category

Fig. 1.- Ernbankment Costs (Page 23)

- iv -

LIST OF REFERSI'CES

ACE, Khowai Project, Feasibility Report, February 1968.

EPWAPDA, Upper Kusiyara Project, Feasibility ,tudy, 1966.

FAO, The Regional Pattern of Land Use and Agricultural i velopmentPotential, IDA Sector 5&tudy, Mimeographed Report, 1971.

HUNTING TECHNICAL SERVICES and SIR M. MACDONALD AND PARTNES, DaccaNorht Project, Preliminary Note on Proposed Development, June 1971

ECI, Dacca Southwest Project Feasibility Report, August 1970, plusIDA Special Projects, Appraisal Report, 1971.

IECO, Meghna-Muhuri Water Transfer, Prefeasibility Study, August 1971.

IECO/RAAL, Karnafuli Irrigation Project, Phase I Study, 1971.

LEEDSHILL DELEUW, Chandpur Project, Feasibility Study, 2 volumes,1969.

PAKISTAN TECHNO-CONSULT, Belkuchi Project Report, 1971.

PAKISTAN TECHNO-CONSULT, Belkuchi Project Report, September 1968.

PEGG, John, Embankment Maintenance, Memoranda Reports, July 1971.

SANDWELL, Sangu Project, Feasibility Report, January 1965.

SANYU, Pabna Project, Draft Summary and Conclusions of FeasibilityReport, January 1971.

SCHILSTRA, J., Distribution of Flood-Depth Classes in ZRst Pakistan:Typewritten Report, 14 pages, 8 tables and 3 plates, 1971.

SIMONS, D.B., IDA Sector Study, The River System, 1971 . Tech. Report 25.

ANNEX 1Page 1

DRAINAGE AND FLOOD CONTROL COSTS

1. Introduction

1.01 Until recently, the people of Bangladesh have adapted to the fioodconditions as best they could but there has been very little modification ofthe flood environment. Cities, villages and homesites are located in higherareas or on builtup mounds to reduce the frequency of flooding. Farmers plantrice varieties which take advantage of the normal flood conditions at diff'erentperiods of the monsoon season. However, if flood depths are reduced, it willbe possible to ef'fect a considerable increase in crop production.

1.02 In addition to the direct damage they inflict on crops, floods hamperrice production in other ways. For example, no rice can be grown at all ondeeply flooded lands (over 15 feet in the Meghna Valley). Only low-yiedicngbroadcast aman rice can be grown on lands that are flooded from 3 to 12 feet.Where flooding is from 1 to 3 feet, farmers grow higher-yielding aus and trans-planted aman rice, accepting risks f'rom occasional higher flood or from drought.It is therefore important to identify present depths and extent of flooding andto determine locations where flood depths can be decreased to enable the use ofthe higher-yielding rice varieties.

\ AL/ I O 7VA . L A U % A ; Ji AV M.JAIL L_'L U.C A iA _J + A A C W A .L _ L

classes with different flood depths. These classes were lands flooded:

a) seasonally or intermittently to a depth of less thanone foot;-,

b) to a de.pt of4 one to three feet;

cL) to a depth of three to sixA feet; and

u) tu o Udepth11s oLf more -Llian six feLet U.

VIA the bai ofthscasfcto,teln ra alng i n classes (c) and.

(d), (some 7.7 million acres) were studied to assess the practicality ofreuduc-ing f"loodu dUe.pthl's by.-1-- dring i-,lrvrXn work or by -lo -oto -and . _' - _-reUul.~L1I .1. ±LiUUU~JU1J~Li U.-Ld.I.LrAd:; _LLljJLiUVt:11AIILII. WvunoUft,Li uy ±±JUUU ULVIIU.UL±V dJiu

drainage development.

1.0 4 The flooded areas along the Chittagong coast were not included :Ln theSchiAl.stra stud'y ardl were, thilerefLore, excludted Lfrom1 theR mink.U anaI.l.ysis cU-r.IdL

out. However, at a late stage in the study some detailed information onpotential proJects (H afld..a Zaru ±lic.faiiW-I) .11 i dIjLO arLea UbLeWI-, available. Th1'e

results of a preliminary analysis of the new data are incorporated separat.ely.

ANSEX 1Page 2

1.05 This volume summarizes the flood depth study and the resultantcategorization of drainage development potentials together with cost estimatesproduced for input to the IBRD Sector Study development sequencing modelanalysis.

1.o6 The potential benefits from the categorized drainage and flood controlworks and the integration of such works with irrigation were not a part of thisstudy and are being considered by others in the Sector Study.

1.07 The direct results of this study, therefore, are (a) the identificationof areas where, if projected agricultural benefits warrant it, detailed studiesshould be undertaken, and (b) a basis for the establishment of priorities forthese studies. These detailed studies should then be incorporated in the termsof reference for the four regional studies currently under consideration.

2. Land and Flooding

2.01 The analysis of Schilstra (1971) summarized, on the basis ofinformation in the "Reports on Reconnaissance Soil Surveys of Districts andSubdivisions. The distribution arid area of various flood depth classes andidentified areas where improved drainage could lead to increased rice pro-duction.

2.02 On the basis of a more or less identical percentage distribution offlood depth classes, the 49 Land Development Units (LDU's) distinguished fromthe Soil Survey data were partially grouped together or, where necessary, sub-divided to form 18 Broad Land Development Units (BLDU) as indicated on Plate 1,and listed in Table 1.

2.03 The resultant areas of each of the four flood depth classes existingin each BLDU are presented in Table 2. The total flooded areas by depth classin relation to percentage flooded over three feet are summarized in Table 3.

2.04 The percentage distribution of moderately deeply flooded land (overthree feet) and deeply flooded land (over six feet) is indicated on Plates 2and 3 respectively.

2.05 The areas of the four flood depth classes within each of thenorthwest, central, eastern and southwest regions are detailed in Tables 4, 5,6 and 7, respectively, and summarized below:

ANNEX 1:Page3

Regional Distribution of Flooded Areas

Flooded AreasNet Areal/ (million acres) Percentage

Region (million acres) 31-61 6' Total of Net Area

Northwest 6.75 0.67 0.57 1.24 18Central 4.25 , 0.75 1.05 1.80 43Southwest 6.62g/ 1.17 0.47 1.64 25East 4.961' 1.55 1.46 3.01 61

Total 22.58 4.14 3.55 7.69 34

L/ Excludes active river flood plain, homesteads and watertanks.j Excludes LDU's 9, 10 - Tidal inundated land and Sunderbans.j Excludes LDUIJS 8, 9, 11 - Chittagong coastal areas, hills and hill-tracts.

3. Categories of Drainage and Flood Control

3.01 The 7.7 million acres identified as having drainage improvementpotential were studied using the limited data available and personel knowledgeof informed individuals. A preliminary categorization was made of the fresh-water flooded areas by type of construction works, if any, considered practicalfor drainage improvement. The categorized areas are indicated on Plate 4,.Estimates of cost; were based on typical estimates for each drainage category.

3.02 The resultant categories are:

Category : (450,000 acres)

Areas with no significant drainage or flood control problems, i.e.,less than 10% of the identified areas (Schilstra, 1971) are subjectto flooding over three feet in depth, or areas where drainage im-provement would not be beneficial in relation to the existing landuse.

Category 2: (713,000 acres)

Areas subject to flooding by rainfall only where a significantreduction in the extent of flooding can be obtained primarily byimprovement of natural drainage channels and by construction ofsmall cut-off embankments and control sluices. No pumping plantsfor drainage are considered necessary. (Cost range: Rs 120 -Rs 185 per acre)

ANNEX 1


Areas subject to flooding by both rainfall and overbank spillfrom rivers adjoining the area where the construction of peripheralembankments would greatly reduce the extent of flooding and improve-ments to natural drainage channels (as for Category 2) would be ofadditional benefit. No pumping plants for drainage are considerednecessary.(Cost range: Rs 270 - Rs 660 per acre)


Areas subject to flooding by rainfall and by overbank spill fromrivers whose high water level is caused primarily by tidalfluctuations. Improved drainage could be obtained by constructionof low embankments, natural channel improvements and the installationof sluices at stream outlets to limit the effect of the tidal cycle.No pumping plants for drainage are considered necessary but regulatorstructures may be required. (Cost range: Rs 155 - Rs 350 per acre)

Category 5: (1,087,000 acres)

Areas wherenatural drainage is severly restricted by high water levelsin surrounding rivers. Flooding is caused both by rainfall and over-bank spill. Drainage improvement requires peripheral embankments toeliminate overland flow and pumping stations to evacuate the excessrainfall from the area. No major problems in embankment constructionand maintenance are envisaged. (Cost range: Rs 1,000 - Rs 1,075 peracre)


Areas similar to Category 5, but where the peripheral flood protectionembankments adjoin the major rivers. The large peak discharges neces-sitate high embankments. Riverbank movement and siltation are thegoverning factors in location of the embankments and pumping stations.The feasibility of such schemes requires very detailed study byspecialists in river morphology and earthfill embankment design con-struction and maintenance. (Cost range: approximately Rs 1,200 peracre)


Areas where no practical solution to the flood control and drainageproblem is presently envisaged. These are very low-lying areas;areas subject to very high intensity rainstDrms; areas where drainagewould be of little benefit to agricultural production; areas whereflood control requires works outside Pakistan and the flood plains ofmajor rivers. These areas have the lowest priority, technically atleast, for drainage improvement.

AINEX 1.rage 5

Category o: (182,000 acres)

Areas in the coastal belts where flood-control development is at anadvanced stage by means of the "Coastal Embankment Project%.

4. Potential Works

4.01 The areas identified as having drainage improvement potential(categorized by type of construction works considered practical) are indicatedon Plate 4. On this plate the work categories are superimposed on the LandDevelopment Unit (LDU} areas to provide a common base with the Land Use andAgricultural Development Potential Studies.

4.02 Potential for drainage improvement works on a regional LandDevelopment Unit basis are outlined by category in the following sections.Active river floodplain units have been excluded from the study.

Northwest Region

4.03 General Description. The northwest region is the region leastaffected by flooding, (Plates 2, 3 and 4). The general gradient of the landis steeper than in any of the other three regions and interior drainage ofmuch of the area is accomplished, without significant flooding, by many smallrivers.

4.04 A prime factor in permitting the rivers in the eastern section ofthe region to drain naturally is prevention of overbank spill from the Jau=naby the Brahmaputra Right Embankment, constructed in the years 1964-1968. The135-mile long embankment extends from the Tista River in the north to theHurasagar River in the southeastern corner of the region. Unfortunately,, theembankment has not been well maintained and, in fact, has recently beenbreached by the Jamuna in at least two locations. Remedial works and establish-ment of a permanent maintenance program are an essential pre-requisite to anyinternal drainage improvement works.

4.05 The areas in the region primarily affected by flooding are LDU 10and the southern part of LDU 5 in the southeast portion, at the confluence ofthe Ganges and Jamuna Rivers. Here many of the rivers have converged to forma single outlet - the Hurasagar River - and outflow from this river during thewet season is severely restricted by backwater from the Jamuna.

4.o6 The restricted outflow from the Hurasagar in turn causes deepflooding in LDU8s 5, 7 and 8a, a low-lying beel area in the Atrai River Vlalley.The northern portion of LDU 9 is also affected by the high river levels :LnLDU 8 a but much of the flooding here might be alleviated by improvement ofexisting channels.

4.07 Backwater effects from the Jamuna also cause flooding in thenortheast of the region on the northeast extremities of LDU 3 and LDU 4a.Here three major tributaries rising in India (the Dudhkumar, Dharla and TistaRivers) join the Jamuna in a 35-mile stretch and overflow their banks at peakflood levels in the Jamuna.

ANNEX 1Page A

4.08 The only other area in the region where major flooding occurs isin the southwest corner adjolning the Bangladesh/India border. It comprisesthe western extremity of LDU 9 and LDU 8b. This area is primarily drainedUy ithe rWUIdIlaiUd I-VUeI iloWdi% -LIInto Uthe uiigC uut au peak r-i-vr levels tuhe

Mahananda is partially fed, through the Pagla, by the Ganges in India.SigiLficant drainage _iro-vement is therefore iot conlsidered practical atpresent.

4.09 Local flooding occurs in low-lying beel areas in LDU's 3, 4b, 12,11 _~ 2 , I 'L. . ~ - e e _ _ n -- t_ 1-L_ r,s -_ e L_ 1 - 1 n - - - -- ..- _ n t _ _ _.L_) an4U 14/ U a.LL d UeC, J - U LI1AEI W/O Ul ULIU UUUL..L dgU91-LU..LULLAd± alr*a k6U1LIu

140,000 acres in an area of over 3 million acres) and so no works have beenass-urrmed. hlle active river floodplain, LDU:s Ila aid lIlb, excluded from thestudy, comprises some 600,000 acres.

4.10 Analysis of Region. The areas within LDU's subject to floodingover three feet in depth and the areas which could benefit from drainage,with or without flood control, are summarized in Table 8. The potentialdevelopment areas are summarized by work category in Table 9.

4.11 The work proposed, or the reasons no works are proposed, aresummarized as follows:

LDU 1: Less than 0.5% of the area is subject to flooding. No worksare proposed.

LDU 2: Less than 0.17' of the area is subject to flooding. No worksare proposed.

LDU 3: Less than 3% of the unit area is subject to flooding. However,50% of the flooded area in this LDU is located in one localityat the confluences of the Dudhkumar and Dharla Rivers with theBrahmaputra.

It is considered that some 19,000 acres of flooding inthis area might be alleviated by a Category 3 project,i -e fllnori ebnhankTnents and grai ty drainage throughcontrol sluices. The length of embankment required ishiah in relati.nn . +he are hbnefit.te.A hiut. if nreoliminnaryinvestigations confirm that gravity drainage is in factof benefit and that prmning is not req ired, detailedstudies could be considered.

LDU 4a: The majority of flooding in this unit occurs in an areaCat the 4 c.o.nfluencIe of the Dilarla a4. Tista -vers with the

Brahmaputra, adjoining the area described in LDU 3. Again,so.me 19000acres flo odi4ng m,ight Ice allleviated bky a Category

3 project subject to the conditions set out in the previousp_-_ag~raphl for TU T3

The oks otlie for; n! e dand TTaI fo., -a part of' 4theWAPDA K rr am..J4.no 'ju. Projec .LJLJUu I.J± ii1 a jJd.±4 - 44140

WAPDA Kurigram Project.

A1NEX 1Page 7

LDU 4b: Considered as part of LDU 13. No significant flooding occurs.Category 1.

LDU 5: Flooding occurs over about 275,000 acres, or 48% of the netarea in this unit. The area is flood protected from over-bank spill from the Jamuna by the Brahmaputra Right Embank-ment but considerable flooding occurs from rainfall anddrainage congestion.

Some 119,000 acres flooding in the northern portion of theurit could be alleviated by a Category 2 development channelimprovement. However, alleviation of the 156,000 acresflooding in the southern portion requires a Category 5development - flood embankments and pumping plants - as theKaratoa and Gumani Rivers overspill due to backwater fromthe Jamuna in the Hurasagar River.

Fairly extensive feasibility studies (1968, 1971) for theBelkuchi Project in the southeast corner of the unit havebeen carried out bv local consultants but the 1971 reportis not available for this study. Remedial work andcontinuous maintenance of the Brahmaputra Right Embankmentare a pre-requisite for any drainage (or irrigation) worksin this unit (Pege, 1971).

LDU 6: Considered as part of LDU 13. No significant floodingoccurs. Category 1.

LDU's 7&8a: These units are very low-lying areas in the Atrai River

Valley (Chalan Bil). A draft feasibility report wasprepared for WA\PDA in 1970. The technical problems ofalleviating flooding in these areas are so great thatdrainage improvement works are not envisaged in the currentstudy. Category 7.

LDU 9: Flooding occurs over about 270,000 acres, or 35% of thenet area, in this unit. About 82,000 acres in the westernextremity of the unit, close to the border of India,flooded primarily by overbank spill from the Pagla and Mahananda,Mahananda, are considered to be Category 8.

Some 112,000 acres in the central portion of the unit,draining into LDIW's 7 and 8a, are subject to flooding,partially by high water levels in Calan Bil, but it isbelieved that some alleviation by channel improvementmay be possible. Category 2.

The remaining 74,000 acres at the confluence of the Gangesand the Jamuna in the southeast corner of the unit are partoF the proposed Pabna Project. Flood control and drainagewould be by embankments and pumping plants. Category 6.This area and the flooded areas in LDU 10 would be one project.

AMNLEX IPag e M

TU 10: Floodin- occq ps over about 9-4-14 a cres, or 7,-/ fthe unit area. Prime causes of flooding are backwaterin the Hurasagar Cfrn the nf'ffe,+4ng +he -rnal rnd

the Ichamati and overbank spill from the Jamuna.

Preliminary data from the Pabna Project studies indicatethat about 190 m les of flood emb-e,nkkent end fourp

ing stations and drainage channels (most already ineV -tennce) wul be required for Major r-nainage mn-r-,vrent

The amb-n.rb'ntsa along t-ha T-- nA an ,-anges Pi;vnr wou,lA

require the establishment of a permanent maintenance andflood=fighti- n org- -ztion in v-ew of the hazds causedby river movement and high river levels, (Pegg 1971 andSmon)sL.1 -L7 I -L9 . ThI.Ls dVev.Lop,mL.1eU iLs, the1re.LVfore, vLaODU Cas

Category 6.

LDU's lla& III_ Actv rle lodli.NodT a rfod-otoK L.L±J l ,LV _ L.VtJ. ±ULJ_UUY)._LII. INOu U4.1.J.JIar't kiJ IAAJVU-uVJIIL,.UU±

works envisaged.

LDU's 12,1). 9~

14: There are no single large areas affected by flooding in4-these unt4 -S. A ta4-l o-a of t 140,000 acres (ofo over 3,000,000ULl ,J LLIL .,U JL LA _L,. LJ ..L4,J, 'JJJ cLI~~ 1, "J VJ J JJ , 'JJ

acres) is subject to flooding but insufficient data areavallable to categorize drainage w-orks. It ls probablegravity drainage, Category 2, would alleviate flooding inpart of thie area butu au uubtedly ria of the -waUer iscontained in low-lying pockets of land (bils) and is pos-sbl.y better lef f"or dry-season use.

Central Region

4.1 Thiue uentral reglon slopas gradually from fooUtills 0on bIle Indiianborder to active floodplains on the Padma River in the south and from thecor.stantly migrating east bank of tlhe Uar-ura River ln the west to thre westernexrtremity of the low-lying Sylhet Basin and the Meghna River in the east.

4.13 There are no existing flood-control projects in the region otherthan the i5,000-acre Dacca-Narayanganj-Demra polder-type pumped drainage/irrigation development adjoining Dacca City.

4.14 The majority of flooding in the region occurs in lands betweenthe Jamuna-Padma and the Madhupur Tract (LDUis 9, 10, 11) and lands adjoiningthe Lakhya River (LDU's 13 south and 3d) the major outlet for Old Brahmaputraflood discharge and the Meghna River (LD-UGs 8a, 8b). The high wet-seasonlevels in these rivers necessitate flood-control and drainage developmentsimilar to the D--D project (Categories 5 and 6) to alleviate the almost 90%flooding in these areas. The location of embankments and pumping stationsis governed by river migration and sediment load and poses major technicalproblems (T.R. 21).

A 1CAN77

Page 9

4.15 Flooding in the northern units of the region is much less severeand, in light of the current cropping patterns in relation to topography andsoils, no significant drainage works are recommended for LDU's 3b, 3c, 4,5 and the greater portion of 13.

4.16 The lands below the foothills defining the Bangladesh/India border,LDU's 14 and 2, are subject to flash flooding from severe rainstroms butflood protection is not considered a practical development.

4.17 Lands Ln LDU 3a,. north of the Old Brahmaputra River, are subjectto limited flooding from the very heavy rainfall and restricted dischargechannels in the area. However, flood control and drainage may requirenumerous embanked polders and high peak-capacity pumping stations so thisarea is considered of low priority. Detailed study in a regional context isrequired.

4.18 Analysis of Region. The areas within LDU's subject to flooding overthree feet in depth and the areas which could benefit from flood control anddrainage are summarized in Table 10. The potential development areas aresummarized by work category in Table 11.

L.19 The works proposed, or the reasons no drainage work is proposed, aresummarized in the following paragraphs:

LDU's 1,& 12 Active river floodplain, totalling about 500,000 acres, on

on the bank of the Jamuna and Padma Rivers. Riverchannel movement is such that flood control or drainageworks are not envisaged.

LDU's 2W These units, situated below the foothills of the Bangladesh

/India border, are subject to intermittent flooding over about100/g of their area. The flooding is primnrilv r!alised bvflash runoff from the hill streams and flood control isprobablv not practical. Some reduction of flooding byembankments and gravity drainage might be possible.Presently classed as Category 7 but should be studied inthe future.

LDU 3a: Some 13% of this unit of over 600,000 acres is subjectto flooding. Detailed information on the area is notavailable but it is believed that polders and pumping ina number of separate iinits would he requiired to nrovidesignificant relief. It is probable that the relativelyhig,h pimping capacity neGessrvy because Of the hiogh

-intensity runoff may give such works low priority in thetotal development program nand the uinit has been nl ,ssed asCategory 1. Again, an area to be fully studied in regionalplanning.

ANNEX 1Page 10

LDU's 3b, 3c, h& 5: Flooding in these units varies from almost zero to about

20% of the unit area with the majority shallow flooding.Advice from land-use specialists is that no significantoverall benefits would result from drainage improvementworks in these units. They have therefore been classedas Category 1.

LDU's 3d, 8a& 13 (part): Major flooding, primarily from overbank spill from

the lower offtakes from the Old Brahmaputra River and fromthe Middle Meghna River, occurs in these units. Over200,000 acres are subject to flooding and flood embankmentsand pumping stations are essential for relief. The potentialworks are classed as Category 5.

It should be noted that while these units require major worksfor drainage relief, the surrounding river banks are (forBangladesh) highly stable and no major technical problemsare envisaged.

LDU 7: Flood control or drainage improvement works are notpresently envisaged for the unit on the border of thedeeply flooded Sylhet Basin. This is more fully discussedunder LDU 3 in Section h.31.

LDU's 8b, 9, 10& 11: These units are the major flooded zones in the central

region due to restrictions on surface drainage by the highflood levels in the Jamuna-Padma River and overbank spillfrom distributaries off the Jamuna, principally the Dhaleswariand Buriganga Rivers. The units are bounded to thenortheast by the Madhupur Forest high land which increasesthe runoff congestion. All flood control and drainage worksare assumed to be Category 6 in view of the major technicalproblems imposed by embankmaent of the Jamuna and the heavysilt content of the rivers.

Comprehensive studies covering most of these units have beenundertaken in recent years, and are continuing, for theDacca Southwest Project (Feasibility Report 1970, AppraisalReport 1971).

Flooding in LDU 9 north of the Dhaleswari River is lesssevere than in the Dacca Southwest Prolect area. Some floodrelief in this area could probably be obtained by gravitydrainage from an embankment along the left bank of the Jamunaand construction of major control sluices. However, thepossible conseauences of double-embankment of the Jamunarequire much detailed study in the future. It is, therefore,considered for this study that this portion of LDU 9 beclassed as Category 6 for priority purposes. The proposedregional study will give priority to the problem.

ANNEX 1Page 11

LDU 13: The major part of this large unit comprises theMadhupur Tract, an area of relatively high land.Flooding from rainfall occurs in valleys but nomajor drainage relief works are considered necessary- Category 1.

The southeastern corner of the unit is bounded bythe Lakhya River, a amjor outlet for Old BrahmaputraRiver flow and runoff from the higher lands to thewest; combined with high river levels in the Lakhyacauses major flooding. Flood control and drainagerel:ief is currently under study for the Dacca NorthProJect (Hunting/MacDonald 1971). Flood embankmentsand large pumping capacity will be required but nomajor technical problems are envisaged as the Lakhyais stable. These works are, therefore, classed asCategory 5. About 112,000 acres would benefit directly.

LDU 1L: This small unit comprises foothills on the Bangladesh/Indiaborder. No works required. Category 1.

Southwest Region

4.20 General Description. The southwest region slopes gently from theGanges-Padma Rivers to the Bay of Bengal. Until recent vears the major partof the region was subject to extensive flooding by rainfall, overbank spillfrom the Ganges and its distributaries and tidal inundation.

h.21 The extent of flooding has recently been considerably reduced byflood embankment construction on the south bank of the Ganges and the westbank of the Gorai above Kamarkhali as nart of the Ganges-Kobadak Project andby the Coastal Enbankments Project. The present distribution of floodingis indicated on Plates 2 and 3.

h.22 The maiority of flooding now occurs in the Faridnur-Sureswar areasand depressed areas in the Khulna diLstrict (LDU's 4 and 5). Over 55% ofthese units is moderately to deeply flooded for a considerable part of eachyear. Much of the floodwater is due to overbank spill from the Ganges-Padma andthe Madhumati Rivers with drainage restricted by constantly changing channelsand tidal effects in the recipient rivers to the south.

4.23 The Kushtia-Jessore areas (LDU 3) while largely freshwater storagereservoirs will be a subiect for detailed studv in the future.

4.24 Analysis of Region. The areas within LDU's subiect to floodingover three f'eet in depth and the areas which could benefit from drainage,with or without flood control. are summarized in Table 12. The notentialdevelopment areas are sunmarized by work category in Table 13.

4.25 The works proposed, or the reasons no drainage works are proposed,are summarized in the following paragraphs:

ANNEX 1rdge JV

LDU 1: Active river floodplain, totalling about 270,000 acres,on the southr banks of the Ganges-Padma Rivers. Riverchannel movement is such that flood control or drainageworks are not envisaged.

LDU 2: These areas, comprising about 200,000 acres, are naturalpolders formed by reasonably efficient side drainingchannels of the Lower iveghna River. Flooding over threefeet in depth is negligible and flood control and drainageworks are probably of low priority for agriculturaldevelopment. However, over most of the areas such workscould be provided at comparatively low cost by smallembanloments (four feet to six feet high), interior channelimprovement and tidal sluices. The northern polder betweenthe Madaripur Bil Route and the Arial Khan River might,however, require drainage pumping due to restricted internalriver outlets (IECO Master Plan, Vol. II). The unit has beenclassed atppresent as a non-flooded area (Category 1).

However, data at the bottom of Table lh indicates the areasand percentages in this LDU and in LDU 6 subject to floodingof between one and three feet - more than 87% of the unitareas. The relative simplicity of flood and drainage relief,if required in these units emphasizes the necessity fordetailed study of the development sequence for this unit andLDU 6.

LDU 3: This large unit of over 2 million acres is located betweenthe Bangladesh/India border and the Gorai River, bounded on thenorth by the Ganges and on the south by the northern limitsof the Coastal Embankments Project.

Some 500,000 acres, or 25% of the area of the unit, are subjectto intermittent flooding. In recent year, construction of theGanges-Kobadak-Kushtia Unit, Phase I, provided a flood-controlembaniknent on the west bank of the Gorai River and cut-offembankments eliminated spill from the Ganges. The majority offlooding now occurring in the unit is therefore caused byrainfall and drainage congestion. Some additional flooding iscaused by overspill at low points on the banks of the Mlathabahangaand Bhairab Rivers flowing into the drainage area from India.

Drainage relief over much of the flooded areas could, therefore,be obtained by channel improvement, minor embankment construction,control sluices and siphon or regulator structure constructionwhere canals of the Ganges-Kobadak Project have obstructeddrainage.

In the southern area of the unit, west of Khulna, adjoiningCo4stal Embankment polders, high backwater levels in the streamflowing to the Bay of Bengal may obviate any benefits fromchannel improvement and embankments and pumping stations mightprove essential if major drainage improvement is required.

ANNEX 1Page 13

However, flooding in this portion of the unit is be-lieved to be very slight and gravity drainage improve-merit is assumed for the entire unit.

The strip of LDU 3 around and south of Khulna may besubject to flooding by accummulation of overspill fromthe Madhumati and its offtakes and limited channel capacity.Some 49,000 acres have therefore been classed as Category7 although relief by dredging may be possible. Furtherstudy is required.

LDU 4: This unit of about one and a half million acres isbounded on the northwest by the Gorai and the Ganges-Padma Rivers and on the east by the Lower Meghna.

Almost 900,000 acres, or 60 per cent of the unit area,are subject to perennial flooding from overland flow,poor natural internal drainage and tidal or capacityrestrictions on drainage at high river discharges.

Flood and drainage relief over 47 per cent of the unitarea requires the construction of about 350 miles ofmajor embankments and numerous large pumping stations.The cost of flood protection for the entire unit is in-creased by the necessity of maintaining the MadaripurBil Route and the Arial Khan River for hydraulic andnavigation purposes. There would therefore be doubleembankments along the Arial Khan and along the Goraiand Madhumati Rivers if full flood protection developmentwas undertaken in the southwest region. In addition,the embankments along the maJor rivers would have to bedesigned and constructed to take into consideration theembankments necessarv on onnosite banks of the Gangesand Padma for flood protection development in the Pabna andTDaGe-a Southwest areas. (Pahna and naGna Southwest Rennrts-)

Potential develonment of the major nart of the unit istherefore classed as Category 6.

Some 190,000 acres of flooded land in LDU h are locatedwest of the Madhlumati River and north of Khl1na and itis considered that flood relief could be obtained byconstr-iction of a fl ood embankment al ong the west bhankof the river and internal drainage channel improvement -both Categorv 3 works. Outfall condiitions to the Gnoastl1Embankment Polder region will probably govern the feasi-bilitv of this tvne of drainage improvement.

T 5: TMhis llnit. of about half a million acres ceomprises threeareas where extensive flooding occurs (some 46 per centof the total area) but full drainage development is notrecommended (IDA Sector Study) because of the extensivepeat deposits. Undoubted>y local dranage rmIprovemenot

ATNEX 1Page 14

would be of value in specific areas but would necessitatedetailed stuuy in relation to developmiienlt plans for adjoiningLDU's. The unit is therefore classified as coming underCategory 7.

LDU 6: This unit, the Barisal Project in current development pro-grams, is similar to LDU 2 in extent and type of flooding.it is estimated that less than 2 per cent of the 500,000acres is flooded to a depth greater than three feet. Nu-merous channels drain the area with tidal range the governingfactor in depth of flooding. Flooding could be alleviatedby low embanionents and tidal sluices but again agriculturaldevelopment of the unit should proceed before extensivedrainage improvement development. The unit is thereforeclassed as Category 1.

LDU's 7& b: Flooding is limited in these units and flood-control and

drainage works (embankments and tidal sluices) are welladvanced under the Coastal Embankments Project - Category 8.

LDU's 9& 10: These units are classified as Category 7. No agricultural

development is envisaged. However, eventually, a regionalwater shortage might lead to study of estuarine closureto form freshwater storage reservoirs.

Eastern Region

4.26 General Description. The foothills of India form the northernand eastern boundaries of this region. The western boundary is approximatelythe district boundary between Mymensingh and Sylhet and the Bay of Bengalis the southern limit.

4.27 The region has the highest annual rainfall in the country and,excluding the Chittagong Hill Tracts, the largest area of land subjectto major flooding - over 63 per cent of the net area available for agri-cultural development.

4.28 The main reasons for this high proportion of flooded land arethe Sylhet Basin area, lying at 10 to 20 feet above sea level, and subjectto inflow from intense rainfall in its catchment area and overbank spillfrom the Meghna River draining the Basin, and the Gumti River which issubject to flash floods from high intensity rainfall at its headwatersin India.

L.28 In the southeastern part of the area the Little Feni and MuhuriRivers cause flooding In the Chittagong area, the Halda and Ichamatitributaries of the Karrafuli River and the low lands along the Sanm_ Riverare also subject to annual flooding.

8.29 Much of the land adjacent to the Bay of Bengal was subjectto flooding and saline intnision but. constn.-ition of GIoastal EmbankmentsProject polders has provided considerable alleviation of these conditions.

