001 reservoir plan

8/3/2019 001 Reservoir Plan

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U&T 1 RESERVOIR PLANNING.1 Introduction

Objectives.2 Reservoirs

PurposeClassification of Reservoirs1.4.1 Singlc Purpose Conservation Reservoir1.4.2 Slngle Purpse Flood Control Reservoir1.4.3 Multipurpose ReservoirStorage Zones of a Reservoir1 .5. Normal Pool Level1.5.2 M ~ n ~ ~ l i u r nool Level1.5.3 Dead S oragt:15.4 L~ver Useful Storage1.5.5 Surcharge Storage1.5.6 Bankstorage1.5.7 Valley Storagc1.5.8 l'risnl Storage1.5.9 Wedge StorageMass CurveI .h .1 Reservoir Capacity from a Mass Curve1.6.2 Yield from a Mass CurveFilling Capacity ofReservoirs

Trap Efficiencies

ing m a n s an orderly consideration of a reservoir project from the originalpose through the evaluation of alternatives to the final decision on a co ursee basis for the decision makers to take up or abandon the project. This unitrstanding the various components of a reservoir and the various factors

this unit, you should be able to :describe Lhe purpose of reservoirs,classify reservoirs,usc a mass curve,define trap efficiency,explain reservoir sedimentation, and


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i>.us~~:i i I ~ L W I i n 1.2 RESERVOIRSRcsurvoirs are artificial lakes created by the con structio ~l f dams across rivers They aralso called stora ges. Th ese are dcvclop ed to re ta n exce ss water during periods of high fot use during periods of drought or deniand.

Reservoirs inainly servc thc purposes of water conserva tion and flood control.A coliservatlon storage reservoir is meant to save excess water carricd down by a riverduring the wet season when the demand is less and release it (luring the dry season w heriver flow is less than the deman d. The storage may serve any of Uie following requirem

1) Doir~esticwater supply,2) Industrial water supply.,3 ) Municipal water supply,4) Irrigation,5 ) Hydroelectric power,6) Navigation,7 ) Recreation , and8) Fish and wild life conservation.

A flt x~ d ontrol reservoir holds some of the flood waters when the iiver discharge is sucto cause damage to the cities and inhabitants in the vallcy downstream if it is allowed toflow dow n and release them at a slow rate when the flrmd recedes.SAQ 1 .

i ) What are the various uses of a rcservoir'?ii) Wh at do you uridersta~ld y a coliservatlon and a Hoot1 conLrol proje ct?

1.4 CLASSIFICATION OF RESERVOIRSReservoirs ]nay be classified as :

a) Single purpose conservatioii reservoir,b) Single purpose flood conlrol reservoir, such as,

i) Retarding reservoir,ii) Detention basin, arid

c) Multipurpose reservoir.l'hese may brletly be described as follows:1.4.1 Single Purpose Conservation ReservoirSucll reservoirs serve only a l e purpose which could be for supplying water for domesllanid ~t~ ( lusu ia leeds ot a tow n, or for irrigating a spec ific area, or for generatinghytlroelectric power, and s o on. In all these cases the requirement of w ater may he asseslor diftercnt parts of the year wlth as much accuracy as possible, based on w h~ chhecap;rnty of reservoir may be estimated. When m aking an estimate of water required, thg,.n)wth n denl'md over time must be considered.1.4.2 Single Purpose Flood Control ReservoirSuch a reservoir helps Lo reduce, in the dow nstream reaches, the peak discharge of a floby ithsorhing a part of the flood volume, while the flood 1s rising and rclrase tllc saiileclua~itity,while Lhe Htx)d is f;tlling. I t reduces the flood levels a id hence the ctnisrquell


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in the basin. The schedule giving the largest total bcnefits from the various intendedpurposes without interfer~ngwith the lower or upper limits of storage is adopted forpurposes of estimattng. Baseti on the actual experience these tables can be modified.

1.5 STORAGE ZONES OF A RESERVOIRThe storage zones of a reservoir are shown in Figure 1.2.The water stored between differentlevels of the reservoir have different purposes, and these various levels and zones may bedescribed as under:1.5.1 Normal Pool LevelIt is the maximum elevation to which the reservoir surface will rise during normal operatingconditions. This corresponds to the elevation of the spillway crest or the top of the spillwaygates as the case may be.

