stilling basin design

1. i,tV
CHrPTIIR t3
Sp illways
I3,1 INTRODUCTION
.
'--fhc sain frrnction lof .u spirrrvav is ro dispose off surplus
'watcr Jrom rire reservoir. The spillway rvorks ,." ,oi",1.
.valves for rhc dam and adiacer
. Depign
", ,ouil,,;.1'f,?,#-i:,r:H::,
"k on trrc projecr
r3.2 . FAGTORS AFFEqrrNc DESIGN
c)l.i-i
.. so!ct2. considcrations ioni.sistprt,
l!,!i. cc,onom)_ IvIany failures of
d a m s ir a vi' "
rg
i:l-f.o ;'r'"trp+io*.J,'i;, i g o. a s p il rv a ys o r
spillrvavs of ia-"ad.fiit" capaciry. It properry designed,
structrire .of adequ4te capacity may be
:found 'to
b""onr'
1od1a1ely
h.igher in .oi, than a srrucrure of inad,equarc
capacrry.
G1r:{@;l':,,i__,fuGi rn" spiurvay design and its
capacity depend on :
{i) Inflow discharge, it.s frcquency and shape of hycrro-
graph,
(ii) . Heiglrr nf cr.rt,
(iii) Capaciry of r.cservoir at various level, ancl
(iv) Geological and other site conditio.ns.
-
Important topographical . featyres rchich . aflect spillrval.
design are :
llst'

2. COMPONENTS OF SPILLVAYS
0 r' ,r 'rrr 1r-
-
rtil--,
(i) Steepness of terrain :
(ii) Amounr of
"*.f,,on and
,///
a-"": embankment material :
(iii) The possibilities of scour :
(i") Stability of sropes, bearing capaciry of soir erc.
For exampie, in case of narro], valley darru, side or chute
channel spilly,a;, is ver), ,.iio'ri, porriir.. ilri, may be as
much a .dfrFdqr"r." of thc stccpncss of rhc banks ,, of ;;;;
insu-ffi cient sr abilii1,.
influences rhe design flood
dams have ro bc provided
55r
- ?-/
' '6't l;"
poritritiry of irr urc as
-?t!li'
+_
T1pc nf dam The type of dam
.,,r-i and spillway.
.
Earth and rockfill
f rr'ith amole spillway capacity.
?,
*e::;i-j1"rrlgi*;s.*:iE).,Jl.gpurposerorwhich
the dim is designed m;i,-ry;;;,*iil.'fri.''f.i;;'i"*r",0 i" ^
gated spillrvay, and the type of gare most suitable
,@!{rl liy'",.y;l dr[) The .rise in rhe downsrream
l,evel rn heavy^gp+ and irs, coruequences need careful
consideration. ceitain 'spilwayr-1r,., greatly rhe shape of
floods hydrograph downstream of spilriay- -Thus ,iohoo
spilrvays reach their maximum discirarge ,#t'"rr., p;t;;
ilg
oI_".1,"
.u, their maximum .rp^.i y unrit a.j.;^iogl
This gives rir:-lb"-wa.v/ertray_gtli"g io*r,r,r."- i" ;" ;;:
rvhich is deteririidiltai to'ffihgfil;-" and fishing-gnd may carue
damage to popll1.l:::lL Oeveioned
^0".
do"ffi
( Naturc and amourt of sotid mai^-iiiUU-jn-Ol> Trees,
no^ti"[" a
"iriii,
-,
"Ji;k;fiffi u.,, ion or rolli ng on b ed, affect
?u
I3.3 COMPONENTS OF SPILLWAYS
spili*'ays can be buirt as part of the main dam or separatery.
concrete or masonry overflow spiilways can be built in the
river section rvhere rock foundarions are suirabr.e ,",r.r, ;;"ro
adjacent sections of the dam ooay be
-embaak."renr
,yp".
Separate spilirr.ays
1r. required, for muitiple aich d;;;;;
for all rypes of embarrr.ment dams. Ev"n in murripre'";;

3. 562
SPITL1VAYS
l:.,,
.t:
'lt l
.:i
dams, there are certain designs rr-here the spillryays ha*e been
provided on rhe buttresses,of rhe arches.
.-' Major componcnts ,f spiilu,ays There arb
., components as follorvs :
three major
(") An entrance structure which admits reservoir rvarer to
rhe spillu'a): and controls the discharge.
-
(b) A conduir rvhich .**. the spiilrvay discharge from
' the entrance structure to a Jorv ievel outlet downstreari of the
dam.
(.) An outlet strucrure to dissipate the energy of the high
velocity flow from the conduit and conveys the v/ater to tie
chan:ael downstreasr.
13.4 TYPES OF SPTT.T.WAYS
spillu'ays are ordinarily classed according to their most
prominent feature either as it pertains to the discharge carrier
or some other ao[porr".,t. Ther', are .also referred to as
.
controlled or uncbntrolred dependlng on ryhether they are
gated or ungated. Common types are :
- (r)' Overflow or Ogee spillivay,
,) b) Straight drop or free overfall spilirvay,
' (c) Siphon spillway,
(d) Shafr or glory hole spill way, ( Drup inlti l
(.) Side channel spithvay,
, (f) Gate spill'*'ay,
i (g) Chute spillrvay,
.. *(h)
Tunnel sp;liway t (or,./rr/ c..:-;! a2.,- .,' -r7;:li1:r.,-t;
,ogcc or orcriliow spitlaaL (Fis. r3.l). .This t)-pe comprises
a control u'eir which ii ogee or S-shaped. Ttre ogee ,hrp"
conforms to the profile of aerated lower nappe and falling from
a sharp crested weir. The upper curve at the crest may be
made eirher broader or sharper than tle nappe. A broader
cur'e wili support the sheet, and hydrostaiit pr.rr.rres rvill
occur along the cont4ct surface, The suoport sheet thus
creates a back warer effecc and reduces irra coefEcient of
L
a

4. TYPES OF SPILLWAYS
discharge. The sharper crest on the other.hand
negative pr*ssures, increases the effective head and
rhe rlisc han; c.
563
creates
thereby
+
/]. r !-r. octt-op oyffiftow sptLlwAy
Fig. 13. t
Frtc ooufi, o-r straigrtt drop (Fis. r3.2).. Jn iti, type the
florf drops freelv from the crsti-T.hit-do;.''-J;-iffi'
^r.r1Ja-&=n"r" a'r** a crest rvhich has a nearrv
verricaFace or a f.." rul I
in ffir,Sing lip to direct r*"i,'"d'^'::r;t;
ar'ay from rhe face of the overlall section. ffr._,r!ai"riJ""oi
the naP-P-e ' is' vsnt-i-l3te@ pr"*r..,,--3* p-ursating
fluctuatin_g j:: --=---r-.-'r'-:.'-'
t l.-,:
_-
. F_g E E oVERFAL L
OR.STRAICHT
DR OP
Fig. 13.2
--.IHPoAl
I i sA))Lt slPt1gS1
SPIIIWAY
Fig. I3.3
siphan spillway_ (Fis. I3.3). A siphon spillrvays is a closed
cond r ri t s),stem form ed in_t-he_ shape-_of-_:l_igyg5!S{--U tube.
1" ,'] t
-diXhg8-qs- 21 e s i rn i I e r m - tl-,,r, *-of-
"--* "ir,-UEf r-iEE'- .
in the
_O:"9_"t.:iL. =l"r-!.ir ira:manralby the flowing warer,

5. 564 SPILLWAYS
siohonic action starts and continued flow is. g-r-11nta!q9{-by
-'J".ii""1m";'l-Ga t.-ctetr^'rp"n nr*-&il;1iiq Iorter- Ieg' ) -
Drre inlct or glory ltolc spiUwalts (fig- t?.*l' ILIIs lyPj'o-:-
spillwl y .wa t sr---entenry-betizontal circulat-g:lt . 11{-
drops shaft -"."q then fJorvs
dorvnstream througlt a horJzontal-condu[ or trrnnql'
ll
MORNIN.G OLORY SPILLWAY
{ FiE., I3.4
idc zltaxl
arttr
ttillin1 6ttin
i.N-
TYASAL SIDE CHANNEL ANO CHUTE
5PILLt"/AY ARRANGEMENT
Fig. t 3.5

6. TYPES OF SPILLIAYS 5&i
ir anilthen
-tulf_ a@rlgh
turru a
rnto
.
' The spilir'ay is suitable ro dam ;ites in narrow ?r:r){*
Another ad"an[B_?
l r"tati-'sjy t"w l*"ail-ntJ-rypc is, rhercforf-ia"-r *r"*
maximum.spillwai' overflorv is to be limited.
sidc channcl spillway (Fig. I3.5). The conrrol rveir i
he control rveir is placed
1lo"S _1!g .rde_of and approximat;l
arong the side-of and approximattlym
p"i!,
portion ,of the
I?J:ron .ol rhe seilIwlscharge channEll--Flo
.to, f"Iir ir,o . r e,are'i
l_(
l?f ,n aisclrargc Crai. Floiv i"-t" sia
side oniy or both sides, ancl over trrc cncr of rhe trough.
Sischarge characterisrics are similar to ordinary overflow
wcir except that ar high discharge it may parrly submerge rhe
crest. rr is not hydraulicail! effi.cient nor inexpensive bur ir
has the follorr.ing advantages.
(") Narrow discharge channel or tunncl due ro precipitu-
ous abutmenls. i
(b) r-rg overflow crest to Iimit the discharge intensity.
Gatc or barragc tlpc spihutass: (Fig. I3.6) rt corursrs o[ a
jgries of g^rp. scpar^red l''y liers rvith floors Tfr-bliirc-in-im-l
ji=-te S".h typ es
""o
b"
tetlor 6a!c
lcnttl, tS ,7,
ictc/ptesr)
ueilbt ,a.Jo ,n
G ATE OR ts ARRAGE T YPE SP IL LWAY-
varuruELLE geanacE ( r eaNcE)
. Fig- 13.6
D.5,xalet

7. 566 SPITL1YAYS
part of dara as has been done at Ahrora Dam in U.P. or can
also be built separatel,v.
Chttc. spitlutay: (Fig. 13.7)
:
A spillrvay rvhere discharge is
conveved from the reservoir to ie dor,rrrs'tr €{tr 'iive? Ieve
.Efie- "*psl annel placed along a damEutment or
EFCdls=.qrght pilhvay'.
ar-e mosd1-us.qd with earthZamslnd have the following
used with
tn"in advantages.
(i) Simplicity of design,
(ii) Adaptability ro all t,vpes iof
(iii) .
Overall economy by use of a
excavation.
t on l,'t -1r?
CHUT E ,5P IL LWAY
trig. 13.7
foundations,
large amount of spiilwaY
Trr-nt[ oi condu;t sprlluTa;ts (Fig. t3.B). Vhere a closed
clra n n el i s us@ is cha rg e, t h e sp ilfw-a-,/-ayr s-r.;IIA
i ruanel or cofrIi ilall.,-,The closed channel may be a
vertical or inclined shaft or hoiizontal tunnel through earth or
rock. Corrtrol structures are almosr o.f all types and overflorv
crests, vertical or inclined orifice, glory holes or side channel
control etc. Tunnels are usuaily designed to run partly full
except in case'of a glory hole- Ample aeration is provided.
This type is mainly suited to dam site in narrotv canyons.
'<trlvotr
^J