ANNEX 1Page 15

4.30 Analysis of Region. The areas within LDU's subject to floodingover three feet in depth anrd the areas which could benefit from drainage,with or without flood control, are summarized in Table l1. The potentialdevelAopm.ent- a re1 as a ree -- m' -d by w--k, calor.yr in Table l

1) MI1 Th-ok rpsd r 4th-e reasons no driaework Jis p-posed,'-4 * 1. LL VY'JL r~.O jJ.A. UO U0 'JL. Uzi ± a0Jk I'. UJ. VV'J±Lz ~-L . IV0 H'

are summarized in the following paragraphs:

LDU's 1QC II.L XlCLL 1%kL_, -,Y ,, JV ;X WLil aBr ,tU l/ic 0 iIt,lLU"5M LIU_ UUI'Ut I I

No fLood protection or drainage works required apart fromloca:L worrk on thIie tuea estates or, the h 'loupest. CaLtgUor-y1.

.Lu 2: Overv onie Ult1JULiI acUres of1 landIU, of W-whUii bUoU-u (U ptr centIiL

is subject to flooding from intense rainfall and flash floodson the catch-ments of the streaims and rivers draining thehill lands. The two major tributaries of the Meghna -the Surma and Kushiyara - flow through the unit and the broadvalleys of the rivers are subject to heavy annual flooding.iMiost of the smaller tributary stream basins also flood dueto restricted capacity in relation to frequent flood peaks.

Floocd relief works in the major river valleys are not consideredpract;ical at present and will be the subject of a major studyin the context of regional development. Local flood controland cirainage works (embanknents and sluices) may be feasiblein some of the tributary valleys such as the Upper KushiyaraProject (Feasibility Study, 1966). However, improved dry-season irrigation works would undoubtedly have priority andthe entire unit has been classed as Category 7.

LDU 3: This unit of over one mlllion acres primarily comprises thelower Sylhet Basin, or Meghna Depression, in which thenatural Meghna River outflow is subject to tidal influencecombined with backwater effects from the Padma. Floodingis extensive (over 75 per cent of the unit area) and apractical method of alleviating the problems cannot be developedwithout comprehensive studies of the whole northeasternregion.

Benefits might be obtained by construction of submersibleembankments to delay the onset of flooding or by constructionof a low barrage-type structure to form a storage reservoir.The technical and social problems involved in either suggestionare formidable and it is improbable that much improvementwill be obtained in this area for many years. The unit has,therefore, technically, the lowest priority for developmentof flood control in the Eastern Region (perhaps in the wholecountry) and is classed as CategorY 7.

LDU 4: Again a large area (over one million acres) subject toflooding varying from averages of about Q6 per cent in the

ANNEX 1P,a 1 __

northern section to 70 per cent in the southern sectionadjoining the coastal recl-m.ation works in T.TT ln on theBay of Bengal.

Flooding in the upper section, north of the Gumti River, isprimariEly cue to overb-k pill fro-m thei Mi ddle~ Meghnanjlr *t.

The central area flooding is due to high river levels attIIe confluence of thILe MegI-a and the Dad.c -. A to overbark

spill from the Gumti River which is subject to extremefOla s h floodsA from ra-infPall or. Jts hill catch,.ent inTnda.w± oi .L.LUVJ O . 4. 1)13II .3 a.L±a4.± 4.3.1 4. v1 II _L.L..L 30 U_VI.. II C1 LI 4.1t.L.

F~lood- contlrolI and4 drai.ag re-1iJef in these areas woulId -E.? ±I3U Ai L. '4 OIU uJ. .L±. L~4 ~_LLC I. 4.1 VI_70 0. 4 II _L3.A .3

quire formation of many polders by embankments and provisionof regulatLaJors and HumpInL.L11 0I'vation. Prelimary s. 1_L.Lt. O 3UUdles

of developments of this type are in progress (IECO 1971)lor th1'e arreasu of iUi.i- UUi Rive. iiieue d.Le nIU trALm1e1t:

technical problems and Category 5 type development tore'Lve flooUdiig over about .5,000 CLUreU UUU lUull±lU1rtU

practical.

It is possible that flooding in the southern section of theunit could be alleviated by embankments with gated sluicesand regulator structures rather than pumping stations.DiLcnstharge WUU1U bC geared tU wUi -dUd lc yle. MIuUci U.U±l±lU

study of surface runoff characteristics; river levels inrelation to tidal effect and =rainfall; outfall conditionsin relation to coastal reclamation works and total developmentconcepts, will have to be undertaken before the relief bygravity drainage assumption can be fully confirmed. However,one project of this type - Chandpur - nas been designed andconstruction commenced. Optimistically, therefore, the alle-viation of the estimated 272,000 acres flooding in thisportion of the unit has been classed as Category 4, andthe completion of currently authorized studies (lECO 1571)and the Chandpur project will resolve the uncertainty.

LDU 5: This unit is also under study as the "Little Feni RiverProject" but, again, no conclusions regarding drainage areavailable.

The outlet from the Little Feni River is presently con-trolled by a regulator and 17 sluices in the coastal embank-ments forming the southern boundary of the unit. Thesestructures are currently operated to prevent saline intrusionat high tide and also assist in reducing flooding by controlleddischarge at low tides.

Considerable flooding does occur, however, and whetherit can be alleviated by major embankments on the Little Fenitogether with a larger regulator and dredging of the riveroutlet or whether pumping is required requires much study.The gradual closing of the Sandwip Channel which is occurring

ANNEX 1Page 17

naturally as a result of coastal reclamation works and theresultant westward movement of the main Lower Meghna currentsuggest that gravity drainage may becomae increasingly difficult.On the basis of IECO's work to date, however, alleviationof the estimated 166,000 acres has been classed as Category 4for this study.

LDU 6: The maior nart of this deenlv flooded (96 ner cent of area)unit bordering the Meghna is considered impractical for floodcontrol development for the reasons outlined under TDITT 3.

However, a natural Dolder of some 50,000 acres (Meghna-Dhonagoda) (IECO Master Plan) at the confluence of theMerghna and Padma couild be nrstected by embankments and drainedby pumping. Preliminary studies of this development are inprwgress (IET.0 1971) A (ategorv 5 tvne area

TJ.J 7: Thiqs un:it (209,0n00 aGts) Gomnr'iqP t.he maPn small val leyis

between the foothills forming the eastern Pakistan/Indiaborder. FMtooding in the area ns no t. ex+ensi-vre n+. isfrequent due to high-intensity rainstorms on the catchmentsin Tn in n mhinA~ LTi+-h hjpke-w.i+.av. afa~. fwAmr +_hp TT no~.

nn India cohnd..t ac. ffc- from. th.e UpperlMe;hna and its tributaries.

Embankments and gravity drainage sluices might provide reliefin some KT~i alleys (e.g.,r~ Kh i Project) but\ hii+Tr.lh study isr -~

required.

An assumnption of alleviation of flooding by Category 3 develop-m,ent fLor 10,000 acres h'aCs bleen .madue.

TrrEt t _ QJ.LU ' U

& 9: These uniits were excluded from the Schilstra analysis of flooddLs Ur.LIL ution and I'lave therefor-e bUeen excluded fLromi l-able15However, the northern end of LDU 8 is currently under study(I4U Uri River Project - 11",000 acres gross) and some alle"va-tion of flooding would result from the proposed Feni River'n -_ Ll. n _a. _1mu4%|5_ t_ _- .Reu:Lator. ml4s MILinJ puu0c-fUUOU UL UIL4 fLt:;gu±CLoUr, I-UWUVt., ±

irrigation. Preliminary designs incorporate a "fuse-plug"sectior tnlo safe6guard theu stractureu duL1-11r FCC&& flood discharIge .It is possible that full drainage would require pumping -Cauegoiy 5. NDo reliabule±u UdisribUUL..LUII VL UUof L.b .Lfr urtt.iIage

and flood-control benefits can be made at this stage in thestudies, but the unit cosB per acre is likely tio be high(assume 50,000 acres benefitting).

Studies, including drainage and flood control, of relativelysmalv project areas on the haida (4u,000 acres in two polders),and Ichanati (4,770 acres) tributaries of the KarnafuliRiver are in progress (IECO/RAAL 1971). Preliminary reportspropose combined irrigation and flood control projects by

ANlEX 1Page !io

Category 5 type developments. Lengthy embankments in relationto project area, are required and the unit cost is relativelyhigh.

The remaining area where some flood alleviation is Dracticalis in the lower Sangu valley (Sandwell, 1965). The conceptjis a major storage reservoir with hydro-power generation.The costs for flood control (120,000 acres) only by this develop-ment are nrohibitive and nower and irrigation will govern theviability of the project. However some flood relief (20,000ares_ ) ciould probably be readiilv nrovided bv embankments;tidal control sluices and gravity drainage - Category 4.Earilu s+udyris - w-r-rqnted=J

Most of +.th coasta.nl s-trin is mirrrently rProt.e-ted bI, Coastal

Embankinents Project development. The potential developmentareas in T.flTT R e indicated aS an addendum on Table I..No drainage works are assumed necessary in LDU 9.

Summary of Potential Developrnent Areas

4.32 The total flooded areas and the potential development areasresulting from the study are summarized by regions and by works categoryin Tables 10 and 17 respectively.

L.33 It is apparent that drainage in over one million acres(Categories 2, 3, 04) may be improved without major polder embankmentconstruction or pumping stations and should have priority in the develop-ment programrh Priority in polder studies should be given to the 1.1million acres (Category 5) where embankments and pumping stations wouldprovide relief and riverbank movement is not a critical problem.

4.3b An additional 20,000 acres in Category 4 and 105,000 acresin Category 5 in LDU 8 (East Region) are also potential developmentareas.(

ANTJEX 1

Page 19

5. Basis of Cost EStimates

5.01 It must be emphasized that these cost estimates were prepared.for use in the development sequencing model utilized by the Sector Studygroup of the Special Projects Department, IBRD in the 1971 Land and WaterDevelopment Study program. 'wnile the estimates are based orn data fromavailable project study reports, they cannot be applied on a 'per acre'basis for specific project estimating.

5.o2 The cost estimates are not precise - the detailed hydrologicand topographic data required for good estimating is simply not available.The estimates are solely intended to indicate the order of magnitude ofcapital investment required to obtain significant flood relief for landareas presently subject to annual flooding to a depth of 3 feet or greater,as defined by Sc:hilstra (1971).

5.03 The estimates indicate the approximate cost per acre of floodrelief within each regional Land Development Unit and, when integrated inthe sector mod.el with irrigation costs and potential agricultural benefits,should provi.d.e a reasonable basis for the establishment of priorities forfuture project s-tudies. mn ex.change rate of US$1.0O a Rs h.7(K was used..However, in the Land and Water Sectior Sequencing Model 'T.,t. b) the foreigncosts were shadow priced at a rate of US.Sl.OO = Rs.9.52.

5.oh However, the per acre cost data developed.for flood control anddrainage works and applied to a Land Development Unit is very sensitive tothe actual area benefitting. For example, where relief from flooding bygravity drainage is assumed feasible, it is hardly practical that the totaLflooded area within an LDU will benefit. Extremely low-lying areas and'bils' will always be subject to flooding in both gravity and pump drainagedevelopment. Also, the analysis by Schilstra does not define the locationwithin an LDU of the actual flooded areas and, while this analysis could berefined from Land. Capability Classification data, the non-availability ofbasic data on topography and on the cause (rain or river), annual depthsand duration of flooding obviates detailed.project planning and costestimating in this study.

Estimating Proce(ure

5.05 The areas d.efined.by Schilstra as subJect to flooding over 3 feEtin depth were reviewed in relation to available knowledge on topography,overland. flows and discharge restrictions. The type of works considerednecessary to provide relief were categorized as d.etailed in Section 3 and.indicated. on Plate h.

5.o6 The prime sub-division in drainage and flood.-control works ismethod.of water disposal, either by gravity drainage or by pumping,Peripheral embankments may be reauired.for either method, dependent onratio of overland flow to rainfall as source of flooding.

ANNEX 1rage 2Y

5.07 Cost estimates for gravity type drainage works are based onLat UVcos's per acre developed 'rom±UI a vaiLabLe± I. "JP.j L, t.LV Ur Ua Cda.

5 .o8 The eI -- ed costs of wo'-ss required, in addition to basicdrainage channel construction or improvement, such as cut-off embankments,exJ1iusting e-uaiurieuu ±iiovwrien. ad. control and oute l- ± ce were applieU

to the total flooded areas in each LDU to give an estimated capital costper flooded, acre.

5.os Tne percentage proportiono of the capital cost per acre -whichshould be attributed to foreign exchange and to unskilled labor was estimatedfIo' use i1n ecVoiIQLLc auaLysis.

5.11 Similarly estimates of annuai costs for operation and maintenancewere developed.. The annual costs do not include the investment cost.

5 .12 Provision was made in the capital cost estimating for contingencies,generally 200 assumed. in view of limited, data available, engineering at lU01Z,establishment costs at 5%, and for interest during construction at 12% per annum.

5.13 Cost estimates for pump-drainage type works were also developed ona unit cost per acre basis. Pumping capacity was estimated on a drainagecapacity requirement of 0.6 inch of water per day or of 0.75 inch per day,although much detailed study oI rainfali frequency, storage/eievation, etc.is essential in future project studies. The effect of installed pumpingcapacity on capital investment and operating costs is a key factor ineconomic analysis.

5.14 The prime 'unit cost per gross acret variable in a 'polder-type'development is the embankment height, length and cost. However, in applyingthe unit cost data developed to various 'polder-type! project areas, andincorporating the gross cost per acre for embankments, the total unit capitalcost per acre was generally in a + 10% range. This range accomodates avariation in embankment costs per acre of about Rs. 200, or ± 50 miles of 10ft. high embankment in a 100,000 acre project area. It is considered.,therefore, that the application of the calculated total unit costs per acrefor large polder developments to similar type areas is well within the overalllimits of accuracy of the sector model analysis. Small polder developments,under 50,000 acres, would be much more sensitive to embankment cost anddetailed estimating is necessary.

5.15 The per acre costs for large polders are much more sensitive tothe actual area benefitting. For example, within a polder, drainage channeland pumping capacity has to be provided for excess run-off from the grossarea yet the net agricultural land area benefitting might be only 75%. Ata gross cost per acre of Rs. 1200, the net cost per benefitted acre wouldbe Rs. 1600, or 33% greater. However, the model analysis takes account ofthis factor.

ANNEX 1Page 21

Estimating Data

T___ ____ r___ rin al----

Data Sou-rce Gost, /acre- (,R3,

Pabna 60Rurarl Wsorks Pr-ogram. 81Upper Kushiyara 77

Halda (East Pblder) 138Halda (West .>l.r 106G.K. - Jessore Ph. III 100

m"he bnre >-dw.Isnl of the G.Sy" Jessore, Ph TTT est4-t s ie. elw

ms+al Area of drain-age unts =35 ,15,~ acres

r. -1 ' Co4t,/Acr

1~~~~~~1 .1t- n ALI 1n An

EsIt. cost of% drairnage c.arune Rs' .J.18L, Ps. 39.5

it ,~1 -- 4. . -- 4.. en,t7 Ln/A , r'C! c-LIMerts & 1foot bridges 6,0,V L400 18.5

It~~~~~~~~m -P1 4r%s a rl )Qn r_ t

a, t LdL- O-L.kU ' U, l ,1 C./ UV

LUIJL.rU± ~~~~ILUL±UL CV,U)94, I (U Ij UV

'1i rL r1 u- r ve L U a LU U I LC I I U VII UIUe U I,.± rw. 0(2

IV ULLJ LI. i±L

Lar. - 0.5% of area at Rs. 5000 per acre

70 L pulU L~. XW. O

T o Uwal nso 9

Appro=Lmately, Rs 100/acre

5.16 It is considered that this estimate takes fuller account thanmost oI the other estimates of the various pancillary work items requiredbeyond. the basic channel work. However, natural channel density is probablyhigher in areas outside Jessore and.a figure of Rs. 80 per acre is consideredreasonable for general estimating purposes. The possible cost range is large,however, and. this subject requires much fuller analysis in future projectstudies than has been the practice.

A-IIEX 1Page 22

5 .17 Annual operation and maintenance costs have been assumed as2) of th 4 1,e cap-;tal cost.

4. tJA. ~Jl ..aWLQ .At U.

FImbankments

IC ml, e-iIIU1JAent cost.s utl lzed are shown on F i,gure el. Ty arebased. on a unit cost of Rs. 90 per 1,000 cu. ft. of fill covering excavation,

p.L i g, eU meciL "LidIUdJ PUIUdI;tL,LV11 dLIiU L1i-..Ii. l,diU LU%4.JLL.O±U.LViI UVUO .

are also indicated, assuming a 5 ft. borrow pit and a 50 ft. or 100 ft. wideUema, b'e'uwreen thl'e tUoe ofL the t,,mb~LrULZ1,n andl theU borroL-w pit, andU -lnd1I costs

at Rs. 5,000 per acre.

5.19 A significant allowance for embankment maintenance, based onrecent ~ ) DcaSJ. stuies ha b--1een rinclued in the annula' costs.recen.uii-lc J.IV LU U.LI-, 11Ld) LJ -L ±LKU.UtU IL ULI L 0

-Pumping Stations

U.20 TIle cost of pumllping st6ationls was based on pu-mping criterEiadeveloped from very limited information and on recent project costs(Chandpur bids and Dacca S.W. estimates).

~).21 AssOWuming a reUqU § ICU pumpUinp g aUpacity of v 0. inch 1UP ady Uo

0.025 c.f.s. per acre, a 50,000 acre pumping plant is estimated to costMS. 290 per acre. At 0.75 inch per day- the capital cost wo-uld be nS. 320per acre.

5.22 Annual pumping costs are subject to considerable variation withrairnfall intensity, duration, river levei, energy cost, etc. The assumedcost is based on a rainfall of 70 in. during the wet season, an evaporationof 20 in. and storage carryover of 5 in., leaving an average 45 in. excesswater to be removed by pumping. Assuming a pumping head of 15 ft. and anenergy cost of 16 paisa per kwh, the annual pumping cost is estimated atRs. 15 per acre. This could vary by ± Rs. 5 per acre with physicalconditions and. be much less if secondary energy could be relied on.

5.23 Annual operation and maintenance of the pumping plant is estimatedat 2-1/2% of the capital cost and replacement costs at Rs. 8 per acre(Dacca S.W. assumed. typical).

2'oreign Exchange and Unskilled Labor

Foreign exchange assumptions:

-umping Plants - 50,%- Mean for polder project: 30%

Embankments - 5%

Unskilled. labor assumptions:

Pumping Plants - 20%- Mean for polder project: 45%

Embankments and Channels - 90%

.Oa -SI LAmN L----------

1 -4-4

C\j (D

F .-7

.10;ool00

z ju

It 7

X LC :4

7.7 K No Li F, 4% r- -/ER-

A%ilEX 1Page 2.4

Category 4: Gravity Drainage and Embankment and Tidal Sluices

(a) - LDU 2 & .6, SW (2% over 3 ft and 87% 1 ft to 3 ft) - Barisal -16,000 and 882,000 acres

(i) Over 3 ft

Channels and sluices - 16,000 ac @ R 75 - Rs 1,200,000

Say 4 ft embankments, 10 mi @ R 50,000 - 500,000

Total - 1,700,000

x 1.35 - 2,295,000

Cost per acre - R 140 + 12% IDC - Rs 155/acre

Operation and Maintenance

2% x 1,620,000 - Rs 32,000

10 mi © 5,000 50,000

Total - 82,000

Say Rs 5/acre

(ii) 1 ft - 3 ft

Channels and sluices - 882,000 ac -

@ R. 75 66,000,000

Say, 4' embankments - 1500 mi

@ Rs 50,000 - 75,000,000

Total - 101,000,000

x 1.35 1,O0000,000

Cost/acre - Rs 216 + 18% IDC - Rs 250/acre


2% x 66,000,000 - 1,300,000

1500 mi. © 3000 - 4,500,000

Total - 5,800,000

x 1.35 - 7,900,000

- Rs 9/acre

Say Rs 10/acre

ANIEX 1Pagye 2q

(b) - LDU h, E. - Noakhali/Dakatia/Feni

Calculation 1:

Flooded area - 175,000 acres

Embankment 28 mi. @ 600,000 - 95'DegLao 1 S4 5,0,00 =3

Major Sluices h no. @ 1,000,000 23R. 255

x, 1. 3D RnR

1cl Tnh0 fl'Nn/* 'c- -V I J2-'

Calculation 2:

From IECO Interim Memorandum, Dec. 1970

Stage 1 - Project cost per L. Feni Dakatiaacre (excl-udglrWater Transfer and Rs 268 Rs 134Distrir±bution)

Full Dev.-Increase in projectcost per additional Rs 525 Rs 4c,0acre

Assume difference is cost ofdrainage and flood control: Rs 257 Rs 356

Adopt, rn R /a - o ..- regior,Adouput R ,' crt jo unisL rug±Luii

ANNEX 1Fage 26

Category 5: Medium Embankments and Pumping

(a) - LDU 5, NW Belkuchi/Ullapara - 160,000 acres

Embankment improvement - 32 mi @ R 50,000 - Rs 1,600,000

New embankment (over 12') - 96 min~ D on n(Vn OA pnr% rrn' it -R300,000 - 28,800,

Chann.el-mpoe,,n 160,000 ac r- RD An -n 12,0"00

Regaulators - 2 I R 10 m - °,ooo.ooO

Puuin)Lg- Plant's - u 160,00 ac. @. R 9 6'o,o

Total -) , 100 ,000

x 35 1-3, 00 OA

Land - 96 .mi I Rs '160,000 - .A .nr, Gonr

Total - 39,200.000u_pi *a ngos _ _ -rs - .1 ,u C _ t ,f ,- / _ '

ImP t , I ucr ,flnacrbeRk)| b tbUN 1U1dUlt nJur tIU0WJ-i. - ybI ,U9U/,U'U

Say Rs 1,050/acr-eOperation and Ma''n-0enance

Drainage Channels - 2% x R 12 8 m x II 35) - Rs 3U,00

Embankme -96 128 mi R 14,6o0 1,7)402,000

Pumping plan-cs - 2.5% x R.,40.4 x 13T _ 13,600000

Rs 35778',0uo

-Rs 2V/acre

Energy cost 15

Replacement costs o

Rs L,7j acre

Say Rs 50/acre

ANNEX 1Page 27

(b) - LDU 9 & 102SW Pabna - 318,000 acres (Empoldered 450,000)

Calculation 1:

Embankment (14h average ) - 188 mi @ R 400,000

x 1.35 - Rs 101 m

Cost per acre - flooded, Rs 320; g2rossR 225/acre

Drainage channels - Rs 80 x 1.35 - 110

Pumping plants - Rs 290 x 1 .35 - 390

Total Rs 725

Land 188 ml @ Rs 200,000 - 120

Total - Rs 845

+ 18% IDC - Rs 1,000/acre

Calculation 2:

From Sanyu draft report, Vol III, Nov. '70, Table 6-1

Zone II Area - 55,980 acres

Basic costs: Embankments - Rs 11 .9L m - 214h/acre

Drainage channels - 3.36 m - 60

Pumping plants - 17.62 m - 315

Total Drainage and Flood Control cost - Rs 994/acre

Adopt Rs 1OOO/acre


Drainage channels - 2% x R 110 - Rs 2/acre

Embankment - 188 mi @ 15,000 - 6

Pumping plants - 2.5% x R 390 - 10

Energy cost - 20

Replacement - 8

Total - Rs 46/acre

Say Rs 50/acre

ANiEX 1Page 28

(c) - LDU 13, C - Dacca North - 112,000 acres flooded, 150,000acres gross

(From Sir M. MacDonald preliminary note - June '71)

Estimated capital cost, drainage and flood protection -Rs 140 m

Gross area - 150,000 acres

Cost per acre - Rs 935

Flooded Area - 112,000 acres

Cost per acre - Rs 1,250

It is suggested that in this area with considerable highground a mean figure should be adopted - say Rs 1,075/acre

Assume Operation and Maintenance - :Rs 50/acre

ANNEX 1Page 29

('a+ ory 6_a,or jor rm.e+ts and ,mrping

(a) - LDU 8a, 8b, 9 (p.o.), 10,11 - C - Dacca SW - 334,000 acresgross

Drainage channels and sluices - Rs 80/acre

Enbankrnents - 155 mi @ Rs 83.5 m

r U.IFLJ.LII ~ ~ 1fl. u iii(D'w Riv Lepo) rt I5

~rurnping plant-s - TRLs( 10.8 r,.(DSW Report) - 330

Total - Rs 660

x 1.35 -Rs 890

Land - 155 mi ( Rs 280,000 - 130

Total - Rs 1,020

+ 18% !DC - Rs 1,200/acre

Operation and Maintenance - Rs 50/acre

AiHNEX 1Page 30

Additional Estimates

(a) - Gravity drainage and long embankments - Kurigram and UnnerKushiyara type projects, Brahmaputra left embankment.

Kurigram: Gross area - 345,000 acres,Cost ner acre - Ps 500

(LDIJ 3 and La. NW) Flooded area -38,UuW acres,Cost per acre - Ps 2;200

.Kushiyvra Bpnefitting area -

(LDU 7,E) 80,000 acresCost per acre - Rs 660

Brahmaputra Left emb2nkm.ent:(LDU 9,C) Benefitting area

Cost per acre - Rs 600

(b) - Small Pumped 'Drainage Projects - e.g. Halda and Ichamati

Ichamati - Benefitting area - L,770 acresCost per acre D s 1.5

V~~~~St 'DO-1~ ~W L~. 1.

Halda, East Polder =Benefitting area -

23,000 acresC ostU per acre TS- Rs 1

Halda, WV OLest P'older - Benef Fitti area -

17,000 acresCostu per acre II's 1,38

ANN&C2 1Page 31

0. Potential DeveloDment Costs

6n01 R.egional Analysis by Tand Develonment IUnit. The estimatedcosts, on a "per acre" basis, applied to the potential development areas

-rp indiaont.rî hv regi on_ -nt.aorv nf davel onmont and nercentage of TDIJbenefitting in Tables 18, 19, 20 and 21.

6.02 The "tcost per acre" for gravity-type drainage development(categories 2,3 and hi) are based on the p.ti-matd flooded areas_

6.03 l'he"costs per acre" for pump -type drainage developmentCategories c and 6) generally reflect the cost of benefit-ting the floodedareas althouigh the -.co prn, acre. ae baiscd on t.he total 21 emporie

area. These costs are, therefore, slightly optimistic, as the total area;n~ t uni~- + ' not ccn ec i Iair -kb =r+ +o fl noodi nas cd fi neld ea rl er

i e., over three feet deep. However, as virtually all of these unit areasYVJ.i 1JS- 4iA .1 f i A. 4P 0 fS I A..A -JA fr otA Si AJSJl *_ U ~ ~ A ~ A +n n Q~ qnwould benefit fro flood prt- ction, i+ is consldered- thecotda

developed can be used for the Sector Planning Model analysis.

6.o4 The Categories of development used in Tables 9 to 21 inclusiveare restated below.

CATEGORY DESCRIPTION

1 No significant drainage or floodcontrol works required

2 Gra-vity- drainage works

3 Gravity and embankment

L4 Gravity and embankment and tidalsluices

5 Medium embankments and pumping

6 Major embankments and pumping

7 No significant improvement practical

8 "Coastal Embankment Project" works

ANNEX 1

Page 32

Analvsis'h bv flatgorv of Development

6 os As indirated in Summary o±f Potential Development Areas (p.r 1 ),Tabel 18, the potential gravity-type drainage developments total 1.41million acres, the pumped drainage developments total 2.75 millionacres and another 0.2 million acres will be covered by Coastal Embank-ment Project ..+-orks.

A oA The -tirated costs for the works n velopment

categories are summarized below.

GRAVITY TY'PE

Cateqorv LDU Cost/Acres-Rs Notes

2 5.rN7 185 Tncluding embankmentimprovement

6.NW 120 Basic channelimprovement

9.MN 120 Basic channelimprovemelCnt

3.SW 160 including embankmientimprovement

3 3 & 4a 2,000 (neOt) v7rv hiah proportionNW 500 (gross) of embankment

4.SW 270 Including mediumembankment

7.E 660 High proportion ofembjanOI-L 1-4LL 4

ANNEX 1Page 33

CategorvL LDU Cost/Acres-"Rs Niotes

4 __S.\? 155 Tnclud±rCr m4nor

enl'-anisLc':Itz4s

4.E 350 Includinc, n;ediiim5.E 350 embankments8.E 350

PUMP TYPE

5 5.Nw 1,050 Variations in categories_ll 1 l-on0 5 and 6 pr-nmarily diue

8a.C 1,000 to embanrkments13.C 1,0754.E 1,0005.E 1,000

6.E 1,0008.E 1,400

6 9. NW 1,000 Embank-nents subject to1O.NVI 1,000 river bank movement8b.C)9.C )

ll.C

If c SW 1, vv

Ai\TNX. 1

Page 34

7. Conclusions

7.01 Specific conclusions on the sequence and priority of drainageand flood-control works in the planned development program cannot bemade from this study. However, integration of the cost data with projectedbenefits in the model analysis will provide a ranking. This ranking, onan LDU basis, must be viewed with caution, however, because of their ratherlarge area and the possible wide variation in density of flooding withinany one LDU. As indicated in the Introduction, much more detailed andorganized data rGOp 1reetton is a vit_1 prereouisite to decision ma;king onmajor drainage and flood-control project development.

7.02 However, certain indications of areas within regions whichmight have ponornitv in flt;ure studiles are apparent. - bjehiprct always tojustification by agricultural benefits from drainage and flood-controlworks, and are omtlined below.

Northwest Region7.03~ Gravity Dralnage. The -ctlon of TTTT -n aa

the portion of LDU 9 draining into Chalan Bil, totalling 230,000 acres,appeIar proomising, -with no new -makmet -equlred.

7n0) Tr - - -fp * The s portio of TnTT 5 = +1t,h 1e1_,-Ch1-.-

Project area and an area to its west - should have priority over thePCabrna Project area.

7.05l G-rav-it r a The only area n this region w,dich mlay

possibly benefit is the region between the Jamuna and the Madhupur Tractnorth of the Dhaleswari offtake. * owever, this is very dependent on aBrahmaputra Left Embankment and much detailed study is required

7.o6 Pumped Drainage. Priority should go to the areas which adjoincomparatively stLabU'le riverbanks, e. g. LDU1 3d ardi 'a, totalling 25,ooo

acres gross and 227,000 acres flooded, between the Lakhya and MeghnaRivers; and the southeastern portion of LDDU 13 - the Dacca North projectarea. The presently planned partial development of the Dacca Southwestproject area should aiso have priority as a key trial major polder project,however, the priority ranking of this development in relation to alternatecapital investments requires re-appraisal on completion oI the Sector Study.

Southwest Region

7.07 Gravity Drainage. Priority should undoubtedly go to the floodedareas in LDU's 2 and 6 - the Barisal project area - although low-liftpump irrigation works investment should precede investment in drainage.Although the large Kushtia/Jessore area - LDU 3 - appears favorable, it

AMINEX 1Page 3.

is probable *that drainage works are of low priority in relation to investmientin co.mpletion of the existing Ganges-Kobadak Irrigation Project and inwater management development.

7.08 An area worthy of study is the southwestern portion of LDU 4,west- of an e:xt-ended 'Gorai er.ban-kent.7.0 The large aridpurSurewar are,a- lTnT Ta 4apparstl

priority but must be a major consideration in the proposed RegionalConsultJ ant'...I s s.IVU uu dL i eJs.

Eastern Region.

7.10 Gravity Drainage. Possibly the most promising I ar, sor11e440,000 acres, in the country for gravity drainage and flood-protectionworIKs is in LDU 4' south of tihe DakLdatia Ri-ver andU U 5 - jULle FeniL.The current project consultant should be requested to accelerate study oft1-l as ec , _ L I -S -u- 11 1- 1r -a C_-GniS dbpECCi 01 flJub contract commitmlents.

7.11 The area in LDU 8 known as the Sangu Project shouid have somepriority over possible pumped drainage developments in this region.

7.12 Pumped Drainage. Priority in pumped development should go tothe area in LDU aL Detween tne Dakatia ana Gumti Rivers presently understudy. The area north of the Gumti will have some priority in the proposedRegional Consultant;s drainage studies. The current studies of the Haldaand Ichamati projects in LDU 8 indicate favourable returns from flood-control but costs appear high in relation to other potential worksin the Eastern Region.

Summary

7.13 Priorities for the country as a whole might be:

7.1l Gravity Drainage. Southern area of LDU 4, East - the Comilla-Noakhali project region; Barisal area in LDU 2 and 6, Southwest; south-western portion of LDU 4, Southwest and the smaller areas in LDU 5 and 9,Northwest. Investigation of small projects in the Eastern region e.g.Khowai and Kushiyara, should proceed. Also study of the BrahmaputraLeft Embankment.

