IS 5477-2: Fixing the capacities of reservoirs - Methods, Part 2: Dead storage

16 Pages·1994·1.6 MB·English

by  Bureau of Indian Standards

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IS 5477-2 (1994): Fixing the capacities of reservoirs -
Methods, Part 2: Dead storage [WRD 10: Reservoirs and
Lakes]
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee””
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
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“Knowledge is such a treasure which cannot be stolen”

IS 6477 ( Part 2 ) : 198'+
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REAFFIRMED
. JUL200~
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)
Indian Standard
FIXING THE CAPACITIES OF
RESERVOIRS- METHODS
PART 2 DEAD STORAGE
( First Revision)
UDC 627-815-6
e SIS 1994
BUREAU OF. INDIAN STANDARDS
MANAK BRAVAN, 9 BAHADUR SHAH ZAPAR MARO,
NEW DBLHI 110002
D,cember 1994 Price Group S
Reservoirs Sectional Committee, RVD 4
FOREWORD
This Indian Standard ( First Revision) was adopted by the Bureau ofIndian Standards, after the draft
finalized by the Reservoirs Sectional Committee had been approved by the River Valley Division
Council.
Byproviding extra storage volume in the reservoir for sediment accumulation. in addition to the live
storage, it is ensured that the Jivestorage,although it contains sediment, will function at full efficiency
for an assigned number ofyears. This volume of storage (in the fixation ofwhich the minimum draw
down level is also a major criterion in case ofpower projects) is referred to as the dead storage and
is equivalent to the volume of sediment expected to be deposited in the reservoir during the designed
life ofthe structure.
The distribution pattern ofsediments in the entire depth of a reservoir depends on many factors, such
as slope of the valley, length of reservoir, constriction in the reservoir, particle size ofthe suspended
sediment and capacity inflow ratio; but the reservoir operation has an important control over other
factors. However, a knowledge ofthis pattern is essential. especially, in developing areas, in order to
have an idea about the formation of delta and the recreational spots and the consequent increase in
back water levels after the reservoir comes into operation.
This standard ( Part 2 ) was first publisbed in 1969. The present revision has been prepared to incorpo
rate the latest knowledge in this field in this revision an additional figure for determining the type of
reservoir has been incorporated in addition to modifying Fig. 1and 2and some tables.
This standard consists offour parts, Part 1 covers general requirements, Part 3 covers live storage and
Part 4 covers flood storage.
For the purpose of deciding whether a particular requirement of this standard is complied with.
the final value, observed or calculated, expressing the result of a test or analysis, shall be
rounded off in accordance with IS 2: 1960-Rules for rounding off numerical values (revised )'. The
number of significant places retained in the rounded off value should be the same as that ofthe
specified value in this standard.
IS5477(Part2) :1994
Indian Standard
FIXING THE CAPACITIES OF
RESERVOIRS - METHODS
PART2 DEAD STORAGE
First Revision)
I (
1 S(~OPE record covered by the survey will then be equal to the
total weigbtoftbe sedimentdeposited in the reservoir
Thisstandard (part2)covers the methodsfor comput
plus thatwhichbas passedoutofthe reservoirbasedon
ing the sediment yield and for predictingthe probable the trapefficiency.In thisway,reliablerecordsmaybe
sediment distribution in tbe reservoir below normal readilyandeconomicallyobtainedon long-termbasis,
(full)reservoirlevel (F.R.L.).
4.%.2 Thedensityofdepositedsedimentvarieswiththe
2 REFEREN(~ES
composition of the deposits, location of the deposit
within the reservoir, tbe flocculation characteristicsof
Thefollowing IndianStandardsare necessaryadjuncts
to this standard: clay content and water, tbe age of deposit, ell". For
coarse material (0.0625 mm and above) variation of
ISNo. Title
density with location and age may be unimportant.
4410 Glossary oftenus relating to river Nonnallyatimeandspaceaveragedensityofdeposited
(Part6) :1~83 valley projects : Part 6 Reser materials applicable for tbe period under study is
voirs(first revision) requiredforfindingtbeoverallvolumeofdeposits.For
4890: 1968 Methods of measurement of sus this purpose the trappedsediment for the period under
pendedsedimentillopenchannels studywouldhavetohe classifiedindifferentfractions,
Most of the sediment escape from getting deposited
121M2: 1987 Guidelines for determination of
into the reservoir should be from tbe silt and clay
effects of sedimentation in plan
fractions. Insomespecialcaseslocalestimatesofden
ningand performanceofreservoirs
sitiesat points inthe reservoirmaybe required instead
3 TERMIN()IJ()(;Y ofaveragedensityoverthe whole reservoir.
For the purpose oftbis standard, tbe definitiousgiven 4.Z.3 The trap efficiency mainly depends upon the
inIS 4410( Part6 ) : 1983sballapply. capacity-in-Dow ratio but may vary with location of
outletsandreservoiroperatingprocedure.Computation
4 MEASlJREMENTOFSEDIMENTYIELDS
of reservoir trap efficiency may be made using trap
efficiency curves, sucb as tbose developed by Brune
4.1 Thesedimentyieldinareservoirmaybeestimated
and by Churchill(seeIS 12182: 1987).