8. ]'YPES OF SPILLV YS 567
TUr.J IIEL .SPILLwAY
Fig. 13.8
Yhen the closed channel is carried trnder a dam, it is knorvn
as conduit spillrt'ay. These are generally most suited to dams
in rvide valleys as in such cases the use of conduit spillrvay
enables the spil)rva1, to be located under the dam near stream
bed.
Saddtc spittwoy In 'some basins I'ormed by a dam, there
may, be one or more natural depressions or saddles in the rim
o[ the basin rvhich can be used as spillwal,. To be useful as
a saddle spillrvay it is usually necessary for the saddle to be
on 6nn rock. Thc siie rvhich has saddle is a very desirable
and e,:onomical iayout.
I3.5 ENIERGEIT{CY AND SERVICE SPILLryAYS
'here feasible, the provision of emergency spillwav in
addition to permanent service spillrvays may restrlt in reduced
cost of construction as rvell as an increased factor of safety
against or,t.rtopping of dam rvithour inrparing the eflicierlcy
of normal rcscrvoir operations.
13.6 DESIGN PRINCIPLES OF OGEE OR OVERFLO1Y
,
SPILLWAY
Shape of the cregt
Three t),pes of spill*'av profiles 3're usually adopred for
overflorv scctions as given below :
TtPc / (Fig. l3.e)
A
(
+

9. 5bu
(
C4IST f otp tow HclrD
Fig. 13.9
'l'his is suitablc for lorv ogee..
crests.
SPILLWA}'S
. - u'U,tt oct t P,eoi t4 r
Fis. 13.10
spillrvays as for cirute spillrray
TSpi II (FiS. 19.10) (usual ogee profite)
I* tiris type thespilrrvay.surrace starrs tangentialry. rrom the
upstream face of the dam and'turns smoorhry rising upto the
spillway crest and thereafter Ialls in a' .t.rrr.- '
TS,pc III (FiS. l3.l.l) (overhang on rhe upstreanr)
-
The spillway surface exrends upstream of the dam face,
thus.crearing an
-overhang.from tr,i uoay of the dam. The
ovcrhang 'is continued verticalry to "t r..rt r/3rd rhe head
over the cresr and then joins the upstream face of the dam in
a slope of 30" to the veriic"l.
OVfPXAtJe ,plLLVAy -ro, tt/y.l, Xt/D
Fis. l3.t I

10. DESIGN PRiNCiPLES OF OGEE
' The follorving profrle (f,g- t3'12)
Corps of Engineers malr bE used for
for the dorvnstream Pro6lc.
SPILLYAYS
as given by U.S.
finding coordinites
s69
Army
(*, y)
(r3.I)
rvhere
+
-x
sJ.nts.Ltvtt
11.8s.: ! fl.o.as t
-- -'-
Ha : design head over the crest'
't
I
oetctx.oF cooRbrflATES
_---
-
--r, x
[, oollltSfPttLt
t' '3 - ZHr
Pq.orlL ?
?.ty
.rP57rlAu
PEOilLT
o
l.t
t + o 2to xa y,"+.b t26 )Jt- o tlt ttl'''rt ( x + o zto nt)' al +
o?824.t^ro atr/tts '7r'DE J
a
+! nt
.L
OVTR,II,IFJ , TYP€ 2
Fig. 13.14
faced overhang, the verrical depth of
be equal io 0-.5 Hr (Fig'- 13.1+). Tbe
-ivr-
, IJPSTREA}4 AND DOWTISTRilM PPOflLI OVIPqIOW
SPILLWAY-
Fig. 13.12 ")
Dcsign crilcia for oacrhangs and upslrtam proflc
The maximum desirable projection from the crest line is
0.315 H, (Fig- 13-t3) and the verticai depth of the maiimum'
'bulging is 0.25 Ha. I
-
tl
t
-r
'ry
J.
ig. 13.13
In case o[ a vertical
the projection should
c:5 rd
[J

11. 570 SpILL'AyS
If/i ratio should nor be .lers than 0.5..unless this value is
zero. For ht/N ratio berrveen 0 and 0.5, florv conditioru are
extremelv unstable.
For upstream pro6le, u.s. Army, on the basis of latest
analytical studies and laborarory tesr results, has recommend-
ed the follou,ing equation, (Origin at rhc crest)
* ,* : o.zzffi$*t, + 0.126 Ha
,- 0.4315 Hro'us (xf 0.270 H3)o.e :: ( I3.2)
-I}re curve extends (0.270 H.r) upsrream and (0.t26 Hr)
dou.nsrream from the crest point)-' :
Dcign oitcia lfor prcssurcs
'oL,cr
spiil,,^a1
For medium high spillrval' negati.v:e pressures of abour- l-5m
of water ma,v be permitted. rf rve keep head I.33 rime5 }ra,.
the *alues of negative. pressures rvill be about 0.6 Hd rvith
pien (u-s. Arr,ryrequarion)- und.erpartial openings negative
pressures of the order of 0.1 H.r ryere recorded. U.S.B.R.
perrrits negative pressures of the order of-4,8 m head of
water, rvhereas Indian Standard. specifications permit a
negative head of 3 m of water. Hoyerer, it is preierabie to
avoid sub-pressures as they invoive the following disadvantages.
(r) an increase of the overturning moment,
(b) an increase of the lil-ring forces ,in the case ol'gates,
(c) a decrease in capabilitl. o.f automatic control,
(d) vibrarions expanding evenrually ali over the rvhole
structure,
(*) r.ibrarioru desrructive to rhe
o.usi.ng cracks rhar necessitate
for the stone [ining etc.
mortar and rherefore,
special anchoring bolrs
Dischargc cotficicnt
m!
'l-he rireorctical r.alut t,f co-c{Ilcirnr oI tlisc]rargc disallorving
an)' reducrion due ro friction etc. ii 2,96: But thir value is
difiicult rcl achierjc. 'I'rre. pracrical Iimit of coefiicienr of
dischirge, rvithour altorving subatmospheric pressures is 2.21.

12. !;?
DESIGN PRINCIPLES OF
'l-he various factors rvhich
llelorv :
(i) Tlrc natrtc oJ Fotrlc at thc toP
This is the most imPortant Part'
2.76 have been attained rvith suitable
OGE,E, SPILLVAY 57'l'
affect the coeflicient are given
Coefficients as high
design.
neglect ed.
coefficient of
(ri) Thc sloPe oJ the rcar glacis
f-he effect is not. very considerable and may
(iii) Elfcct of dQth oJ aPProach.
fith rlecrease i1 depth of' appro'ach, the
discharge decreases (fig. 13.15).
be
*
1r
L
i
o
u'
!
(,
}.
a
o
h
)
22
2t
q/
t l.?
2
1.9
r-8
t7
r.6
.o
OtscitnCE COEFtctENTs toR OGEE C.PESf
UP57REAl4 FACE VtRTttcAL
Fig. 13. ts
:
(ir) Efccl of htads difering fron dcsign hcad
A rvid.ened shape o[ crest rvill result in positive pressures
along t.he crest coltact surfac.g, thereby redtrcing the discharge;
rvith a narrover . crest shape negative pressure along the
srrrfaie u,ill occur, resulting in an increased discharge' FiS'
13.16 shorvs the variation of the coe{ficient as related to valttes
of Hr/Ha, rvhere H, is rhe actual head being considered.
'vALUEs of ,/rt

13. s72 SPI LLWAYS
a5
*?
t(.
d.
lro
I
I
I"
P
t
a8
L.
t
t,
t
>r
[il:
"*
ll$
r r -li'
i s ill
'u i "1"
q
cga)
b+#
:cfFr/c;{Nr
06 0
v,tlaas'€4
OF O/|i.rrJlpoa ,op Cg-e'-SHT.DED c.?f 9T
and downstrcam
(r) Effcct of upstrcan facc slopc
For small ratio of
overflow rcsults 'in an
For large ratios the
disclrarge (FiS. 13.I7).
!o1
too
Fig. 13. t7
(ri) Efcct ,f dounstrcam apron intcrJcrtncc
sub-mcrgtnce
''hen the rvater level belowan overflorv w:eir is'high enor.rgh
to affcct the discharge, ,thc wcir is said to be submerged.
F/Hr, . sloping the upstream face of rhe
increase in thc coellicicnt of rlischarg,'.
effect is a decrease in the cocfficient o[
l'J
-
/ !'ot
,2 ri ta t
*.ri4 5. O?,pd rr at

14. l
DESIGN PRINCIPLES OF OGEE SPI LLVAY J/J
k
1.
t
p
Fr
ql
I t,lu
!i
It
IT
l.(
o
1., O
lJ
q
b
e
Q
ir
it
oq
o
S
.
k
t
t
o
tstt
*9t
3 x,
iJ
)
ttS
ei
^o
Iu
- L,
iu
?l
(
:
e
o
L
k
o90
'o I
-t-]
_T__-1,
I
I
-
PosrtloN'or Dott''Ji ltf't !
oF Dr5€,l1R6t ccfrflc'l^'ls o"c
J'
Fig. 13-IB
Fie. I3-tg
?o ,t,PcH tlFFcT
. &,!rtO
o2
A,
DEGPTE Or suBvr4Ceeccfi
oF otSctf'Ror coEFilcrtNTS OUz 7o 7,.rL *A7tr2 ltttCT
R/7rO

15. 57+ sPILl,lVAl.'S
''ere the hydraulic jo*p occurs, the decrease .in
the coeffi-
cienr of discharge is due to rhe back prorrr.*;;"; Ir,nu
dor*'ns11s2m apron and is ind,ependent ;i;;;' *'i;.;_ence
effect of dor+'nsrream apron ..cond,itions on ,rr" .o"m;il;;i
discharge. lthen the value
"f +*+d exceeds about l.l, the
dort'nstrearo floor postirion rr^,
^,,,,r"
effect on the coefficienr,
bur there is decrease in the coefficient caused by rhe tair rvarer
submergence- Fig. r3-r9 shorvs rhis
"n".i.
F Dcsign.rf
@
!----'-"'-'--- -
when cresr piers and abutments are srraped to cause trre
side contracrions of the over flow, the effecrive length wi[ be
less rhan the net lengrh of rhe crest. .The effect of end
coatractions may be taken into account by reducing rhe net
cresr length as below, in equation 13.3.
L
tvhere
L
L'
N
Kp
Ka
Hd
-l'-2(NKp*Ka)H,
t
: effective lengrh of cresr,
: length of crest,
: number of piers,
- pier contraction coefficient,
.abutment contraction coefficient, and 2
total head .on crest including head due to
velocity' of approach,
coefficients are as follo,vs
square nosed piers
round nosed piers '
poinred nosed piers (90. cut lvater)
(r3.3)
Average pier
For
For
For
8.02
0.01
0.01
The aburmenr contraction 'coefficient is affected, by the
shape o[ rhe- abut*".,r, rhe
"";i;-;;,*"". the upsrream
approach *'a, and the axis of floiv, the head in reration ro
the'desigp Ha, and,rhe approaeh velocity.
A*erage coefficients (Ka) ma' be assumed as follorv :
Iror sqtrare abutments with lread rvall 0.20
Forlrounded abutments ivith head rvall 0.10