7.14 Pumped Drainage. The areas between the Lakhya and Meghna inLDU 3d and Ma Central; the Belkuchi project area in LDU 5, Northwest;the area between the Gumti and Dakatia Rivers in LDU h, East; the DaccaNorth project area in LDU 13, Central. The major polder project plannedin the Dacea Southwest area might have priority over some of these projeci;sas a trial development.

Table 1ANNEX 1Page 36

Bangladesh Sector Stmav

Broad Land Develonment IJnits

T Part. of Tista, Alliivil FanI Part. of Tista Alliivi. Fan

DTI Part of Northern Piedmont Plnain

IV BTarindl Tract

V M a d hi-ur Tract

TYrr PaA o- f th KaratayV- a,,n Ta.,na a.d Old ta Flood Plan

UTT1 Part of the Old PT- 1mnrni+ra- Flood Plain

Vi C PDarts of the Old and vouang B-a>-,a-t- (Ja...-a T9- od Plain

VITTA SJylhet B-sln

VTTD Vaster . - Ku'shiar Tlo -laV lL) I, 24 0tA U i U ± iSS±. 1n S .LL-.4_4.".

VTTI Pat oiddl e G;anFlood Talaina and Old>n EstIMFutr.e 'Flood P1la-ins~TTT( TT) -- d,~~ M-l,- fl,-1 -4 T71 4 -,I, C1A :l31-4-~Dl ~ V -l ISP K01U.455 IS UJ0.±1U5240, Si 0.455U44.0 1.J±UA 5.54.5.. 15±'ul 0.A4iSS0.HLU V. 12 L-uS.U I Lal xJ

VIIIT Parts of Ganges, Atra4 and Lt44tle Tamr.n.a FlloodAlanVIII 1 0.. 1,0 5.51 u 0 U 0.1 011 U U..L: r .vv r K ..L0.j 110

ILA 170.11,0 U I £'0.10iLIi0.1AU0 CLIIU U0JIIrUD £- I uS E -La-1I0

A IT "~dII~ UI~~ U . -- AU -'.JI --

xi Young Meghmna- Estua-rine Fl' o-od Plain

XII Saline Ganges Tidal Flood Plain

BANGLADE3H SEC1'OR TUDYr;RO,AD LAND DEVELOPMENT UNIT AREAS IN RELATION TO F'LOOD-DEPTH CLASSES

Flood Depth in Feet = Homesteads + . _ er-all-road Land Loss than 1 nw 1- 3 < 3-6(ndE4ver6(df) Water-tanks Total Flood-path

_eveloprr.ent Unit _ sqms m % _m%m _ s m '% scr m Concdition

I 1001 61 515 32 3 _ -_ 115 7 1634 Practically noX .271 12 2012 87 1G 0.5 9 0.2!5 9 0.25 2317 moderately deepxir - - 2719 88 - _ _ - 379 12 309B and deeply floodedIIIB 450 41 587 54 - _ _ _ 47 5 1084 land

II 1430 39 1802 49 105 :3 7 _ 332 9 3676IV 2036 67 583 19 85 :3 101 4 226 7 3031

V 785 54 289 20 66 4 234 16 93 6 1467 20--30%VIB .568 36 670 43 138 '3 39 2.50 149 9.50 1564 mcderately deepIx 2164 45 1.063 22 979 20 278 6 357 7 4841 and deeply floodedXI 198 18 374 34 275 25 10 1 24:3 22 1100 lardIIIA 101 17 280 48 147 2.5 27 4 32 6 5&87

VI. _ -_ _ 163 8 __ 840 43 538 27 270 14 160 8 1971 [1 40. rr.cJf + dfVIII .349 8 1.143 26 1376 31 1251 28 2 89 7 44c0 60-G5GVIID 55 1 512 17 1190 39 766 25 544 18 30c•7 c.d:E + dfVIIA 191 8 345 14 934 37 858 34 185 7 2513 ,0-- 80VI:- 23 4 39 6 131 21 340 54 9:3 15 626 m'oderately ceepVIIC 15 3 43 8 65 12 338 63 7:2 14 533 and deeply floodedVIIB - - 410 22 419 23 1014 55 3 - 1846~_ __ _ __ _ _ _ . _ -- - _ _ _ , _ __ _ _ _ _ __ _ _ _ _ _ _

TOTAL BLDU's 9800 25 14226 36 6467 16 5542 14 33293 9 39363

Not included: nf = veryactive flood plains shallowly f;LoodedLDU's INWIla, llb; Cl12; S)l - 2209Sundcrbans (LDU SW10)- 1900 sf = shallowly floodec.Hills (LDU's C14;Ell)- 878Water +- Urban areassU . eyeC - aeas2063 rrdf mr.oderately I JI01V~atcr +-Ubnaestuncr,:cyed 914 deeply flooded 1 CD(inclucaing large 914 deeply flooded CD

e~~~tuaries) - - - ~~~~~~~~~~~~~~~df = deeply flooded Hr\Chittagong + iill -i__ ._ 7798'r:r . c _'>t - 79I

TOA'L.' Bangladesh 55b _

Table 3A KIThT"' -1

Page 38

BANGLADESH SECTOR STUDY

SWUiLIZIARY OF E LOjTD.L.C. COL'DITIO.-S ON C0.U .1 .k.TCULT' '.ALli.'2

A_ eas in Sc,uare !ie ru2

Group nf + sf mdf df Total

Practically no moderatelyor deeply flooded 1-nd 13,406 209 117 13,732

20-30% moderately deep and

deeply flooded land 6,492 1,605 588 8,683

40% moderately deep anddeenlv floodRd land 1.003 538 270 1.811

60-65% moderately deeoand deeply flooded land 2,059 2,566 2,017 6,642

70-80% moderately deep anddeeply flooded land 1,066 1,549 2,550 5,165

TOTAL Bangladesh 24,026 6,467 5,542 36,035

nf = virtually non-flooded (less than 1 ft

sf = shallowly flooded (1-3 ft )mds = moderately deeply flooded (3-6 ftdf - deeply flooded (oVer 6 ft )

i Areas mentioned at the foot of Table 2 excluded2 Exclusive of homesteads and water (tanks)

BANGLADES3 SECTOR STUDY

BRChD L_AND DZVEWPM4ENT UNIT APEAS IN RELATION TO FLOODDE>TH CLASSS IN THE NORTIVWEST REC10NI

1. -_ Flood Depth in Feet }[omesteadsEi Total [Cverall Ploocd-Depth

Broad Land Less thanL 1 (nf) I - 3 (sf) 3 - 6 tmnLdf) I y,er 6 (df) E. Water Conditions in N.WU

Develonment Unit. sq m % qr srn q a sq m y;q in sq m Legion

I G101 61 51S 32 3 - . _ 115 1634 Practically no

midf + df- land

II 131.3 37 1779 50 105 3 7 _ 316 9 3520

19 2036 67 583 19 85 3 101 4 226 7 3031

ProfIA- - 36 42 32 __ 10 12 _- I .l . n _lPart of IX 511 36 3001 21 305 22 143 10 152 11L 1412 3et0een 3: ano 5Ca

Pa1rt o:F VIA _ _ 36i6 42 324 3 7, 105123Se E0

~~~~~~~~~~~~V-_ _ _ _ _ _ _- - - -Part oE VIII 311 3 139 14 227 22 329 52 92 9 11018 over 73% rdf and

df lend

Total of BLDU'S in

N,W. Regiort 4892 42 3683 32 1049 8 8835 8 986 9 11495

Note: nf very shallowLy flooded

sf = shallowly flooded

rdf = moderately-deeply flooded

tf = deeoly f looded

*1 .1- r-k- X ICD

\"ci H_

BANGYLAJJEh kSECTOR S'TUDY

BROAD LAND DEVELOPMENT UNIT AREAS IN RELATION TO FLOOD-DEPTH CLASSES IN THE CENTRAL REGION

-_ _ _ _ _ FlcodDe.t h in reet Homesteads 'Total COveroll Foocd- ept;,Broad Land Less than 1 (nf) 1 - 3 (sf) 3 - 6 (ndf) OVer 6 (df) & water Conditions i:i theDevelopment Unit sCT m - sq m sq m sq in q m % - sq m ' Centril RegionPart of II 117 75 23 15 - _ -1 :6 10 156 Practicali.y no r.df

_ - - _ . _ -_ _ ____ -_ _ _ _ _________ _______ __ _ _ _+ f la_d

VIB 568 36 670 43 138 9 39 2 149 10 1564 IC)wcen 10 and 20't

rnd' + df l.andv 785 541 289 20 66 4 234 16 93 6 1467

IIIA 101 17 280 48 147 ;25 27 4 :33 6 588 13Betwcen 30 and 500rm3f + df land

Part of VIA 163 15 474 43 214 20 165 15 7 5 7 1091

Part of VIIA 84 8 1.50 14 399 :37 367 :34 77 7 1077 ilore thin 707- i.lf+ df land

VIC 23 41 39 6 131. :21 340 54 93 15 626VIIC 15 l 43 8 65 .12 338 63 72 14 533

Part of VIII - . - - 15 10 123 80 15 10 153

Total of BLDU'S in

the Central Region 1856 26 1968 28 1175 .16 1633 :21 623 9 7255

Note: nf = very shal'Lowly floodedsf = shallowly flooded

nrdf = moderately-deeply floodeddf = deeply flooded

CD F-H


BPOAD LAND )EVE OPM Pr UNIT AREAS IN RELATICN TO FLOOD-DEP'TH C]LASSES IN THE SOUTHWEST REGION

____=______ Flood Devt in Feet _ Homesteads Total Overall Flood-Dcpth

Broad L,and Less than I (nf) 1 - 3 (sf) 3 - f (A,f er 6 (dC) I & Wa1ter Ccncitions in theDevelopment Unit sam m sm % sq m M sq m % sq m % s(I m S.W. Region

x 271 12 2012 87 16 1 9 9 - 2317 Practically noXII - - 2719 881 - - - _ 379 12 3098 mdf and df land

Part of IX 1653 48 762 22 674 20 133 4 205 6 3427 20-30% mdf and

_________ _____ ~~~~~~~~~~~~~~~~~~~~~~~~df 'Land

Part VIII 318 10 1004 31 1134 35 599 19 184 5 3239 50-70% mndf and

Total of BLIDU'S in

S.W. Region 2242 19 6497 54 1824 15 741 6 777 6 I 12081

Notes: nf = very shallowly i-loodedsf = shallowly flooded

mdf = moderately-deeply flooded.

df = deeply flooded

.i (ONN X |I C

BANGLADESH S SJTOJ STIJDY

E3ROAD LAND DEVELOPMENT UNIT AREAS IN ]RELATION TO FLOOD-DEPTH IN THE EASTERN REGION

_____________r_ Floocl Depth in. FetM: Homesteads Total OveraLl Flood-Dc-tl

E3road Land ILess 'than 1 (nf) 1 - -l (sf) 3 - 6 (mdf) Over 6 (df) & Water conidit-ions in theDevelopment Unit sqm m sm % sq mn % sq m SC I m sq m Ea:;te:rn Region

IIIB 450 41 587 54 - - 47 5 :L084 No indf and df land

XI :L8 1.8 374 34 275 25 10 1 243 22 1100 20-30%i mcf & cif1 and

}art of VIIA :L15 8 20;L 14 531 37 488 34 101 7 1l436 71ore than 70%m.-lf tdf land.

VIID 55 1 512 17 1190 39 766 25 544 18 :3067VIIB - - 410 22 419 23 1014 55 3 - :184G

Trotal of BLDU'S in"astern Region 818 10 2084L 24 2415 28 2278 27 938 11 6533

Notes: nf = very shallowly floodedsf. = shallowly flooded

ndf = moderately-deeply floodeddf = deeply flooded

I a'ND I H-

" I CDRJH-

BANGLADESH SECITOR STUDY

ANALYSIS OF NORTHWEST REGION

]otential ResidualNet Areal Flooded Area Developrment Areas (1.000 acres) loocl.CC. Al:rea

LDU (1000 acres) (1000 acr s) 1 % c,f Net il 3'-6' .1 >61 Total 0o Net (1 0 eO CJ '_

:1 199 1 0.5 . NIL _ 1;2 799 0.5 0.1 - _ NIL _ 1:3 1,361 40 3 1]9 _ 19 1.4 214a 434 31 7 1]9 _ 19 4 124b 181 See LDU 13 -- - NIL _

5) 581 275. 48 2C)7 68 275 48ID 75 15 20 1]5 _ 15 20 -

7 37 37 1.00 -. N I L, _ 37Ba 203 203 100 . _ NIL _ 2038b 24 5 20 -- - NIL, 5

9 832 268 35 124 62 186 22 82:10 334 24a 73 11]3 131 244 73.lla,,b (605) (605) 1.00 -- - NII _ (605).12 192)

).13 1,332) 117 7 _ NIL , 117

)14 170)

.___ __ ___ _ __ __ 261 ._ __ __-._-I

TOTAL 6,754 1,2373 18 497 261 758 11 479 (79il

nuiill.teS L.UdULt CtitU WdcLt fu±uueL U $utl;

2 Active river flood pla.in Active river f lood plain, excluded (D

BANGLADESHi SECTOR STUDY

POTENTIAL DEVELOPMENT AREAS BY WORK CATEGORY - NORTHWIEST1 REGION

Flooded Areas (1000 acres)LDU Category f1 3'-6' fl >6' Total ° Net Area

3 3 19 19 1.4

4a 3 19 _ 19 4

5 2 82 37 :L19) 21275 418

5 125 31 1L56) 27

6 2 15 15 20

9 2 75 37 112) 13186 22

6 49 25 74) 9

10 6 113 131 244 73

TOTAL 497 j261 758 1L

8 PCDI(H

BAiN D IJ S, 1CTOR STUDY

ANALYSIS OF CENTRAL REGION

Poterntial ResidualNet Area' Flooded Area Development Areas (1000 acres) Flcoded Areas

LDU (1000 acres) (l__OO_crES) % -f: 6' fl> G' Total _ a c- ._ s

12 (45() (4i50) l10 _ _ _ _ (450)2 187 52 28 _ _ _ _ 52 283a 624 34 13 _ _ _ _ 84 133b 242 50 21 _ _50 203c 272 :32 12 _ _ _ _ 32 123d 119 106 89 30 76 106 89 _ -4 117 NIL _ _ _ _ _ _ _5 164' :35 21 3 _ _ _ 35 2i6 17 6 4 9 28 _ _ _ _ 49 237 35'jh 3'354 79W' _ _ _ _ 390 798a 137 1:21 89 27 94 121 8'9 -8b 73 73 100 8 65 73 100 _-_9 656) 4'5 0 68 1 60 2930 450 G613 -10 1 25 1:25 100 1.4 1l11 125 10( - -

112 28E :28 100 3 :25 28 10( -12 (55) (55) 100 _- - (55)

113 946) 19'6 20 1.9 933 112 12 84 814 3 5 1 0 28 _ - - - 10 28

_ _ _ ~ ~~~~~_ _ __ __ ___ __ __ _ KTOTAL 4,2563 I,8( 3 43 261 754 1,015 24 786 19

1 homesteads excluded2 Active river flcodplain ' ilo

3 Active :river floodland excluded ~iHj9h Conflicting data - Brammer/Schilstra (does not influence potential development areas)

RANGL4.DESHi SECTOR STU]DY

CENTRAL REGION - POTENTIAL ]DEVELOPMENT AREAS BY WORK CAT:EGORY

Flooded Areas (10&00 acres)

IDU Category f1 3'-5' f1 >6' Total _% Ne2t

3d 5 30 7 6 106 89

8a 5 27 9'4 121 89

13b 6 8 65 73 100

6 1]60 29 0 450 68

10 6 14 l:l 125 10 0

11 6 3 :25 28 100

.13 5 19 93 112 12

TOTAL 261 754 1,015 24

o(ID H


ANALYSIS OF S'OUTHWEST REG:ION

Potential fResidualNet Area. F:Looded Area Dcertv-1o]2ment, Areas (1000 acres) Flooded Areas!

LD)U '1000_acres) l1o00 acres) % f 2-' f.3>6' Total N t _____uu __.-r.s iA

I ~ ~~2 21 (272) (272) 100 _ . K (272)2 208 14IL NIL _ .3 2,032 516 25 381 86 467 23 49 24 1,436; 1361 60 578 .283 861 60 _5 542 :248 46 - . 24 8 4 6 8041 16 2 16 16 2 - _7 1,321 NIL NIL _ . _ . _8 274 NIL N IL _ . _ _9 (220) )NA - _ . _ .10 (1,020) NIA _ - . _ . _

~~~~~~~~~~_ __ _ __ _ __._ _ _____ _ ._._.__

TCOTAL 6,617 1,641 25 975 369 1 344 20 297 5

1 Homesteads and water excluded

2 Activ& river floodplain

Excludes active river floodplain and LDUT s 9 ancd 10 - tiLdal inundated land and sunderbans


SOUTHM:EST REGION - POT'ENT'IAL DEVELOPMENT AREAS BY WORK CATEGORY

rFloodod Areas (1000 acres)LlDU Catecgry _ 1 1 3 '-6' _f 1 >6' Total _ Net

3 2 381 8 6 467 23

4 3 135 5 6 191 13

6 443 227 6710 47

6 4 1.6 1 116 2

TOTAL 9 75 369 1,344 20

i1 1 '-31 :El U 3'-6'

2 lEl _ 18:1 874

6 _71 1 El 717 87

: F i. oCCDV (DH


ANALYS:IS OF EASTERN REGION

Potential ResidualNet Area1 Flooded Area DeveloDrnent; Areas (l000 acres) Flooded. Areas

LDU (LOOC acres) (1000 acres) % fl 3'-6' f15-6' Total %J _ (l000 a.c.res) _ J_ I---_ .- ____ __ __ ____l

1 !287 NIL . _ _ _ _ _2 1,0C55 750 70 _ _ _ _ 750 703 l,097 820 ,75 _ - - - 820 754 1,Cl96 824 ,75 504 320 f324 75 - _5 237 166 70 123 43 L66 70 - _6 273 262 96 25 25 50 18 212 787 209 1.0 5 10 - 10 5 - _82 (714)2 NA . _ _- - - -92 (50)2 _ . _ - - - - -

10 705 182 26 176 6 IL82 26 _ _lla 2 ( 500)2 NIL . _ _ - - - -

~~~~~~~~_ __ ,_ _ _ .. __ _ - . _ _ ! _

TOTAL 4,959J 3,0143 61 838 394 1,232 25 1,782 31

Homesteads and water excluded2 LDU's 8,9, lla were excluded in basic data (Schlistra)

3Excludes LDU's 8,9, 11eL - Chittagonc district and hills and h:ill tracts

*t 1t:;1 '-

(D W i-~, (

4:1 F

BANGLADESH SECTOR STU)Y

EAST REGION - POTENTIAL DEV]ELOPMENT AREAS BY WORK CATEGO]RY

Flooded Areas (1000 acres)

LDU Cate-Tory fl 3'-6' f1 >6' Trotal % Net Area

4L 4 202 70 272) 25)82 4 75

5 302 2150 552) 5o)

5 4 1-23 43 166 70

6) 5 25 25 5 0 .18

.7 3 10 1 ( 5

L0 90 1]76 6 18:2 26

TOTAL 838 394 1, 23:2 25

ADDENDUM:

8 (Szangu.) 4 NA NA 2 0(Muhur i) 5C NA NA 5 0(Icharnati) 5 NA NA D

(Halda. E) r5 NA IA 2 3 I(HaLlda. ) W) NA 17 tJ° t F

1 3~~~~kC

TOTAL 111,

_______ TC)TAL ____ ___1,347 2 7

Table 16ANNEX 1Page )3T

Flooded and Potential Development Areas -

Samma.ry by Region

| egio~ I~et A |~d A Residualk RegiLon. ,hel Area v Flood-ed Ar-eas rot. -ev. Areas I F-loouded Arelas

im ac m ac m ac m ac

SNrth-West- 6.7f5 . C.4 18l 0 .7 1 1 0.48 7

iCentral L r.25 o- 1.80 I4 , .o1 2 I U. 070

sSouthwest 6.62 1.6h 2.34 20 0.30 5

LEast 4.96 3.01 61 1.23 25 ! .78 36(5.67)*. ( .36)* (27)*

1----------------- !--- ----- -- ---.Total 22.58 7.69 34 4.3 4 i9 3.26(23.29)*l (h.L7)*

* Including known potential development areas in LDU 8 (East) - totalflooded area data not available.

Table 17AXTNNEX 1Page 52

no+ on+ a 1 Tb,l - ,n+ A p-nn _

Summary By Works Category

| Category j Flooded Area Per Cent of Per Cent of lI ~ ~~~I /I nn - - T I'Ml A-- I To.. A.,-.

| | I1,0uu acres) F.LooUdeud Ar.ea Po Dev. Ara l

1 450 5.8 j 0

2 713) 9.3) 32

| 3 239) 1,106 | 2.1) 18.3 l

14 454) 5_ _9) l l

5 1 1087) 1 41.2)llI I 1,8) 2,751 1) 35 9 I LI I6 11,664) 1 21.7) l l

| 7 2,8il! |37.6 l 0

1 8 1 182 2.14 4 l

Total | 7,683 100.0 | 100 1l l ! l l__ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _

BANGLADESH SECT'OR STUDYCATEGORIES PLND COSTS ]3Y I..D.U. - NORTHWEST REGION

Pei, CaEital Cost Rs Annual CostsI _ _ - _ _ _ - .~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0. T-VLDU Cateqories s of LLU - Ac re % f.e. 2 Lab A cre % f.e.

K 1 Lv 1.00 0 - -

V ] I001- 03 1 98.6'' 0 _

3 1.4 25,(200 5 80 1L2 . 15 l 95

4a 1 95.6 03 4 . 4 2, 20 0 5 8 0 :L2. 1 9 5

(500) *

4b 1 1.00 0 b -

5 1 52 02 21 185 5 80 1 0 1 9 55 27 1, 00 30 45 50 10 '0

6 18 0 0 ---

2 2 0 1:20 5 90 2. ; _ 9

7 7 1-00 -

8a 7 1|00 .

8b 7 .100 - -

*Small per-cerLtage of empo1ldered areia suab ject to flooDdiric c,ver 3 feelt. FigureOs ii., bracl;;ct:.are c(Dst for- gross acrcacTe emso:lde:red.,

(C o ' un . !

BANGLAIDESH SECTOR STUDY

Canital Cost Rs' Annual CostsPer Prer ___-

LDU Categories % of LDU Acre % f.e. % Lab Acre __ f.e. T Lab

9 1. 68 0D _ --

2 1.3 120 5 90 2.5 _ '56 9 1,000 30 45 50 10 -07 1.0 NA

10 1| 27 I) - - -

C, 73 1,000 30 l5 50 10 n0

lla 7 100 NA

llb 7 100 NA

1 2 J100 0D

13 1 00 0)

14 1 4 100 0I

USTDL - Rs i4.76 ;1,|-

0

BANGLADESH4 SECTOR STUI)Y

CATEGORIE,S AND COSTS B3Y L.D.U. - CENTRAL REGION

Per Xital Cost IRs Annual Costs

LDU Categories % cf LDU Acre % f.e. % Lab Acre ° f. e. %_Lab

--X -1~- -- - t -- -- F -t -____ T-- i_

1 7 100 L42 7 100 053a 7 100 |43b 1 100 313c 1 10 0 3d 1 11 -

5 89 iL,200 30 45 50 10 50

4 1 100 __5,6,U7 7 10 0

Ba 1 11 -

5 89 :1,r000 30 45 50 10 1508b 6 10 0 :1 ,200 3 0 45 50 10 50

9 1 3 2 j -

6 6 8 1, 200 3 0 4 5 50 10 5

10 6 100 :L,200 3~ ~ ~~~~~~~~0 4 5 50 10 50

1US$1_ Rs h.-76 \

BANGLADESH SECTOR STUJDY

. _ _ ~ ~ ~ ~ -_ _ __________- -_ _ __ _ _ _ _ _ _ _

ajLta2L Cost Rs; Annual CostsPer Per

LDU Categories % of LDIJ Acre %i. e. % Lab Acre 2 f.e. % L,Db

11 _ 6 100 1,200 30 45 50 10 5012 7 1008.13 1 88

5 12 1,075 30) 45 50 10 50

.14 7 100

U'S$1 Rs 4.76

td D F

(D b lH

P1 HCD

0iF C,-

BANGLADES-1 SEC(TOR STU:DY

CATEGORIES ANiE COSTS BY L.D.U. - SOUTHWE3ST REGION

Capital Cost Rs Annrual Costs

ILDU | Categories % of LDU Acre % f.e. % Lab Acre f. C. Lab

1 7 1.002 1 003 176. 5

2 .235 1-60 5 80 5 1 ] 95

4 1 373 13 270 5 80 i 1 9 56 47 1,200 30 45 50 10

5 7 1.00

6 1 9 8 4 2 1-55 .5 9 5 1

7, 8 8 1.00 38 0 5 80 10 1 9 5

9, 1.0 7 1.00 _

2,rE6 1 13 1if ~~~~~~~~~,~~CD F

2, e | | 1 3 _ T~~ ~ ~~~~~~~~ ~~ ~ ~~~~~~ r , i n . D|t.|1 . 1 4 ______ ___ . _J___ _ n 1_

I US.$1 Rs 4.76

BANGLAI)ESH SECT,OR STUDY

CATrEGORIE,S AND COSTS BY L.D.U. - EASTERN REGION

Canita:L Cost JRS 1 Annual CostsPer IPer

LDU Cateqories of LDU Acre ___%f.e. % Lab Acre % f .. % Lab

1 7 100 52 7 100 ]3 7 100 -

4 1 25 .

4 25 350 5 95 10 1 °55 s0 1,000O 30 45 50 10 50

5 1 30 -.

4 70 350 5 95 10 1 905

1 4 _. ,6 5 18 1.,000 30 45 50 10 so I

7 78 _.7 1 95

3 5 66)O 5 80 12.5 1 95

8 1 NA _ _ _ _ _ !N4 3 350 5 95 50 1 955 15 1]400C 30 45 50 ' 10 507 NA -- - - -

9 7 1C0o -l

10 8 ClO .380 5 80 10 1 95

1 US.1 Rs 4.76 N

(NA - not available)

AINN11X ni

h) .OALI LAN4D1'4 DLEVELOUTUV'L ' I VTS1I PART OF TISTA ALL.UVIAL FAN VI PARTS OF GANGES, ATRI1 AND LITTLE

I PART OF TISTA ALLUVIAL FAN . AVUNA FLOOD PLAINS

I aPART OF NORTHERN PIEDMONT PLAIN PARTS O MAHA'NAN. ' NGANGES

tlb PART OF NORTHERN AND EASTERN X NON SALINE GANGES TICAL FLOOD PLAIN

PIEDMONT PLAINMBARIND TRACT Xi YOUNG MIG,TNA ESTuAiNLE F6LOOD PL'AiN'

M MADHUPUR TRACT IM SALINE GANGES TIDAL 1'LOOO PLAINPAPTS OF THE KARATAYA. JAMUNA AND

~~) 1i~~~ \~'~~ II OLD ~BRAHMAPUITRA FLOOD PLAINS

Pl t 0. A1 / J I b FPART OF THE OLD BRAHMAPUTRA___ __~ FLOOD PLAIN

*' M Z/b.c PARTS OF THE OLD AND YOUNG''4 8 \ S k k\ EBRAHMAPUTRA (JAMUNA) FLOOD PLAIN

. o A I n \ R-rs ax o X 57NnURSYLHFT BsASIN\t/tt \ \> ) > n[\&; / lb EASTERN SURMA-KUSIYARA

A b_ yA rx v\ > ~~~~~~~~FLOOD PLAIN.> ~ <Y). (A \ E ; I _ MARTS OF THE GANGES, 4MUNA AND

I . t R \\ ; giJ1 OLD 8RAHMAPUTRA FLOOD PLAINS

i | ( > r - t w1 MDDLE MEGHNA AND MEGHNA ESTUARINEi . . . / . 1 1 SAL /. I A f FLOOD PLAINS

K4STJf,, wt< 0b N

rv j ,~~~~~~~~~~~~~~~~~~~~~~~~~~~"~~~'""'

>? "->,\A 0 .'> ~ A ~ ~ K «f 1 r ,><.>

'''r''tE,_ S 'tS~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I

'-'''-'' "'X'o'k' s s U ' 'i1=) ' iNs 1 '' I~~~~~~~~~~~~~~~~~~~-

o' ,.>2J lf /\i 2^ 't I . -§ . , ., .. , . Z il }~ S f i Vv..................................... s e -s :'~~~ ;~ -¾L .73 -,,',:/

,,. F 5 v ,. '.

Plate 2

r h ' ; v BROAD LAND DEVELOPMENT UNITS Page OUF -- -. A _ _ _I PART OF TISTA ALLUVIAL FAN N PARTS OF GANGES, ATRAI AND LITTLE1 _ \ _ tS ~~~~~~~~~X PART nF TISTA Al LLJV!'A1 FANI JAMUNA FLOOD PLAINS

X Ia PART OF NORTHERN PIEDMONT PLAIN II PARTS OF MAHANANDA AND GANGESlb PART OF NORTHERN AND EASTERN FLOOD PLAINS

PIFDMONT PLAIN X NON-SALINE GANGES TIDAL FLODO PLAIN

op I } \ \ \ | 0_ 8ARINO TRACT I YOUNG MEGHNA ESTUARINE FLOOD PLAINMADHUPUR TRACT fM SALE GANGES TDAL FLOOD PLAIN

,I', 1- -.. - IX ( a PAPTS OF THE KARATAYA, JAMUNA AND2 / l Xt \ V E l OLD BRAHMAPUTRA FLOOD PLAINS

Mb PART OF THE OLD BRAHMAPUTRA LEGENDS ! \ ) \ \.^L \ \ ' 2 FLOOD~~~00 PLAIN - --PRACT CALLY NO

r- c PARTS OF THE OLD AND YOUNG I I FLOODED LAND_BRAHMAPUTRA JAMUNA) FLOOD PLAIN 20-30% MODERATELY DEEPLY AND

ZbEASTERN SURMA-KUSIYARA 30-50% MODERTEL DPLY ANDFLOOD PLAIN DEEPLY FLOODED LAT D

3c PARTS OF THE GANGES, JAUNA AND 50-70% MODERATELY DEEPLY ANDOLD BRAHNMAPUTRA FLOOO PLAINS r -- DEEPLY FLOODED LAND

Id MIDDLE MEGHNA AND MEGHNA ESTUARINE jjOR 70% MODERATELY DEEPLY AND

~~~~~~~~~~~ A~~~~~~~~~~~~~~~~~L

..-- -

7 IK w- iiw-ta-eXMX'0

'R~~IL, ... L[= R tS - r j H M .C.; \t -, ____

I ._ - - ' X4 S I R-p __a

b'~~~ ~ ~~~ .; a

snlDISTRIBUTION OF MODERATELY DEEPLY AND t2 ... % DEEP.LY FLOODED LANDW(ORE THAN 3 FEET) ;..