> 1.5.2 Minimum Pool LevelIt is the lowest level to which the reservoir is to be lowered under normal conditions. Thislevel may be fixed by the elevation of the lowest outlet in the dam or by co~id~tlonsooperating efficiency of turbines in hydroelectric reservoirs.

4SURCHAR GE STORAGE POOL LEVEL DURING DESIGN FLOOD-.

\

&L p''d.3.a !2r-/~?. .. USEFUL STORAGE I \ \


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Reservoir I'lanninythe permeable reservciir harks when the reservoir fills, and thiswater level in the reservoir is lowered. The hank storageapaciiy of the reservoir over a i d rtbove that indicated by th e'he volume o f hank storage depen ds on the geologic con ditions c!f

cupied in a natural stream ch a~ m cl nlenng the r5servoir.

tween a plane drawn throii~gli line drawn pm ll e l to the stream

tween a line p;rr:=~ielo the stream bed arid the actual water

SA Ql;lt 110 you understa~iu y normal pool level, minlrnum pool level, dead storage,t ston ; L ~ c .nd valley storage''

1.6 #ASS CURVEI

A Inass 4 jrve is a cumuliativc plotting c!f net reservoir iotlow against lime.servoir Capacity from a Mass Curve

3ws a mass cur ve for a 4- year period, to llelp determine the appropriatecity recluired to satisfy a specified dem and. Th e slope of the mass curv e at anysure o f the inflow rate at that time. Dernand curves represent a uniform rate of

OBSERVEC NFLOW XIJUSTEO Fa)EVPPORbTIWM iD REPURED RELEASES FOR DOWNSTREAMLbER

Figure 1.3 :Use of M a s Curve to Determine the Iteservuir Cnpacity Requiredto Prtduce a Specified Yield (Example 1.1)


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I ) ;~IISnd Reseno i l s demand and are straight lines parallel whose slope represents dem and rate. Demand linesdrawn tangential to h e high poinls of the mass curve (P,Q) represent rates of withdrawal ofwater from the reservoir. Supposing that the reservoir is full wherever a dzin;u~ dineintersects the mass curve: therefore the maxim um deviation hetween the demand line ant1the mass curve indicates the reservoir capacity needed to satisfy the demand . The ordinatebetween succe ssive tangents represents water spilled ove r the spillway. If the demand isvarying , the dem'multl line becom es a cur ve b ut the princip les und erlying the analy sis remainthe same. But, it is necessary that the demand line for varying demand coincideschronologically with (he mass curve. i.e., March d eman d coincides with M arch inflow. etc.Example 1.1

For the inflow shown in Figure 1.3, what should be the rcservoir capaclly lo assura yield of 75,000 ha-n1 per year?Solution

Tangents to the mass curve at A 'and B have slopes equal to the demand of75,000 ha-ndy ex. The nlaximurn ordinate occurs at C which rep rese nls a volumnc of56.000 ha-m. This is the required reservoir capacity. Such a reservoir woulcl be full atA, depleted to 34,000 ha -~ nof slorage at D. and would be full again at E. Betweell Eand B the reservoir would remain full, and all the inflow greater than the de ~n an tlwould be wasted downstream. At C, the reservoir would be emp ty, and at F ~twould bfull again. 11 may be noted that in this case the slorage must carry over 2 years.

1.6.2 Yield from a Mass curveMass curves may also be utilised to find the possible yield which Inay be expected Iroln areservoir of specified capacity (Figure 1.4). Here tangents are drawn to connec t high pointsof the mass curve (X,Y) such that their maxirnuln deviation lion1 the Inass curve is less ha1the specified reservoir capacity. The yields lhat can be attained ill each year with thespecified storage c apacity is indicated by Lhe slopes of the resulting llnes. The slope ot eachdemand line is the yield for the period. A demand line should intersect the mass curve whonextended forward. And, if it does not, the reservoir will not rerrll

-30.000hn-m

r 600

Figure 1.4 :Us e ofMass Curve to Determine the Possible Yield fmn~a Reservoir of Specific Capacity (Example 1.2)

55 0

If a reservo ir of 30,0 00 ha-m capacity is provided at the site for which the masscurve of Figure 1.4 applies, what will be the yield'?