16. ... ,-:. .-
-'!
'
a
I
l
ti
St
it
tI
'l t
I
It
t;
o'
o
t
{
o
DESIGN PRIIiCiPLES OF OGEE SPIi,LVAY 575
[ ,9---
*r-2,
1.o
50 ' 55 ao 6)
A?|UAL VELOCTTY OF FLOw s.e rn/Scc
vf LoctTY AND ttR E HT.e"tNlo wr7:'e DEPrn oP
SPltaw,aY FAcE Fop DtFr.tPENt o/5c)Jl.oG.fs
Fig. 13.20
t2-O
t50
rC'o
uo
zlo
21 0
,ao
as
t
u
I
o
nl
<
-
J>
ti
Ir
vrS
qi
Y
eq
tt
t
q,
:
I
i.
/-
)
It
,l ?
)
I
a':"
,.
)
/r
(
ti
:
I
i
ir
t,
li/l
I
r
" .,
90'
/) t50.o
r20
NE'-
.DEPTfi
OF T*ATTN d IN
^IITITT
ACTU4I VELOC/TY ,tNO 'tO(/D tytTEft DEPTI{ ON
srllt tv/lY FrCt roR otFF?/arN7 D'/t ctt/tPGES
I'ig. 13.21
I

17. 576
Dtign of sidt walls
SPILLIVr}'S
I00 m
5
12.5 m
3m
horiz: to I vert-
good
8500 cumec
'The pro.le of. florv
.on spilrrvay ,rrrf".u detcrmines rhe
ireigirt of side wars requircd tt retain the florv ;;;;rp_,;_,;;:
The profile deterrnined by rigid calcuration is nor the rrue
li:T;"::1"_::-,r1".". i1i.:"j1"inment
oc€urs in the norv gi,ing
t)re phenomenon of whitc lyater. r. ai"-"^ 'vrY 5rtIrg
.g"*
. The pressure on rhe ,r.rnii_g
rr'all is taken as
_the
co*]@t of *eigrrt or *u",u, normar to
t^e surface of florv. The flow pro6lcs rvirlr
""d ;ri,;;;t";;
cnrrainment ar.c givcn in figs. r3,20 and 13.2r rvhich .o, rr:"
trsed in the design of height of side ,."i"i"g ;"trr. ir,. ;;:
Army W.E.S. coordinates of
d es i gn ca r cu r a t i o ns o r .s ;; f',,,llJr" iJ:ffi ;LT,: lrli,ln'
' depiE.
13.'; HYDRAULIC DESIGN OF OGEE SPILLWAY &
BUCKET TYPE ENERGY DISSIPATOR
Deeign Erample I3.I
Uesrgn ogee spillway with. the Iollowing d,ara :
t. Height of spillrvay cresr from river bed
2. No. of spans
3. Lengrh of each span (clear)
+. Thickness of each pier
5. Downsrream slope of spillway glacis 0.8
6. Tail water curve is below Dz.curve
7. Rock conditions
B. Discharge (design)
Dcroigu.
.A. Head over cregt and coefEcieut of dischargb
t..'
I
Cleaf waterlvay :. 5 x 12.5
Intensity of discharge
: 62.50 m
8500
62.5
: 136 rns/sec/m

18. I
I
I
I
I
i
HYDRAULIC DESIGN OF OGEE' SPILLYAY 577
e a coefficient of discharge 2'1' hence
I-et us assume-a """:;":;; ( llr,,
CL : C L HUr - 2'l x 62'5 :
or 8500 : I3l I{3'?
l[r:r -- 6']'9
(lf Il'
-
v"v
fl:16.2m
Themaximrrmcoefficientofdischargeisz.2|,ifnotaffeated
byot}rerhydraulicParamet'erslikesi,bmergence,velociryo[
approach etc' To get *";;; Jt]"t,
:.f.
C" the effe{ts of
dilTercnt Paramotc" l-'"l'" to l>c rvorked out'
J.
(d Efcct oJ oPProach dcPth
P : height of sPills'aY fronr
' P 100
- tr-l-&z-
(i;) Elfcct oJ hcad duc to
' r"io.ir* of aPProach
This
ri*cr bed : 1.00 *
6"2
iry oJ altProosh
As this is more. than 4'-0' there is no effecr o[ approach
depth ,r,d .ntifiti"tt of discharge rnay be taken as 2'21'
ucloc
:
li
;
I
!
I
.l
1. .f
'1
'l
il
(iii)
In
and
Elltcr of tail watcr conditioru
this case d * ha :
Ha
ha*d
tr
8500-
--;
@*%
8500
---
i /+'r x II6'2
* 0-98 metre/sec
Head due to velocitY of aPProach
(0.98)1_
'2x9.8
-
oj9 : o-o4e m
20
is very small and is neglectcd'
100+16-2 : 116'2 m
: 16.2 m
11 6.2 , oE
I6.2

19. 578
SPILLWAYS
This is more. than 1.7; rhe discharge coefEcienr is nor
affecred
.b1:
rail warer condiri<lns
(ir) Efcct El^ hcads otht rltan dcsign hcad :
The c.resr is designecr for fu* design discharge to avoid
sub-pressrrres along spillr+,a1- surface. At discharge higher
rhan design
L"10, so1e negative pressures may b.;p;;:;,
bur. thev wirr be u,ithin ltto*"tr" limits.
-il-.,r[;";:
less rhan rhe design-discharge, rhe coefficient of discharge rr.iu
be reduced proportionateli"..o.aing ro (H1Hd) ratio.
(r) Eftct { upstrtam itacc slopc
The
'psrream face of the dam is proposed ro be kept
'ertical- A batrer of r in I(r rvi[ u" p.ooiaed from stabiriry
considerarions in Jorver .parr. This batter being small rvill
have no eft"ect on coefficient of discharge.
Effective - I- ength of Spillway
discharging Iength or effecti'e Iength rvi[ be less rhan the
actr.,aJ length due to end contractions.
cut water (90)" nosed piers are proposed to be used and
also rounded abutm ents- The
"aluer' of kp- f ;;; ;;
Ka : 6'1- Irence effecrive'rength of spirhvaf wi, be
L, : L-Z (N,Kp * Ka) H,
: 62.5
- 2 (4 x0.01 + 0. l;-H,
: 62.5-0.28 H.,
Since the effective length is Iess rhan net clear span of the
spillu'av, a design head equar to t6.5 m is assumed. Hence
L. = 62.5 * 0.28 x 16.5 :62.5:+.62 : 57.88 m
Ifence q -
Hence alrighr
The crest profile
2.21 x 57.88 x 16.5&,
128.0 :< 67 - €570 cumec > 8500 cumec
:
rvill be designed for Ha
= I6.5 m
Downctrearn profiIe
The profile recommended by yaterlva)-s Experiment Starion

20. *'^{: r"i -: ..t'- :
:j:
HIDRAULICDESIGNOFOGEESPILL'AY579"
Yicksbtrrg Ilississippi U'S'A' of'U'S' Armv is
/xr'as
-"/v
(nJ :=H-,)
,
or 11.E.1 :2Hao'8ty
' x1'35 1l'Bi
-
xl'8$
The calculated coordinatcs lor the dorvnstream profile are
x (m) Y (m) * (m) (Y) *
00
I 0-046
2 0.167
3 0,354
4 . 0.603
4.575
6.02
7.BB
9.7+
r l.B5
14.35
t2
I4
l6
iB
20
22
5
.,9
IO
0-905
I.710 i
2.684
3.240
23.5 15.73
Tangent Point, Coordiuateg
Theslopeofthedownstreamglacis:0.Bhorizontaltol
vertical. Hence dy/dx : (l'0i0'B) : l'25'
DilTerentiating .equation of the dorvnstream profile
I
g
-
l-85xo'ts :1.25
A; 21.6
1-25x21.6 ' r
or xo.8s-ffi:14.6
:23.5 m
orx
Y : 15'73 m
Llpstrca rr' Profile
The r.rpstreirm profile ir given by the equation

21. 580
Sincc
SPILLVAYS
0-72+ (x*0.270 Hr)r'as
Hao.!?6 y (xf 0.270 Ha)o'crs
I-i.r : 16.l-r nr, llence
O.72+ (x * 4.45;r'as
)- - ,#ff +2.08-t.233 (x**..liyo.ara
'fiic c.oordinatcs oI tlte profrle arc found out as rrnder
| ,. -,-
f+.ss;,'"
x x*4.45
0.72,1
.1
l0.u /
(x+ 4.45)t'63
lr** l,.rrrq*-,.
|
4.45)o ct;
la.+s1o'r:s
- 0.5
- t.0
- 2.0
--_ 3.0
- 4.0
- +.45
3.95
3.45
2.45
1.45
0.4s
0
r2.73
9.90
5.29
r.99
0.23
0
0.850
0.oo+
0.35+
0.133
0.015
0
2.360
2. t60
1.7s0
r.262
0.607
0
9.91
2.66
2. r6
1,56
0.7s
0
0.0?0
0.06-{
0.27+
0.653
1.345
2.080
Thc upstream profile extends upto
: - 0.270 H,r : - 4.45 mctre
)' : 0.126 Hd : 2.08 metre.
Pressures
The maximum negative pressures expected on Y.U.S.
profilc arc just dounstream of gate and are-0.03 H6 - - 0.03
x 16.5 : - 0.5 m of rvater head. At head eoua] to I.33 Ha
i.e. 1.33 x 16.5 i.e. 22 rn of head over crest, negative pressure
is-0.6 Ha i.e.-10 m of tvaterhead. 'This is hieh and hence
acration arrangemerlts are necessary.
Aeration
To control negative pressures and _co11eg13ntly cavitation
du*ry_o-_1gg,iqn pipe Z5 mm dii-if-3 m cElaldng th'd
spfl-*af fi.. b.l"w gate lip-rvould bc providedl These pipes
rvill bc connected to a bigger size header.