Plate 3ANNEX 1

. ~~~~~~~~~~~~Pazere 61A ' X . , BROAD LAND DEVELOPMENT UNITS

X 9 8 I PART OF TISTA ALLUVIAL FAN VU PARTS OF GANGES, ATRAI AND LITTLE

- - _ . A X PART OF TISTA ALLUVIAL FAN vIAMUNA FLOOO PLAINSlJ PART OF NORTHERN PIEDMONT PLAIN O PARTS OF MAHANANDA AND GANGES

No PART ~~~~~~~ FLOOD PLAINSjib PART OF NORTHERN AND EASTERN X NON-SALINE GANGES TIDAL FLOOO PLA * . ~~~~~~~~~~~~PIDMONT PLAIN I O SLN AGSTDLFODPAIN

I BARiND.-X_"CT 3D YOUNG MEGHNA ESTUAFIINE FLOOD PLAIN6 ' - ? v\s . > MADHUPUR TRACT 31 SALINE GANGES TIDAL :LOOO PLAIN

7 la~~~~o PAPT'S OFt ITlt KARtiA IOA,JAMUNA ANUI, . k t uOLD BRAHMAPUTRA FLOOD PLAINS

mb PART OF THE OLD BRAHMAPUTRA LEGENDa. r1 amAe~TIr~i -I V M X .rFL Pl;rT!rALLY N.FPI Y

If e15[ - / t. N u | X . t. cPARTS OF THE OLD AND YOUNG FLOOOED LAND\ > ^/\ //1 t;i , , YltzSY~~~LHE AI 10 -20%IDEEPLY FLOODEDLN__ 2 ~ ~~~~~~~~BRAHMAPUTRA (JAMUNA) FLOOD PLAIN 7 ] OQ DEPYF)EDLAND

RI EASTERN SURMA-KUSIYARA 20-30% DEEPLY FLOOOED LAND

yMc PARTS OF THE GANGES, JAMUNA AND i 30-40% DEEPLY FLOODED LAND9 ' Ht 12 t \ 1 Y9\ 8zX 't 1 .Y OLD BRAHMAPUTRA FLOOD PLAINS L7_

, 'V;MIDDLE MEGHNA AND MEONNA ESTUARINL F-7 OVER 50% DEEPLY FLOODED LAND

A ;?