OBSERVED INFLOW AOJVSTED FOR EVAPCRATION AND- REQUIRED RELEASES FOR DOWNSTREPIN USERS


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I)ams and Reseivoim compare d with the reservoir caplicity, lhe useful life of the reservoir gets rcduccrl. Reserplanning rnust cor~ siilerhe probable rale o f sedimentation to determine whc thcr the uscflife of the proposed reservoir will be suft'icient to justify its c3nstructioli. Thc useful lifethe reservoir may be calculated by determining the total time needed to fill the storagevolunle by the sedime nts. If the aver ngr se dime nt load of a stream is &own the11 the lifethe reservoir can be computed. Various reli~tion s,n this regard. as applied to Indiaii riveare given as uncler :

FINE SED~MENTS

Figure 1.6 :Sediment Accumulation in aTypical Reservoir1 ) A. N. Khosla's Formula

'?The annual silting rate = 0.036 Inillion In' per 100sq km of catchment.area. ...2) D. V. Joglekar's Enveloping Curve

-Hie annual silting ratc = Y = 0.5 97 A-".24 ...where, Y is ihc sedimen t yield in million rn3 per 100 sq km, nd A is the catchmenarea at the dam site in sq km. and

3) R. S.Varshney and M. d;. Haichur's FormulaThe ir re la li ~n s avc been clevclopecl for rivers north and south of the Virld liyas sinc:the two systznls of rivcrs show their o wn distinct char;acteristics.

For North Indian Riversa) For mountainous rivers with ca tch ~ne nts pto 3 30 sq km ,

y - 0 39 5 A - ~ , ~ ~ ~ ..b) For rivcr in plains with catchment areas upto 173 sq kmY = 0.3')2A- ".20" ..

c) For catch~ nent rcas over 130 sq km.Y = 1.534 r).264 ..

For South Indian Riversa) For rivcrs with calcliments upto 130 s q k ~ n ,

Y - 0.46A- 0.468 ..b! For cnt ch~ nen t reas over 130 sq km,

Y = 0 . 2 7 7 ~ - ' . " ~ ..

SAQ 6What arc (he elripirical rclations for estimating sedimentation rates of Indian ri


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n t i i C the iztflowi~lg ediment that is retained in the reservoir is a funclion of thest:rvoir capacity 16 total inflow aici is known as tlle trap efficiency of theThis trap effiaency gets reduced with age as the reservoir capacily decreases byeposilion. Complete t'illing of a reservoir takes a very long period, however, the)C the reservoir 1s lernllnalecl when the capacity occ~rpied y tlie sedinlcnt

reservoir from serving the desired purpose.

hat (loyou understand by "trap elficiency"'!

ONMENTAL EFFECTS OF RESERVOIRSous have some adverse lnlpacts on Lhe environment of thc area where they areci. Tliese adverse environn~ental frects should he mmlnused while plannlng axr poject by studying alternative plans of dams and reservoirs.

nt consists of all the external factors and conditions that affect the lives of livings. The environmental requirerncnts of different living beings are interrelated, and

each crealure is dependent on and affect the othcr creature. Enviro~lmental ffects iueto monetary evaluation, dilferent people evaluate the degree of i~iiport;ulce f)n~ilcntal o~lditionn a different manner, llence Lle evaluation is purely

ivc. People living in Hie plairls would like the dam and reservoir to be IOcated in theiect them from the ravages of floods whereas Uie hill folks feel the location of a

eir area would deprive the111of land which is the very source of their livelihood.ii!jc)r collcenl are the environmental conditions that directly affect the population. Tlieon~nenlal Sfec(s that bencfit mankind are irrigation; tlood protection, improved land

and water supplies for domestic ang i~~dustrialeeds, power generation, water quality,culture, recreational an d health improve~nents.However, there are various adverseonnlental effects caused by the co ns hc ti on and operation of dams and reservoirs asntcd o u l e;irlier. While some are unavoidahle olhers call be reduced to some cxtenl.

le 1 . 1 presents Ihe adverse effects of reservoirs on the environment.