22. H1DRAULIC DESIGN OF OGEE SPILL,AY 5BI
naPPe Profi'le aDd
'ater surface Profrle is
side vr'all 'height and its
height of gide -q'a11s'
- . -
of intercst in thc dclcrmtnatton
l"rigr,. Belorv are coordinates
att-. 13.22) for different values
uPP"r
The
of tire
o[u
ipiit*utys with bridges
.ot
g^::
l;::'1:r1:':.-il" lJ*t,i"'"' r" w'E's' frofr'e rvith piers
are also given below'
,rito NtPpt
ORIGIN
-x<-: rX
t't'= 2'o H d
I ig. 13.22
+
I
I
I
v/
4-x
Table 13'1
Co-Ordinates of {ater Surface Profi'le
' .'. TYirhout Pl9I5
- --15ar-gtr[Fil-@
E
x/nd j'
ffiJ-g2 -0.941 -1-230
-r.0 -0-490 -0'933 - r'zio -1'0 -0'+82
-0,8 -0-480 -;;i; -1 19? -:: -:ii3
-:':ii :i.lll
:3l :8.iil :;:;;; :iii1 -ie -o^:'.
-::H:i iH
-0.4 -0-+60 -0'865 -f iIO -0'4 -o'+r7 -0'890 -1'165
-0.2 -0-'125 -0'B2t -1'999 -a'2 -0'431 -0'855 -r'12,2
0.0 -0.37I -0'7s5 -i'999 0'0 -0'38+ -0'805 -I'071
0.2 -0.300 -O'Ogf -o'Sr2 0:2 -0'313 -0'735 -l'015
0.+ -0.200 - 0'586 -0'82; 0'+ -0'220 -a'6+7 -0'$++
0.6 -0-075 -0'+55 -0'i00 0'6 -0'0BB -0'539 -0'847
0.8 0-075 -0-320 -0'569 0'B 0'075 -0:389 -a'72r
1.0 0-2s8 -0'l+5 -0'+11 I'0 2V11"
-0'202 -'056+
1 .2 0'+70 - 0'055 .- 0'22; I '2 0'+62 0'015 - 0'356
l.+ 0-705 0'29+ o'ooi 1'+ 0'705 0'266 -0-i02
r.6 o-e72 o's63 o'1i I : ?':11 : ::l 3:r#
I '6 v'Y t L
I '8 1'278 0'860 0'465
I.B I -269 0'857 0'.53l *

23. 5trl
SPiLLIYAYS
Al*g Pierr
3-
xIlId
- I.0
-0.8
- 0.6
-0.+
-0.2
0,0
0.2
0.4
0.6
0.8
1.0
I.2
1L
t.6
1.8
- 0-495
-0.492
-0-490
-0.482
-0.4-40
-0.383
- 0.265
- 0.185
- 0.076
- 0.060
-0.240
0.445
0.675
0.925
1.177
v/Hd
-0.950
- 0.940
--0.929
-0.930
-0.925
-0.779
-0.651
-0.545
-0,425
-0.285
-0.12t
0.067
0.286
0.521
0.729
-- 1.235
- 1.221
- 1.209
- t.2tB
- I .2.t+
- 1.103
-0.950
- 0.821
0.689
-0.il9
-0.389
* 0.215
- 0.01I
0.208
0.438
- -T: f Pp e coordin"to
as oelow :
Table l3A
m
- I-0
- 16.{J
-0.8 - 13.2 _0.932 _ I5.4 _0.940 _15.5
-0.6 9.9 _0.913 _ ls.t _0.929 .- 15.3
-0.4 6.6 _o.BSo _ 14.7 _0.;;; _ i;;
-92 3.3 _0.8s5 _ t4.t _o.rzs _ 15.2
0.0 0-0 _0.805 _ r3.3 _0.77s _ 12.9
4.2 3s _0.735 _r2.r _o.i.i _i;.;
o-4 6.6 -0.il7 - to.i o.a+s _ 9-o
0'6 9-9 *0.539 - 8.9 -0.415 t_ 7.0
? zBS - q-7
r.u lc.s *a.zoz _3.3a---1i21 j 2.0
I .2 i 9.8 1 0.0 r 5 0.25 0.067 t. I
t.+ 23.1 0.266 4.4 0.286 +.7
i g 26.+ o.sz t 8.6 0.s2r 8.6
l.B zg.z 0.860 t1.z a3ig ,r.o
#
,- -i
/
,t'
--;
-)
t

24. HYDRAULiC DESIGN OF OGEE SPiLL'AY 583
'['he velrrc:ities
t'n the splllrval'
13.20 and I3'21 .
(o :
and depths of rvater (rvitlr and without air)
face can also be evaluatcd lrom the figures
an' 'i' - )
,/
,-/-
h (in m)
head belorv
crest
veloci.ty
in m/sec.
d':depth of
water and
air mixture(m)
,d
I a.p
I solid w
th of
ater (m)
j
10
20
30
40
50
60
70.
BO
90
20.9
94n
2i.+
28.7
32.8
36.0
38.+
41.0
+4.2
5.5
5.0
+.2
4.0
3.5
3.2
3.0
2.8
2.6
5.90
s.50
+.75
+.60
4.10
3.70
3.6s
3,60
3.55
Provide a 1.5 m free-bo3rd over the rvater depth rvith air
entrained
Shape of Pier
90" cut water rosed-piFr-is- hydraulicall;' efficig-L-1ld -
gives.
minimum ..*i[.iion ioef6cienr. This shape t,f pid is adopted
in design. The design of cut rvater is shorr'n in figure I3.23.
}L,,,;
,CUT
WATTR SHAPE Of FITPG{ON{TPY
Fig. 13.23

25. fvr,_r l?l ;: E_s z.n,
5S4 t,. . t { r: **" SPILLIVAYS
";) 1
Tirickness of picr - t : 3m rl -k! 5' c*)
Radius of cut lvater - l.6t: 4.Bm
t / f , n.,
spittwa2 dischargc raring cutoc (.-r r ::
/ l^;
- :, (_.{ ,. . .7,-1 }
-
{ith lhe help of figure 13.16 the varues o_l coefficienrs of
-
(
discharge for heads other than design head can be evaluared !
and discharge calctrlated from the ef,uarion ,,,
A: Ca (62.s-0.20 H) gsrr L'p ?*,* .
Enrrgs, dissipation-Ski jump buckct'
C J = .*?,
4"1/4
since foundation rock is good and the tail rvater level is lorver
than Dr curve (i.e. curve giving values of depthr f.r formarion
of jump at dilTercnt dischlrgef.), ski-jump
-Ju*",
is an ideal
and economical solution.
Bucket 'itvert
,,/
The invert for ski-jump can be ar any erevation, rvirrr rrre
proviso that a rninimum cover of r.5 m olconcrete is required
ovcr good rock. The bucket can be provided i* the body ot-
tlie dam at a high elevation. Thi; rvill increase impact
on rhe downstreaml The bucker invert i., irrii .rr. is providecl
at rhe river bed Ievel asrumi,g sound rock to be 2.0 m berorr.
thc river bed.
Bucket radiu.s
(') From varshney's c*rve : The vertical distance.Fetrveen
I;ucket
_and
upstream pool elevation is i 14.5 m. The bucket
radius from varshney's curve in figure s.3a (page r32) rvorks
out to be 23 m
(b) From the relation given in equation 3.6 rve get
(*-
(
*1
R - 0.6/lmx t65 : 24.4 m
(c) To evaluate radius of bucket by
tlte velocity' at thc toe of the spillrvay
: r'i9^6El0e.zs
Ven Te Chorv lorrrqrla.
has to be determineJ.
^/2x
e.Bt (TTm=.5
: .16 m/sec.
-l

26. H1'DRAULIC DESIGN OF OGEE, SPILLVAY r8r
;-. From figure 3.32, rve get by extrapolatir.rn VrI!'r : 0.98.
Hencc "1 - 4Gx0.Iltl - .15.1 tn/set:.
Using ren Te Chorv's relation, equation 3.7 rve have
45.I+6.+ x I6.5++.BB
:
-
: I U j
Y 3.6 x 16.5+ I9.5
It:0-305xl0p i '
: 0'305 X 101'0;5 : 29 m'
(d) l-rom R. S. Varshne,v's formula re have,
"/iT
: 0-0e (fr) + t-ou (rrom cquation 3.8)
+
. t#:il41p3/sec/m
1-) ' t'l-1
D,: Il+
-?-53m
45.1 - -'vv rrr
Ft:=-!l-:9.05
y'g'B I x 2'53
/e.os :0.0e
++ t.e6
or R:29.5m
,.r,i)._"i.:,-
R. S. Varshne.v and tr[.L. Bajaj's formula (egn.
9.05 - 13.0 R1/r-i9-5 .'. R : 23.3 m
The least of the abovc values viz 23.0 m is adopted. The
bucket rt'ill be circular.
Erit angle
The usual exit angles are 30 to 35". An angle of 30" is
selccted as bucket lip angle. Checking from R.S. Varshney's
forrnula (equation 3.12). rvg,}r21'e
3.os : - o.ooooer.# {,+t.a
. ? r to
9::fl
Lip shape
1'he Iip rt'ill be a sloping one rt'ith 2 horizonral and I vertical

27. SPiLL'AYS
3q
qr
o
a.
o
n
l-
t
a
q
o
I
o
f-:-
I
a
-l
_:
1
i
586
ta
'4
!-
o
a
t-
Yr
k
-i
r -:
I _.
.-
1n
-.
/
l--!
l{-r
:'=r
F
ocr)
q
() (,
vto
t.)
't
l+ (
qcc
T
>L:r
.
tt
t
o
o
i
tr
6
E>
I l'[
I rr
I qU
I i
tt
I :'r
Nli
: tlr
'-rr'
-Nt
--/
. $r).-/
I-+-j- - -
- 'i...---
o)
./.
:.4
4,,
1;:
j
'ki
,..,.......,
.r, '..t ';::
..' r' .t i.'-)-
al
-l
:
o
tt
o
o
}r
f
3.-
?
o
J
o
n+
-^ I
iol '
ol
xl
-. F
o b^
+ l--
HI
r-It
i
o
l,
x,/ ,/,
./.
a(-/'
ot 1-r:'
,/,/'.tr
/ /;.:' 'i
-lv.- i "'
{.:' l"
:"
3
r. I
|Jv
(
vl
'-i". r'
. -.,. .")-'l'li
q.
ij'
o^
r ":
q.
ttr
:
t8
o
k
- -l-i
lr
i
,4
/':'. ' .
'o'-'
--j{.'.'-. j
:o
-:- ---- :
::
!o
:
! 'o
+-3:-
a F.
:P/
f e--
9!J/
g/
^Yr/
t
o!/
:./
)-a-r-4
tx : /
!+ /
oA/
: ': I
r^ rr'/ r
. I ./ L-
/ iE
colt'
;,V ,}l
::tl ,/
!l ,/
i,v _,/_:.
-l:l ,/ I +
'i)/ t
tn-{ o-
:,I i :
'l:--i-
r;,
r: -{
i "*.
T ;i
Ilr
-u
k t-(
ii yW
r: !/ /i,,
y (:0,,
,:,,,,
,l
3
i
u.t
-
k
t
t
L
{
-+
/
l-r
i*i
o
o
o
d
o

28. .,r'..;s:i'&l
587 ,
H"DRAULIC DESIG}i OF OGEE SPILLVAY
I
tl lNVERT
I
P,<OFtL f
aucKEr d !lF PROF/ttS
I
I
-1 I
(
T.t
+-
I
I
a
30 8c
t
/1
/1
lrt it-
90" Cut
13.21 Ogee
I
I
I Jooo
-+--
I
I
I
lVater Pier Nose Geometry
Spillrvay Llydraulic prr-rfiles
o'8
l.Fr, "
"J
t ''.
's:', ./
. ..
a ? 'v-. ./
'.ir ,'
1{ r- . .' ,/
-J-
:.
rI .-.
N 1.25.5t.< '::N
_ _ __r
-s.-
i
Fig.