| h, . . + | . | 'M'/ r \ - s\

~~~~~~~~~Lc~~~~~~~~~~~~~~~

,...c~..*** r7r..

I ;1 DISTRIBUTION OF DEEPLY L X - ,|t FLOODED LAND (MORE'THAN 6 FEET)',. J

Flate 4ANNEX 1

[ ~~~~~~~~~~LEGEND Pg d-W %LNo MAJOR DRAINAGE OR(Z~~~T.~~L~~~~- FLOOD CONTROL PROBLEMSI' 1~~~~~~~~Vh ~ ~ ~ ~~~~ ~IMPROVFMENT BY GRA'VITY

7_ r =15-S 5,; l-' t-l..Z.J DRAINAGE DEVELOPMENT

____ -IMPROVEMENT BY EMBANKMENTAND GRAVITY DRAINAGE

1 r__ r:\ '.iIMPROVEMENT BY TlDAL SLUICESANDF ! ,, , } , ll \i>S.; 5Ss '3j ,,' r 8EMBaNKMENT AND GRAVITY DRAINAGE

z - L s q \ ' x ME ̂ f . | Xt e ., 7, IMPROVEMENT BY MEDIUMi-.-.'I EMBANKMENTS AND PUMPING

-j -; IMPROVEMENT BY MAJOR~~~~j\ ~~~~~~~EMBANKMENTS AND PUMPING

SEVERELY AFFECTED BUT NO MAJORIMPROVEMENT CURRENTLY PRACTICAL

: >. .._ \ \tf 4 *- _) J ss COASTAL EMBANKMENT

L S 7 8 i '; \ ;4 DEVELOPMENT

K_-~~-1

. < ! \ I ' t:----.- m :: -, :: 1 .. iN

|'~ ~ ~ ~~~~~~--Y~i I *4 i1; #t

1~~ ~~~~~~' ' p.jmS r

:n- )n

, ,a,4 -V . .t-, \w- , J }, l [ 4 , E , t ',: . : ,; \ .~~~~~~~~~~~~~~~~~~~~~..... ...

L r r.?R -- j , >8..........I ...... .I '''- ".-': I \\ 4 t:-/,.'.::''.1~~~~~~~~4

POTENTIAL DRAINAGE WORKS t A{IIi B Y CATEGORY N. -- p J

RMSTRICTRT)

INTERTL&TIOTJAI. BPA?TK FOR RECrOTTSTPTTUGTIONM A NM ThELOT.flPMvNT

TNTURT.ATTONAT. D EVFLOPMPNMT ASSOGITATTON

BANGLADESH


VOLCTMAE 1TTTI

TIE~ F'T1'fAT) DPfAnT3i'M

PP"TVTTr AT DMI'AD(P A ES.LL.'4LL1. . ±lJ. iLk .LV * j

~T)T1TVD QVC!1L'MT A1iTATVcQt'

Decerriber 1, 1972


BANGLADESI-I - SECTOR STUDY


TECHIUCAL REPORT NO. 25

RIVER SYSTEM ANALYSES

TABLE OF CONTENTS Page No.

Summary and Conclusions . i

I. Introduction *..........* L ......a.. ..... a.............

II. General Aspects .............. 2.

A. Geomorphic Aspects 2..........I... ***..... * , 2B. Types of Rivers soo.oooo.o............................... .3C. Flow Mechanics ...................... *.. ......... .3D. Sediment Processes o.so.s..... .$.0......... .. 00.... 0.0..,

E. Transport Relations @**000600*S00000e00000 )F. Effects on Mechanics of Flow ............................

III. River Training oo............. .. .. ..................... o7

Ao Embankments ............o o fo...........o..o...........o...ooo o 7

Frequency Analysis ...0......*..*0.00.....* ......0o ..... 7Peak Discharge with Embankments 9River Hydraulics I.ELSediment Transport 12.. ... 12Stage-Discharge Relation 13Location of Embankments .......................... ...... 17

Risks to Embankments ....... 18Coastal Embankments ..................................... 29Double Embankments ...... 29

B. Low-Water Channel Stability .............. 21

C. River-Bank Stabilization ............ 22

IV. River Response to Enbankments ............ 23

Predicting Response 23

The Glase of the Mjsjissippi- - 26Changing River Forms 26

Corncl usion- 28

V. Suiimmarv of Tlanrea Southwest, Fmbhnkment Studi - -28

A. Flood-freqoue.n.cy S+udies -28

' This report was prepared. by Dr. D.B. Simons, Colorad.o State University.

-2-

Tabhl nf CThntents (conetd .)

Page Ifo.

C. Rttivip+er rdr~.... e s p o nse..... 3

FV. Augest. fr--+re+i. ,

ft - j--L~~fUM~ a.~A~t . . 0 J .~ *.*..a ........

VT, Q A --- 4- -A T+ --A -P-- T-,--

BIBLIOGRAPHY

Figure 1 - Relation between Food.Recurrence Interval and.Probabilityof th liidben aaceded daua4 SelectedaAAA,,. ~aa Periodsn

ig-are ° ~ ql, c , -1T = -J-'I fle of± the ro..fl. ' x Overland.. .ooA.L i ng P a,.ob 1 em.S , i n

Bangladesh

Figure 3 - Effect of Embankments on a Flow Hydrograph

Figure 4 - Initial Response Response for Rigid Banks

Figure 5 - Response for Erodible Beds WIater-Sediment RelationIJrlL4g Onei HI-dUrogId4JL

Figure 6 - Stage-DischarLge Curves for the MIsiLUsL pi Rlver at Arkalsas City,Arkansas (after U,S. Corps of Engineers, 1971)

Figure 7 - Stage with Embankments

Figure 8 - Stage-Discharge Curve for the Padmna River at Bhagyakul for 1966/after - EC!-ACE, 197a)

Figure 9 - Channel Response to Levelopment (after W.E. Borland, U.S.B.R.)

Figure 10 - River Response to Enbanikments

Figure 1 - Mississippi River Flows at Vicksburg

Figure 12 - Stage-Duration Curve for the Mississippi River at Vicksburg, Miss.

PANGrTLDRqS - S TOR ST !JDTY

fT1TnTMV VTTTT - TH' PTr)ODT PpfLnT.rM

T'rw'MNT RT'.PnPT mNO 2tr

PTITTin Ss.ST7M AMA.VqPqSE

SUNMARY AND CONCLUSIONS

i. InT 101.6 -Xse P01- for flood -4-tro an dainae rojct-LAI -L.7'J4. 0.Ii. e £ L0±I . -LJ± . J.A U' 1AJ.L UJ. -JJ. 0Lu J .AOa~i' -

was prepared.by IECO and., in the same year, J.Th. Thijsse reviewed. thehyd-rolog4cal conditons o° -gldes and- oulied te hagewic

might be expected.in these conditions as a consequence of completion ofprojects for f-lood, contlvro"l, drainage,_ -r_-io,r.o=lcri oeand. navigation.

ii. In his review of IECO Master Plan (1964), Thijsse emphasized the.tmost of t.ih1e proposed, .-lood. UUILU± po.UJects WU'.LU, IdVa a cUoLsi.eU,rableU1.

effect on hydrological conditions. Thijsse outlined the hydrologicquestions -wh:.ch shLo-Idu.dbe answereu, before worik on those projects is bUr,ed.

These were c:Lassified as: (a) the high-flow problem of the rivers; (b) thelUow-flow problemltj (C) the sbiUiUt1by prbUlemj aIU kU.) cUda L P1l prolUems

In this repo:rt, the high-flow and stability problems are reassessed.. In theper,ou between 1964 and. the present, much inIornmation pertainlig to thesetwo problems has been collected. and. analyzed..

iii. The general aspects of the river system in Bangladesh are reviewoed.first. Ihe high-flow river problem has been reforimilaued. into a discussiLv1of flood, protection with embankments; embankments being the only method.considered. feasible for flood. protection on tne major rivers in Banglad.eshat this time. The problems of embankment location, height and maintenanceare considered. The effect of douile emDankments along the major rivers isassessed.. The anticipated. response of the river system to development isstudied..

iv. The river staDility problem has been divided into two parts.The first part deals with the movements of the low-flow channels and.howthese movements affect the avaiiaoility of water for irrigation systems.The second.d.eals with the bank erosion problem and. bank stabilization thatcould.be employed in Bangiadesh. A concrete application of the principlesoutlined.in the paper is presented. using the Dacca Southwest Project asexample. Recommendations for future river system investigations are made.,

v. In general, river training pertains to engineering works builtalong a reach of river in ord.er to confine the flow to a prescribed, channel.Types of river training discussed. in this report are high-water trairangaimed. at providing a sufficient cross-sectional area for the expeditiouspassage of large f-loods, and bankline training aimed. at preventing the losSof bank-land, areas to river flow erosion.

- ii -

vi. In Bangladesh, the only currently feasible method.of trainingthe manjor rivers to prevent vast overland. floonding dring penk riverdischarge is by construction of embankments along the river channels.Fa^tors crritinnl fnr a sucsf'i flood. PTmnhn nm0nt prnotectiorn system areembankment height, embankment location, and the maintaining of an adequateembankme.nnt cross section by mnninte-nnnce. The eff ect of constructing theembankment is to increase the main channel discharge during high-flow and.reslilt in nan increased stage and depth. These increases are dependenton the decreases in bed form roughness in sand bed.channels which usuallyOCCriiv' ra -d +. jn r'cnnQrl cljz cn!n*r-,occlpwih *mceased. disch_rge.

vii. The main conclusions regarding embankment design and locationare: a) The design height of the embankment should. be economic heightnl,s a f--r-barA. ol o-ance. The nrnavi+ of the f-reeboard, llow-ace shou'ud

depend on the uncertainties encountered.in establishing the jointprlobb 1i;ityr Aof stage h,,. l;ve ri4de Up 4d ,; 1 1 U - ona,

policy decisions. b) For the Ganges, Brahmaputra and. the Pad.ma Rivers,the reco. m-en-.ed 4-1-,-,set-back Js one 0 1-4' .,;'e. M_Ths d4 stance

will provide adequate time should rapid bankline erosion occur. Formeanderi.Lr rv.J.erVs, the UdlsaIe iL V'yL one-quarter i,ieTe sC.I,e

distance is recommended. for smaller rivers with essentially straightch-mnrrnI ca!nd Coh lesiva baMklsc0.At'. fl4tLt 0..Lt. '. tJLAt.'J .A VC~kJ,AJ *o

BANfLADETST A- TS' COn - I

VOLTIOXT VIIEI - TIM FLOOD PROBLE4

1 CIRCAfL RPORT NO . 2

IRIVER SYS"TEMI ANALYSES

I. INTRuDuCTION

1.01 The river system and the land resou.rces are the source of lifeto the people of Bangladesh. Conversely, the rivers are capable ofinAnlicting great damage during periods of f-looding. The destructivepowers of the Bangladesh rivers were well described by J.A. Krug in aReport of tu-e united Nations Technical Assistance Mission (1957). In1964 a Master Plan for flood control and drainage projects was preparedby IEC0 and, in tne same year, j. Th. Thijsse reviewed the hydrologicalconditions of Bangladesh and outlined the changes which those conditionswill undergo as a consequence of completion of projects for flood contrcl,drainage, irrigation, hydro-electric power and navigation. Thijsse statedthat the u:Ltimate aim in Bangladesh is to completely control the riversystem. In this completely controlled ideal condition,

r... the river flow is confined to a stable andfixed bed at all stages of discharge, allowing ofefficient inland navigation. The water in theland between the rivers as well as between therivers on the one hand and the sea on the other,is completely controlled. It is kept at the mostfavorable level. When there is too much, thesurplus is evacuated; when the crops and theraising of cattle need more, the rivers supply theshortage. The coast line is continuous and asshort as possible. It is interrupted only by asmall number of mouths of the principal rivers andby the entrances for navigation to the main harbors.A sea wall prevents flooding, even in exceptionalconditions."

1.02 In reviewing the IECO Master Plan (1964), Thijsse emphasizedthat most of the proposed Master Plan projects will have a considerableeffect on hydrological conditions. Thijsse outlined the hydrologicquestions which must be answered before work on those projects is started.The problems were classified into: (1) the high-flow problem of therivers; (2) the low-flow problem; (3) the stability problem; and(4) coastal problems. In this report, the high-flow and stability probl-emsare reassessed. In the period between 1964 and the present, much infor-mation pertaining to these two problems has been collected and analyzed.This information, mostly in the form of hydrologic data, has helped toformulate some of the answers to the high-flow and river stability prob:Lemsposed by Thijsse.

- 2 -

1.03 The general aspects of the river system in Bangladesh arereviewed first. The high-flow river nroblem has been reformulated intoa discussion of flood protection with embankments; embankments beingthe only method considered feasible for flood protection on the majorrivers in Bangladesh at this time. The problems of embankment location,height and maintenance are ronsidered. The effect of double embankmentsalong the major rivers is assessed. The anticipated response of the riversystem to develonment is studied.

1_04 The river stabilitv nroblem has been divided into t-wo narts.The first part deals with the movements of the low flow channels and howt.hese movements affect the availability of water for irrigation systems.The second deals with the bank erosion problem and bank stabilizationt+htf could be emplnyed in Bangladesh. A nrrntp annpnlicatinn of theprinciples outlined in the paper is made using the Dacca Southwest ProjectPs examnli. Winnlv rpronmmprrinti nn- for futmrp rivpr 'qvtenm inventi crn±.; n:…_are made.

!I. C-ENTA-L ASPECTS

9-n1 Thi in-" ,-v -r, --- -f -- t Cy n e A +.ha v X

the Upper Meghna and combinations of these three rivers. The Ganges andBrahmaputvra River-s merge together in-+^--- +he -- Rive , ui, -;+

joins with the Upper Meghna to form the Lower Meghna River. The Lower

water and sediment into the Bay of Bengal from a drainage area of approxi-Aately 600,000 square niles T nu peak flood is of the order of

5 million cefs and the estimated annual sediment load is approximately 1 to2 billi1on tons per year. Flood waters Pror, snow r,elt4 ir, the 1-1-imayas andqI.. J_.L'I JL ) * 1 J.LJ W- v ± C L ± 4I LIW iL. LI .L± ULI1 ILLALIO.LO:.J~0 O lCuLt

monsoon rains over Bangladesh and over the subcontinent combine to inundateclos to athLrd ofL thie 'land area each' -year.

A. Geomorphic Aspects

2.02 The principal geomorphic feature of much of Bangladesh is thedeltaic deposits of alluvium brought down by the rivers from both the northand south slopes of the Himalayan Mountains. Geological studies revealthat most of the surface of the country is composed of recent alluvialdeposits. The delta is relatively flat and slightly above sea level, withlocal variations of relief on the order of five to twenty-five feet. Thematerials brought down by the Ganges and Brahmaputra Rivers are mostly finesand, with lesser amounts of silt and clay. These materials are not homo-geneously deposited in the delta. Deposits consisting chiefly of siltsand clays are called nodes. Nodes are more resistant to river erosionthan sandy deposits and therefore affect the migration of the rivers onthe delta.

2.03 It is difficult to reconstruct the migration of the river systemon the delta in quantitative terms. Coleman's (1968) studies of channelprocesses and sedimentation in the Brahmaputra River show that the migrationof the Brahmaputra has been relatively minor since the Brahmaputra abandonedits former channel, the Old Brahmaputra River, to the Meghna River and has

- 3 -

developed a new channel, the Jamuna River, to the Padma River. Withinreeent geologic timey river ohannel shifting on the delta has dlstributedsediment along many miles of the shoreline. Within the last few hundredyears. the fanges River has shifted from the western edge of the deltanear Calcutta to its present location where the Ganges joins the Brahma-putra River. The Ganges water and sediments are now begin di sc-haroed onthe most eastern edge of the delta via the Meghna River. The sedimen-tation processes On the delta are fairlv wel1 inderstoodn in qualitativeterms. In the model river delta tests at Colorado State Universityreported hv Chang (1967), +he p.hysical prcesSeS hy whi h a uver migratesacross the cdelta are clearly described.

B. Types of Rivers

2.04 An alluvial river is one whose channel is formed in the sedimen;;scarried and deposited by the river. In the deltaic region of Bangladeshall major rivers are alluvial rivers. Alluvial rivers can be straight,meandering, or braided in plan view appearance (Leopold and Wolman, 1957).Rivers which exhibit combinations of straight, meadering, and braided riversare termed transitional rivers. In terms of river engineering, the banklinebehavior of meandering rivers is the most predictable. Braided and straightriver banklines are the least predictable. In Bangladesh, most of the reachesof the major rivers are braided. Many minor rivers, the Kaliganga for example,meander.

2.05 On the delta, many of the minor rivers are distributaries of them^lajor river,. .1That is, the minor rivers are supplied with water chieflyby the major rivers. The distributary rivers are generally either decreasingor increasLng theLr capacity to carry- water and sediment. The old Brahdma-putra River and Dhaleswari River are distributary rivers which may beabandoned (Coleman, 1968). Some rivers drain precipitat1ion Irom the delitawatershed, but may also serve as conveyance channels for overbank flow fromthe major rivers. Tnese rivers serving a combined function are less likelyto experience rapid changes in size with time than distributary channels.

C. Flow Mechanics

2.06 Di an alluvial river, there is a complex interrelation betweenhydraulic variables and geometric variables. Alluvial rivers are subjectedto great variations in the magnitude of flow and generally, the flow isnon-uniform. Channel boundaries are mobile. Resistance to flow can varyby a factor of 3 to 4 during the passage of one hydrograph. There is aninteraction between the sediments supplied to a reach of river and thehydraulic variables of the flow. The changing ability of the flow totransport sediment results in scour and deposition on the bed and inbankline migration. The overall state of knowledge of the mechanics offlow in alluvial rivers is summarized by the Conmittee on Channel Stabili-zation, U.S. Army Corps of Engineers (1969). Other documents on aspects

-4-

of the mechanics of flow in alluvial rivers emphasize the complexity ofPeach facor of the flnW process +hat carn 'h isolatfed For examen1P thecomplexity of the resistance to flow in alluvial channels has beenstu2iedPr ancd repnortedi 'hyx qiT.nns andz cih2rrdson(96)

2.07 When each isolated comro.nent of the flow process in alluvi1lrivers is complex, the integrated effect of all components in a reach ofrierpr cnn +t1ak on manyr forms. Fonr nyemprle, +the s+tuies of +the RPin G.mnrian

by Nordin and Beverage (1965) reveal that at one section, "... the depth,water-st-1rface slope, bed shear stress, resis.a+ncer to flow, and h bed-te.r;al-

size increase with increasing water discharge..." At another section,". water-surface slope an.d bed-mate+ri4 nc Ihanrac titi cs are appro) dlnat+ltr

constant, flow resistance decreases with discharge..." On the IMississippi,q tA in ^nnr, "non )lo , ^-f +I,0 .- wn ov"a M'hA -; + -',n" 0+nn+ ci nv-.o n-,ne n.c . nnrl

decreasing slope with increasing discharge (U.S. Army Corps of Engineers,1071).

2.0 '-JU LLIC findings u-L NorLn and Bever age, theII CrULP U.J Loif11C a'Urs, and

of others reporting on the mechanics of flow in alluvial rivers, indicateUhat u hie b)ehavio--0r ofL flIowV in a- r--each Lof allu-iV-al riv er is best Uete 1:;iLLL,ne

from the study of the data collected on that reach of river. The mechanicsof f-l ow 4ln 4the B-1-Spu+ra an-' Pad.a bvers have Ibee-n stidiedA - Mr by EC- ACELuL .L .L/I -LU ULIC li.L '_JLLII.u.JL bi c 1A I alAIIlc& :LL V Ci. a jc'.V LSCJIU a u-" K DUL '.. J 1J? I U±Ii

(1970a) during the preparation of the Dacca Southwest Project FeasibilityReport. T - aAd4 tion - he effect of se-ment-4 traspote by1- -lveLtC~~J'J± -. " 111 LU.L U-LulJI9 UIIC Z%ii. CU 0 U.± Dt5CLLL_CIIU u1±o.I UIao u~u. UY ul it- I -LV tC,L

system and the response of the rivers to the proposed Dacca Southwest…2 -..~~~~-.2 Lf-rr A /IT' I 1 7n1_ water resouarce dlevelop,mLent were considered (C-E,1970b).

D. Sediment Processes

2.09 Sediment transport in sand-bed rivers is complex in comparisonwith rigid systems in that the interaction between the flow and the boundaryis not simply a function of the roughness-height, viscous-layer-thicknessratio. In sand-bed rivers, once the general movement of bed material hasstarted, the water and the alluvial boundary interact in a complicatedmanner. Salient features that differentiate flow over sand-beds fromrigid boundary flow are:

(a) In sand-bed channels, the flow, transport and boundaryshape are interrelated. After general movement of the bed has started,the sand-bed is distorted, giving rise to bed forms. The shape, size, andrate of movement of these forms and the geometry of the channel vary withthe flow (for example, Simons and Richardson, 1966).

(b) Roughness size represented by the bed forms can be of thesame order as the depth of flow in some phases like dunes and antidunes(for example, Coleman 1969).

(c) A sand-bed is not impervious. There is a possibility offlow, however small, penetrating into the bed. Thus, the turbulentfluctuations normal to the flow do not always vanish at the boundary.

(d) The boundary, in the case of sand-beds, is moving at boththe grann and he bed. foim scales. Grains rolling at the bounaryn mayintroduce additional shear by their rotation and change the turbulencelevel clos to~ +1"e bo r by- thi *nes p. movem.ent o'f bedfoms

on the other hand, creates unsteadiness of flow at a vertical due tothe ^hang-Jng bed e&e1Vatim+ and flow1 patte.-

(e)i ~Tbse mappitude of t1he sn.eer s+ress and -Lhe to,,bule.r.ce ofthe flow are affected by variations in the concentration of fine sedimentor Va- s bA ndC- - y vria - o4-4- - . te..rature of +1- .ater.seo4mon+

'.JI. W~i.j .L -LJAU. O..L&" LJ.J V -~.L .L~ UL'.J1J.LJ LL WAI,IJJUL -A VLA.I. V '.31. II a- VS3~ 3i3A41

mixture.

(f) The bed material is thrown up in suspension. The presenceof4 par 4i-c'le 4in, 4upnso afet h urbuflence charactesti4-c;s ofP 4the_L ULJJv0 JI.L DU ±LLO1±. CLL. U, UILL UU.J.L U L I±. I 11AJ. UV.1 t ~ U- '.34 UJl-

flow.

(g) As the bed forms achieve dimensions comparable to the depthV.±uUeb/, vhe Mlow is no longer--uniform,. Both the depth and velocitychange along the main flow direction and across the section.

2.10 The trcnsport and resistance to flow functions are not alwaysI _ - - - ' 1 _ - -1 -- m - q I , __ __ 1 _ _ ~ - _ i L- h _- - .3 - - - _ single valued. Ine Ifow o-i water anu sediment over a sJanU-UeU may reuZlt

in lower regime, upper regime or some combination of lower and upperregime loUW.

E. Transport Relations

2.11 Numerous transport relations have been theoretically and/orempirically derived but because of the complexity of sediment transportphenomena, neither the theoretical nor the empirical relations completelydescribe the processes of sediment transport. Their agreement withobservations in the field is highly dependent on how close the conditionsof the stream in question agree with the ones for which the empiricalrelation was derived or on how close the assumptions made for the theoreticalsolution come to the actual river conditions. For the rivers of Bangladesh,it is suggested that the modified Einstein procedure (Colby and Hembree,1955) may be used to estimate the unmeasured sediment discharge. Thisincrement of sediment discharge added to the measured sediment dischargewould give a good estimate of the total sediment discharge.

2.12 In the absence of any sediment data a rough estimate of the bed-material discharge can be made using the Colby (1964) procedure. Thismethod simplifies the problem in that transport is estimated as a functionof velocity, depth, size of bed material, concentration of fine sedimentor wash load and water temperature. For the particular case of large riversfew of the existing relations can be applied with certainty of good results.Therefore, when possible, it is advantageous to develop the necessarysediment transport relations for a large river from field observations.

- 6 -

Using the most simple approach, it has been documented that in many casessediment discharge correlates well with mean velocity or discharge.

F. Thli(e s o1n ' ri of1-i1C5 Fl oLU-w

2.13 Sediment processes are depen--dent on many variables some of wr-uchare again dependent on the sediment processes. This dependency and inter-dependency of variables makes the problem oI determining the sedimentdischarge and its effects on the mechanics of flow complicated. Some ofthe effects of sediment processes on tne mechanics of fiow have beenidentified; others have not. Some processes that have been identifiedare described below:

(a) The concentration of bed material in suspension affectsthe fluid properties by increasing the apparent viscosity and the specificweignt of the water-sediment mixture. Tne presence of sediment in theflow may dampen the turbulence, alter the velocity distribution and theresistance to flow.

(b) The concentration of fine material (wash load) also affectsthe fluid properties by increasing the apparent viscosity and the specificweight of the water-sediment mixture. The resistance to flow and bed-material transport is sometimes decreased in the lower flow regime andnearly always increased in the upper flow regime when fine sediment isadded to the flow.

(c) The effect of temperature variations on the sediment dis-charge has been identified in field observations (U.S. Army EngineersDistrict, Omaha, 1969). In summary, the effects are: (1) for a givenwater discharge the sediment discharge increases as the water temperaturedecreases; (2) at low temperatures the friction factor of a river channelis less than at high temperatures; (3) at low temperatures the bed formsof sand-bed rivers may smooth out and become less rugged than at hightemperatures. Studies by Simons, Haushild and Richardson (1961) indicatethat much of the effect of temperature on sediment discharge can beexplained by the decrease in fall velocity of the sediment grains astemperature falls. However, the mechanism by which a change in watertemperature changes the bedforms is still obscure.

2.14 The foregoing effects are significant but of even greater impor-tance is consideration of the long-term response of channel alignment,channel profile, the characteristics of the bed material, and the hydrauliccharacteristics of the flow in terms of sediment and water dischargeconsidering the development of water resource project which will involvediversions, controls, embankments, and possibly channel stabilization.

- 7 -

III RIVER TRAINING

3.01 In general, river training pertains to engineering works builtalong a rea-b of river ; An orde -r to c no +he flow +M a prnsoev-

4oA

channel. Itjpes of river training considered in this report are high-water trainitg aimed at proid-ng a su-ficient cross-section.al area forthe expeditious passage of large floods and bankline training aimed atpreventir.g se+1- no of nPalrflan arfas +n r + ivra P1 ervoson.

A. Embanknents

3.02 In Bangladesh, the only currently feasible method of trainingthe major rivers to prevent vast overland flooding during peak river dis-charge is by construction of embankments along the river channels (Latif,1969). Factors critical for a successful flood embankment protectionsystem are ernbankment height, embankmaent location, and the maintaining ofan adequate embankment cross section by maintenance. Embankments placedalong a river channel prevent overland flow and storage of water on theflood plain. Thus, within the main channel, flow rates are larger withembankments than for the natural river condition. Not all portions ofthe main channel hydrograph are affected. The elimination of overland flcwand flood plain storage affects the main channel hydrograph only for thosedischarges greater than bankfall discharge. The important considerationis the amount that the natural main channel hydrograph is changed byembanking a river channel. The aim of this section is to present anacceptable methodology for determining embankment heights along the alluvialrivers of Bangladesh. The factors which determine the flood stages forembanked river channels are discussed. Reference is made to flood frequerLcyanalysis and the increase in peak flood flow due to embankni.ents. Also the!effects of increased peak flood flows on the river hydraulics, sedimenttransport, and peak stage are considered.

Frequency Analysis

3.03 The design of embanlkments must be based on discharge or waterstage frequency analysis for the river. Selection of a design frequencydepends on economic analysis and policy decision. Designing for any flowbelow the maximum possible flow involves a calculated risk. The mosteconomical degree of risk can be determined within the limits imposed bythe amount and accuracy of the available data and its analysis. Theacceptable r:isk to human life is a policy decision. The aim of the floodfrequency analysis is to determine the return period distribution of peakwater stage events. Sometimes, in alluvial rivers, pronounced shifts inthe stage for a given discharge render stage data inconsistent for frequenxcyanalysis. It is usually recommended that the analysis be made in terms oldischarge and that the results be converted to equivalent stages by usingthe most recent applicable stage-discharge rating curve (Linsley, Kohler,and Paulhus, 1958).

- 8 -

3.04 It is important that all the discharge data for the study periodbe true, unbiased observations of those discharges. For example, manydrainage basins have undergone recent or continuous development. Earlydischarge records reflect the natural or undeveloped drainage from thewatershed. Later discharges are affected by man's works. The completedischarge records for such a watershed are not elements of a stationariprocess but elements of a process that is changing in a biased manner.Adiustments to the later records to account for developments should bemade before the data are used for the frequency studies.

3.05 The log-Pearson Type III method has been recommended for adoptionas a base method for flow frequency analysis in the United States. Themethod is described by the United States Water Resources Council (1967).The base method was adopted with nrovisions for using other methods whereadequate justification is presented. The log-Pearson Type III was recom-mended after a study of long-term records at 10 IU.S. test stations wascompleted. The 10 test stations had records ranging from 97 years to 40years.. The 1argest drainage area was 37.;000 square milps! the smallest.16.4 square miles. Six methods were applied to the flood series. Of thesix methods, the 1oog-Pearson Tvne TTI distribution was rhose-n as the hasemethod because that method showed only a small bias in fitting the floodseries data and the method was more flexible than others having about thesame bias. The log-Pearson Type III distribution is recommended for floodf1 ow frequency ana1rsis for Bangladesh rivers iintil -it i9 shon thatanother distribution is more suitable.

3.06 Many of Bangladesh river discharge stations have only shortper' ods~ of ~'vre1crs not. of swff-'i ciet 1eng+h1 for fl ow frqec 11rtu';es-

It is recommended that efforts be made to develop the basic frequencycvilrre for the group-s of rivers +h. ha.vei An -in-l fl ood-producing harac-

teristics. For example, the Hardinge Bridge flow records on the GangesRiver are of sufficient length to definea good flood-frequencyrecords on the Brahmaputra River are less adequate. If the Ganges andBrahmaputra Riverb inans are homogeneous *ith respect to flood-produc;g

characteristics, the two rivers will have similar frequency curves of aboutequal slo-e or s t e epness. IT is +)nIn+ +tha the Brahmaputra an C-ang

River basins are not homogeneous in all flood-producing characteristics.Hll.owever, 4 Id. eregional sttisticl44- -approa, 4t4ie ir.t l1 4-.. records

may be a better alternative than extrapolating short-term flood records.

3.07 The interpretation of the flood-frequency curve for a river stationshlLou Lu begin with I-L an LLUth eIJr LLLg of e .LLLrL,U1Uu _UJllJV0tU Lid Ully h 1ion LLI

record length. Studies have shown that long-term records are necessary toaccurately predict even the average annual flood. IL the table below, fromDalrymple (1960), it is shown that 40 years of records are required to

_~~~__ .... . L.-~£1...1 ...4 2£ I I %, f AM11predicLC Lhre miaDgniitude of Lue miean r ±udealaLuaUl f'lVood e-ven' wi 14vti IVJ70 of Uhe

correct value 95% of the time. T'hat is, if 100 records of annual peak--. . .- - __ n __ L ~ _r _~ .~ -._ _ -L- - ,

fllOW, UUc 4V yYaS in lenlglh, Were aValaldUe, 795 of UtheUs ecorUs wouldyield a mean flood within 10% of the correct value and 5 would not.

For the Hardinge Bridge, flow records on the Ganges River (1934-1970),the table incdicates that the 50-vear flood cannot be oredicted within25% of the correct value.

f TLe.ng+h o,f rec t-r'd {>yqers) r h-irprd tn i-rwiGntthe magnitude of the chosen event

Magnitude of flood within 10% of the within 25% of the(retu^rn rpeo-i ;w~ in co-rn'rect1-. value QE5 I GorrevC+ value 9%Qyears) of the time of the time

2. (me arâ1) 40 1210 /90 18

25~~~~~~ ~ 105 31

5'0 110 391 of) 11r I .

_________I .,- I_______3.08 ~~Ann-II, n i ue.o'l real ation for, 1n-Ia,n,n--#v pe.g sheI~ flood na , f un-rr

data is that shown on Figure 1 (from Crippen and Rantz, 1968). The curveson 1ELgure 1 are IIL1he grapn".J J aJL present.a.iIn i.ofno the 4U uat4n.

P(n,T) = 1- 1 gn

where P(n,T) is the probability of a flood of T-year return period beingequalled or exceeded in the next n years. For example, there is a 407chance that the 100-year flood will occur in the span of 50 years (point A.on Figure 1). Figure 1 also shows that there is a 31% chance that the100-year flood is in the 37-year record (point B) at the Hardinge Bridgestation on the Ganges River. It must be kept inmindthat there is a 1%chance that the 100-year flood can occur in any one year (point C onFigure 1).

Peak Discharge with Embankments

3.09 To this point in the discussion of flood frequency, it has beenassumed that the river flood flows are uncontrolled; that the river basin.is undeveloped. After embankments are built along a reach of river floodflows in that reach will be changed. The flood frequency curve will alsochange. The magnitude of the change in flood flows due to embankmentsmay be deternmined from a water balance study. It is necessary to establisha water budget balance on the area affected by embankments in order toassess the effects of embankments on peak river flows. The embankmentsprevent overbank spills which means that storage and overland flow on theflood plain on the land side of the embankments are elitinated. In reachesof rivers bounded by valley walls, the water balance budget is relatively

- 10 -

easy to accomplish. On the Bangladesh delta, the water balance duringpeak flow is nearly impossible to determine accurately. There is nodistinct boundary to the area through which water does not flow. Theproblem is illustrated on Figure 2.

3.10 The area (-igure 2) to be poldered receives flood water fromthe main channel of the minor river, and overland flow from -the uplanddirection, in addition to flow resulting from precipitation. Water islost from the surface of the area by overland flow at the downstream end,to return flows to the main channel and to the minor river and to ground-water storage, evaporation, and evapotranspiration. At any instant oftime, the water budget for the area to be poldered can be written as

Change in Net main Overland Net minorsurface = channel left + inflow - river rightstorage overbank spill overbank spill

+ Precipitation - Overland - Losses to groundwateroutflow storage, evaporation, etc.

Usually measurements of precipitation over the area are available but noneof the other variables of the water balanced equation have been measured.The water budget for the main channel is:

Change in M4ain channel Main channelchannel inflow + Precioitation - outflowstorage

- overbank - overbank - storage, evaporation.

In th- - 4 -- i-- --- precipitatlon, losses to gr- -eters+ora,evaporation, and evapotranspiration are dropped from consideration forbDrev+-.y of .analrysis. A.l - the -. ter b udget terr^.s for +1o ahe -.. ver are

14.IV4.Lj 'J ..hi1J.J .4. 1 d4- 0J , ~.1- VIa.VI- kin '- I.0',4 1 IU. -.4 L1 JIM M.J± ±...V1± I!'

the same as that for the main channel. Discussion will be limited to them--in charr.nell only. "Supposee for lllustrativ purose 4t.hat 4- main char.nl

*CI.4.± ~ ~ '441I4. 'J±.L)I* .U.~jJ4.44 414 . L4.4LLLI.4 40.14V 14 jJ~4ijJUA JW0' UtLa.k 14 111' IUf IC1 k.LIOdJ.I.L'.

inflow is measured and that of flood frequency analysis is available at thest--tion. GeneraL'Q-, +Ile chann.el storage can be estmated4 b,ut o4.her 4items

in the main channel water balance equation are unknown. A second discharge4L .OJJ .L1 .4 14. _4L'1 A' _ 1411 '.14 14.LIV '1. '.4± 141 1!C-1 UI.IJ..L . W L U. UO V'4±U'IU. .01JILt_ctW ~ ~ LI '1X#, Gtil L I -li out_ W .L U *W- U_tl V1L tLle mainX *_IX;6IaIUsc wVkU.L_ Li va Uau

only if the sum of the absolute values of the errors in the dischargemeasu± 01110111tus at)J both s l is at least one order of Imatp.Llit±ude s,11allerthan the net overbank spill from the main channel.

3.12 One effective method of obtaining a water balance in the mainchannel is to m-,Xeasure all i'…t…la except t -- s t;I 1has 4. larget.5 magnt ude

The largest item may be computed in the water balance equation. All signifi-canlt t.erml-s in the -water balance equation oI the main channei and the area tobe poldered must be estimated before the effects of the embankment on themain channel flows can be determined. in the main channel (Figure 2),the maximum flood peak with embankments is given by the equation:

- 11 -

Maximum peak flood flow in the Main channel inflow peakreach wi+.h embanlkmpnts = writhntt emhankments

A part of the Net left Increase in net right+ overland inflow + overbank spill overbank spill

Part of the overland inflow may be carried by the minor river. Of thatlract'uion of the overland inflow aadded w t rte mainl eLIarelug inloUw ea partwill be lost from the main channel due to increased peak net right over-bank spill. Net left overbank spiii is prevented by tie embankment; apart of this spill goes into increasing the net right overbank spill andthe remainder is added to the main channel inflow peak. Tne estimatedpeak flows with embankments are assigned the same frequencies as that. ofthe corresponding main channel inflow peaks without embankments.

3.13 in terms of the flood hydrograph, the poidered area will havethe effect of increasing the peak flood for all flood flows above bank-full discharge except for large floods of long duration for wnich theeffect of the loss of overbank storage is zero at the peak. The peakmay be shifted slightly with respect to time, depending on the timedistribution of the overland inflow and left and right overbank spill.The increase and shift in peak fiow are illustrated on Figure 3. In themain channel, the important factor is the percent increase in the peakflood discharge caused by the embankment. As far as embankment heightsare concerneci, it is the increase in stage caused by the increase in peakflow that is of interest.

3.i4 For the problem illustrated on Figure 2, it is likely that thepeak flows in the minor river would be increased a greater percentagethan in the main channel. Also, an increased flow in the smaller riveris likely to have a more pronounced hydraulic and geomorphic effect thanthe same percentage increase in the large river. The water balance studyfor the main chamnel, for the area to be poldered, and for the minor riverwould indicate which river will be more greatly affected by embankments.

River Hydraulics

3.15 The increase in peak flood discharge caused by the embankmentshas been determined from the water balance equation. This increase indischarge may result in an increase in stage in the embanked reach ofriver unless the increase in stage due to increased flow is countered bya reduction in resistance to flow or by a decrease in channel bed elevation.If the river were a rigid boundary channel, then the increase in stagecould be computed directly from Manning's equation. The geometry of thechannel is fixed for all stages and the Manning ts roughness coefficientand the slope would be essentially unchanged throughout the reach. Upstreamand downstre&m of the embanked area backwater profiles would exist in thetransition from the natural stream water surface to the water surfaceprofile in the embanked reach of river.

- 12 -

3.16 In alluvial rivers, other responses are possible because theboundaries are erodible and because increases in discharges can signifi-cantly decrease Manning's roughness coefficient and consequently the depthand the velocity of flow. The immediate response of an alluvial river isusually the same as for the rigid channel. That is, the embanlkmentsincrease the discharge per unit width of channel, and an increase in thedepth and velocity results. In the alluvial river, the hydraulic depth canbe increased by a lowering of the bed, or by increasing the stage, or by acombination of bed lowering and stage increase. The velocity can beincreased if the bed configuration roughness decreases. The response ofthe hydraulic variables to a discharge increase in an alluvial river canbe better explained by examining the corresponding effects of discharge onsediment transport.

Sediment Transport

3.17 For the graded condition in the undeveloped reach of river,sediment transport and water discharge have established a quasi-equilibriumcondition so that, on the average, the water is able to transport throughthe reach those sediments supplied to the reach. There is no sigiificantaggradation or degradation within the reach for the graded condition.The balance of water and sediment transport are illustrated on Figure 4a.The point A represents the long-term average of the peak flood unitdischarge q, and peak sediment discharge per unit width of channel, qs.The long-term average peak depth and peak average velocity are associatedwith the above values of discharges. The long-term average peak floodwith embankments is represented by the curve q + 8q; Sq being theincrease in q due to embanlments. For a channel with rigid boundaries,the conditions associated with the increased average peak flow (point B onFigure 4a) can be computed directly from rigid boundary flow equations.Assume Sq as the same order of magnitude as q so that q + q = 2q. Asstated in the preceding section, there would be a slight increase in thedepth and in the velocity. In the rigid boundary case, the increased stageis directly proportional to the increase in depth. For the embanked reach,the transport capacity of the flow is increased because the average depthand velocity have increased. The amount of sediment being supnlied tothe reach is still only q so the rigid boundary channel could transportthe sediment through the reach without any trouble. Tn fact. there is anexcess of transport capability for the amount of sediment being supplied.

3.18 In alluvial rivers with erodible banks and beds and multiple bedrnvwhness. the Tigid ihonnncarv exPt-ensinn is not. validL (',enPra1v +.he.immediate response of a sand-bed channel at flood stage to an increase inimit diienharge wniilri be thlat more of +he reivpr hbed attains a qmoot.her hbdconfiguration. If it were possible for the roughness to decrease whilethe boumdary remained rigid, the condi+ion with eTmbannr.ments would be rep-resented by point C on Figure 4a. For these hypothetical conditions, the

- J *F_an U. _*S 4. - d -

case (point B). If the main channel had rigid banks with an erodible bed,the 1on--tem response of tie rieW tr.ba-m.entS woulhd `be the conitonr,epresented by the point D on Figure 4b. The path of the response wouldbe fr-P A +t r' 4-t. -T. 4-.nA4 -- -espon,se 4 n incr,,e-as 4in . 44-harger. .nJ i Ld L .LJA J.1M1L3t..C& t~ . Ld (iX ..LLL,. ~i, J ELI UAL.. ..LJVMCJ

is a decrease in the roughness and the temporary conditions representedby point C. At C, the capacity of the channel to transport sediment isgreater than the rate at which sediment is supplied to the reach; there-fore, degradation of the bed occurs. Once the bed has eroded to a depthwhere the transport capacity has been reduced again to q (path C to D),a new equilibrium has been achieved. The depth is now gieater than beforedue to bed erosion and increased stage. The stage for conditions at D isless than for conditions at C due to bed degradation.

3.19 When bank erosion can occur, the effect on the flow is to decreasethe unit discharge. It usually is not possible to predict the final equi-librium condition from the depth, velocity, unit discharge and unit sedimenttransport curves. The new equilibrium condition for the channel withembankments could be point E on Figure 5a if the bed were rigid and thebanks erodible. For Bangladesh rivers which have erodible banks and beds,one of the possible equilibrium conditions for an increase in dischargeof bq is point F on Figure 5a. Here, the unit discharge at point F isslightly greater than the unit discharge in the undeveloped river; thedepth is greater; the velocity is essentially unchanged; and thesediment transport per unit width is slightly less than before (due tobank erosion).

3.20 The four-variable plot described above is a useful way ofillustrating the effects of sediment transport on alluvial river flow.It is difficult to project the relations into a design criteria forembanlment height because for aWy one flood hydrograph, the flow-sedimentrelation usually follows one curve on the rising portion of the hydrographand another on the falling portion. One curve would represent scour inthe reach; the other deposition. Considering a single hydrograph, atypical flow-sediment relation for a deep-narrow reach is shown on Figure 5a.Efforts have been made to define a numerical value for the conditionsequivalent to conditions at point A on Figure ha or Figure 5b. That is.the graded conditions on a reach of alluvial river have been described bya long-term weighted average of discharge. This discharge is a nunmberwhich is the basis of describing the depth, velocity, and sediment transportfor a graded alluvial river. The set of equations relating the long-termweighted average discharge to the other variables are called regimeequations. Regime equations which are developed from field data are usefulin predicting the direction of the changes in depth, velocity, and sedimenttransnort for embanked river channels. Thev are less useful in predictingthe amount of the change in stage. It is felt that the stage for theembanked condition can be predicted from the known stage-discharge relationand the correct interpretation of the hydraulic and geometric relationsfor the reach as accuratelv as by any other existing method.

Staoe-Discharge Relation

3.21 The stage-discharge relation for a reanh of graded i l1 iiv-i1 riveris not the same every year. Each annual stage-discharge curve depends onthe dsthrihii+non of fl1ows and channel response during +hat year. The

- 14 -

upper portion of four annual stage-discharge curves for the MississippiRiver at Arkansas City, Arkansas, are shown in Figure 6, (U.S. Army Corpsof Engineers, 1971). For comparison purposes, the year-to-year variationin stage for a discharge of 1,000,000 cfs at Arkansas City are given below.

Year Gage heights for a discharge of 1,000,000 cfs

Maximum Minimum Rangefeet feet feet

1967- 30.0 28.8 1.2196 85- 30.5 26.8 3.71969-- 30.9 26.7 4.71970* 30.7 30.1 0.6

Notes: 1. * indicates one single peak above 1,000,000 cfs.2. "-- indicates more than one peak above 1,000,000 cfs.

3.22 These four years of records show that the maximum gage height at1,000,000 cfs varies from 30.0 to 30.9 feet and the minimum from 26.7 to30.1 feet. Ihe effect of multiple peak stages above 1,000,000 cfs isapparent. The range (maximum gage height minus minimum gage height) isgreater for multiple peak hydrographs than for single peak hydrographs.If annual stage-discharge relations were available for a long period oftime, the average maximum gage height curve and gage height variationsfor 1,000,000 cfs and higher discharges at Arkansas City could be estab-lished. The river's immediate response to embankiments would be an increasein stage, predicted from this average maximum stage-discharge curve,corresponding to the increase in discharge determined from the water balanceequation. The expected maximum value of stage corresponding to the increaseddischarge resulting from embankments would be the mean maximum stage plusthe increase in stage due to embankments plus the variation from the averagemaximum stage due to yearly variations in stage for a given discharge. Thegraphical presentation of the maximum anticipated stage for the embankedchannel is given on Figure 7. If point X represents the maximum averagestage for the design discharge in the undeveloped river and Sq representsthe increase in discharge due to embankments, the immediate response of theriver to embanknents is the increase in stage,, Sg. The anticipated maximumstage for development is the stage for point X plus iSg plus the maximumvariation of the stage from the maximum average stage represented by thepoint Y.

3.23 The difficul-ty with the above approach is that neither curve Anor curve B in Flgure 7 are defined for extreme events greater than thosein the period of record. For example, on the Brahinaputra River atBahadurabad, the 1 00-year flood is estimated to be 3,600,000 cfs; whereasthe highest recorded peak flood is only 2,700,000 cfs. If the 100-yearflood were to be the design flood in this case, there is no data to definecurve A in Figure 7. As a consequence, curve B is also not defined for

- 15 -

the 100-year flood. Curve A in Figure 7 can be extended for higher stagesand discharges from the knowledge gained from the study of the hydraulicand geometric properties of the reach of the river from past flood hydro-graphs. For example, the stage discharge curve for the Bhagyakul stationon the Paclma River has been extended (ECI-ACE, 1970a). The extension ofthe stage-discharge curve is, however, not arbitrary. Extensive study ofall the data on a reach of river usually limits the extension of thehydraulic and geometric variables to one narrow range of possibilities.

3.24 The lack of hydraulic and geometric information on alluvialrivers at extreme event discharges has lead to the detailed study of yearlyvariations in stage, velocity, etc., for a fixed discharge. Efforts havebeen made to describe these year-to-year variations with both deterministicand stochastic models. The advantage of the deterministic model is thatless data are required to estimate the variations than for the stochasticmodel. Most of the variations in the year-to-year rating curves foralluvial rivers occur at very low flow or in the regime between dunes andtransition. At low flows, the geometry can be remnants of higher flowsand therefore not directly related to the low flow. The variation in therating curve in the transition region is due principally to the changes inbed roughness that occur in the transition region. Other variations aredue to local scour and deposition which are dependent on the magnitude and.duration of the higher discharges.

3.25 Theb confidence that can be placed in the estimate of the maximumanticipated staze for an embanked channel depends DrinciDallv on thefollowing considerations:

(a) The amount of data available to define rating curves forthe river reach.

(b) The magnitude of the increase in disrharge naused by theembanlment.

(c) The ratio of the yearly variation in stage at the designdischargPe to the chanpe of stage due to the increaseddischarge.

(d) The slope of the stage-discharge curve at the designdischargee.

3.26 WJhen the behavior of an alluvial river can he HnociimentecP withfield data and can be explained with the most current knowledge of themerhanics of sediment and water f'lowq there houild be no unePYnectedoccurrences in the river behavior. If the magnitude of the increase indischarge due to embanking is qmall i;n co-mparison to the uindeveloped peakflows, the year-to-year variation in the natural river flood flows willovers.hadow th2 PeffP1-.+q of +he 1mhnnn+.e Tf +.ho ehnnr in +neo Aie +the increased flow in the main channel of the embanked river is only afrac+lon of_ _he _h..v1 . y eary variation ;_ stage at _ s- _i-.. dishage

it would be nearly impossible to detect any change in the river's behavior

- 16 -

due to embanlkments. For all practical purposes, the behavior of the riverstage has remained unchanged.

3.27 In large alluvial rivers, the slope of any annual stage-dischargecurve is very small at flood discharges. For example, the slope is of theorder of one foot per 500,000 cfs for the 1966 peak flow in the Padma River(see Figure 8). The maximum river stages are relatively insensitive tovariations in magnitude of peak floods. According to the confidence criteriadescribed above, it would appear that the maximum flood stages due toembankments on small rivers would be more difficult to predict than on themajor rivers. First, generally there is less data available to define therating curves for small rivers; emphasis has been on data collection forlarge rivers. Second, the relative magnitude of the increase in dischargedue to embankments along small rivers could be much larger than for majorrivers. Third, the slope of the stage-discharge curve at design dischargeis generally much larger in small rivers.

3.28 Once the design water stage has been established for the reach ofriver, the addition of an allowance for wind waves and for imponderablesestablishes the embankment heights. The occurrence of wind waves can betreated as a statistical problem in the same manner as the flood discharges.When wind wave height data are available or can be computed, an annual maxi-mum wave height frequency curve can be established. For the chosen embank-ment side slopes, the wave height-frequency curve is converted into a waverunup-frequency curve. This curve, along with the stage-frequency curve,establishes the limits of the recurrence interval for combinations of stageand wind wave rideup. One limit is determined by assuming complete depen-dence for the two events (rideup and stage) and the other by assumingcomplete independence. A study of the time distribution of the peak floodsand peak wind waves will help establish whether the complete dependence orcomplete independence assumption is the best approximation for the jointprobability distribution of stage and wave rideup. The economic height ofthe embankment is determined with the stage plus rideup-frequency curve.