by anyoneofthe following twomethods:
a) Sedimentation surveys of reservoirs with 4.1.4 The sedimentation rates observed in adjacent
similarcatchmentcharacteristics,or reservoirs also serve as guide while designing dead
b) Sedimentloadmeasurementsofthe stream, storage capacity for a new reservoir, the rate of
sedimentation observed in similar reservoirs and/or
4.1 ReservoirSedimentationSurvey
adjacentbasinshouldbe suitably modified keeping in
viewthe density ofdeposited material, trap efficiency
4.%.1 Thesediment yield from the catchmentisdeter
and sedimentyield from the catchment,
mined by measuring the accumulated sediment in a
reservoir for a known period, by means of echo 4.3 SedimentLoadMeasurements
soundersandotherelectronicdevicessincethe normal
sounding operations give erroneous results in large Periodic samples from the stream should be taken at
depths.Thevolumeofsedimentaccumulatedinareser various discharges along with tbe stream gauging
voiriscomputedas the differencebetweenthe present observations and tbe suspended sediment concentra
reservoir l'apal'ity and the original capacity after the lionshouldbe measuredas detailed in IS 4890: 1968.
completion ofthe dam,The unit weight ofdeposit is A sediment rating curve which is a plot ofsedimeut
determined in tbe laboratory trom the representative concentration against the discharge is then prepared
undisturbedsamplesor by field determination usinga and isusedillconjunctionwithstagedurationcurve(or
calibrated density probe developed for tbis purpose. now duntion) based on uniformly spaced daily or
The total sediment volume is then converted to dry shortertimeunits1ataincaseofsmallerriverbasinsto
weightofsedimentOil the basisofaverageunitweight assesssedimentload.Forconvenience,the correlation
ofdeposits. The total sediment yield for the periodof betweensedimentconcentrationagainstdischargeOIlY

t
ISS477 (PartZ) : 1994
be altered to the relation of sediment load against b) The minimum drawdown level isfixed a little
run-offforcalculatingsedimentyield. Whereobserved above the new zero-elevation computed in (a)
stage/Dow data is available for only shorter periods, above. When other considerations like com
these have to be. suitably extended with the help of mand area elevation, providing extra head for
longerdata on rainfall. Thesedimentdischarge rating powergeneration, etc, prevail, thiselevation is
curvesmayalsobeprepared fromhydraulicconsidera fixed higherthanone ofthese.
tions using sediment load formula, that is, modified S.z Severalmethodsare illuse for predictingsediment
Einstein's procedure. distributioninreservoirsfordesignpurposes.Eitherthe
empiricalareareductionmethodor the area increment
4.3.1 The bed load measurement is preferable. How
methodmaybeused.
ever, whereitis110tpossible,itmay beestimatedusing
analytical methods based 011sampleddata oras a per S.1.1EmpiricalAreaReductionMethod
centageofsuspended load (generallyranging from 10
Thismethodisbasedontbeanalysisofdata ofsediment
to 20 percent).Thisshould be added tothe suspended
distribution. In this method, reservoirs are classified
load togetthe total sedimentload.
into four types, namely, (8) gorge, (b) hill, (c) Oood
5 PREDICTIN(;SEDIMENTDISTRIBUTION plain-foot bill, and (d) lake, based on the ratio oftbe
reservoir capacity to the reservoir depth plotted on a
5.1 Thesedimententeringinto astoragereservoirgets log-log scale (see Fig. 1). Figures 2 and 3 give the
deposited progressively with the passage oftime and sedimentdistribution-area designcurvesfor each type
therebyreducesthedeadaswell aslivestoragecapacity ofthese reservoirs. The equation for the design curve
ofthe reservoir,Thiscausesthebed level near thedam
used is:
to rise and the raised bed level is termed as new zero
elevation. It is, tberefore, necessary to assess the ......(1)
revised areasand capacitiesatvariousreservoireleva
where
tionsthatwouldbeavailableillfutureandcouldbeused
illsimulationstudies to test the reservoirperformance Ap• a non-dimensional relative area at relative
and alsotbe newzero-elevation. dis..nee 'p'abovethe streambed,and
=
C,mand non-dimensionalconstantswhichhave been
Thefollowingproceduremaybeadoptedforfixing the
n fixeddependingonthe typeofreservoir.
deadstoragelevel and sill levelsofthe outlets:
5.1.1.1 Thesecurvesare used toworkoutthe probable
a) Thedistributionoftheestimatedsedimentload sedimentdepositioninthereservoiratdifferentdepths.
for the feasible service time of the reservoir This method is more reliable than the area increment
should be carried out and new zero-elevations method. An example of the usage of this method is
sbouldbe determined,and giveninAnnexA.