29. SPI LL'A'S
5Br]
slope in
^
vertical distance of 1.5 mctre,, and thereafter it
rvtrttld nreet rhc rock strrl-acc at slope nrf 45o'
Length and height of trajectorY
Assumirtg a depth of 2.5 m in the bucket invert
vclocitY - 45'l
'r/scc
8500 n
DePth : #I
:' 2'52 nr hence okaY
V2 sirr 2d
x : k
v 'rrrr 'y rvltcrc k is a constallt rr'lriclr acc(r-
urrts for air resistance : 0-95 approximately'
0,95 x 45.1x45.1-sin '60 : 170 metre
x: ---{Er-
-l'he skijurnp will rise to height
y - k Yt' ,i,,? # :. rt *;
'j;:i x (t/'+)
_ o.ss x +1' t_I +r t
. BX9'BI
: 2*.8 sa1' 25 metre
Pressures on bucket
'T[e maximum pressure on t[c bucket (ot t]re invert)
is given by' Gumenesky's formtria ("qt' 3'16)'
- /v! rr.,
Design head ho : (;
"
* t
: [4s.rx49.1 +t z.i;
9.BIx23 ''') -,-
: 10.0 x 2.5
25.1r m o[ rvater i.e- 25.0 tisq m
By Balloffet's forrtrtla'
V2 ( rR-h:)
L1 :n*trlt-t?) l (l'nr
: 2.5 + !,#+ {,_ (%+)1

30. DESIGN N,XAIvIPLE 589
: 2-I + lo3 (l-0.797) : 2.5 + 103 x 0.203
o r) + 2l - 23.5 m rrf lvater
L.
. The bucket shall be designed for a pressure of 25 nr head of
rr'at er.
The h1'draulic design of spillrrzy is shorsn in figure 13.2+.
Design F.xample 13.2
Evaheation of Dl.aamic Force oa the Spillrt'ay
Find orrt the d1'namic force on the curved portion of rhe
spillrvav buckct, from thc buckct cntrance to btrcket invert
(Rei 6gurc 13.24).
*
- Solution
t'''- Discharge intensity : Ii4 cumec/m
, _., _Applying
Bernoullis theorem on u.s. and the bucket entrance
( (Section l) and bucket invert (Section 2), lt'e get,
i 16.5 : 8.65 * dr cos 5l.Io Vr!
' Yi {i)
+ Tg:ot= rr ('
But 71 dt : 114 : V, dz
Substituting for r, :
f ^"a
rr: lf i" equation . (i)
rve have
i16.5:8.65*dr.0.6225 r 111
lll-4
r + rs^ozar" ano
I ll-rz 1 l/-
- 116-5: C '
r't'!rr?
..:
Solving by trial, lr'e geE
: r' dt:2.5rnand dz:2.4m
Vr : 45-7 m/sec /z : 47.5 m/sec
Let F, and F, be the componetrts of forces of u'ater on surr,'ed
.section I-2 and Fr and Fr be the hydrostatic force at rhe
rcspectiYe sections (FiS. 13.25)
Pl : *xIx2.5'xcos5l.5':6.25x0.31125 - 1.94t.
P2:]xIx2.4t:2.88t
Yeight I of the rvater florving in this section
' : 1 x # X 2; x 23 x 2-+5 - 5o-7 t
I

31. 590
I
C05 Sr-S'-
7r
Fig- l3-25 Dr:ramic Force on
Applying equalions 3.1+ & 3-15,
Pr X 0-6225-P, i- F, : #
or F' : 223.67 'r
S imilarly
Fr : P, sin 60"-W : 11.63 [0
: 529.4 t
Resultant force :
and acts at an angle =
rbla DESTcN pRrtt{crpr,ES
SPILLWAY
SPI LL1iAYS
Spil lrvay
-D efi ni tion sli erch
rve have
(+7.5
-45.7 )< 0.6225)
- (-47.5 sin 60')l
-J/Jt
: 62. ["
J,
P2
I
/w
529.4
I an-l
223.67
OF' SIDE C}IANNEL
Gerreral
The side channei spillrvav is one in which the control rveir
is placed along the side o[ and approximatelv parallel to rhe
upper portion of the spillrvav discharge channel. . Florv over
the crest falls .inro narrorv rrorrgh opposite the rveir, rurns an
approximatelv righr angle and rlrr,n continues inio the main
discharge channel.
Disclrarge characteristics of a side channcl spillwav are
similar to those of an ordinary overflorv spillwav. However,

32. SIDE CHANNEL .SPILLVAY
' .j*::jtn'{jli-:;ll
s9l
for rnaxinrum discharges the side channel fiorv may differ from.
rftat of rhe r'*e'I]oru spirrrvay in that trre flow in the trough
mav be. resrricted, .,roi, pu.ily ,rb;;; ln. or* over the
crest' Then the florv characteristics rvirtr b;
"":::,Lltll.t_
constriction in the chann"r do*nrrream frorn ;.t::i:"#t ?:r:
consrricrion rna' be a point of criricar fl";l; the chann€J, an
orifice control or a conduit or tunnel .florving firll.
rn recenr )'ears some side channer ,pir;;y designs have
been modified to incrrrde a srrort .,r,"ir section prependicurar to
the channer resrrrting in an i r;"p"; .".;:"'iy.ara,,ric moder
studies ha'e demonstrated that trre energy of flow over the
end-section of ul- L lhrped crest is of assist
'',ater
doi'lt tJre side af,onri.l.
vrLJr r': ur dsslStance in rnoving
Crest sholte
The shape of rrre spirlrvay crest is dependenr on the type of
rr'('ir selected, the head, ,nL treight of rveir (which influences
rhe *elocity of approacrr), and the srope .r,rrr"'upstrea.m face.
fn most cases tJre standrid og." rt,eir.can be rrsed.
Sifu channcl dcsign
I)esign by Julian Hind_"
rhar all the energy of the
cha nnel is ."rr.J entirely
in rhe channel, Fig. I3.2d
I
I
method-The b,
'.
,
*':". fi orving ^:l:.ffi:I;lil^;
by the slope of the rvater lr.fr..
shorvs a secrion along ,h" ;;;;;.
€rrgg7
S UEf4 g 1-
CH, NNltt
oF Fo,e^r oN
cui'vr -sror
t2rt!. wlY
Irig. 13.26

33. 5e2 SPI LLl'A'S
linc of a side cltannel spillway. 'fhe rvatcr surlace falls along
sonre curve from thc point B at the trpper cnd of the cl'ranncl
to a point D opposite thc downstream end of tfic crcst. 'flrc
total energy applicd dorvn to point D is equal to that produced
by the
"ntirc
florv falling through the average lor all the
particies.
Iror a frictionless channel, Hindi has shorvn that tbe theore-
tical ordinate of the water surface ctll've, measured dorvnlr'ard
frorn this line BP is given in the equation
,,: ll("ji + u[)a. ( r3.s)
( r3.B)
rllrcre
V
q
a-
o
- average velocity oI rva.ter in t]re direction o[ florv
: inflorv in a unit distance
: i.rrtal florv at point corresPonding to y
(13.6)
found convenient
I f the relatiops of q and V to x are known, equation'can be
integrated. Since inflorv per unit length o[spilhvay crest'for
design purposes is rr5trally uniform and .the toial discharge at
a seition x from the upper end of the crest rvili be given by
thc equation,
Q-: q *
an equation of the exponential t)'Pe rvill be
for exprcsing the veloqity distance relation :
V _-- .xn (lJ.i)
Strbstituting these valucs-for V and Q in cquation (13.5) and
integrating we gct
v- h,,
rr'here ir, : theoretical velocity head
The spillrvay channel
I3.6, i3.7 and I3.B if
qompletely designed bY equations
cross sectional shape and the values
is
its
o[ ,a' and 'n' are chbsbn. The proper choice of these lactors is
controlled by economic corsiderations, for which Hinds has
specifted that for rninimurh excavation,

34. DESIGN PRINCIPLES OF CHUTE SPILLVAY 593
( r 3,s)
Modified Theory of Desiga
, A ncrr ..t oi fcrrmulae irave been given recendy rvhich rake
into consideration the effect that unequal velocity distribution
in the side channel, primari!y due to florv ovcr the end section
o{'an L s}raped spillrvay has on the momenturn. on the slope
of the rtater surfacc and on the cross sectionai area of flow-
If thc_ velocity in a channcl cros.s s.cction is trniform, thc
qv
II{mentunr is { : . Horvever, if the velclciry is not
rrnilorm, the mornentum rtill alrvars be Sreater than that
determined lrom thc mcan velocitl', and rvill be
vhere p: momenttlm corrcction
greater than l-
( I3.lo)
lactor and is airvays
13.9 DF^SIGN PRINCIFLb,S OF C}TUTE SPILLIryAY
Geaeral :
For earth and rockfull dams, or for dams over which ir is
impossible or undesirable to Pass floods (e.g. arch dams), chute
spillrr-avs are adopted.' The spillrrav pro6le may follow ,1"
natural or exCavated earth or rock lormation to convey the
'ater to the river belo'*' the dam. Factors influencing the
selection of chtrtc spillrt'avs arc the s.implicity of their design
and constructiori, their adaptability' to almost anl' fbundation
condition. and the overall econom)'often obtained by the use of
large amounts of spillrvav excavation in rhe dam embankment.
Chute spillu'a,vs ordinarilv consisl of an entrance channel
either srraight or curved in alignment, a control slructure, a
tcrminal structgre, and an outlet channel ({iS. I3.7). If
necessary, the curvature in the florr upstream is confined to tbe
entrance channel, because there the Yelocit)' of approach is
Ior*'" Ihere discharge channel is required to be curved, its
fic,or is sometimes suPereleraf ed to guide the high velociry flow
(*l) r'': *
'{ = I QV
,g
g
)-