3.29 The design height of the embankment would be economic height plusa freeboard allowance. The amount of the freeboard allowance shoulddepend on the uncertainties encountered in establishing the joint probabilitydistribution of stage and wave rideuD and will deDend on Dolicv decisions.The cost of the embankment with freeboard should be compared to the cost ofthe embanlment at the economic height. Then the cost of iTmonderables andof any policy decisions will be clearly defined.

3.30 Ln many areas of Bangladesh, an opportunity exists to comparenrononsed embanloment heights determined bv PnrienPtring methods wt.-i thecommon village protection schemes that have been in existence for centuries.On the flood plains, vinllages are n man-made moumds nf earth bhiilt up toprovide protection from floods. If the elevations of these old villageswere established and an interview scurvey conducted with longtnme residents,a long-term successful flood protection height in the area could beidentified. The village mounds that have not been overtopped by floods and

- 17 -

wind waves for manly years provide a source of information that includesall the elements of the hydrology and river hsydraulic studies, all theelements of the wind wave analysis, and the elements of economic andpolicy decisions rnade at the most basic level -- by those who will getwet.

3.31 In this section, concern has been with the vertical or stageresponse of the alluvial river to embankments. The immediate responseto embankments is a rise in peak flood stage. Over a longer period oftime. possible horizontal response by the river could result in stagesdifferent than the immediate response stage. Long-terra channel responsesof an alluvial river are discussed in Chapter IV.

Location of EDbankments

3.32 The malor factor governing location of flood-protection embank-ments along the major rivers of Bangladesh is the seasonal migration ofthe brai dpd ihannpls rnl Tman (1909) has renorted lateral banklinemigrations exceeding 2,500 feet per year on the Brahmaputra River. Embank-ments will not st+p la+eral bankline migration so it is neeessarv toprovide a setback distance at least equal to the anticipated maximum yearlymia ration. For +he Gangeqs Brahmanptra; and Padma Rivers; EGT-ACGE (1970b)

recommended that the embanlment setback distance be one-half mile. T,henthe river indicates a pronounined shift toward one banc with subseullentrapid bankline erosion, the one-half mile setback distance will providepnough +ime to consider and implement plans to provide nrotection to theendangered polder before the embanlment is lost to the river.

3.33 The magnitude of possible lateral migration of a river channelis closely related -o +he t+pe of river; migration is greatest in magni-tude and least predictable for braided rivers with sand banks. If theriver isn !-ndriyer but corfir.ed by r elatively cesive bhqn1rz l+e_a_lmigration is slower and more predictable. For these meandering rivers,EC!-ACE (1970b) recoended a onre-quarter -mle setback distance from theedge of the actives meander belt. A one-quarter mile setback was alsorecommended for channels which are essen+ially straight, have cohesivebanks and are narrow.

3.34 Once the setback distance criteria are satisfied, the embankmental; r?myn n + r-n 'hont:A lii-+.oi cl; eh +1 %r +in -:zxrm- r1 wr; 1 neC!~ riTrlum1;ncp! ln

g -ex. v -,- can be a_jus'--t- - v- .w I,_ ---- 6, loZ.__..,t _Cal

depressed topography, and areas with poor foundation materials. In generaL,the alignment should be such that there are long straight sections ofembankment and smooth transitions between changes in alignment. Generally,

tlle rea btweenthe .ai charnel of U.- manor- r_vers and flo-prtectionembankments is not an eIficient conveyor of water. The overbank area doesr-.o prvi,de .much f-lo=apaci-y for 4-me --rive Ala--n- ajorrvers*iJL

1J I> IUL 4...- --- -d"LJLA." U .LJ. JU> 11 V t>J. .t1. L r'JJ .-. IIj- ~.L..V t -.L

embankments setback one-half mile from the channel are subjected to velocitiesr.uc les thn0.',fee per second1, exceptl possib-ly irn so.me local areas.

I'La.e oL tAl flooLd pJlai has trasi

I-ater on the floodi plain has the appearance of a lake. On some minor rivers,

- 18 -

it may be possible to significantly increase the river transport capacityfor floods by increasing the setback distance of the embankments. If theflood plains carry significant flow the embankments must be protected fromerosion by the flow velocity.

Risks to Embankments

3.35 The proposed Bangladesh flood-protection embankments along themajor rivers can fail due to a variety of conditions; some conditions arevery improbable and others have a greater chance of occurrence. The riskof overtopping an embankment designed to the 100-year flood stage elevationand with 5 feet of freeboard is remote. In the absence of water waves, theprobabilitv of overtopping by flood waters in any year is less than 0.0005.The risk of overtopping the same embankment by a combination of flood stageand water waves is greater than 0.0005; possibly 0.0010 in anv vear.

3 6 The risk of failure du]e to the lateral migration of the riverchannel has not been assessed in numerical terms. However, that riskis inverselv ponortionail t-.o the emhYnhm.ent setback disthnce That. is

there is less risk with greater setback distances. A setback distanceof one-half mile on m.ajor rivers is of the same magnitude as the mnaimimobserved lateral migration in a year. There is an economic limit to thesetbhak distance hecs.qme the larnd between the river and the embankment

has no flood protection. Along the major rivers in China, major flood-nroteoti.on emhnnklmpnts we-re set. hbak aq mu,ch as frnr milpe on eaGoh sirie of

the river channel (Todd, 1938). These embankments were known as thetlInfininI Amhnunkmonf.cztt 1? rmp-,.cz n +.hpi-r t-vwn ini+.i-+.rpe -nn.nt. c int.pri

low-level embankments along the main channel so that, for a few years, theycould obtnin more prouctivnity frri-m the land between the official emhqnlnMenteand the rivers. The lesser embankments were called the "people's embank-mentrs ."

3.37 In D, gads 13gr--- eater setback distances wol- l - ---d moresecurity for the embankments. but would leave more land subjected to monsoonm Ioodin-g. Wth the pe.t LJL,1t8J e. - .. a,IL.,,L a4L 6 ,lI,..,, +'-here w'ou WLdA be

sufficient time to build sections of new embankment where the river threatensLWA . A.L .- il IJ.L\1Ii~Ii. -rni UAle .L11LUJ. V~_11..116 UJ..IfI8, IIIJ'J. ~ .LO.IIU .L0 PA ~ I)U U .1.4 iJI4the origna e.m.baa-1-en. In- the 4nterver,in ti..e, more 1-d 4s -4-4-edro

flooding.

3.38 Failures in the embankment cross section and foundation under normal.L±ooU condUUJitUIIons are Uonsidjered ILOUre probabLeD. tLhan f±a lOlures fro,U any Uother

reason. Some consider this type of failure inevitable. For that reason,embank-fent maintelalce and sector flood flghtinlg prugravin are of utmUostimportance. General J. Pegg (1970) wrote that:

"Experience has shown that flood control andchannel rectification works require extensive mainte-nance in order to remain effective for extended periodsof time. The basic reason for this stems from thefact that small failures in these types of structurestend to enlarge rapidly unless corrected as soon asthey are detected. This indicates that a well-organizedinspection force should be activated as soon as projects

- 17

are completed, and definite plans developed foraccomplishing necessary maintenance on short notice.During flood periods embankment failures can oftenue psrvenue'd buy a nominal c,untiuu of r.air,ten^nce if

accomplished timely. Based on discussions bothwith EPWAPDA and general consultant representatives,littie routine maintenance has been accomplished onthe structures in Bangladesh to date. Further-more, there apparently is no definitive plan foraccomp:ishing routine maintenance. Based on theground inspection of the G.K. Project-Kushtia Unitand on air inspections of several other embankmentprojects, there is obviously an immediate need formaintenance of not only the embankments, dikes andborrow pits, but also the pumping plants, drainagestructures, etc. Furthermore, there is evidencethat the embankments are being overgrazed by live-stock; that the few borrow pit traverses are beingbreached, apparently for utilization as waterways;and that numerous structures are being constructedon the embankments. All of these items are detri-mental to the integrity of the embankment systems.In this connection, serious consideration should begiven to curtailing large additional expendituresfor flood control and channel rectification improve-ments in East Pakistan until a definite maintenanceplan is developed and implemented."

3.39 Because of the probability of an embankment section failure,the characteristics of crevasse failures and the resulting effectsinside a polder have been studied by the Ad Hoc Flood Consulting Panel(1571). The causes of crevasse failures, the rate of crevasse widening,and the rate of rise of the flood waters inside a polder have been considered.For sub-polder 1 of the Dacca Southwest Project, the maximum depth of flood-ing would be about two feet after the first day. The panel concluded that"since the maximum distance anyone would have to travel from within thepolder to an embankment is not more than three or four miles, it should bepossible to safely evacuate the area if flooded." The panel noted thatbecause of the high population density and the large number of animals inthe Dacca Southwest Area evacuation of the area would be a major undertaking.

"However, if the structures are adequatelymaintained the probability of a failure is soremote as to make any planning other than of avery general nature neither necessary nor desirable.A general concept including designation of respon-sible agencies should be developed and publicized.This concept should cover policies reestablishingrefugee camps, care of animals, rations for refugees,medical care, and resettlement after the floods havesubsided."

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Coastal Embankments

3.40 It is not yet feasible to design coastal embankments to withstandthe ravages of cyclonic storms which form in the Bay of Bengal. Therefore,coastal embankment failures are inevitable even with the best type ofembankment maintenance. The Ad Hoc Flood Consulting Panel (171) reportedthat:

"In coastal areas subject to tropical storms(tornadoes or hurricanes), levee failure can occurfrom overtopping by the storm surge which causesalmost instantaneous flooding and great damages tolife and property. The only protection against thistype of flooding is either evacuation in advance ofthe storm or construction of storm proof shelters. Ineither event, a dependable storm warning system is anabsolute necessity.

Double Embankments

3.41 As flood-protection projects are developed, double embankmentsmust be constructed. Double embankments will confine more water to themain river channel than single embankments. The effects of double embank-ments on river stages along the Ganges, Brahmaputra, and Padma Rivershave been studied by BCI-ACE (1970a). If double embankments were cons-tructed along the Brahmaputra River from Bahadurabad to the confluencewith the Ganges, along the Ganges from Hardinge Bridge to the confluencewith the Brahmaputra, and along the Padma from the confluence of the Gangesand Brahmaputra to the confluence of the Meghna River, this conceptualsituation of total confinement would give the upper limit to flood stageson these reaches of major rivers. Total confinement means that all waterwould be contained in the channels of the Ganges, Brahmaputra, and PadmaRivers. Accordingly, the 100-year flood in the Padma River would beapproximately 5,250,000 cfs whereas the 100-year flood in this river withno embankments is approximately 4,`400,000 cfs. BCI-ACE estimated that theincrease in stage due to the additional 850,000 cfs in the Padma Riverwould be approximately two feet.

3.l2 The total confinement situation is conceptual only. Blockage ofthe Gorai River, a major distributary of the Ganges, and of the DhaleswariRiver, a major distributary of the Brahmaputra, are not contemplated.Accordingly double embanking of the Ganges below Hardinge Bridge, theBrahmaputra below Bahadurabad and the Padma River should cause a stagerise less than two feet on the Padma for the 100-year flood if the majordistributaries are not closed. Tf the delta of Bangladesh is to be pro-tected from river flooding, double embankments will be necessary. Beforedonbie emhankmnt.s are nonstrncted. the annrehpnsion about double embank-ments should be eliminated. Some apprehension can be removed by stagedde've1lopment of donhl_ Pmheanked reaches of river Thcperience gained fromobserving river behavior with double embankments cannot be repudiated.Be-ause of at-A-it itu anti apnprhensions, many unnustified- it. is the firststep to double embankments that will be difficult to make.

B. Low-Water Channel Stability

3.h3 In the major rivers of Bangladesh, there is a relatively largequantity of water during the low-l"low period of' the year. nowever, it isdifficult to conceive a scheme of permanent engineering works which willassure that the w"ater can be obtained fr-om the low-water channel and deli-vered to the agricultural land. The problem is that the major channelsare braided. Most of' the beds of the major chanlnels ha-ve the appearanceof deserts during the low-flow period. Sand bars and sand dunes, remnantsof sand movement during hngner flOws, Occupy most o' tne cnannel bed. T-lelaw-flow water-carrying channel occupies only a small portion of the bed.The location of the low-flow channel is, generaily, not predictabie. Fromuseason to season the law-flow channel can shift more than a mile across theexpanse of tne river bed. it nas been conceded (,oy MEACI-AWCE, i>970D, IOrexample) that there are serious problems in trying to obtain irrigation waterdirectly from the major rivers during the low flow season. Permanent pumpingplants or intake channels to permanent pumping plants could be located atnodes on the major rivers where the banks are relatively stable and thechannel is deep and narrow. Otherwise, the alternative is floating pumpingplants; a scheme whereby the plant is moved to the water channel.

3.hi4i In addition to the problem of having the low-flow channel in astable position, there is the problem of sedimentation in the intake canalfrom the low-flow channel to the pumping plant. Heavy siltation in theintake channel of the main pumping station on the Ganges-Kobadak Project,Kushtia Unit, has limited the supply of irrigation water to the system toa fraction of design value. Dredging the intake channel has not beensuccessful. The supply of sediment has exceeded the rate of dredging.

3.45 Basica:lly, the low-flow discharges in the major rivers are rela-tively free of transported sediments. The concentration of suspended sedi-ments is only about 200 parts per million by weight. However, in localregions sediment concentrations on the convex bank of a bend are very muchgreater than the average concentration. Generally, during low flows thereis heavy sedimentation along the convex bank of a bend. The sedimentationis reflected in the existence of a point bar on the convex bank of the bend.

3.46 The location of intake channels for pumping plants has been dis-cussed in detail by ECI-ACE (1970b). This report on the river mechanicsand morphology pertaining to the Dacca Southwest Project lists the most favo-rable location as the concave bank of a stable long-radius bend. At sucha location, the thalweg will remain at the concave bank, the bend will notmigrate rapidly, and the heavy concentration of bed load is swept away fromthe outside bank toward the point bar. Other locations may be acceptablebut are less favorable.

3.h7 Generally, the year-to-year migration of the low-flow channel inthe major rivers makes the major rivers a precarious source of irrigationwater even though the quantity of water is more than adequate. Minormeandering rivers which have stable banks provide the most favorable loca-tions for pumping plant intakes provided the low-flows in the minor riversare adequate to meet the irrigation demand.

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3.h8 Minor rivers which are distributaries of the major rivers dependon the major rivers for their low-flow discharges. The offtakes of suchminor rivers must be maintained in order to assure continuing adequate low-flows in the minor rivers. In the ECI-ACE Dacca Southwest Project FeasibilityStudy allowances were made for maintenance dredging of the offtake of theDhaleswari River at the Brahmaputra River.

C. River-Bank Stabilization

3.49 River-bank stabilization on the major rivers in Bangladesh hasbeen accomplished at one location only; Hardinge Bridge on the Ganges River.With the continued use of rock riprap, the Ganges River has been narrowedand confined to a channel under the Hardinge Bridge for more than 50 years.Other river bank protection plans at other locations on the major rivershave not been as successful over a long period of time nor has there been acomparable effort. The problems associated with river-bank stabilizationon the major rivers are numerous: (a) Channels are very deep; in order of60 to 130 feet during flood flows. (b) Main channel velocities are rela-tively large; greater than 10 fps. (c) In the braided channels, areas oflocal bank protection can be rapidly outflanked by changes in the thalweglocation. (d) Proven bank stabilizing materials are either not available orexpensive to obtain. (e) The equipment required to place bank stabilizingmaterials on a large scale is not presently available within the country.

3.50 As control of the magnitudes of the floods on the major rivers isnot anticipated, channel stabilization must be designed for high velocitiesin deep channels. According to Pegg (1970). "stabilization of channelswith the characteristics of Bangladesh rivers is probably without prece-dent." Because the major rivers are braided and the thalweg changes loca-tion readily, "piecemeal" bank stabilization at local areas will not generallybe successful. The thalweg will eventually outflank the protection. Undersuch conditions, a bank stabilization program will require expenditures untilentire reaches of the rivers are stabilized. After many years of exnerienceand experimentation in the Mississippi River system, General Pegg (1970)recorded that " it has been determined that. the most. permanent andefficient type of training works are those constructed from riprap rock."Rock riprap in smfficient. sizes, anialitv_ and quantities are not readilyavailable in Bangladesh. Estimates of the cost of the rock that can beobtained are as high as 27 dollars per cubic yard (Pegg, 1970). nhvionsl vunless the price of rock can be drastically reduced, rock riprap for bank.qt.nhili7.tinn nrnojec+..t ill n nn+. hfas ible

3.51 In 1970, a bank protection plan was devised to protect the town ofSerajganj from destruction by bank erosion resulting from the impinging flowin he main channel of the Brahxnau tra River. The plan has become L-nor asthe "Serajganj Experiment" because the materials (soil cement riprap and ateel=jack jetty field) are uSproven for the conditions existig. 4long te,

river bank at Serajganj. The cost of 5000 feet of bank protection waseSti-mt.,ed as Rupees 33 000.000 or ,'. 66 A00 -per f oot. mTh 500 ft o

bank protection was considered only the initial investment needed to protect4,ii towr,. More bar'- p ection wo-aLLnL'ube req'auired Jin succeeding y32 The

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extremely large cost of an unproven bank protection scheme was undertakenbecause of the economic importance of one town and for political reasons.The protection of farm land from bank erosion with such costly programscould not be considered feasible.

3.52 One of the important benefits of resumption of trade relationsbetween India and Banpladesh will be the possibility of bringing in rockfrom Assam. A re-evaluation of the Serajganj scheme and a broader studyof the implications of construction materials imports from India forBangladesh river control are urgently required.

TV. RTVRR RESPONSE TO EMBANKMENTS

),.ni The tjmp- 1 for a river RvstPM=I rAsnonsA to a change in evi-ronment is relative. For example on the geological time scale rivers adjustrapidlyv to al tered cl imatoltogical annd hydrol ogic conditionj hbut thhe newequilibrium conditions may not be achieved during a man's lifetime. Also,in the geologcal s~1ceWnse, t.he u1lti.mat. fntsP rO1 any reservor buli t. on ariver is complete filling with the sediments carried by the river. Waterdevelopment program s are designed on +-he eot.ominc tim.e scale which is moreor less analogous to a man's lifetime. Discussion in this paper is limitedto re spor.nses a.icipated 4,ingr the ecor.n,

4l of rir ant.

4,r enlrk.

ments.

4.02 In Chapter III, the inmmediate vertical response (changes in stage)ofL Ul4Lt ULbaJ1I.SL.d Li.LVer.L £L Ndec was. et lished beas t,e1 vet-tLcal res-onse

can be an important factor in establishing the embankment heights. In thiscl' a-'er cn.ea ions gi.ven to the -aea _-.Pns ofth ewa-eLlIP Lu tVHl±UUV. I±ULL ±aU5_CIL LA) LL10 .J..L V.A.L~ ,?ILJ MIL11EUM

river reach, and to responses occurring in other segments of the riversystem due to0 the embanked reach. Tihe po3sible lateral responses arechanges in channel widths and changes in river form within a form (increasedmeander belt width for example). * nese lateral responses in turn willaffect the river stage. Long-term stages in rivers which widen should beless than those computed by assuming nonerodible banks. Long-term riverresponse is difficult to predict because many factors are involved.Experience gained from large river systems wnich have undergone develop-ment are very useful guidelines to selecting the proper response. Forthis reason, examples of the iMississippi River's response wo over acentury of development are given in this section.

A. Predicting Response

4.03 In a previous section, the prediction of the maximum stages anti-cipated due to embanlkments was based on the premise that the river channelbanks would not erode. Bknban]ments increase the sediment transport capa-bility in the reach and it was assumed that sediment would be eroded fromthe bed only. Any bank erosion that could occur would usually result instages less than those obtained by assuming non-erodible banks unlessresistance to flow increases, as a result of channel widening, that compen-sates for the reduiction in unit discharge. The non-erodible bank description

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of the responsA process is nn expedient simplification. Generally, thealluvial river reach achieves a new equilibrium in response to increaseddisqhnrarp hv dparnrintion in cnnmbinntion with later erosinn.

n1, Tf' tfhe normnl yeanr-to-vPnr variations in erosion And depositionalong the bankline of a river are, to all appearances, random in magnitudeand position, the river banks are sa id to be unstable The major reasonsfor river bank instability are: the variability in the composition of thebanks, rising a.nd fnhln I stag seveanl hraidedi hnrnols, impingemen.t ofthe thalwegs on the banklines, deposition of sediment, the formation andmoveme.n.t of sand bars, bark slmmping and the presence of old river channelsAll of these and other related factors greatly affect the bankline posi-tion and river configuration.. In the undeveloped state, iinstablh ar.A s+.ablreaches of river bankline tend to remain so except when subjected to catas-trophic changes -n both stable and unstable reaches.

LcE The an -. A ;PA Q;A t; .-hA ; +1,n A an.-e oh ., , n PAP+- + +1,-

rising and falling stage, the braiding of the channels, the erosive power.ad position onP tIheO t weg,s, tAhe depositio ,of Me+-Ient an( tAhe fo..ation

and movement of sand bars. In meandering rivers, the erosive power andposition of the thaw eg and t;he formiation ald ,movement of sand bars arepredictable if the bank materials are homegenuous. For other conditions,

LJCILMLJ-LU V~.LU. IOA± LU L C .LU V '~.LWQ J..IJLA UCL WU J AV .kJ L k.L LA~& U IVL UIJ.LLLJ J.L1 UL

local regions and for very short periods of time. The changes in rivergeomietry due to developm,Vent re usual-ly predicted with regime t ypeequations. Regime equations predict the average changes in the riverreach and not the local changes due, for example, to variations in bankmaterial along a reach.

4.06 Channel response to development can be predicted with the regimeequation represented in Figure 9 (after Borland, see Lane, 1955). Tneequilibrium conditions for a graded alluvial river are represented by adelicate balance between the sediment size, the sediment load, the streamdischarge and the stream slope (Lane 1955). The balance is of the form that

Sediment Sediment Stream Streamload size discharge x slope

The immediate response of the river reach to embanakment is the eliminationof the spill from the bucket. The amount of sediment on the palletcorresponds to the sediment transport into the reach; the amount remainsunchanged by embankments. If the bed materials are very fine sand, thesediment size will probably remain unchanged. Therefore, according tothis model degradation will occur until the stream slope can flattento achieve a new balance.

4.07 The degradation and stream slope flattening can be accomplishedin more than one way. Efforts have been made to refine the predictionequation further to give insight into adjustments in width, depth, andmeander wavelength that can occur. The set of equations were developed bySchumm (1969) from studies of 36 alluvial rivers. These equations are

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apnn1iGe.h for Gase of nn increase or decrease in discharge or bed-materialload alone and are useful for interpreting changes in channel width andreprhn, ShunnAml s ernnations nre 2S follows:

St.rp-.qm Strem,qm Meander

Stream < width x depth X wavelengthrA; !zhPrr>

Streamsl onpe

and

Stream Meander StreamR,;mzr. +. e TATi; A+1. X %Tn-=rc.l nr+.h X sl opnn

loadStream Stream.depth x Sinuosity

4.08 For the! embankment problem, the increase in stream discharge ishb-avaed i-n t.rAmo hwr a A'r.risn. hrn lryno ::nA Jn nq-r .cz in hcith Wiidth nnri

depth and, if the river meanders with the reach, the meander wavelengthWTAI' 4-,crease. 'Pe earnder w-,veleng+h4 +.he d44+stnne -a t,e consecuti

meander loops. In equation form, the new equilibrium balance is

Stream' c width x depth x wavelengthdisch"age

Streamslope

The superscripts indicate ijncreases (T) and decreases (-). If the streamlwere straight with non-erodible banks, a greater increase in depth and de-crease in stream slope would be predicted than for a meandering stream wi-.Lerodible banks.

4.09 The sediment transport equation is not applicable within thereach because the sediment transported into the reach remains unchanged bythe embankments. However, downstream of the embanked reach the streamdischarge is unchanged by the upstream development but tne sediment load ischanged. The sediment, removed in the embanked reach while the embankedreach is adjustirlg to the new regime, is passed on downstream. in the down-stream reach, some adjustment occurs. The sediment equation predicts tha-t theresponse in tne downstream channel will be a decrease in depth and sinuos:ity,and an increase in width, meander wavelength, and stream slope or

Stream+ Meander+ Stream+Sediment+ f width x wavelength x slopedischarge

Streamdepth wA UUOIL U.±

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Sinuo ,i+ j 5i9 a charact-'istic of meandering cinels def-ned as the ratioof channel length to valley length.

4.10 Upstream of the embanked reach, a slight rise in bed and watersur-f'ace e-levatli own shoi 'd re ML't du e t o thie b a Ck-W a t er e ffPe c t c au ss ed by thIe

embanked reach. A pictorial representation of a straight reach of riverndiL iL 1.s response tuo embd.±aLlnig LO i V g L1e .Ln F1g e 10. 4r. mary reaches .o

major rivers in Bangladesh, conditions are such that the average degrada-tion a U n d U - 11 e p T'U 4 -- -3 widening would not be p. Deail are gVC1 en n a

succeeding section.

D. L±ne Uase of.L e u ±l± pp±

4.11 Tne vI4ississippi River and its tributaries have undergone progres-sive development for over one century. The developments have been in theform of: reservoir for flood control, irrigation, and power; river bankprotection to help maintain channel alignment; river entraining works tonarrow the channel widths to provide navigable depths; meander loop cut-offs to provide shorter travel routes for river traffic; and river embank-ments to protect the flood plain. These many forms of development on theMississippi have been staged over the years so that it is difficult toassess the response of the river to any one development factor.

4.12 The results of the integrated types of development on Mlississippidischarges and water stages at Vicksburg, Mississippi, are apparent (U.S.Arnmy Corps of Engineer, 1971). 'The ten-year average of the maximum, meanannual, and low flow discharges are shown in Figure 11. Peak flood dis-charges have decreased over the period of years due to increased reservoircapacity on tributaries and possibly because of changes in watershedcharacteristics and in precipitation. Possibly there is a trend of decreas-ing mean annual discharges. Since 1930, the trend of the low flow dischargehas been upward due probaoly to low-flow season releases from upstreamstorage.

4.13 The overall effect of the river system development on MlississippiRiver stages at Vicksburg is illustrated on Figure 12. Tne percentage oftime that any (but the lowest) stage is exceeded has decreased throughoutthe years. Since the mean annual discharge has remained about the sameover the years the conclusion is that the overall effect of the develop-ment is towards stages lower than those t.hat occurred before development.

C. Changing River Forms

4.14 If the main channel flow was increased sianificantly by construc-tion of embankments, it is possible that the river form would change. Alarge change in discharge is equivalent to doubling the water on the bucketside of the scales (Figure 9). Wiith such a large change in discharge theremav be no way that the scales can rebalance. The result would be a newriver form; one that would accommodate the large increase in discharge. Forthe river in transition. it is nossible that the sceles are delicatelybalanced. Any slight change in discharge or sediment load may unbalancethe snnlhs.

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) he capacity l s otheM scales -for tMe offerent river -o-

have not been adequately defined. It is difficult to predict the exactcontdtit.i.onS 4;hat w4'l cau-s a tle +o change its + .4 -^b. thl T-l

natural discharge, by trans-basin diversions for example, has destroyed.,i.enVd e-lg sturearis andU th1LVir ri.Lv VdL.ly . 4-,le saI.e result hLa o1curred

when small stream channels have been used as wasteways for the drainagefro, irri:gation syster.s. In sor.e cases, man has changedt.erv-fo._LI (J l ±1 I-LLJL ~ L~CI V LI fUIIlD Ilde.i1 L1d.1 LUL%v1~u ULIU ±JLV..V - 'J.L11

For example, meandering rivers have been straightened by excavating cut-.P e L a,L -s to h |1 P _ |s _ 1-1 _ _ _ A _ 4i __ i ,.L . i) v V Jutofl. X X C ie eV C IUI L ffect L eL;L aOLA1t UlJz LIJJ WIU. VILLD1I. ULit 1GBU-U jhiu L

supplied to the river, the sediment size and the water discharge areeent'i L a'LJ..- unchangedL, 4iJ.I scales arOe Unbac1LaneU aUn bJCLIMr soIUr anWUoLr

degradation occurs. In small river systems where cutoffs have been construc-ted, the apparent response has been for the river- to atte-mt to r-etu-n tc(its former natural condition. The original condition is usually notrealized because further investmenits in structures and retaining worksare made to hold the river in its altered form.

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D. Conc'lusions

4 .i0 nmanimenus along an a-Luvial river reachi e±u.Uinaue Uverlandflow and flood plain storage on the land side. In terms of the mainchannel flow, overbank spill is eliminated and the main channel dischargeis usually increased. The increased main channel discharge usuallyresults in an increased stage and depth. The increase in stage anddepth are dependent on the decrease in bed form roughness in sand bedchannels wnich usually occurs witn increased discharge. if bank erosionoccurs due to increased discharge, the stage rise will be less than forfixed banks. A combination of bed degradation, channel widening, anddecreased bed roughness could result in decreased stages for embankedreaches. To determine stage response a careful analysis is required.

4.17 In heterogeneous alluvial deposits, all main channel cross-sections will not respond in the same manner. Increases in width anddepth wilL be different at different cross sections. For example, atnodes, the increased discharge may not be capable of increasing thechannel width. the response of the water stage will be more uniformfrom section to section than either the width or the depth. Experiencehas shown that embankments may increase the water level stages initiallybut usually, in the long run, stages are less on developed than onundeveloped rivers which carry a large portion of the flow in a mains%nd-bed channel.

V. S-WMMA-RY OF DACCA SOUTHWEST PMBANKMTN1 ST1UD1ES

5.01 The hydrology and river hydraulic studies which provided thebasic design parameters for the Dacca Southwest Project (abbreviated DSWProject) embankments were presented in the Dacca Southwest Project,Feasibility Report, Volume IV, "Hydrology and River Hydraulics,"August, 1970, prepared by Engineering Consultants, Inc. and AssociatedConsulting Engineers, Ltd. The report contains: studies of the occur-rence of floods and the historical flooding patterns; discharge andstage frequency relations for stations located along the boundary riversof the project area; detailed hydraulic analysis of the Brahmaputra andPadma Rivers for the DSW Project condition and for the condition of totalconfinement of the Ganges, Brahmaputra, and Padma Rivers. In this section,the DSW Project studies relating to embankment location and heights aresummarized.

A. Flood-frequency Studies

5.02 Flood-frequency studies were done for stations located along theboundary rivers of the DSW Project Area and for upstream stations on themajor rivers. Discharge frequency relations were developed where dischargeswere measured; stage frequency relations were developed where stages onlywere measured. Frequency relations were extended to the 100-year returnperiod by fitting the Gumbel distribution to the data. Discharge-frequency

- 29 -

relations were established for the Hardinge Bridge station on the GangesRiver, the Brabmaputra River at Banauurabad, and the Padina River- atGoalundo. The maximum recorded or computed discharges along with theestimated 100-year floods at tnese three stations are given below;

Maximum recorded 100-yearor computed flood discharge

Station Date discharge (cfs) (cfs)

Ganges River 1 Sept. 2,585,00Oa/ 2,720,000at Hardinge 1961Bridge

Brahmaputra 1 Aug. 2, 800o00o/ 3,620,000River at l955Bahadurabad

Padma River 4 Aug. 3,880,0002i' 4,400,000at Goalundo 1954

Notes: 1/ From WAPDA records.2/ Computed from the maximum stage recorded in

19,55 and the 1966 rating curve.it Computed from the maximum stage recorded in

1954 and the 1966 rating curve.

The recorded length at other discharge measuring stations were consideredtoo short for frequency studies. Stage frequency relations were establishedfor the following stations: Dhaleswari River at Tilli and at Kalagachia;Kaliganga River at Manikgani3 Buriganga River at the offtake and at Dacca3

and the Meghna River at Satnal.

B. Water Balance Studies

5.03 Water balance studies for the DSW Project Area. the major riverchannels adajacent to the Project Area, and for land areas adjacent to theProject Area were described in the Feasibility Report. The river flowsoverbank spills, overland flows, and changes in storage were estimated forthe 1966 flood. The data which were available, especially for overlandflows, were extremely limited and many of the conflicts in opinion as tothe origin, (irection. and magnitude of overland flows could not be resolved.

- 30 -

For the DSW Project Area downstream of the Dacca Aricha Road the waterbalance equation for the 1966 flood yielded the following estimates:

(a) The flow into storage was less than 30,000 cfs measuredduring the peak of the flood. This flow is less thanone percent of the more than 3 million cfs measuredflowing in the Padma River.

(b) The peak overland inflow was 45,000 cfs (measured) andthe peak overland outflow was calculated to be 82,000 cfs.

(c) The net left bank spills from the Padma River and netright bank spills from the Kaliganga and DhaleswariRivers into the area were computed as 67,000 cfs fromthe water balance equation.

(d) The DSW Project would prevent this 67,000 cfs of netoverbank spill which represented 2% of the peakflow in the Padma River.

(e) It was concluded that the DSW Project would increasethe peak flows in the Padma River by approximately 2%.

C. River Hydraulics

5.Ch The behavior of hydraulic and geometric properties of the rivercross-section at five discharge measurina stations was established forthe 1966-67 water year. The five stations were Bhagyakul and Goalundoof the Padma River and Mathura, Serajganj, and Bahaduraoad on theBrahmaputra River. The sources of data were the discharge measurementsummaries for these stations. For the five stations. it was shown that:slope increased with increasing discharge; Manning's roughness coefficientdecreased with increasing discharge: and the stage increased about onefoot per 5C0,000 cfs at the peak flood discharge. Discharge measuringstations are. for exnediencv. located at nnrrow sections of rivers. Narrowsections scour during the floods. At Bhagyakul for example, local scourbeenme aDoarent when the discharge reached 2;000C000 cfs. SGOUr Gontinl1edduring the remainder of the rising portion of the hydrograph. The cross-section filled again during the hvdro1rpnh recession so that at the end

of the water year the bed elevation was the same as at the beginning ofthe year-

D. Sediment Transport

5.05 A sediment discharge rating curve was established for the Baruriachannel of the Padma River On p G-oa'uqdo* The 1966-67 water year datawere obtained from published WAPDA records. The plot of measured sandload in suspension versus water discharge indicated that a sin.gle curvewould describe the sand transport, water discharge relation for conditionsbefore aniu after te peakc. JInu.Lca.iUU were tt the beU lUau tL rasport

- 31 -

was large in comparison to the bed material load in suspension. Generally-,studies in smaller sand-bed rivers have shown that most of the transportis in the form of suspended-sediment transport.

E. Staze-Discharge Relations

5.06 The 1966 stage-discharge relations at the five discharge measur-ing stations were extended to encompass the range of the 100-year flood.The 100-vear flood was specified as the desien flood for the Project.The natural condition 100-year flood discharge was increased by 2%to obtain the desigrn discharge. The 2t is the increase in neakriver flow caused by the Project embankments. The stage corresponding tothp dtzsign discharge was obtained from the extended stage-discharge curve.The design discharge water surface profile was established from the stageEsobt_inAd at the five discthqro,. m-esi3rino, StatiOnD. The mqximnm rec,ordedstages at all stage-gaging stations along the river were compared to thedie-ian water sirfare nrofil. These mTYiml]m rPnorded stnags were less

than the design discharge water surface profile at all stations.

5.07 The 100-year flood profile for the undeveloped river was 0.1 to0.2 feet lower than the profile for the r)w, Project condition_ qhoe mTarinlumvariation in the year-to-year stage for a given flood discharge in the major-4vters of Bar.glad*sh w*as estte o be 2D fee+ or plsor .- ,usonfoot from the average. These numbers were determined from published stage

(A se1harge c-armres for thle BrLahMJC-,%AputrLa R. ver.

F:. 41ML 'bal-l ,. Lent Heig,hts and "lKImarlwnt

5.o8 along Ile PadILUma ar.L A-aJ1U a iVL, RIve- VJeULd -bu,et LL' c,-es

elevation was established 5 feet above the design discharge water surface

_r: nn . A r I_ ___ 1- - _1 _~ _ __ 1__ _: ___ , t_ __ __ _ ~ _ 1|_5

;l-Vl 1 Gj ireiG D= Wti;> d.LU E .we:u UU III WaV t: UU 1 u 1iU L 1 tIU .U D ± IlLpU1IU i eUal*,

5.09 The em,barnkment -was set back s-ufficientlDy fromr the ri-vers so that,it would be relatively safe from river channel shifts and subsequent%A;.-Lect atuackA Lb t.Lh floW "L lLve mai charmLel. The se-U-back d-l.,tance

along the Padma and Brahmaputra Rivers was approximately 1 mile and alongUlle MlieL V G iL- JJt1U AtL L gd16L tLLVA.- V U e IZ rA11UWjALIiL"iU aD ;tJ UZt;L[ .L7 LU *.v

mile from the active meander belt.

G. Anticipated Response

5.10 The DSW Project embankment will increase the flood discharge in theadjacent Paduma and Braimiaputra Rivers by approximately 2%. Tne increasein peak stage corresponding to a 2% increase in discharge is only 0.1 to0.2 feet; much less tnan tne year-to-year variation in stage for a givenflood discharge. Normal bank erosion and deposition rates along theBrahmaputra and Padma Rivers can be very large. For example at Serajganj,the 1969 rate of erosion was approximately 60 feet per month. Therefore,the year-to-year variation in channel width for the undeveloped river ata cross-section can be large. The small increase in width anticipatedfor increased peak floods should be entirely overshadowed by the normalyear-to-year variations. In general, the 2% increase in main channel dis-charge should result in responses undetectable from the normal year-to-yearvariations in the undeveloped river.

- 32 -

VI. SUGGESTED LINES FOR FUTURE INVESTIGATIONS

6.01 Flow of water and sediment in alluvial rivers -and regulation ofthis flow is a complex problem involving many disciplines. Many of ourpresent problems are the results of too simplified an approach to theoriginal problem. The innumerable variables that affect any given riversystem or river at a particular point in time may be grouped into sevenbroad classifications: time. geoloev, soil chemistrv and soil mechanics.hydrologic, geometric, hydraulic and man's activities. The variables inthese c-lassif~itions cannnot be oon.sidd-rPd indepnndentllv since thev dependon each other in varying degrees. An understanding of this dependency isneceSSay-r< for- a wo-rkcncg knnowle*dge of river andr rlvp-r qv.stPTns.

6.02 The major geologic, soils, geometric and hdrv-auilic variablesthat are important in any detailed analysis of streams are listed in thefolloing p Tagraphs. Th.e elical variable s are: th.e general r eliefof the region, the slope of the river, the characteristics of the bed andb& Wmaeral th Ye' type % %Id JA dept of the surace ar.d Qmlbsurface a'uvi-formations, and the groundwater characteristics. The soil variables ares4-4-1-- 4to 4the geologlc varlables ard 4-clude 4the 4-,-- -of so-ls 'I the."UI1L-L.LOJ ULJ V4IL 8u. .,LU LdIJJ.V. 'L- -LLAL-LA%V * 11 U 1 YY O ULJ OVL-O LU1±

heterogeneous distribution of the alluvium, the chemical and physicalproperties of the irdiidua soil t -pe , -ai -- Io -h silts ar.d cl-s.-j.J.VI ' L %L~L V UL I .. fl'A.VL.JO. ~J.L U QWri -frC4.S.L.A.&J U W OA.L..L CU0 WL%A %..L.CVJ

The degree of channel stability, bank sloughing, vegetative growth andL~. ~J. ... .1.L V~J. . U.LUJI 0.Z. J. V-L k U "L U' 1v0J.. V 0~ - . .J -L JL~lateral rive r r a t ion- a 4ereaed At4o 4the so;ilvraes

A no q_ .* - … _ … 4_W..) eL1; Va aes e ciU I dl U.v LI tJ±±z gyILU- lm.- UJ. vLi U ull" ICUI1O ±1LXUUt;

depth, width, sinuosity, radius and degree of curvature of bends, widthof- r,.ear.der belts,- d1-c e4--.,erdrlop,dstrc eter aU! JI~.1tAWJ.L &VL UO, kLLLOk Lid.L1I LtJUM liW i 1J1t;CLU1Ue.L ±UUj9I, %UJL0UdiUU1 &JU LWULI IJtLL

formations, general alignment, the longitudinal profile of the rivercarLLel UIA1 t t t.e geor,eJry Uo UbU ±LrLuIL WIar Ucars, WIU LdLLU WldytJ sp actUors o.f

channel cross sections. Every geometric variable is a function of dis-charge; when the discharge quantity or duration is altered t'he geometicvariable of the river system is changed. The hydraulic variables are:slope, velocity, turbulence parameters, fall velocity oI bed and bankmaterial, the sediment discharge and seepage forces. These variables arethe most dependent and the most changeable of all stream variables. Tneyare constantly adjusting in an effort to keep the river system inequilibrium.

6.o4 F'uture studies of river systems should consider:

(a) The adequacy of geologic, hydrologic, geometric andhydraulic data for analysis of the development and response of therivers and river systems of Bangladesh and adjacent countries,principally India and China.

- 33 -

(b) The development of data storage and retrieval systems toassure accurate, complete and easily accessible data for those involvedin the analysis of river systems and related problems.

(c) The development of detailed geomorphic and river mechanicsreports that could serve as a reference docament for the plamners andengineers. These reports may be supplemented in time by the developmentof mathematical models of the river systems. However, it would be essentialto adequately test such models under a wide variety of field conditionsbefore using them for more than identifying possible alternatives in theDlanning staee. The development of such models would reauire an adeauatedata base and a thorough understanding of physical and stochastic processes.Continuous model upgrading is a necessarv requirement because the systembeing modeled will be subject to contirnual change. Unless the effort isto be a continuing one. it would be difficult to iustifv the large invest-men-t required to develop, and calibrate useful river system models.

(d) How changes in a river system may cause progressive changesthroughot the system. and its ri1nt-I iev i VNorm_lly, any ch.anap will c-ausea reaction upstream or downstream to a point of man-made, hydraulic, orgeolo1caiml cn.r%+vnl.

{a\ TPh nro+.tn+tql mannn I psn+. And prnonnposei act+ivritie si% +.n upsetthe regime of the rivers. If regime changes in rivers are predicted, fulldevelopnmen.t river systems can be realized.

BIBLIOGRAPHY

Acres International (Overseas) Limited, 1970, "General Consultancy,

Data Status Report", Volume I. (Draft)

Ad Hoc Flood Consulting Panel, 1970, "Draft Agreement Between EPWAPDASogreahl, Memorandum dated 16 November 1970.

Ad Hoc Road (sic) Consulting Panel, 1971, "Embankment Failure by Crevasses",International Bank Office Memorandum dated May 20, 1971, toMr. Picciotto. (Draft)

Chang, Hai-Yain, 1967, "Hydraulics of Rivers and Deltas"l, Ph. D. disser-tation, Colorado State University, Fort Collins, Colorado, March.

Colby, B. R., 1964, "Discharge of Sands and Mean-Velocity Relationshipsin Sand-Bed Streams", U . S. Geological Survey Professional Paper 462-A.

Colby, B. R. and C. H. Hembree, 1955, "Computations of Total SedimentDischarge Niobrara River near Cody, Nebraska", U. S. GeologicalSurvey Water-Supply Paper 1357.

Coleman, J. M., 1969, "Brahmaputra River: Channel Processes and Sedimentation",International Journal of Applied and Regional Sedimentology, Vol. [II,No. 2/3, August.

Committee on Channel Stabilization, U. S. Army Corps of Engineers, 1969,"State of Knowledge of Channel Stabilization in Major Alluvial Rivers",October.

Crippen, J. R. and S. E. Rantz, 1968, "Interpretation of Flood-FrequencyData", Selected Techniques in Water Resources Investigations, 1966-67,U. S. Geological Survey Water-Supply Paper 1892.

Dalrymple, T., 1960, "Flood-Frequency Analysis", U. S. Geological SurveyWater-Supply Paper 1543-A.

Engineering Consultants, Inc. and Associated Consulting Engineers, Ltd.,(ECI-ACE), 1970a, "Dacca Southwest Project Feasibility Report Vol. IV,Hydrology and River Hydraulics", August.

Engineering Consultants, Inc. and Associated Consulting Engineers, Ltd.,(ECI-ACE), 1970b, "River Mechanics and Morphology, Dacca SouthwestProject, East Pakistan", prepared by D. B. Simons.

International Engineering Company, Inc., 1964, EPWAPDA, Master Plan,Volumes I and II and Supplements A, B, C, D, December.

Krug, J. A., Leader, 1957, Report of the United Nations Technical AssistanceMission, United Nations --- Nations Unies, Technical AssistanceProgramme, Water and Power Development in East Pakistan, ReportNo. TAA 'Pak' 15, Volumes I and II, June 3.

Lane, E. W., 1955, "The Importance of Fluvial Morphology ir. HydraulicEngineering" Proc. ADUC, Vol. 'L^ No. 7h5.

Latif, Abdul, 1969, "Investigation of the Branmaputra River", Journal Ofthe Hydraulics Division, ASCE Vol. XCV, No. HY5, Proc. Paper 6793,SeptemDer.

Leopold, L. B. and M. G. woiman, i -957 "River unannei ratterns: Braided,Meandering and Straight", U. S. Geological Survey ProfessionalPaper 2t -r2.

Linsley, R. K., M. A. Konier and J. L. H. raulnus, i958, Hydrology forEngineers, McGraw-Hill Book Company, Inc., New York.

Nordin, C. F. and J. P. Beverage, 1965, "Sediment Transport in the RioGrande New Mexico", U.S. Geological Survey Professionai Paper 462-F.

Pegg, J., 1970, "rEast Pakistan - Individual Findings as a Result of 6-22November Visit to Dacca and Vicinity". International Bank OfficeMemorandum dated 29 November 1970 to Mr. Robert Picciotto.

Richardson, E. V., 1970, "Hydrologic Data and PC!!, East Pakistan",Memorandum dated Dec. 10, 1970, to Mr. Robert Picciotto, InternationalBank for Reconstruction and Development.

Schumm, S. A., 1969, "River Metamorphosis' t, Journal of the Hydraulics Division,ASCE, Volume XCV, No. HY1, Proc. Paper 6352, January.

Simons, D. B. and E. V. Richardson, 1966, "Resistance to Flow in AlluvialChannels", U. S. Geological Survey Professional Paper 422-J.

Simons, D. B., W. L. Haushild and E. V. Richardson, 1961, "The Significanceof the Fall Velocity and Effective Fall Diameter of Bed Materials",U. S. Geological Survey Professional Paper 424-D.

Thijsse, J. Th., 1964, Report on Hydrology of East Pakistan, May/October.

Todd, 0. J., 1938, "Two Decades in China", The Association of Chinese andAmerican Engineers, Peking, China.

U. S. Army Corps of Engineers, 1971, Vicksburg District, personal communication.

U. S. Army Engineer District, Omaha, 1969, "Missouri River Channel RegimeStudies", M. R. D. Sediment Series No. 13 B, November.

U. S. Water Resources Council, 1967, "A Uniform Technique for DeterminingFlood Flow Frequencies", Bulletin No. 15, December.

rigure i

200j \\ X \ 'NJr \\ \ A \ _ _ _

100~~~~~~~~~0,l

C I \\ \ X >o X I40 2o 10 S

grae than tha haigte niaercrec

Point AN indicates that there is a 40perC)en

0) L l ')

Pechance proabiit the 100-yerrneoa flood wl eecee

greate than th-yat having the indicateardo recurrdc

(Point A indPicateCsos that there is a 4 ecn

I percent chance that the 100-year flood willoccur in any one year.

Figmre 2

Main Channel Overianid Inflowinflow

ItI It _____

,,/t I)\A; Area to be A VPol d'ered >)

0CZJ

-\\J T '- ,, - n[- c 0Wtf w

k4ovlulin C.!

O i i2

TYPICAL EXAMPLE OF THE COMPLEX OVERLAND FLOODIN'G PROBLEM

T-N BANGLADESH

When the area is poldered, flood flows in the main channel

and in the miOnr river will be increased.

X X ~~~~Br nki.f(lll Di sc h rrgecC) ~T

AA

01I

o_ X1 ____ ___ ___ __\ ,__,,

| XBX Timne

EFFECT OF EMBANKMENTS ON A FLOW HYDROGRAPH

Curve A is the main channel inflow hydrograph. The net rightand left overbank spill is represented by Curve B and the

overland inflow diverted to the main channel, by Curve C .Curve D is an estimate of the main channel hydrograph for thedouble embanked reach (sum of A, B and C).

we; -' 1:D- --

elocity;r, f Ps 10 I Voci tyf Cp 10

4-c4 -x -h

INITIAL RESPONSE RESPONSE FCIR RI'GID BM3R

CuLrve Y is the rigid boundary exten[siorn Whern the barks a.re rigicL, thie responlseofP theg ma.in c;hannel peak flood conditions to embankmen.ts i.9 along the path Aassuming constant roughness. Curve X tc, C. The firial condi.tions at; D aLrei'3 thse rigid 'boundary extension assuming an i.ncreased. q, increase!d deepth, loTorera decreases in roughness. velocity, an.d th.e saxie q[s.

V E~~~~~~~~~~~~~~~~~~~~~~~~~~~Lqu IlIbItri u mL \ I I I \ \ I: X | Transport Cu,v e>'

:0 ~ ~~ ~ ~ ~ ~~~~~~~~~~ f t Pec r. J/

XI&!5î ~ ~ ~ ~ ~ ~ ~ I 4'tfD OIVlct,fs1

Sa~~~~~~~~~~~~~~~~~F Sb r

Wh.en A,he b,edand banksare erodil,e, t,heT>e bEbSoes anclfter peak PiPeck~~~