NoI.: m=xy S !
r....J~ ..7 mII ioro1.5.oTfFlE:1v(GOA::
I~
l/l r-,
: ~
V ~ ~~ V m•1.5to2.51YPEIII(Hlll)
V x L--~ '~ I
~
.......~ L......- II ~ 1
- -I ~ -- ~"m. .I 25to3.5TVFtEIi (flOD[ I~NFOOTHILL
........- - I.' ~ II"""~ ...... L....o ,.., m.3.5to4.5 TYPE I (lAKE)
II /"
~ ~..- _I--"" ~ t.- IIIII~
III ~ ~~ I- ..... -~~ I
!/lI'~~~ I-~~1~..00---~1- ~
l..oIII'"
~~~ ~~"..I-'~ ~
....
~
CAPACln(C)
FIG.1 C~IFICA11ONOFREsERVOJR
pFYTH VERSUSCAPACTYRaAnONSHIP
2
IS!477(Part%) : 1994
!.2.2 AreaIncrementMethod
2.8 Thebasicassumption in this method is thattbe sedi
ment deposition in tbe reservoir may be ap
2.8 proximated by reducing the reservoir area at each
reservoir elevation by a fixed amount. Successive
2.4t----tt-......-IV Ap;:1.486P-0.25 (1_p) 1.34_ approximationsaremade. Averageend area(orpris
III Ap. 16.967p1.15(1-p) 2.32 moidal formula) is used to compute the reservoir
2.2 t--.......---4~II Ap=2.487 P0.57(1_p) 0.41 capacitieson thebasisofreducedsurface areasuntil
2.0 I Ap=5.074P1.85(1_p) 0.36 tbe total reservoir capacity below the full reservoir
level is the same as the predetermined capacity ob
! 1.8 tained by subtracting the sediment accumulation
with time from tbe original capacity.
L5 1.6 Thebasicequationinthis method is:
ex:
-c
~ 1.4 VI• Ao(H - ho)+Vo ••••••••(2)
where
1.2
VI- thesedimentvolumetobedistributedinthe ,
IX
1.0 reservoir inhectaremetres,
0.8 Ao- tbearea correctionfactorinhectareswhich
is original reservoir area at the new zero
0.6 elevationofthe reservoir,
H• tbe reservoir depth below full reservoir
0.4
level (F.R.L.)in metres,
ho• tbe depth in metres to which the reservoir
iscompletely filled withsediment,and
0.0....--'-.--.I""'--.....&-.--............-......-......._~~~
o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Vo• the sediment volume below new zero
RELATIve DEPTH ~ elevation inhectaremetres,
,(MEASUREDFROMBOTTOM) 5.1.2.1 In other words, the equation mathematically
expressesthat the total sedimentvolume V consistsof
s
FlO.2(SBEDT~DISTRIBUTION- AREADESIGNCURVES two parts,namely, (a) tbe protion which is uniformly
ONREsERVOIRSTORAGECuRVES ) distributed vertically over the height H - 11 with an
0
'00
~~
r-
TYPE1""\/ ' J •
TYPE11--;\ ~V ~ /" j
r\ V ~
/ V/I
/" V
~
/ / Y \ V
/ ~
I ,/ / ~ V LTYPE III
I /
/ v: ~ K'
/ V
./
II~/ ~ \
/ -TYPE I'
~ t
,L
~
~
o 20 40 60 80 100 120
PERCENT SEDIMENT DEPOSITED
FIG. 3 TYPECuRVESOFPERCENTSmlMen'DEPOSITED V,.ASUSPER(~ENT
REsERVOIRDEPlHBASFDONAcrue,Oa:uRRENCES •
3
IS5477 (Part1): 1994
foraparticularreservoiranditsanticipated
area equal toA and(b)theportion V below thenew
o o sedimentstorage,
zeroelevation ofthereservoir.