35. 594 SPILLWAYS
around the bend, rhus avoiding piling up of florr. toryards the
outside of rhe chute. !
The main design considerations rvould b" to. fix the longitr-r-
dinal bed profile of the channel and its section dirnensions. The
eaergy of the flo:rv has ro be suirably dissipared at the outler,
before the florr' enters the dorynsrream channel-
Crest
Tbe qlee pro6le for lorv'rr'eir as recommended by U.S.1V.E.S.
conforins to the follorving equarions..for different rarios o[
h.IFIa,
Value of
h"/Hd
Applicable P/H6
rangc
Equation of the
dorvnstream profile
0
., 0-08
0-12
> 1.0
r.0-0.57
0-57
-0.30
xl'a : I,852 }fa.o ;s ,
x}-zs == 1.869 IIa o-z:
,
xl-?r; : 1.905 Ho o.zr;,
j -- r.' i :l'. ' ;:
TEC c'oo-rdinateS of
of h"/II3 are given on
**,rg: in a 45" slope
iir" Lprt.".* profiie for differeiit
next page. The profile upstream
(Fig. 13.27).
vilues
should
T-
.l
1I
a
I
lg
1
urzfR rrlrrt
64iqp.tt+t/7ft
-
D.s
Pr€rtt
oProtN q
2^ o-45 l
{iu.s.
PFv/tt
.l
Fig, 13.27 Lorv Ogee Crests.geometry

36. r arR:-;-LLl&!
CHUTE SPILLYAY
XiH,
hn
il:
s95
..,..,..---
0.t2
I
0.00 0.08
flHa
- 0.000
-u.020
-0.060
-0. t 00
*-0,120
- 0. 1+(l
-0.ts0
-0.t60
-o.i;:;
- 0.1 90
- 0.t 95
- 0.200
0.00.00
10.0004
I
0.0.36
0.0103
0.0150
0.0207
0.0239
0.0275
0.03.33
0.0399"
0.0424
0.04s0
0.0000
0.000+
0.0035
0.0t0I
0.0147
0.0203
0.0235
0.0270
0.0328
0.039s
0.0420
_----
0.0000
0.0004
0.003s
0.0099
0.0t4.1
0.01e{)
0.0231
0.0265
0.0323
0.0390
The toe crrrve radius equal to 2Ha may be provided.
Longitudiual stope aud control section
The aim of the design is to provide the most economical
Iavour lor r'e ch*te. The srope in the iniriar .;^;;;';h""rd
preferably be more than critical, so ,tru, ,t. .hannel does not
afTecr rlre rliscrrarging characteris.tics of rhe crest and tlre
conrrol sectirrn should rernain at t]re ...rr. .-
The side slrrpes have to be verrical at the crest rvhere gates
rt'orrld bc pr.vided for controiling reservoir levcrs. In uncont-
r,lled crests, r,rrtical sides rvill .ot be
'ecessary. Downstream
ol-tlre cresr, ,h: steepesr lslopes permissible in the formations
ma)' be adopr ed to minimise .,r,iing. iiri;,,rj';;;";;: *
kept in mind rh:r. the slope s'o,lJ be such ,h;r-;;;;;;;;;
()ccur' Berms and drains may be provided ro contror sriding
damage. ,
----vvu ru
Hydraulics of d.ischarge carrier
' Discharge generaily passes through rrre critical stage in the
spillrr'a' control srructure and enters the discharge channer as

37. s96 SPILL}'AYS
srrpercritical florr'. To avuid a ltl,draulic junrp l-ornration
irelqrv tlrc cre.st the fios'mtrst remarn at the sirpercritical stage
tlrroughout tlrc Icngth of charrncl. The flotr" in the channel
nray be rrrrifnrm or ir may be accelerat ed or deceleraterl,
depending on the 5llrpcs and dimensions of cirannel and
on the total drnp. Fl,,u' at any poinr along t]re.channel rvill
drpend iri>on tlic spccific energy (d X Ir,1) at the p4rricular
point. This energ), is equal to the drop in heaci fr,,m upstrcam
rr';rter lcvcl to thc fioor of the channel at tlre point minus the
lr,';rd lrrsscs- I"or tlt:tcrlrrirtirrg dcllths ,rl' [io',v irr a c()n('!'r.tc
lirrcd t'lrinnel a valrrt' ol' N ol'about U.016 ro 0.UIlt rrr;rr bc
asstrmed t() ar.coilllt lrrr air srvellt vave action etc. l'or
dctermining sllccific crtergl' of flow needed for d"signirrg the
tlissipating <levices, a valr.re of N of :rbour 0.00{J to 0.01 irrav
Irc assumcd.
P rofile
Sharp convex and concavc vertical curves shoulcl be avoitled
to prevent unsatislactory flow in the channel. Convex curvcs
shotrid have a sufEcientll'long radius of curvature ro mininrise
rlre dynamic forces on thc floor brought about by tlre..n,r,f,,-
gal forccs u'iiich restrlt from a b,hange in' the direction of fltlrv.
To.avoid the tendcncy.[or .
rhS warer to spring avay from rlre
llrro.r and tlicreby reducc thc surface contacc pressure, rhe floor
slrapc for.convc crrrvature should be made substantialll'flatrer
tlran the trajectory of lfree-discharging jer issuing, under a
lrcad cqual tt> the specilic encrgy of che fl,olv. as.it enters the
cirrve; The crrrvature should approximate to the parab,llic
s)rape as giyen lrv eqrratiqn l3.i I
o
4
(i3.1 r)
.)':=-xtanO- k [4(d*h,)cos?0y]
rr'here,
'6 * Slopi: lnglc of thc floor.Lrpsrream
k': I.5
For the concare curvatrlre, in .no case radius of itrn'ature
slrould be less than l0 d (d being depth of rvarer in'm).
Convergence and divergence
A fiare or rvidenirrg at thc extreme lorver end is sometimes
providcd .to reduce the endrgy pcr' unir lengih of the ryarer
(

38. CHUTE SPILLVAY .597
ent'ering :r. stillirg basi,. 'l'hc rnaxi,runr pcrmissibre sicre wart
divergence is 1 in 3 F (F is Froud" N.,,j, if cross r+.aves of
exceqsive hcight are lo bc avoicled,
Free Board, l
The following expression giv-es a reasonabre incrication of
desirablc free board, for tLe side training rvalrs of the .rrrl..--
Frtcboard:0-61 + 0.04 x Vdr,3 ( r3. t2)
)
rt'llerc, v and d arc mean verociry and cicprh in rhc chure
rEach under consideration in rn/sec and metre rqipecrively.
Corctruction dctails
(i) Foundations : The chute channel floor can b, .oo-
srructed on any r1'pe of foundations provided pr";., ;; i,
' exercised. In
-
case of good rock, ,ro tr"ut.r,"r,i i, necessary,
except some lined' section just downstream of the crest.
. Ih
weathered rocks or l'ose material the lining of the chute
section becomes obligarory; s.ch formations should not settle
much under loads; orherrvise lining rvill .be d"T."S:d-
. ...,
rhickness **"iit
given varics from I0 cm ro 75 crn rvirir 38 cm as an
""*^g;-
This applies als, to rhe srope paving if used at the sides of rhe
spillrvar'. The slope liningrgl")' be rhinner at rhe rop tban at
tl:e bottonr of the slopc
(iii) Reinfo-rcemenr and. paners : Abour 0.25 p.c. rein-
forcernent each l'ay in the top of the sl;rb is th" general
pracrice, Thc amount sh6uld be sulEcienr to avoid.s"pi.r.tion
if a crack occurs- In case conrraction joints are not given,
then 0-5 to 0.6 p.c reinforcemen! of hilh elasric Iimil sreei
rvith concrere of about 2c0 kg/cm3 srrcngth mav be provided-
f'o avoid cracking the concrcie should
panels u'irh ronrraction joir,ts on all sides.
l5 rn rvit]r 9 m as average have becrr used.
(ir) ioints The tr-pe o[ conrraction joinrs on ail sides of
rhe panels. varics..r*ith. rhe conditions
"t rhe site- There
be poured in sq-
Dirnensioru 6 ro

39. 598
SPILLYA}'S
should be no heaving or sertlement of the found.ation normal
to the direction of flow, r-,rherwise water can seep through and
cause uplifc.
Joint fi!lers capable of expansion and..contraction.rnust be
provided in all joints. Thev mu-st be strong enough not to br:
puiled out of the joint by the high verocity florv. Nletar or
rubber sealing ma)- be used to make the joinis rvarer tighr.
(') c"t'oft Three t)?es of cut-offs are necessary in chute
spiilrtay,s
(") A cut ofl at the upper end ro prevenr entrance o[ head
r'ater pressure ro the underside of the lining-
(b) In the absence of stilling basin'a curoffar the d.oyn-
stream end of the paving, consisting of a concrere filred bench,
to prcverir undrr cutting of the lining.
(c) Expansion and conrraction due ro changes in rempera-
ture tend ro make rhe concrete paving paders creep, ir b,ritr
on slopes- rjnder;uch conditions. a cut-off ar rhe .rp.,r"u,*
end- of '
each panel is necssarv ro prevent such movement as
u'eII as.to prevent florv from one paner to another along the
underside of the lining- This is absolutely necessary rvhen the
lining res* on gravei- A trlpicar cut-offis shorun in fig. 13.28.
>rn ;rP.airr.otJ JEltf7 ,rtl2'2
€mo
+4r<__j_
50o
I lrPX.Ll
l. ,ttzr 1
i+e:trur4.s2.*.*.
r-F--
'/
.'--- -J ,
+U.ooF 4oo-+{r*l loo
Y:l-r-t, 'l)
.3*aval
fyprc:tt
lul orF
Frg- I3.28
("i) Drainagc A drainage svstem is necesssarv rrnder the
lining ro prevenr up)ift,from grdund water.or.rvatbr ,;;-;;;
its rvay through the paving during operation o[ the spiilrvay.
The s1'rtem'usually cortsi:ts of gravel fillecl trerrcles u.<ler the
l<ow

40. -*z-;l.b'i.Ll i'l
H}'DR.4,ULIC DESIGN OF CHUTE, SPILLWAY 599,
paving with bpen tiie drain embeded in tlie
rocks or previous foundarioh may be provided
gr.r.vel under the entire Iining.
(;ii) Anc^orogts Anchorages are sometimes provided by
gr()uting anchorrods in the foundation a.nd embeding these
in rhe lining.
r r'pica) hydrauric design of chute spirrrvay is given in
para io follorv
'*i.'
I3.IO Iil'DRAULIC DESIGN OF CHUTE SPILL'WAY
Desiga Exanrple I3.3
Design chute spillrr.ay, rvirh the follorving data :
l. Height of bpillrvay crest from stream becl
2. Spillu;a1, cresr elevation
3. I)esign flood
+. No. of spans and clear span rvidrh
5. No. of piers and their thickness
G. l)orynsrream r,ater level lor 4000
7 . Irlanning,s rugosity .oaffi.ient for
of discharge carrier. i
D esign
,. A1>proaclr Channel and IJeacl O*.r.r Crcst
Assurning ;r coeflrcient .f discrrarge eqrrar ro 2.r7, head over
crest is given I:r, the relation (e : C.L'H.r/)
rv | +ouo 2/3
r;ro' :(so;zizl : (36'B)2ra : I l'2 m
Ievel : 500.0 + ll.2 : 511.2 m
: 500.0 - 6,0 : 494.0 m
:511.2-494.0 : 17.Zm
gravel. .poor
with a layer of
)
6m
500.0 m
4000 rn!/sec.
4. each .12.5. rn
rvide
'3 piErs each
'
3 m thick
cunrec 402.0 m
dusign
O.OI B
Hence upstrealn ,ater
River bed level
Hence 1,arer deprh