final response to embabnkments coul,d be caLte unequal t;ransport for the saineth.e point F where the q is increased, di0sche ge. Wi.th non-equiibriumthe depth is greater, and the velocity, transport the section will scour/depositand qs are less thLan a.t A. dTing onef paat o ther hyecrograph and

ritcomni tA/.r nur trhric ng thA r the.1 n.hpr -

32 - - - v --- 1__--

2 2' -

32D1 - 2- 3 8-.-/ F

r. 2X 2D X 0

i4C 6°l)t 9C

19 67 2-1968

___/ )__ !I t I- 1O L L JI 4 1 L1 1_I I l l

0$.ê 0_i. j.3 1.0 1.2 1.4 0.4 0.6 0.8 1.0 1.2 1.438 - . -~~~~~~~~~~~~~~~~~ 338 -

- ~34-

- CS 30 L

2A 6

~22; 22-7~~~~- ~

i 4 1 ~~~~1694 9C

0.8 0.8 [~~~~.0 1.2 [.4 0.4 0.6 0.8 [.0 1.2 1.4

D~sc:~rc~~, i;c: i c~ cf Discharge, millions of cfs CD

STAfIE-DISCHARGE CURVES FOR THE MISSISS)IPPI RIrERAT ARKAN[SAS CITY, ARIKANSAkS (ztfter- U.S. CORPS OF ENGINEERS, 1971)

Figure 7

r.7 1K

z/-B~~ ~ ~~~~~~~~~~~~~~~~~~ .. . . ....

A <E

Cuv / the maiu eryvrainOKh tgSTAGE WITH EM4BANKMENTS~

Curve A is the long-term average maximum stage andCurve B the maximum yearly variation of the stagefrom the average stage. The embanlments increasedthe.discharge by 5Q, and the average maximum stageby aSg. The maximum anticipated stage withembanlkments is stage Z plus the maximum yearlyvariation Y.

C-.--

A t e r °e a k Discharge,--== , -

y - Before Peck Discharge

,7D~~~~~~~~~~~.

c 4

C 02 0C.. 4 0.6 0.8 1.0 i.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Dis2lh ore in i'villions of cfs

STAGE-DiSCiiRC-E CU'RVE FOR THE PAXMA RIVJER AT

B--LAGYAKUL EOR 1966 (after ECI-ACE, 1970a)

(D

= ~ ~ _ ______ l, - - - eE

__ _01 FINE FLAT.25 STEST E P CjDrA>l,0~~~~~ P q 'LO PIE

G- --71 | |

8-

Ag 1\

i:t_

CHANNEL R1ERNSE TO DEVEILPMNT (after W. E. BORLAND, U.S.B.R.)

The increased dLscharge resiulting from embankments upsets the delicate balance inthe graded river. New equilibriium can be achieved 'by increasing the sediment sizeor sediment loali or by a decrease in thie stream slope.

CD

'I

Figure 10

l l

_ _ _ _ _ _ _ ~~~~~~~ / /

I .-Bank Erosion

Plcmi View

EmhonnlkPd

Reach

IDecrecoscd S lp

l i- l---ncr-eosed Stoi)c

DN,\~~~D o) .- o da' i lon|

-~~~~~~~~~~~~~4¢ i Cerl,crlii;C- Proli le

RIVER RPVNSE TO EnBAN1GN'NT

In a straight alluvial river reach, the response to embankmentsis increased channel depth and width (degradation and bankerosion) and decreased slope (increased stages). Downstream,bank erosion and aggradation occur along with an increased slope(increased stages). The upstream reach is nearly unchanged byembankments.

W gyure 11

1.6F I1.55 A -Averoag Mo:aximum

1.4

1210

0 7 L --- Averaqe Mearn Ann.al

-' 0.56 - ~ _ _ L~0.5

C)

0.3

C |2I- . ,/-Averaicq Low F Io)J

0.1 1--K~OO0 i0- 1920- 19-1- L

1909) 1"9 1132- 1937 Ic;39 fCŽ50;C

Yeas, Uy lO- Fccr FYriod',

MISSISSIPPI RIVER FLOWS AT VICKSBURG

The average maximum flow has decreased over the years due todevelonment. Hnwever; the average mean annual and low flOWShave remained nearly constant.

rL

40K

L .\ \ \1900-1936

6<

202

0)

-0 1

0 20 100C 80 100

Perceinl of Tihie *Flcit ,heGcrJ a Ilci2h!-t VEx r-cae(e(

S_AGE-DURATION ChPTRVE TAnR TH (zSE .- TSSIRrDTrTAT VICKSBURG, MISS,

River stages at Vicksburg have decreased as development progressedon the Mississi ..i River and its upstre_m trbutaries. A givenstage occurred for a lesser period of time during the 1960's thandurîng the -eriod L-om .M ?onn t^ ' 014

RESTRICTED

TN1TRN.ATTnNAT. RANK FnOR rGM,'PITTrfTTnOT ATMT Trw7Tr LPM.ENTT

TNTFRNATTOnA T. TEVR.VOPM.nT T ASSOGnr.TATTON

BANGLADESH


VOLUME VIII

THE FLOOD PROBLEM

EMBANKMENT MAINTENANCE


nDece-.beO r 1,. 1797

BANDGLADESH - SECTOR STUDY



EMBANKMENT MAINTENANCEri

T5hle of nî+.=ntc

Page No.

SUIMARY ......................................... i

T TNROTIICTTON- ............ 1

TT- TN~PPLTTOwS wa--- ................... 1

Police inspections ... 2H4igh water inspections = 2

TTT - TjTflh WATER MATNTETA.IATr. nR FTnOD FPTrHTTNTT PRPflCETlITRRS-

EME3NKMEINTS 2

Drainage of Landside EDabankment Slopes 3Sl oughsanolAl rlP 3Bamboo Matresses ...Board rNtte =.=

Sand Boils ..................................... hToppi ........ ..................5Topping with Hauling Equipment ................. 5Tcnni nc? wi th D'-rrik RnsQt. nnti Rror- - -1- -rr--- t> -'-- ' --- . -............

Sacked.Earth ... .000 ... 6Cut Crown Toppinga -- 6Board Fence with Earth or Sack Topping ......... 6,L.a ir e W L.^roh ........-.-.--- .. * ---=* ==*-=-*--............ 7Scours ... o 7

Burrowing Animals .............................. 8B u r r o w i n g A n i m a l s 8

Treatment ................ e*..*..... 9

j This report was prepared by General John Pegg, (Consultant)

Table of Co-n-tents (cont= )

IVi. CLOSURE OF flRVl¶rAss5 TN pAVnMRtK,'NTrq..................... -.,

General A9Timber Trestle ........................................ 10T .T d Box TM 11

V. REGtULATOR; OPEPJuTION ANi,D ~AMf.ljTErMGJCE ,,............................, , 11

General *...*****,************. 1*1

Piping ..................................................... 12

VI. ORG-ANIZATION AND ADI'INISTRATION; ....................................... 13

Organization for a ,ingle Emban kment System 1l

Personnel ****.*........*........................... l4Fac;'ities2 ... ****.... O *....... ........... .......... 1)

Equipment .. .................................

Procedure for Obtaining Equipment and Supplies. 16

A,4--r -- ; -nr, +rs -- e -Ie s .rnn 1 X4

OPerasionl a Mn aus 16

Figure 1 - CoJi1~.) L~L. Euipmnstctio J1n UIaUU .L a J .I. f High . aer B,b I 0 trFigure 2 - Construction Methods for High WJater .,and BoilFigure 3 - Construction IIethods for High Wlater lid BoxFigure a - Lumber and Sack ToppingFigure 5 - Construction M,ethods for High ,4ater Sack ToppingFigure 6 - Construction Methods for High Water anve iash

Protection Portable BulkheadFigure 7 - Construction Methods for Hiave ash ProtectionFigure 8 - Board Fence Save Tash ProtectionFigure 9 - Construction Methods for Deflection DikeFigure 10- Stone Crib for Caving Bank ProtectionFigure 11- Crevasse Closure


VOLUME VIII

THE FLOOD PROBLEM



SUMMARY

i. No matter now carefully designed and constructed, embankmentprojects are of very little value and in some cases could be a menaceif not properly maintained. Embankment failure can result from a numberof causes and failure at some location is not only possible but probableduring the life of a project. If embankments are properly designed andconstructed.failure is less likely to occur as a result of overtoppingand direct attack by the rivers and is most likely to occur because offactors such as slides, seepage, sand boils. scour from wave and excesscurrent actions and piping through tunnels created by burrowing animals.These Dotential structural failures can be held to a rare occurrence ifan adequate maintenance program is provided..

ii. In view of its overriding importance, a maintenance and floodfighting nrogram must be included. as an integral part of the Dlanningand implementation of embankment projects. It is essential that plansinclude fuind-ins and orsani7 zational arrn naen-ts as i,qwpll as assiLrancethat an adequate program will be implemented and continued throughoutthe life of the nrojiect.

iii. This renort outlines the malor comnonents of an embankmentmaintenance and flood,fighting program. Included, are the need.for op-eration andr mnintenanceP mTnmql.s for -aoh nronipt.- flond qtag'p fnorAnqt.and inspection programs, outline of work required during the dry season,likelyv fod. season problhems and. suggested qolititons organizatioAn- ari-ministration and. requirements for personnel, training, facilities,equipment and supnnlieq- e= ecRius of the variety of si7ze and compleiYtiesof embankment projects, an attemrpt is made to develop a set of maintenanceprinciples and a t+ynicnl organizational anLd admininstrative arrang mentthat could.be tailored to each individual embankment system and to theconditions of Ba-plade1sh

- ii -

iv. A program must be considered in two phases: first, ordinarymaintenance that must be performed during the dry and wet seasons asa routine operation and second, maintenance and flood fighting proceduresthat must be implemented during flood emergencies. WIhile these are in-terrelated, of necessity the routine maintenance, if properly accomplished,will materially reduce the requirements for emergency operations duringthe flood season.

V. The suggested nrocedures. if meticulously followed, should insure theintegrity of the embankment system against structural failure. However,until the banks of the rivers are stabilized. a constant vigil must be main-tained to relocate the embankments well in advance of direct attack by theriver. For even a limitpd bank st.ahilization nrogram; it will bh necess-rvto implement a flood prediction service and to obtain large quantities ofst.one, Thesp items mulst be accomplished with the nnopermtion of Tndia where

over 90', of the flood waters originate and where stone is available.


VOLUME VIII

THE FLOOD PROBLEM



I. INTRODUCTION

1.01 A water resource development system, no matter how well designedand constructed, can not adequately serve its purpose unless it receivesproper maintenance after it is completed and placed in operation. Amaintenanceb program must be considered in two phases: first, ordinarymaintenance that must be performed as a routine operation and second,maintenance or flood fighting procedures that must be implemented duringflood emergencies. While these are interrelated, of necessity the routinemaintenance, if properly accomplished, will materially reduce the require-ments for Extraordinary operations during flood emergencies.

1.02 It is evident that the flood control system in Bangladesh willultimately consist of a number of interrelated embankment systems. Asthese embankment systems will be of varying sizes and complexities, it willnot be practicable to attempt to develop a standard organization for theoperation and maintenance of the facilities. While a set of maintenanceprinciples can be developed, their application would need to be tailoredto each individual embankment system.

II. INSIDECTIONS

2.01 rMe keys to an effective maintenance program are dependable riverstage predictions and an effective inspection and policing force. Beforedependable river stage predictions can be made, it will be necessary toobtain adequate hydrologic data upstream of the international border. Theinspections should fall into three categories:

Low water inspection

2.02 This should follow each monsoon season. The inspection shoulcd beaccomplished by a team representing both the engineering and constructionbranches of the organization. It should have the capability of makingdecisions on the type and urgency of maintenance items, such as repair ofscour, repair of wave wash, rehabilitation of drainage structures, repairof borrow pit traverses, repair of drainage facilities. etc. The resultsof this inspection should be used in developing the maintenance program,which should be accomplished prior to the following monsoon season.

-2-

Police inspections

2.03 During the low water season, sufficient inspections of theembankments should be made by individuals in authority to control excessgrazing, enforce the removal of all structures from the embankments, andprohibit the placing of structures on the embankments; prohibit thedegrading of embankments for drainage purposes; and prohibit breaching oftraverses in the borrow pits to permit their use as waterways.

High water inspections

2.04 These should be scheduled, as necessary, to warn of any impendingfailure of any of the facilities. These inspections should, of course, beginas soon as the floodwater is against the embankment, and should be intensifiedas the staoes increase. During periods of extreme flood, the embankment shouldbe under almost constant observation. During flood periods, it will benecessarv to expand the normal oneration and maintenance organization intothe flood fighting organization, and have each element prepared to accomplishemergencv flood fighting measures instantlv. Under certain conditions, adelay of several hours in initiating corrective measures may mean the lossof protection.

III. HIGH IWATER MAINTENANCE OR FLOOD FIGHTING PROCEDURES-iMBANKMENTS

3.01 Prior to the start of the monsoon season. the following preliminarvwork should be undertaken.

3.02 Fill up bad washes or holes in the embankment crown and slopes.IWherever new construction has been completed during the year; rain washes withdeep gullies may have developed. The necessary labor and equipment should bemobilized and serious deficienGies repni red. Tf the new embankmoent is qlnongan exposed reach, preparations to combat wave wqash should be made in advance.

3.03 Gaps, where road crossings have worn the crown below grade, shouldhp ranni rprl Tn filling thp rnri c'rn.qqinc annps, it. may bh neacssnry to nhtninmaterial from landside borrow pits in order to raise the embankment sufficientlyhigh Any filling will be thoroughly tamped.

3.Oh £11 roads alon1 the emba.nkmaent crowTn should be put in a state ofgood repair. It will be found that many access roads previously used havebeen fenced off and are not now passable. These roads shold be repaired andput in good condition.

3.05 All drain ditches on landside of the embankment should be investigatednnd hesedr -ns s1ho '~d bke opened where obstr~uctio. est. Peaetcu

the necessary drainage ditches to expected seeps. No attenpt should be made,hlowevver, 4o dr a.Jin tbe em;b LaLlknJJLUent sl'Lopes until seepage actul, CaIl..Y. take pla

on the slopes.

3.06 All dynamite and other explosives of any kind should be removed fromtlle vricijiy 0f. - Lulhe ORD1.ir..iLuLI. UidUer. 1IU 4_±1.1U) L-, IUtane should ULY Utes

permitted within one mile of the levee line unless an artificial crevasse isplanned.0

-3-

Drain.a.e of . Landside VAILUCULUIMIfLU S-LopJeJs7

3.0 7 T'- - of 4the-' -c3nsid slop -' s one of the 4 ost -4-,zotn 4high- - ,L/ VI .AL CL.r±age, L.I IJLIU .LOA.UO.LUW D.%p;LO VJILV VJ± ULA;L WQ iU .I.LILWJ±t. VUL1I U 1&1water maintenance operations and its function must be fully understood and.

a'o± Ju. appredivd

3.08 Water seepilg through an embaInIenLt first appearstas a a wet spovon the slope. As the seepage increases the wet spots spread until the wholesl'ope is wet aniU. the seep-water slowly flOwS UUWIn 11 a sIhteet CUIlUnUe

exposure will cause the slope to become more and more saturated and. soggyuntil it is liable to slide Or even flow out, resulting in an embankUentfailure or requiring extreme measures to prevent a failure.

3.09 The purpose of draining the slope is to concentrate the flow ofseepage into directed, channels which carry it rapidly downi the slope -and awayfrom the levee. The-;result is that the slope will often become dry and.firmbetween the drains and sometimes the drains themselves even stop flowing.Sometimes, however, drainage will not cure a wet slope and the slope becomesless and less stable0 If this happens, the slope should be carefully observedfor signs of sliding or sloughing and.the maintenance forces should be preparedto construct a matress imiediately.

3.iO Tne first drains cut should be i2 to 15 feet apart, V-shaped, notmore than 6 inches deep, originate at upper or highest limit of seepage, runstraight down the slope and lead across the landside berm into whatever systemof take-off drainage is available or can be provided. Then to secure bettercoverage of the seeping area, additional drains spaced 4' to 6' should.be cutbetween the first drains and Y'd together and into the first drains. (seeFig.7).

3.11 in no caseshould an attempt be made to cut slope drains until seepageactually appears. All traffic, animals and people should be kept off seepingslopes.

Sloughs and Slides

3.12 Where seepage appearing high on the embankment slope cannot be con-trolled by slope drains as outlined in the preceding paragraph, and the con-dition grows progressively worse, there is danger that slough or slide maydevelop. A slough is a condition in which the material in the embankment, isexcessively wet and soggy and is inclined to flow or fall away from the slopeand.heave or pile up at the toe. A slide is more apt to occur on steep slopeseven when the soil does not appear to be extremely wet. In a slide, the slopebreaks away in a clearly defined crack or cleavage plane and.moves outward.taking the toe with it.

3.13 In any case where it appears that slope failure is likely or hasoccurred., the treatment indicated is a reinforcement in the form of a buttressof the berm, tapering up over the failure. A brush or broad mattress is alwaysplaced under the buttress and.constructed.in such a manner that it will permitdrainage, provide a stable but flexible base for distribution or uniform pressure,

bridge the failure, and anchor it against further movement.

Banboo M4attresses:

3.14 Figure 1 shows a simple method of treating slides developedby LeedsU.D1iJl--Leu wLI L- Jfor Duse LCtUtl . iter UJ _JAJ UslLope I 1d hVt;a UbUee

cut, place a single layer of bamboo or several inches of any small trees or- -'L. - 4. L 'L u_ _ _- 2__n_L n --L:ILJiS Wi butts uap Uhe slope and. tops Udown andi per-penicular to centeri ne

of levee. The bamboo should extend onto the dry slope several feet abovethle softU area a far enough onto the berm lar,Uwuaru VI Uie le-vee tU proUv±uea base for the buttress. A second layer of bamboo or brush is cross-laidover the first layer to help dlsbrlbute the load and. to prevent sacks fromfalling through. If brush is used for a mattress, all leaves and small twigsrrfust be removed to prevent stoppage of drains.

3.15 The mattress is then loaded with sand or crushed brick filled sacksin the form of a buttress as required to hold the failure, having the heaviestpart of the load on the berm, not more than one layer near the top and no loadat the very top.

Board Mattresses

3.16 lWhen bamboo or brush is not available or impracticable to obtain, aboard mattress may be constructed instead of the brush mattress. Any width of1" lumber may be used, but either 6" or 8" probably wil1 be more available thanother sizes.

3.17 To construct the board mattress, begin by first draining the embank-ment slope and. berm as provided above, making the slope ditches up and downthe emoankment slope and as far across the berm at right angles to the leveeas considered necessary to hold the slope mattress in place. Fill in betweenthe first boards with paral el boards up the slope and across the berm leavingabout 1" cracks between boards.

3.18 Place the top layer of boards across the bottom layer and parallelto the embankment leaving about 2" cracks beginning at toe of the embankmentand working up and down. The top boards should be random nailed to thebottom boards with at least two nails to each board. On embankment slopes1 on 3 and steeper, 2" x 4" stringer should be placed about every 3 feetin the top layer to prevent sacks from skidding down. The mattress is thenloaded in the same manner as the bamboo mattress.

Sand Boils

3.19 It is difficult to evaluate the seriousness of sand boils. Anyboil which enlarges and increases its discharge of material, especially iflocated within 200 feet of the embankment toe, is considered to be a threatto the embankment and should be controlled.. Treatment of boils, however,is not limited to those within 200 feet of the embankment toe. Boils runningclear water, unless they have an excessive amount of discharge may be onlyanimal or soil boring holes and. need no treatment except to be watched and toditch the water away from the embankment.

3.20 The treatment of sand boils consists of building a sack looparound 4~ ,them lo raise Ile wJater l Lev e-lw -ui..h4in 4he loop -UL. --- 4Jj- toJ a he4ight s --tcie

to stop or midnimize the discharge of material. A low place is left in theloop for a sp- ,way- on 4the sid tow4._ard 4-1 3-- -stua -riae 1,T- bo Ih 'd.L~JJ .L a J.i.LJVCdJ ViJl Uti1- C)LUO UUVWd.L U 1iiaUU±..LC U1C. 11%C il*J L~U.L_. DLIVLJU.

be sacked high enough to completely shut off the water. To do so probablywill cause it to bre UIC'L Vout again.4 JLkust AUJV I outsideU theVP san loop.1 Fiure 2shcws

typical methods of sacking sand boils. If a single boil requires treatment,L.di,Ke care 4. -iIdI' .4k i4I,IE 'LoUp ar-Uo_aU i it suf.±C±lent J _.LL ±s-Xe LUV 4VU±U 4II U U't.Lr4 U.LV G

area immediately surrounding the boil.

3.21 If a number of boils close together require treatment, a sack sub-levee sho-uid be b-uilt around. the entire nest of boils, rising to a heightnecessary to control the most serious boils. In locating -the sub-levee,topograph-y- of tuhe grounid should be corsidered, taking ad-varntage of the etm-bankment toe and. any high banks or ridges.

3.22 If, at any time, sand boils either inside or outside protectionloops show signs of discharging with increasing force, indicating that con-siderable material is; being displaced, preparations must be promptly madeto raise a c:ounter water level.

Topping

3.23 Immediate consideration should be given to the embankment grade lineof each sector. Up to date profiles will show reaches where low embankmentsexist. A new line of levels should be run over any reach that appears to bebelow the predicted flood crest. Emergency topping should be undertaken atonce to a grade line whlch will afford at least three feet freeboard abovethe predicted flood-crest.

3.24 Topping material may be placed by hauling equipment, derrick boatand barge, with sacked earth and by cutting back of crown to raise front ofcrown in this order of preference. The method of placing and type of structureused, will of course, be governed by local conditions. Speed is essentialand the more use that can be made of machinery, the quicker the job will becompleted. The use of lumber of bamboo faces and/or boxes will greatly recucethe amount of earth required.

3.25 Figure 3 is an adaptation of the Lower Mississippi River IkIud boxdeveloped by Leedshill-De-Leuw utilizing materials readily available inBangladesh. 4" x 4" and 2" x 12" lumber, if available, can be substitutedfor the bamboo.

Topping with Hauling Equipment

3.26 This method should receive first consideration in raising long lowstretches of embankment known to have insufficient freeboard to safely w:ith-stand predicted stages. No heavy equipment should be allowed on the embank-ment when the water is near the top as the vibration might cause a failure,

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especially to sandy embankments. An ideal outfit for this work consists ofa small draghlne capable of transportation by heavy duty trailer, a fleet oftrucks, and a bulldozer. The material dumped on the levee crown should bespread in layers not exceeding one foot in thickness and thoroughly rolledby the bulldozer. Loaded trucks should be run over the topping as the workprogresses to give additional compaction. Great care must be exercised intraveling up and down landside slopes to avoid damage to the slope or sodand in no case may be done when the embankment has commenced to seep.

Topping with Derrick Boat and._Barge

3.27 If there are abandoned embankments within a reasonable distanceof the topping project, a derrick boat and barges may be used. to good ad-vantage for transporting material to the job.

Sacked Earth

3.28 This is a dependable method and has been used more than any other.It is particularily adaptable to Bangladesh where there is an abundant supplyof labor. The height of sacked earth topping is limited by the base areaavailable, therefore, an embankment can usually be raised only a few feetby this method.

3.29 In laying, the sacks should be lapped about 1/3 with the bottom endon top of the open end and joints of adjacent rows broke as in laying brick.Successive layers should be stepped back to batter the outside edges and tohelp break joints. There should be some cross-wise layers to tie the rowstogether and prevent overturning of the outside row. As each sack is laidit should be tamped into place and workers should walk over the sacks as muchas possible to increase the density of the structure. Figure 5 shows theusual method of laying sacks.

Cut Crown Topping

3.30 This form of topping which consists of shifting material from thelandside edge to the riverside edge of the embankment crown will never beused except as a last resort when material cannot be secured from othersources. When this method is used care must be taken to disturb as littleof the sod as possible and. to excavate in such a manner that thorough drainageis provided.

Board Fence with Earth or Sack Topping

3.31 The use of board. fences in connection with any of the various types ofearth topping serves several purposes. It protects against wave wash, reducesthe amount of topping material required, provides for greater height, makes thetopping material more impervious, and provides a more stable structure generally.

3.32 If material is placed mechanically, the fill is brought to gradefirst then the fence is built and finally the space between fence and earthtodnino is filled bv whatever means is available. Stock piles Dlaced alongthe landside slope by hauling equipment would facilitate filling by hand.

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The braces of the fence preclude arvr halV n pfrer being places. Bracesare not required for a two broad (2 feet) bight but over 2 feet wouldrequire b--rae as shown on F g,ur .

3.33 If~AL top. is require toJ aSA heigh+ ove 3tA to 4 eti+w4Opoal

j. J..J .L.J VW.Vs.F ..±1 .11 ..Vt.JLC~LJ.J v1d 1.11 0. l. l u* U 1.) _J. .5 ) 14 .1..1 4.- VI JA.. r*1)LC.4

be more economical to construct a mud. box as shown on Figure 3. The riversidewaLL should be lined, with sack VJa teril , tar paper or some sm 1ar matealto prevent leaching.

WIave Wlash

3.34 Rxperienced maintenance personnel can usually predict the localitiesWhIere wave NashL1 -Ls JLd.aLbLUe UV ourlU. In1 d..LL. CZ ±e±Li 1e' such rau t t u' can be eter,IL.eIiduin advance, filled sacks and other material should be kept available for anemrLergenIcy .DU __ng per ids of_hig 1ind a_d _ -- L- _L. L _CllttSl-GUlUJ, 1- |sU 61- | Ub |L1 W E 1U UisU WdVt:;. WI v i1PL -tt UV1L 'jIIU U J dI

by and experienced watchmen should observe by sounding the submerged. slopewith a lorng pole where the -wash outs are beg'iLlig Sacking for -wave washcannot be placed effectively in advance in the face of a rising river. Sincethe cutting action is at the water surface, before the sacked zonie cari bemade effective the water level will rise above and overtop the upper sacking.

3.35 Several types of wave wash protection have been used with success.Figure 6 sho-ws a tUype of movable protection. These igatesr can. be mLade inadvance and held. in reserve. Figure 7 shows a protection made by staking

I - - -- _ ---. __ - __ I __ - - __ - _ r £1 , - -1 I I _ _ 0 r- _ -uown b-urlap cotstonu bagging and -weighting with filled sacks. Figure u showsa horizontal board fence which offers a method of rapid construction. Asthe wave action may loosen the posts in the ground, it is necessary to weightthe fence with filled sacks placed on the intersections of braces and posts toprevent it from floating out.

Scours

3.36 Scours are particularly dangerous due to the insidious manner inwhich they develop and the difficulty of detection until almost irreparabledamage has been done. Tne chief danger, oI course, is that the scour re-sembles the caving bank of a river in action and appearance, in that iterodes under water and has a vertical caving face. Wnen the water is nearthe top of the embankment and by the time the vertical caving face appearsabove the water surface, a large portion of the embankment is gone.

3.37 A careful observation will be made of the riverside of the embark-ment, in the borrow pits in all reaches where an unusually fast current isapparent, and where the profiles show a steep high water slope. Turbulencecaused by shallow water is a pretty good sign of no scour but should bewatched. If the turbulence unexpectedly becomes quiet, scour may be sus-pected and soundings should be made immediately. Conversely, in deep water,scour may be indicated by turbulence and eddies. Trouble may be lookedfor below sharp outside angles in the embankment, at the ends of all dikes,road crossing ramps, and traverses across pits.

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3.38 Threatened embankment and dike ends can be protected by the con-struction of defl ection dikes J Fir re 9 shows a te of deflm ection dieconstructed of wired stakes filled with brush and filled sacks or brick.Several dJkes may be required to stop the scour egn w4it, th-e f-is+ d-i,k

below the scour, working upstream into and above with additional dikes.

3.39 Rock cribs (Figure 10) are very effective in controlling scourwhien pushiAe d di4rectl int the ara The -rb can be -osrce at theM,__4, -- '--4 ~LL~~L ~.4OA4~U U-LL UL,y .LIIU ULAJ I.AA d CLI ._ . LLA4 L L -_ _ .1 0 .UC~ V%'- JU11 UtLLLUL U-U a U UAIR;

site on the embankment or bank and pushed where needed by bulldozers. ForcoritrolU 0f' sco ,Mt in; .'the borrow.-L Ukd p4its near thIIe elU, aIAlr UI1eiLAt use of.- roc,k crisb

(Figure 10) as described in the next paragraph, is very effective. The.1. U .LLQ ZJ2'U.LU U JL. U ..i Li tLJ b4 L1, c nc n raSJi.,i 5140 LJI J .LJ5 4i L1Ec;bs sho,f ld b,e pl -.a ced J11 the- scouLr wiLthL cocetrtorn of 'load in thLe

direction of the embankment to insure that further scour development willb-e away from raller th"an ''ar the er.bar-,-en 4

L. L4k isW LUt L L±L) CIj ±±±tU VW LL5,1I IUrli. ilU.l U .Iui 4 .Vr.O ide e ± ±ui-) 1 . TAE - . -I -l

3.X0 ~~-LurL,b 1-ibs flewhrock- or conicrete blocks have beern foundito be very effective in retarding the caving of banks. (Figure 10). Cribsare -usiii'y ±U- A ±U0 x -LU', insiUde UUmensions, constr-ulU U Uof UUdo-Ubl Uhic-

ness 1" x 4" x 12' lumber, equivalent to 2" x 4" pieces, lapped rail fashion|~~~~~~~~~~~~~~~~~~~~~~~~1 A4n5_ 4 A _A A ! 4 -A_i4-.:Ai4_-rA, *__s_+

0.5 O, LiuI. ' V1 11S i) 1 LU w ll 5 Ui LiAJI lJlt. L. LLJO dl V UL V_LUt- U LIILU _L %J L {L % UIIItUd. LLtIUi1D

by two cross walls constructed in the same manner as the side walls. ThefLUUoor anlU covetr1s alte UU-Lu u.p of UUUbLte L A 4!1 UbUards spcdut aUbU 79 UCc .

Under the floor, perpendicular to the direction of the floor boards, are5 equdlLy spadutU pairs ofU! x. A boards abo-ut 2UUU / c-c. OLL Uop Uf cUVtrL,

perpendicular to the direction of cover boards, are 3pairs of top boards,placed over each side wall and the partition wall. The cover can be builtdirectly on the crib or separately and placed on the crib, in either caseafter the crib is filled -with rock,' bricks, or concrete blocks. All nUter-sections are nailed with onae 20d nail and each intersection of walls offabricated crib is securely fastened by a loop of 3/8" strand, tightly twisted.The wireloop is put in place loosely before filling with rock and twisted intoplace to include the top after it is in place.

3.i1141 The 10' x iO: x !o" crib wiii noia approximately 5 tons oI stone orconcrete blocks. The weight can be adjusted as desired to meet existingconditions by increasing or decreasing the depth of crib. If rock or concreteblock is not available, the cribs may be filled with sacked earth, gravel,or other suitable material. In launching the cribs, it is sometimes adviseableto tie them together to keep them from separating and so they will help pulleach other off the bank.

Burrowing Animals

3.142 General: The embankments, generally, will probably not be infestedby burrowing animals, but in locations where they do appear they are a seriousmenace. Control of these pests is effected by poisoning and trapping but sincethese are tedious processes they could rarely be accomplished during a floodfight. Every effort should be made during low water season to rid the entirearea by working with local land owners. If serious leaking burrows developduring high water, immediate corrective action is mandatory toprevent a crevasse.

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3.43 Treatment: There are two general methods of control: one to stopthe~~~4 op-n on. the rse d and the othe torn h adsieoeigwtL.4I, Uptui.LL1 iJ UU l.1~ L-_VeL.L-Z_Ut dLJlU IA1t U U1JAt-.L- UU U1it: alU-0LUt: PUjJILLIlt-, W.L UIL

sacks. Immediate action is demanded because a three inch hole through asandy emib-neRt ncan dueelop into a cre-vae in a -very- s-rt time.

3.2424 wnen a leaking burrow is first observ-ed an effort should be madefirst to stop it from the river-side slope and weighting it down with sandbags. A single sack over the river-side opening would stop it if it couldbe found, but the tarpaulin has the advantage of covering a larger areasince tne intake opening might not necessarily be exactly opposite thedischarge opening. If the hole is high up on the landside slope without a highhydraulic headpsacks tamped directly into the outlet would effectively stopthe flow. It ,would be necessary to cut a small notch or bench at the openingto seat the sacks into place.

3.415 Tne landside treatments, which may be required if the riversideopening cannot immediately be stopped, is to build a sack ring similar toa boil ring around the landside opening with a sufficient base width tosupport a ring to a height sufficient to stop the flow of water. Thisring differs from a boil ring in that it is required to stop the flow ofwater. The time, material, and labor required for a ring emphasizes theimportance of first attempting to stop the flow from the riverside.

IV. CLSUURE OF CREwASSES IiN EfIHANKMENTS

General

4.01 Where it is practical and desirable to do so, closure of crevassesin embankments will reduce the period of inundation of the overflowed lands,prevent the crevasse from widening, and reduce the damage caused by subsequentrises that may occur before the embankment can be repaired.

4.02 Figure 11 is a plan for crevasse closure. Essentially, thestructure is composed of two parts: One, a timber trestle filled with sandbags to shut off the free flow of water and Two, an earth filled mud boxlandward of the trestLe to reinforce and make the structure watertight, ccn-structed in that order.

4.03 A blow or scour hole usually forms in the crevasse slightly land-ward and. enlarges to the landside. The closure structure should be locatedfar enough away from the edge to allow for enlargement of the blue hole andmay be placed either on the landside or the riverside of the crevasse depend-ing on which has the shallower water and the least amount of obstructions.The ends should join the embankment well back from the edges of the breakto allow for caving while the closure is being built.

4.04 The closure should never be started until all required labor andmaterial are available at the site so that it can be made without inter-ruption, for the delay of a few minutes at a critical time may mean the lossof the closure.

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4.05 Closing the crevasse entails considerable danger to the manworking on the closure. Handrails should be installed where needed, andthe project should be well lighted. At least two boats, equipped withoars and ring buoys with hand lines, and manned at all times by experiencedoperators should be anchored just below the crevasse. An experienced firstaid man with complete first aid equipment should be available at all times.

Timber Trestle

4.06 Following the plan on Figure 11, the order of construction is asfollows:

(a) Upright Posts. Drive four 4" x 4" upright posts spacedas shown. The three to the right form the trestle and theone to the left forms the mud box. The mud box post islower than the trestle posts, it being about 6" above thewater.

(b) Cross Pieces. Nail a 2" x 6" cross piece on each side ofthe 3 trestle posts at the top and one 2" x 6" cross piecefrom the center post to the mud box post just above the waterline.

(c) Runways. There will be four runways, two along the top ofthe mud box and two along the top of the sack trestle. Eachrunway consists of two 2" x 10" boards laid side by side. Therunway boards are projected beyond the last bent so men canstand. on them to drive the posts of the next bent. Bents arespaced 4' on centers.

(d) Stringers. Five stringers are placed. One each under thecross piece on the landside posts. center Dosts. and river-side posts and one each just above the water line on thecenter posts and the river side posts.

(e) Hog Wire. Hog wire netting is strung along the riverside ofthe center posts and nailed to the lower stringer by 40d nails,the lower edge of wire is extended nnross the bottom of thetrestle so it will be held down by sacks when they are droppedon it.

(f) fiAre Bracing. 1/Ait wire strand braces are planed on the trestlpepart of each bent, as shown on the plan; but not on the mud boxposts.

(g) q Rndi Rqagc Suifficiont. filled c iiks will be stocrkpnil tocomplete the closure because once this operation is started,it mvust .n.ot be stopped uAntil completed. The first sacks aredistributed across the bottom and banked against the hog wire.The dA' is then brought up on a level grade so that the floT ofwater is distributed evenly over the entire length. The crest

LJC. k/S. LA_ I | LJ. V5At T1 n o A_ 1.1.4 .AL. r; ..L.L 0 ^ LI L/ LIA0 /ULl V _Aca I"o brGo Vu 6sUg UVVGnt av wat er sur~a e fis t ag -s G X' - 1- V; o

netting and then widened on the river side until the dam isbrought to the desired grade and cross section.

I.VuU BD.Aox

u.0 AL Uer thL'e fLree L'ow is cut o by the san bag in the trsle

and as soon as the backwater will permit, the mud box can be completed irth e uol±lowirig oruer:

(a) Base. Clear and grlub the base, removing all debr-is.

(b) Stringers. Nail a 2"1 x 6"' stringer along the inside of thelandside row of posts just above the ground.

(c) Wire Braces. 1/4" wide strand braces are placed at each bentas shown on the plan.

(d) Sneeting. 1`; x i2"' sheeting is driven along the inside of'the wall and nailed to the stringers.

(e) Earth Fill. Earth is dumped and tamped into the box until itsiopes from the crest of the sack dam to the top edge of themud box wall.

V. REGULATOR OPERATION AND MAINTENANCE

General

5.01 "Sudden Failures" of regulators can be prevented by proper in-spection and routine maintenance. Once a regulator fails, closure costsand replacement costs are very high. So, prevention is the best cure.

5.02 Usually the first cause of alarm is a change in the river sidepitching. After a day or two of initial operation, some slipping orsluffing of earth and pitching beyond the river side floor slab may benoticed. This is natural, and no cause for alarm. If the river side charnelfloor block paving remains intact, and there is no evidence of ghogs in thepitching, then there is no threat to the structure. The flow through theregulator is merely making its own stilling basin. After a short time, apool is formed where the velocity of flow and its energy is dissipated safelyaway from the structure. Unless the brick paving fails severely, and the rivers.ude wa1 is bareatened with under-mining, there is no danger to the structure.The depth of the cutoff wall should be known and soundings taken at low stageswitAh a short bamboo pole can quickly show any danger of under mining. Id thisis happening, the vents must be closed until the erosion is corrected.

5.03 Another cause of initial erosion and pitching damage is incompleteremoval of the river side ring bund after regulator completion. This caluseseddies and back-flows that erode the channel slopes. Contractors must com-pletely remove ring bunds before the work is accepted as complete, andverified for final pavment. Brush and piling placed to control river sidepitching damage is a waste of time and money. The erosion should be watchedcloselyv especially at the cutoff wall. When initial erosion has sloweddown, bagged soil-cement or rubble rip-rap may be placed to protect slopes andstabilize the channel0

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Some larger blocks may have to be placed to protect the cutoff wall, because.LfL it -Ls under-m.,rluu pR=I.,LCnent-1 UIdamage or Ja:'-ure ofL ULhe wholeVL: Ie 'ator_C. V-il-l

soon result.

Piping

5.04 A common cause of regulator failure is "piping". Piping is waterIflowing unLder or daiong ventls wh ich washiies away uithe soil backdAJ-fill, oL± .VIIIL1r,

a void or "pipe" in the soil. Regulators are designed to prevent this, butpoor corutlu±uuion can defeat the m1ost caref-ul uesisn. Faulty ju±ini, poorcompaction, missing cut-off walls, and voids in bedding can lead to leaks,loss of soil, and failure.

5* 05 Ivte pip±ing is e-vident, LTmeu±aue seps to stop t t e ten.Some evidences of piping are:

Condit EII rvidence of "Piping

I. Gates closed, high water : Leaking through the R/S Headwall.level in L/S : " Pitcning

: 51 over " Headwall.

II. Discharging Sinking fill over vents.

: Bubbling ghog over vents.lL. Gates closed Leaking in / Headwall.

: Leaking in L/S Pitching.

IV. L/S dry . Ghogs.

L/S - iand sideR/S - river side

•.06 Condition I (Gates closed, leak or ghog). This shows that a "ghog"or channel has developed from the land side to the river side. it occurs whengates are closed to retain a high water level on the land side. Constantdischarge through weepholes, cracks, gaps under the vents, the pitching, or overthe headwall or under the slab and cutoff wall are danger signals. If theflowing water is muddy it shows that erosion is taking place, and the conditionis serious. If the discharge is high, the land side channel should be closedto preserve the land side water level, and then the gates should be closed todrain the structure for inspection.

5.07 To locate the erosion channel, the flow should be observed as thewater level falls. When the flow diminishes, the entrance should be just atthe water surface. This water level should be marked by a stake, and a searchfor the entrance should be made by poking into the ground with a steel orwooden rod, looking for hollow spaces left where the earth has been carriedaway. Large tWavities should be immediately filled by driving straw and earthinto the voids with 2"-3" diameter bamboo stakes. Then a permanent repair canbe made.

- 13 -

s.o8 If the channel is relatively high, it may be dug up and filledwith ranmed earth. If the charnel is through the pitChling or under theslabs, a complete closure and major repair will be necessary.

5.02 Condition II (Discharging, sinking fill over vents). This iscaused by progressive erosion of the soil around the vent, usually througha bad joint. The gates should be closed, and an internal inspection madeby crawling into the vents and examining them with a torch-light. The badjoints can be plugged by filling them with asphalt soaked jute or a damp

mixture of cement and fine sand (1:3) pound into the joint from inside. Ifinspection after 24 hours reveals failure of the plugging, an epoxy compcund.should be used. If this is not successful the vent must be uncovered ove!r thebad joints and sealed from the outside. This can usually be done withoutconstructing a ring bund.

5.10 If the joints appear satisfactory, a search should be made forother channels. Often there is a gap at the riverside headwall just underthe vent where the concrete was not properly poked and rammed into place.This may be closed by dry-packed concrete (cement-sand 1:3), protected byasphalt gunmy-bags until the mortar has set up. If this does not work, woodenplugs may be hammered into the holes. Ine regulator should not be operatedfor several days until the concrete repairs have set permanently.

5.11 Condition III (Gates closed). These clues to piping through thesoil are the same as Condition I, with flows reversed. The same proceduresfor correction are to be taken.

5.12 Condition IV (Landside dry, ghogs). This is due to faulty joints.The vent may be inspected internally, entering from the landside entrancewith a torchlight. Care should be taken to get a good seal on the gates sothe vent does not flood. Caution should be observed in case a snake is inthe vent. Repairs to joints from inside may be difficult to make watertightdue to differential pressure. ]Dctensive permanent repairs to a regulatorwill entail constructing countryside and riverside ringbunds. SUch repairsare beyond the scope of normal maintenance and therefore should be accomplishedby contract.

VI. ORGANIZATION AND ADMINISTRATION

Organization

6.01 A well established organization is a prerequisite of both operationand maintenance and flood-fighting programs. The nucleus of such an orgainizationnow exists in BEngladesh, built around WAPDA. As the entire country is divided.into regions in each of which WAPDA has some type of organization headed, by aSuper-intending Engineer, this basic organization, expanded as necessary, couldbe developed into an efficient management staff for both operation and. maint-enance and flood fighting. The composition of these management staffs will begoverned by the number of embankment systems in the region.

- 14 -

Organization for a Single Embankment S3ystem

6.02 For an embankment system consisting of 50 to 75 miles of embankmentji+ , appurtemnt reg-lator- "AAA A~sys Qte-rms, +.n.n rvnn nn+ c+_ff c hrm1 i1

consist of the following with the Sub-division Engineer and Assistant Sub-'.1--v ~-n~~L1. ~±'JIII..1L"._L.J UL dL-.LLeU. £LI-LLO U1 L_L..[L11r% t:1J_..LUU 01LIULLLU U15 .1± UUUL4 U

12 to 18 months duration.

1 - Sub-division Engineer'I = Ass,istant >>=dvi, o Er.gineer for E-1-al-ents

L Jtx .LO UCJ u 'JULd U4..V .0L.W4A JJJ. AI~_ ~. VI J2ALWJ"4ZUtL v

1 - Assistant Sub-division Engineer for Interior Drainage1 = Assistant Sub-division E-gineer for Structures1 - Survey party consisting of: 1 - Chief, 1 - instrumentman

and 3 - ± '.uiei - chai4wmen

1 - Personnel Clerlk.1 - S-upp.ly ClIerk'~

4 - General Clerks1 - nLadU.Lo L) pd-Ln

2 - Labor Foremen.- if Ud1Cz -uen2 - tinberleance Foremen

1 - Mechanical Inspector8---,.bar',er.t arnd Car.el I-,sp_ecltors

40 - Laborers that have sub-foreman capabilities2 - Vehi.Lcle Mea1rUicsLU0

2 - IMotorboat Operators

6.03 in addition to this permanent stafl, a labor force of up to1,000 men will be required during flood emergencies and lesser numbers duringeach low water period, for routine maintenance.

Administration

6.O4 A highly efficient administrative organization at the field levelis necessary, particularly during times of flood. This organization shouldhave the capability of recruiting and processing personnel, requisitioningand purchasing supplies and equipment, negotiating contracts, preparingand processing payrolls, and performing general administrative functions asnecessary. The permanent administrative organization should. maintain and. keepcurrent a numTber of inventories of personnel, materials and equipment withinthe project area exclusive of that permanently assigned to the project. Theseinventories should be updated at least annually just before the normal highwater or monsoon season. The following inventories should be maintained:

Personnel

6.o5 As discussed above this listing should include supervisors capableof supervising and coordinating maintenance and flood-fighting operations inlarge areas; second-grade supervisors capable of performing these functions insmaller sectors; foremen capable of supervising small groups in construction ofemergency works; office engineers; clerks; equipment operators; and mechanics.The qualifications, permanent assignment, permanent address, and approximatetime required to reach a predetermined assembly point should be tabulated foreach individual.

Facilities

6.06 In order to make this headquarters operational, the followingfac, -ite 4 houl be pro -- ed:-

Au00 r.).(a are feet ofL ofice space3000 square feet of warehouse spaceC,UO squaare Leelu Lor a maintenance sl'opGarage space for five vehicles (jeeps, land rovers,oil p^-k-up tr-uckxs)

Wharfage for:two motor launches, one tug, and four2x' x 100' barges.

z- -7ment

6.07 lLe livetllor-y of equipment should incl-ude each item's locatlion,capacity, owner (whether IAPDA, stock in stores, or private contractors),ax-d a Judgement factior of its condition. Items listed should include, butnot necessarily be limited to, work boats, launches, dredges, barges, skiffs,outboard motors, air compressors, trucks, tractors, bulldozers, draglines,light plants, pumps, and welding machines.

6.o8 Because of the shortage of equipment in Bangladesh and the almost totalabsence of suppliers, the project must acquire and maintain the following itemsof equipment as a minimum:

2 - Two-ton truck mounted cranes with dragline attachments2 - D-o Bulldozers4 - 3elf propelled motor graders

10 - Five-ton dump trucks2 - Five-ton stake body trucks1 - Light sedan8 - Jeeps, land rovers or pick-up trucks2 -. 18 ft. motor launches with 100 hp. motors2 - 15 ft. motor launches with 50 hp., motors.

2000 shovels.50 - Picks20 - Chain saws20 v Carpenter tool sets

3 - Mechanic tool sets6 - 200 KW light plants

10 -6 inch centrifugal pumps with 25 feet of intake lineand 100 feet of discharge line each

2 - 2-way fixed radio stations with minimum of 50 mile range24 2-way radios, suitable for vehicle mounts with minimum

range of 25 miles12 - "Walkie-Talkie" radios.

Materials and. supplies

6.09 This list should include both materials and supplies owned by WAPDA,other Bangladesh agencies, and the private sector. Arrangements should be made

- 16 -

f or the storage o0 signi fiuant quantiti ues of tuhese mat e-la 1sn the

immediate vicinity of the project. The supplies inventoried should includesandbags; l-rDbeL; baLibo -wheelbarrows; small tools, such as shovels, flood-lights, etc.;, protective equipment such as life preservers; precast concreteblocks; and bricks.

6.10 The list of materials that follows should be considered the Mir,,,rmmstock level that should be maintained at all times. If a major flood appearsimminent, orders should be immediately placed to double the stocks listed.

Lumber (2 x 4, 4 x 8, and 2 x 12's) - 100,000 Bd. Ft.Nails - 50 kegs.zacks - il0,O00010,000 tons concrete blocks (1 cu. ft. minimum size)5,000 tons brick.

Procedure for Obtaining Equipment and Supplies

6.11 It can be anticipated that the materials and supplies listed above willbe in the hands of numerous agencies and organizations. Therefore, preconceivedsimple procedures must be developed for rapid acquisition of them during timesof emergency. This should be one of the high priority items for the permanentadministrative unit when it is organized.

Operation and Maintenance Manuals

6.12 The principles set forth above are generally applicable to allembankment projects. However, a detailed supplement must be prepared for eachindividual project and revised and updated at least annually. This supplementmust include:

(a) Location of the permanent headquarters and each sub-office.(b) Roster of permanent personnel by name and position.(c) Communications plan including telephone numbers and radio

frequencies and call signs.(d) Inventory of equipment owned by project and an estimate

of its condition. (For all inoperable items probabledate back in service should be shown).

(e) Inventory of supplies on hand and on requisition withestimates of probable delivery dates.

6.13 This supplement should modify and adapt the organization, materials,and supplies set forth in paragraphs 6.05 to 6.10 above for the typical em-bankment project to the needs of each individual project.

COUNTRY IDE eof RIVER SIDE

Original claps _

I Layer sand boN1t,7

I a~~ ~ ~~~~~~~~~~~~~~re /

____[/~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _ t' ''f2:- /-u

I - Bamboo mat.

ELEVATION

I I~~~~~~~~IA

r ~~~~- ~ ~ rni-DJ/-Jn1 AACTLjrr)

I _ n t -_ _ I I mu ;Y_/ I II~~~ _____ j _________________j________I____! __J1 7,~~X _tA dt ) j \- /t l '- -/'- -- __________ I

')7?7>ffr4/) t(FO H IIG WAE BAM3I

-e t MA'tT'RiS I-- l---~~~~~~' /-( 1l(>;(;- * < ^ - ;~ III II I \ T 3

/7 :,6 L 2>- !

\Drainage Ditches __ -

PLANY _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I I ~~~~~~~~ ~~~~~~~FIGURE 11I flNICTDi Sr'TIflil AACTU/thrC

FOR HIGH WATER BAMSOC0MATT RESS

| ~~Sand 1o3i | | N

j < 'i oI i Sack ill

I Levu ound ŽbAei rla 1ZrX Sack rir:9/r circu 'c

into embktt. If bii is near too

PLAN OF OFVMANKINEKNT

I IC/-ar t no bo ih line r uns crngnt

an d UOII ernbanY r- - - - - I -.

i/eiht ? s.ac hopord psrinshuklre ofl

sufl'iictcnt to slowdon flow through boilfsthat no rnore moterioI is dischY. ng

I -'~~~~~~~~~F-T[N0F v I'iJK -

SECTIONO CO3NSTERUCiNMEHD

Po not sck| boil which runs clear.'Hig of c!,= hoop or ring should be onlysufficlcnt to slowdiown flow thirough boil sot'hat no more material Is discharged.

IDo nct stop flow of water.

I I ~~~~~~ ~ ~~~~~~~FIGURE -2

I CONSTRUCTION METHODSI~~~~~~~~~~~~~FR[IHWTRSN 31~

I * Variabre - i -

-,'Tie Lashing Bamboo Poles__ F 7,1 N N. 17 'K >. ct n '- n "r1 nntrlnnrr.ii-

= ! |0| \ Barnboo Mat "' . - - \rtaintely 3' apart,9 XX iA XX V\ feet inio ground!Iz\ T, \ .nn*A Ea+rth Fll1 \\. g|Ofl

IW) t1ISK \' ' "."\"'.'\'\'\ \cmbo IRIVER SIDE ' F1| \'\ LAND SIDE