W l ~ i trc d ~ effects of a reservoir on the environment'?


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1 SUMMARY ReservoirPlanningroject due care must be given to aspects like sedimentation, andacity of ;I reservoir and the yield from a ieservoir arecurve at tlie site. The classificatioii of reservoirs and theture defining the various levels of the reservoir are features the planner sho uld beThe purpose ol' a reservoir deternlines how thc reservoir should he operated. Theshould he such as not lo dam age the environlnent of the dain slructure. This unit

2 KEY WORDSservation Pro.ject : A project in whicli the llow in the river is conserved tomeet the requirements of irrigation. power generation ordornestic or industrial needs of a town o r a region.

: It is the level below which the reservoir cannot bedepleted any further.: A reservoir for the purpose of tlood control andprovided with a spillway or outlcts is a detentionreservoir.: Aquatic and wild life reyuire a source of water for theirsuslenruice. Any water resources project planned shouldaim at conserving the water body for their needs.

od Control Reservoir : A reservoir that is meant to reduce the damage s due touncontrolled flood in a river by storing the water duringthe tlood season and releasing it slowly after the Hoodrecedes.

h i imum Pool Level11ltipilrpose Reservoir

rrnal Pool Levelervoir Capacity

ervation Keservoir

lley Storage

This is the storage available tb r meeting therequirements of the project.It is the lowest level below which the reservoir cannotbe lowcrcd under normal working conditions.A reservoir that serves to m eet more than on e purpose iseconomical a s the same water can be utilised fordcriving m ore benefits.It is the level in a reservoir at which the water surfacewould be m aintained in normal conditions.The volunle of water that call be held in the spacebehind the dam upto the full reservoir level is itscapacity,A reservoir with a spillway and oullets not regulated bygates or valves is a retarding reservoir.A reservoir that meets any o ne of the requirements ofdomestic households o r industrial needs of an areacovered by irrigation.A reservoir with the only purpose of controlling theflood from damaging the downstream reach es.The ratio of sediment retained in a reservoir to the totalinflowing sedimen t into the reservoir expressed as apercentage is the trap efficicncy.The qu antity of water held in n natural stream chan neland which flow s into the reservoir. '


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ANSWERS TO SAOsSAQ 1

i) Domestic water supply, industrial water supply, n~ un icip alwater supply,irrigation, hydroelectric power, navigation, recreation, fish mil wild lifeconservation.ii ) A conservation storage project saves excess water carried down by a riverduring the wet season when the denland is less, and releases it iluring the dry

season when the river tlow is less than the demand . A flood control reservoirretains tht: tlood waters wlie~ lhe river discharge is such as to cause damage tothe cities and inhabitants in the valley down stream if it is allowed to tlowdown , and releases them at a slow rate when the tlood recedes.SAQ 2

Single purpose conservation reservoir: Single purpose flood control reservoir;Retarding reservoir: De lent ~o n asins; Multipurpose reservoir.SAQ 3

Norinal pool level is the ~llax inlu ln lev;ltion to which the reservoir surtilce willrise during n or ~n al perating conditions. This correspond s to the elevation of I h espillway crest or the top of the spillway gates.Mi lli~ nu tn ool level is the lowest level to which the rese~ voi rs to be lowered- ullder normal conditions. This level m y be fixed by the elevation ot th e lowestoutlet in the dam or by conditions ot operating efficiency of turbines ~nhydroelectric reservoirs.Dead srorage is the water held below thc nlinimum pool level, x id 1s illso ternledas the dead storage level.Live or useful storage is the volume of storage between the minimum and normalpool levels. I11 n~ ulti pu rpo se eservoirs the useful storage may be subdivid ed intoconservation storage and tlootl-nutlgation storage depending on the adopted planof oper;ltion.Valley storage is the volume of water occupied i n a natural-stream channel.

SAQ 4Reservoir capacity and yield l'roln a Inass curve.

SAQ 5Refer Section 1.7.

SAQ 6~' ef t t r ec tion 1.8.

SAQ 7The percent o f the intlow ing sedimen t that is retained in the reservoir is afunction of the ratio of reservoir capacity to total inflow and is know n as the trapefficiency.

SAQ 8Refer Section 1 .10.

001 reservoir plan

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