41. 600 SPILL!VA)'S
: [2.2 rn
. N2V2L 0.0lBz x 3.061x I50
l)r:--- :
-:
"t R.r/r l2:2r.u
Crest Elevation : 500.0 m
Upstream T.E.L; :
:o:.:
+ I1.2 + o.+77 - 0.016
: 5[ 1.66 m
He-:ace head over crest (including ireati due rtr velocitv of
approach)
= 5l I.66 - 500.0 : I 1.66 m
P 6 I"a 0.+77
_:
Ha I r.66
: 0.515 and^-ii : ;i;u : 0.0*l
Hence corrcct coefficiertt o[ discharge,'afl,er taking into
account effect of differcnt parameters (with thg 2!5rrrnption
rhat downstream apron'clevation is maintained such that ir
- 2.1 i x t.Ol (use of Fig. 13.15 to 13.19)
. : 2..13
Assumilg Kp : 0.01 and Ka ='0.1
Etreltive rengtrr:
l[:i [i'':'r.f, TiI; r r 66
. : 50-23-32x0.13 :50-'3.02
: +6.g8 say .17 m .
Assuming I : I side slope of the excavatcd approach
channel, area of approach channel.
: (50+9+17.2) 17.2 : 76.? x 17.2 : I3l0 sq.nr
/elocitl' <,[ approacli : ffi : 3.06 m/scc
Verocit;' rread :
H
: t;z*uT : e.477 nt
Assume lcngrh o['approach channel as 150 rnetre ; h,vdr:ru'
lir: rnean tiepth .. ll : AIP :
l3l0 .1310
.::
59 +48.6 107.t
I;r'iction Iruad lost upto' the spillrvay crest is givelr l.l,v
l"lanning's llrntula. viz,
0.032^1x1-1.03
27.8
0.0162 m

42. o
HYDRAULIC DESIGN OF CHUTE, SPILLVAY
Hence discharge capacitv of spillw.ay c.resr
- 2.13 x 4? >: lt.66a,r
: 100.3 x 39.8 ="S9g2 : *000 cumsc
This r.ilrrt, is :rr:ce1rted.
Design of crest profiIe
+r '?s : l.869H4o.;sy: l.g6g X tt.g[,o.;s,
: lt.By or y:Tl':
I t.B
x (ru)
Doutnslrcant ocst prof t"
Since haiha lies berryeen 0 and_0,0g and p/Ha is about 0 S,
1re use. the fouorving equation for
""^too,irg coordinares x
and 1' for rhe dorvnslream profilc.
60r
y(m)
)' (nr) x (m)
0
0.5
l0
2.0
5.0
6.0
8.0
0
0.025
0.085
0.280
l.4t7
I.930
3.220
10.0
t2.0
14.0
r 6.0
lB.0
20.0
+.75
6.00 .
8.75
' I 1.00
t3.s7
I6,IO
IJprtream, profiIe
Ff, - ll.66m
No. x/H, y lHo x (m)
.v(m)
I
I
2
J
+
5
6
7
(')
o
1l
l0
lt
-0.009
- 0.020
-0.060
- 0.1 00
- 0.1 20
- 0. r+0
-0.150
- 0.1 60
-0.t75
- 0.1 90
-0. t96
0.qoo0
0.000+
0.0035
0.0t0t
0.0t47
0.0203
0.0235
0.0270.
0.032tJ
0.0395
0.Gl20
-0.000
- 0.233
-0.700
: r,166
- 1.400
- 1.630
- 1.750
- l:865
-- 2.040
-2.2t5
-2.275
.0.0000
0.w7
0.0+oB
0. I lBo
0.17t5
4.?370
0.27+D
. 0.3t50':
0.3820
0.*600
0.4900
l+
---?

43. 502 S PI LLIVAYS
elevation
For this
depth
Positior of th9 downstream. apron level
It was mentioned earlier that the apron is at an
such that it docs' n<.,t affect coe{Ecient of discharge.
condition,
ha-Fd
tr>r'7
or ha * d : 1.7 X Ha: 1.7 :< 11.66: l9.B m
llence apron elevation : 5l1.66 - l9.B : 491.86
Discharge intensitv dorvnsiream of spiilrvay pibrs
4000 .1000
: F_ : '";; : 68 m3/sec
s0+9 59
relocity dowrutream : (68id) m/sec if d is $'ater
d * --u=u'= =, : i9:B
' d2x2x9.Bl
or 6r .; 235 : I9.B d3
B.V rrial and error, d : 3.87 nr
Profile of Upf,e. i'Iappe
No. x/Ha Yl}l^a x(m) y(m)
l.
2.
J.
d,
5.
6.
7.
B.
9.
I0.
- 1.0
-0-6
- 0.2
- 0.0
+ 0.2
+ 0.!j
+ l.u
rl.)
+ 1.6
-1- l.o
-0.950
0.930
- 0.925
-0.779
- 0.65 t
- 0.*25
-0.t2t
+ 0.067
+ 0.521
+ o.779
- r r.66
7.00
- 2:34
- 0.00
J 9'-1,t
| 5.v .
+ 7.00
+ I 1.66
+ t+.00
+ 18.70
+ 21.00
: I 1.10
- 10.80
. i ,"-10.80
s-1'0
7.50
+.95
t.+ t
0.78
0.61
0.91
J-
I
I
T
Deeigu of Discharge
.
The florv at the toe
Critica.l depth : ,J*
Carrier
of spillrvay shotrld be strpercritical,
^ [Emu-
:'_1 t-:7.8m
! s.BI

44. 'E:F&ilsisinpf,/a
:
o
I{YDRAULIC DESIGN OF CHUTN, SPILLhI.,Y 603
The depth at the toe of spi[way is 3.c7 nr and hence is
strpercritical depth..
lVith a vierv that the flow at trre toe may renrain supercriti_
cal for certain distance at leasq ttr" ,top. of rhe discharge
carrier should be more than tlie critical.
Critical velo ' 68
crty - zE-
: 8.72 m/sec
D 59x7.8 59x7.8
* 't:5E:p13-*: tr -6-i5m
Critical slope : I'){t :
]{{r!
0.018'+8.72 v.B.7Z
(6' l5;"'
Dcaign of curve uo. I
_ l0-rxq.24x76 I
r I.2 455
t sl,pe of 1l2o is provided in 20. metre distance. Bucket
radius at roe :2}fa : 2Xll.66 :23.32*y ZS.S *
Bed Ievel at the beginning of
'l/200
slope _ 491.86_0.1
T.E.L- : Sil.66_0.1 _i5Ir.55 *
: n" '76 m say 491'75 m
The calculations of r*ater depth etc.'are shorvn in Table I3.3.
The energy slope is found from Manning'r-ro.*ut^.- i;.';;;
slope and elevations are i,.k"., from rhe most economical
Iongiiudinai profire a.,u.*i'J ;;';I,.
";"r,,
of actuar site
.contours
The rvater depth and velocity. of florv in the beginning are
taken same as at the toe of .spillway
"r,tr*.. ryould not be
mtrch change in 20 m distan.".
'
C.rrrr"* .,,rr.,, s]rould be flat
.cnough ro nraintain posirive pressures and ro avoid ,"rl";.y
of separation of flow from th" flo*- c;;;r. curves shourd
hat'e 'sufficiently
Iong radius or .r.ru,*"--r" minimise rhe
dynamic forc"=. o' in"-n;;l.",rght aboirr b1, the centrifrrgai
force resulting drre to change ol. direction of flory.
I
Juncriorr of I
tan0-
in 200
I
I.
200 '^
and
(couver)
I in B slupe
: I-5, d : 3.87 m, hv: 15.75 m

45. SPILL.'AYS
60+
:aEI3.qEq5t
Jocr'ta.-+r-.ic';
=.=.5ooa€Xr:
i.orrr6rrt6ti:=+'+
ta4ar-flE'?=
q1 q .'? (o. ri
=gB8;6EAE
if)lr).r),116!(.q.'i'?
ro(O@O'CO
1+r-t'ccv
&&lcl.i(rlrcr<:
Ecto--6r
;';;'=dddd
=
EE3s=E3E
-Hbirotrie!:--
,r; + ; c.i 6.i c'i $r c{ or
6r'fo@c)c't=
.d.o€FccAcc.tt:
co (t:t $a 6l
EESBEEq?.q
e.rcodqjr-r-aCcD.C
ll=
iE
rl
I'l=
eI .
L la
-) l-
6rl
ZV
II
a
tt) rtt rO v1 .n !O rr) r.t I
r-r-rr-r-rtr-a:
rs c.
g)EcCto"fF)c{C
.(r + + .f + 'f '+ f.'f
O(f,ooO.O"qC ;
u1 OOOseu
=i?6t5rcr€
cc@oorlor)=-
6 ce i6'-.. - to.
d-6t{,r;L?rltr
uorlu^al.l l-
tuouofi
I "
+ooo++t5'n'
r-- co ct{ r cl ci't e. r: r-.
SsduuEsUs
o16OOoqqco.
I s s e d's I = =
ot ol
p?B3S8ceq
dR*si-638
qeas.qP?=e
=R*EsJEBS
sees.qaq=E
d c.t c.; ol ot
;'
o ???????51
Pua eqr ru
p3rEInflEf,
sr, "l'g'.L
(C ler
c.l l-o
cvl
cf)
ll
frt
?l
= *lx
,* 3l*
lq
q) lo,
lla
I
aI
(-l.
od (,
L
c)
riI?,
r;,('
,:$=
al-
!r
ot : €l!
F{
=
tol
-2r
t-
ll
-:
C q.)
?n=
o-
CJ
Acc d
r.O
9o
ct rr
.u
O
qJ
c
I
(o
ll
'^
o
v)t
'l=
G!
'l-
pz+6s:.tl-l*
.Iatawt.t54
l*l'
P6S:"IEi;
Ea-rv I l. I
cll
3l*
-lEI
,1 frlrolrn
I
rpdag E
l-
E
l*
qrBua-I
'oN'ts