~~~~, S / , // / '/ -/ '. <

<4 - z/ £ xi s ti -] E m k t / *I /

I9,"';''""'TS'-' VA;'' r /.-- /,''-.-'. ' -' -''''/

SECTION

BILL ur nmAT£niAL Fv`R 100 Li N E R FEE E THiqht 3 Ft. 4 Ft. 5 Ft.

arnbo o Polos 62 Nos.5' Long 62 hlos.9' Long |62 Nos.8' Lonr] _L. r% - i -2 I% _f- ^0% 6 _ Y hi-- ^ l I _- e^ k 1 _ e^$ I ___-

lernouo rPois uv 1ui0. cv LO-ng 30 IW% cu ouLny UV NQSb. cv 2 un0

Tie Lashina Adequate Adequate AdequateIIBamboo Mat j3' by 100' 4' by 100' | ' by 100I

FIGURE 3

CONSTRUCTION METtHODSFnR HI(GH WATFR MUD BOX Pr.

ONIddOl )DVS CNV u3oWm

t Runouj

,juu t ji id iC,jNu ui 19vinsv j! Tl

cI VVifiI'Is~~~~~~~~~~~~~~~~~~~~~

I~~~ \- NivA --I13 -1;Nu i ,n j

I - - ------ . . . .

A >~~~~~t,Zl X,zl X.1 EJ

Y X,z J

~~~~~~~~~

ii i\*;,/\ (i .L \' ' \

, t'

S ~DOA1 ~o UW~LJ

I F~~~~RIEWRDFCI ~Sd }- i( 2 - - - -_i

I~ ~~ _ i n_4S I )--y<)4_;tr,_fr

I NRIVERWARD FACETE

I Maximnum water surface >_, |

i Eahsc hl efIle prxmtl / ulo_. - - o I

t cne Embalekmenl crown !

'IA1 END SECTION I NOTES: I

4. Each sock shall be fsI led approxImstely 2/3 fu s taofg|2.Place layers of sacks alternately parallel and perpendicular I to center i ne of embankment.|

3. A!ternuat layers of riverw;urd socks will be placed witnhI ends hangirg down. 4.Each sack shall be securely settled In place and staggerecl |

to break a continuous line of joints.

I ____ I| FIGURE 5

BILL OF MdATERIAL FOR 100 FT._| | CONSTRUCTION METHODS Iiaight } St=F nequir F f r GH vv'A SK t\ PHING

I Foot ___ 800II_2 ., ~2400

3 $, 1-4700

E~ Z~I --- 1_ 1_____1_

n ,,-Sramboo poles 5' long I I| I ['Darnboo poles 8' long I I I

'-I F3nrnhnn nnlnc nn,1ln /^rnnt/lH7i

I I '\Hashing I

PORTABLE EULKH.-1).5'.

ivRIVERS!iE COUNTRY SIDE

Saddle bag to hold bambooframe in plcce

\-+. gZr8'8Bamboo nol

Iil o/X /ffi . Existing EmblIt.X/ 'Single/rovi of sand bol

I -j 2 A5, / /

SECTION

131OL.L OF NTEfRIAL FOR IOOFT.I I~~~~~~r l I. nn :C6 60 pieces I10' I ong

20 pieces 8' long

20___pieces _________________ | FIGURE 6

Lashing material

I SANDBAGS -I I CONSTRUCTION METHODS110 Filled Bcgs ' r FOR HIGH IATER Wvv'AV -

WASH PROTECTION IPORTABLE BULKHEAD 1

I River side edge of Ernbenkment crown- IrI Sar!nJ bugs spaced opprox.6'aapart |

I I (Bamboo poles 6'apart) I I Li> 7 &iat~~~~cziiL- 7 Q 1J Lw 1'-0IWNaters edge-,

I I

'<Burlop bagging 42'wide

PLAN

River Side Country Sida

Burlap bagging

SECT'ON

Lay 42' wide uurlIp b^gging lonaitudlina&y alonnEmbankmeg,t and across damaged aroa weight .? i iI.I ~ Sond bags as shw nrv ae ater nately 8t:5,sand bags located along upper edge of bagging additinolbagninn may Ie used

I _I..... ............._ ,Bll of Maierial for lOOft.

Bamboo Sitokes20, stakosi1' long I

Rei-nninn

100' long 42" wide |.

I-,[PFIGURE 7

CONSTRUCTiON MItH I FOR

WAVE WASH PROTECTIONt I

4' 5 TTr

K ilLJ K- I tr°>; . , ./O'/1- i

CS

beh,,d ,b4l/khe-?d

A/0 rTt SOd,cd/ bJ~ tWO Il/ed SdCk-5J CrO.1jtopo boaral of ea~ch _q Su/kbcdd aft'er

to hlep AO/d ' p/ac

x~~~ ~ ~ /0 A 4 Xd

BILL ZoF 4AEnL O010 T1FIGURE 8

24 - /, 4* 6' I ~~~RORD FENCE WAVE WA4SH

24 -b'g t%o PROTECTION

/50 - MIILC x 5ACk

__________________________ FIUR 8____________________

___ lamboo _ _ _ _

=,1 I t -- I --m a2T, I II I, , W A\' Sandbags \>'1

Wire strand to 'f, > ½ Id cirnnn inAIon/ \ " rf,nnA I

.1 -Ir X, of emnbunkment II ~~~~~~~~~~~~~~~~t II

Embankment Section

,,Heavy bamboo poles _,-Sacked gravel or brick;I

I ~e nl fl ,/flF n IE

I /~~I~4Ki j Jr'jI

I~~~~~~~~~~ub,,\,,l,Yg- ____ \,,, Y j

I- i# Vj Li v Bamboo polesto be drivun

ELEVATION

! j FIGliRE 9

I CONSTRUCTION METHODS

I I DEFLECTION DIKE

___av___X______-- j

|IEEF.- _-_ . --- vreried b i""cretse'

I e _ -; -- E or docr-cese /e

F-I - - ---- =-=- .- I- eigr, ,.

rL~~~~~~~~~~-Y

--- i . ---------n j - -1;LH T i

,0.- - /2' 0" -L-e

3 Lb<-3 idd Lom" lVaila1 o-

,5 rt 3/ C n d e r I5 To na | | |i/, |D If op to I-o FIGUREI

tEl ... .- Lr........--.3.irzc±;zz [r doubl- H L.

I ki' r ' 1 - 4 I -I II I __|____ __7b___ ___ i ;j I

I AI- /' I i- I, I 4 I4 , i S . - !

ILi; -_ _j /0

Weight1. _ _ I I c r I, , _ _ _ b ,, J, ,_I_j 1 ,, _1 ,I

__ _ _ _,_!__ _ _1__ _ _ _ _ _ _ _ _-__ _I I I . L ,,1 , _1 I ~ _ _ _______ __ I ,' ! 'j,

lE _ ___ |s 7!,it_____ i.

I LJ L.J U U I aIl Zh ! .id'iiU

|MATER/AL AgFQUIRfp P/ 30 Pc'.,. IJr 4x /2' Lurr,ker3Lba. 20dI Corrn,n Na7ils_

~5 Thrn. AiRop4 X0V^fOrDeINofe: Cibsco,i~rc ld o dobiaFIGURE 10

Jhic Artsy P X ' xI 2 ' /un7 r. tVej/do// -_, __ -- _. I ST(ThNF ('PIR FC)R CAVING I JFC,3fier eoch wsoI/ i',fer.section ,secure/ 2 BANK PROTECTION .......

|Weight of /oo,ded crib er-rox. 5 fonsj

10. f o e- R--

- -_2fl~rW Fi -~,v,rej1 f~e~~ ~'4 .1 ll

~~~2-~1 ?tz , Q1., --_ I A

in L Tfel-np;.yer 5 c ,

t CZ 6 G rusy vt) I5, I<- G -,I- 1 =-

i | . -, 7nU G, ut i 1 l l I)r_f

y v1CROSS SECTIOQN

---- ~~4---'- -4 f Lv 1-

1 T T ; e | A n + H 1 1' [ | T | j j 1 ' t <

Oj~ ~ ~ L~6H | tiI i i IJ

1 10 g a--. 6 ^ 8 <ZvR , j e 1 i -- ' _'~ i ws i-~ }/~~ L

. ,~~~~_ _ . __A{ -im

Pi i w ,?i -s A1~~~~ 'b. 4~~~~~~~~~1., riL _ I 6 - ^ t3 -(:v 7 1 i 6 , 0

SCTIONAU PLAN A-A

RIVERSIDE

* - e - \ _ -

LANOSIDE ( Hole )

- -| FIGURE]]

CREVASSE CLOSURE

Documents

DnrVTMFAMT rFP T?R'1P?ATTnMAT BAmv t-Px … · and flood fighting program must be included as an integral part of the plan-ning and imlementation of eembanlrmennt projects. The reDort