S• totalsedimentinthereservoirinbeda~metres,
S.1.1.1 Anexampleoftheusageofthismethodisgiven
inAnnexB. V(pH)• reservoir capacity at a givenelevation in
NOTE-lbeapplicabilityofthismetboddecreaseswith hectaremetres,
the I.nerease I.n the ran.o of rseesdeirmvoei.nrtcdaeppaocsi.itty. If the H. sthuerftaoctaelidnemptehtroefsr,easnedrvoirfornonnalwater
hundred yearssediment, accumulation exceeds 15per
centoftheoriginalcapacity,amoreexact methodshould A (pH)• reservoir area ata given elevation itthec-
beapplied. tares.
S.l.JMoody:~MetlwdtoFindNewZeroElevation S.1.3.1 Table1givesthevaluesofthefunctionj'(p)for
tbefourtypesofreservoirs(see5.2.1)and Fig.4 sbows
Thismethod isusedtodeterminethenewzeroelevation
the plottingof!Cp)againstrelative reservoirdepth,P,
0, directly without trial and error process. Two
parametersf (p)andf' (P)asexplainedbelowaremade for thefour typesofreservoirs oftbeempirical area
method (see 5.1.1) and also for the area increment
useof:
method (see5.1.1).
1(P). 1- V(p~ ....(3) S.1.J.l To determine the new zero elevation, f(P)
a(P)
shouldequal!'(p).This isdonegraphicallybyplotting
f' (P).S - V(pH) ....(4) the values of I' (P) and superposing this over the
HA(pH) relevantICp)curve. The intersectiongives the relative
deptb of (Po) reservoir at new zero elevation after
where
sedimentation. New zero-elevation may be computed
f (P)• afunctionoftherelativedepth ofreservoir byaddingthe productPo-Hto tbe originalstream bed
for one of tbe four types of theoretical
elevation. After arriving at the new zero elevation,
design curves, either empirical area method (see S.1.1) or the area
V(p). relative volumeatagivenelevation, incrementmethod(seeS.%.1)isused.
(,(P). relative area atagivenelevation, 5.1.3.3 An exampletolind out the new zero elevalion
f' V})- afunction oftberelative depth ofreservoir isgiven inAnnex C.
..
1000-0
500-0
I I
\ rl'VPE I
100·0
50-0 ,
,
\
'"
.~... 10-0 ~
,
" " ,a
"-
~~ ~TlPEII '-
~,~ ~'"....... 1
-
.........
/ .... I ~II~10......- - ~1-...-..-..-..11oo.:: r-----. ~~~'- 1
~:rVPE IV V ""'lIIIIIiiII~.-...,.........;::: """~~
J ~
0·1 '-0.. ..
-.VPE III --
~05 --. -..
,ARE A INC~EME~T "'-~" .""v
I I ~
I ~
0-01
0-' 0-2 &3 ~4 ()& 0-6 0-7 0-8 0-' 1-0
RELATIVE'DEPTH (p)
FIG.4 CURVES TODETERMlWTHEDEPTHOFSFDIMENT INmE REsERVOIR

4
IS5477(PartZ): J9,..
llIble1Valuesofthe FUDdioD/(P) CortheFour1)'peso(Reservoirs
(Clause5.2.3.1)
p 1)pe
II III IV
(1) (2) (3) (4) (5)
0
0.01 996.7 10.568 12.03 0.2023
0.02 277.5 3.758 5.544 O.23Q0
0.05 51.49 2.233 2.057 0.2796
0.1 14.53 1.495 1.013 0.2911
0.15 6.971 1.169 0.682 1 0.2932
0.2 4.145 0.9706 0.5180 0.2878
0.25. 2.766 0.8299 0.4178 0.278 1
0.3 1.900 0.7212 0.3486 0.2556
0.35 1.495 0.6323 0.2968 0.2518
0.4 1.109 0.5565 0.2333 0.2365
0.45 0.9076 0.4900 0.2212 O.21Q7
0.5 0.7267 0.4303 0.1917 0.2010
0.55 0.5860 0.376R 0.1687 0.1826
0.6 0.4732 0.3253 0.1422 0.1637
0.65 0.3805 0.2780 0.1207 0.1443
0.7 0.3026 0.2333 0.1008 0.1245
0.75 0.2359 0.1907 0.08204 0.1044
0.8 0.1777 0.1500 0.06428 0.083Q7
0.85 0.1202 O.IIO? 0.04731 0.06330
iJ.9 0.080 11 0.07276 0.031OJ 0.04239
0.95 0.05830 0.02698 0.01527 0.021 23
0.98 0.01494 0.01425 0.006057 0.008 534
0.99 0.007411 0.007 109 0.003020 0.002470
1.0 0.00 0.00 0.00 O.(X}
5