46. IilDRAULiC DESIGN OF
x
' tr
-
I
'200,
CHUTE SPILL1VAY
.2'
605
I
+ t@lc;m
Since tan I is small, cost ,B rvill be nearly unity
1.5 [+ (3.87
, _ x , xt
,-ld-oTre-2:
This curve rvill meer ih" do*r.rstream
di- I , x I.
c_x 200 ,59 -T
x.xl
loo - JtB-
slope rvhere (dy/dx) :
T x:5e(#-#) :5e(T#) :rya
T]re coc,rdinare.s of the profile Are
5,
: 7.1 rn
7.t
.,
I
x :'0.
)':0,
I, J,
0.0i 35, 0.09 t5. 0.2375, 0.4655
Curve no. 2 (coaver)
.,
rhn.e
= ], k: I.5, .d
- 3.1.m, 'hv _ 24.5jno
xxl
1'
-
I
'B -6TJ+f4E cor,0;cos0ry I.
: j -L' x'
I ' 165
It meers rhe dorr.nstream slope of *
t}..l,xr.
dN I , 82.5 -T
xc
or --:---: J 5x82.5
82 -s- x : :--E- : 30.9 m
o
T'e coordinares of the profire can be found frorn the, eguation
X1!
t.
-
I "
I
-
' B ' 165'
m
rn
n1
X:0
)'-0
t-
r5
m
l0
rn
20 '30.9':
0.13i 0.776 1.857 .
4.g2
.
9.66

47. .
606 SPILL'AY.S
Design of curve No.3 (goncave)
Junction of I in 2 slopc and I in 4 slope
{inimum radius : l0)(d = 10x2.0? : 20.2'sar'20 rn
Design of Euerg'y Dissipator
Since foundation rocks are srratified. a stilling basin of
U.S.B.R. t)?e III rvorrld be provided
. yr : I.B7 m
r : 36.4 m/sec
tr- : 3.5
rl ,_
Hence yr : f fVf+Orf - i) - 0.935 t, t+o *m- tl
: 0.935 (2+-l) : 21.4 rn
Since the tail water fluctiratioru affecr the jump !'er.v much
at such a high Irroude number, the water depth in the srilling
basin should be 5or/" rnore than the calculated conjugate depth.
Hence required r'|ater deprh : i.05x2I.5 = 22.5 ril
Requirtd basin level : 402 .0-22.3: 379.5 m
Since the.stilling basin should be designed for N : 0.008,
. hence ihe stilling basin is approxirnately checked for this also
for N.:0.008;),r : 1.6 m, velocity: (68/1.6): *2.5 m/sec.
Froude number : ;frfu : H : to.7s
)'z : 0.8[ / t3+8 xffi- l] : ,o:8 [30.+- I]
: 0.8 x29.4 - 23.5 rn
Required basin floor level -: 402.0-23.5 :378.5 m
Hence stilling basin elevation is 378.5 m.
Since. Froude numbei is 10.75; iength of jump : 4.3 x :-:
:1 1-t-t!.! - tot m
Churte Blocks
L'J '
:'
Height : rvidtlr : spicitlg : 1;, : I-il7 rrr
Height : 0.2t'.21-5 = {.3 rn

48. .*ad'jli
,t
.
DESIGI{ OF SIPHON SPILL^IAY
Spacing of dents and reeth : ,0.15x23.5 : 3.225 m
Dotvnstreamslope: l: I
Top tlrickness : 0.02 X ).g : 0.43 m
The c)rute derails are shorvn in figtrre I3.2g
607
Structural design
Thickness of lining : 0.5 merre
slabs dime'sions-central trvo srabs each g.5 m rvide an,
tvo on each side l0 m wide
Reinfor.cer.nent 0.25 p.c. each rvav rvill be given.
I3.1T DESIGN PRINCIELES OF SYPHON SPILLWAY
General
A s1'plron spirrrvay is a crqsed conduir sysrem rormed in trre
shape of an in'r"rrld. u, positioned ,o ihu, the inside of the
bend of rhe upper passage *ry i, ut ,rorrrruf
levet- Tle iniii"r iir.i.i.g"r'or rrre spilrrun),,
tXt
;:ljrl;T"l:
Ievel rises above .,o.-.rl ... simiiar ro'flory over a weir.
s-vphonic action takes pr.." afier the air in the bend over
rhe crest has been exhausted. Continuous florv is maintained
by rhe sucrion effect due ro rhe gravitl' pu, of the water in
the lorver Ieg of rhe s1,phon.
Types of syph on
As generaily crassified, rhq syphon spirrrval.s are or-either :
(r) Hooded or saddle !)pe, (FiS. 13.3)
(1,) Circrrlar or /olute siplron (Irig. I3.30)
saddb siphon: I,. crosely resembres an inverted u-tube
rrirh one of irs Iegs longer ,h^r, the other
The discharge is controlled by the dimensions at rhe rhroat,
and rhc pr*sure condirions there. Thc pressure head at the
rhroat section is berow the atmospheric pressure by the extent
.f tlre'eloci11, ]read at trre section. It *,orrrtr th.s be crear that
if rhe r'-xit end vere ,or*er by about t0.35m u.ioru the reservoir
surface. the average absorrite pressure ar ti:e trrroat section
rvould ra, ro zero and rrre extreme trreoreticar Iimit rvourd
.i
I

49. Ia
t
?
I
q
<:l
'rt
in
a
.J
lJ
L
-1
F
U
YI
i
a
I
;l/t
il
l
t
I
:
I
t.
!t
t It
rr ul
tt
r$t
r!i
o
-l
1
1.
.l'
Jr
t
$
t
q
t
tl
I
..{.
n
L
?
q
.x
o!I.
-
l ll"
,r
)
ll
I
(lo
L
t
ix
rq
qie
t
t
t
I
u
fi
t
t
L
t
Gl
al
(f)
.:o
-ra
----
I
r)
t'
{
t
I
t
o
qo
lrr
.lr",
a
-q
rP,
i
!
o
qr
rt
1
a
I
?l
t
:"
i x
l'
I
g
I
{
11
n1
t
lJ
d
I
(
t
q
i
s
t
o
I
t
t
o
!
lr
,{
i'
t
t,
r
.T
t
ir
J.
ii
r_
.r
*.
o
q
I
)

50. DESIGN OF SiPHON SPILLWAY
If h" be the net operative
allorrances for ali Iorses eic.
head. at crown, after malcing
609
r1
OF,UI,JUL
+
vaLUrE -slPttoN
Fig.' i3.30
have reached. The practical limic o[ vacuum ro avoid
cavitation at the throat is equal to rhe atmospheric pressure
minus the vapour. presiure of water i.e. maximum h.g"tiv.
head ot' about 7.63 m, which is alrowed ai the crest.-'The
discharge interuity for a given maximum operative negarive
, to the larvs o[ frec vortex motion, is found as below.
If Vr and /2be the velocities of the florv at the crest and,
crol'n, then we have, frorn equation of continuity
i:' /rRr : VzRz : V:.
(/ is the v'elociry along the florv line having radius r)
Hence discharge rhrough. a rhin 'srrip of radius r and
thickness dr. (Assuming a unit lcngrh of rhe siphon)
:'rnrt r
,/[-h"
DOrrt
Dt, ilp, rP
(
a.
l:
e
{
c
q(
o
E
-l'ourt,7
ou7E4 SffELL
r,. :

51. 610
Integrating bct'rveen the Iirnits ol r as
q : ,/ET" R1 In (R3/R1)
for h,, = 7.63 m (safe head)
9 : 12.2 Ri In (Re/Ri)
In calculating the net operative head
't1r
SPILLVAY.S
:
Rr and R1 tve llave
h,, allorvance should
trt R2
trig. 13.31
'/Tfi,R, +
,r: ) Lo rr'er I t iri i;
//, ,Nt ,7 0 4
OfpFttL
or ir.g i i Loir-er i:tnd {.s) Utrtir.-t
xooo
LtP :-f'
tN tar @ _-tr-
'. ivou7i
.ata { 2 v?t4
LowrP llYA O." lae
tE na
F.tprs of a -l.Do/l ,t,D//o^,
Fig. I3.32
Eooy wtt.t
oF.o) r,,
TlrL w/TER
tro / '

52. -iicll;llS!6,r-:
6I1
(h) Deprimers (i) Body'rvalr ( j) lvater cistern (k) Tra.rh
racks (l) Tudels or off3ets, and- (*) prorecriv. *oikr.
l - Inlct mouth
The inler should have a minimrrm diameter lI D rvhere D
is the diameter at rhe siphon throat.
2. uppcr lip ;
t Th" lip to the hood ar the inlet is best.kept rotrnd,ed so as
to offer Ieast obstruction to florv.
3. Tlsoat i
The cresr of rhe trrroat shourd ha,e as Iarge a radius as
possible. This can be done by giving a lip.
1 Crcst and croutn
Tlt e r",'"t sJr.,.!rJ,l I. . -,^
DESIGN OF SIPHON SPILLWAY
:..,,.. .!. ;.,.r ." ;_-.,
Lii.f-ii ;i riJij-;i.iliiii,,.. .-iii,..,..
times the sides are flared just beyorri the cresr for
distance and again converg.j,., normal section.
)
a short
(;. I-owcr bcnd i
slrarp bend is advantageous rr,Sere vater sear is affected, in
the dorr'rutream or -rorver limb of the siphon to prevent air
getting locked up. If the varer seal is affected outside t'e
lower leg in separate cistern, a smoorh bend is desirabre as it
tsill minimise trrrbulence in the cistern.
7.. Thc outlet
Gr.nerally a separate
disclrarges into the air or
outlet is provided. The outier
into lYater cistern.
I

53. 6t2 SPILLWAYS
B. Dcprimcrs
They arc bcst extended uPto the crown rvltcrc tlte air can
be let in. They should be ail on one side of t1e siphorl only,
facing .the reservoir trPstream' They have, to b.t.9"ard.ed
,grinrt being chockcd by floating debris .by providing rvire
nrcsh all round its morrrh. An arrangement to damp tlre
action of waves will bc necessary to prevent the sealing olT of
the deprimer mouth rvhiie the'siphon is depriming'
9. Bo$t wall
The design of rhe body rvall has to be of necessary section
r*'ithstand water Pressure and vibrations'
10. Watcr Cislun
This is necessary in the tlpe of siphon where the water seal
is'affected at tfie end of downstream'Ieg. It is bqtter to kcelr
the initial water ievel'in the cistern a few cm lower than the
orrilet end'.of the doivnstream leg, so that the air which is
evacuated. belore priming can have free access for escape' It
is better-to build a'toe !^Iali to the' desired. height so that a.
rt,ater cushion of thc required depth is always ensured.
I I. Trash racks
These tvitl be necessary. if the inlet mouth has not becn
taken suffi.ciently deep below the F.R.L-
12. Tudcls or of'scts
.These are given (FiS. 13.33) on the wall in the dorvnstream
Ieg to throw the discharge on to the outer. covering and thus
create a water seal. The offset should not be larger than is
just sufficient to throw off all the rvater hugging over the
surface of the bodY.
13. Protccliac works
Ine energy oldischarge shooting from the dorvnstream leg
of a siphgrl can be dissipated in'any of the foliorving wa)'s:
(^) By adding an inclined outlei dorvnstream
lbl
By forming a vater cushion or stilling basin

54. DIiSIGN O}I SI I'I ION SI)I LI.".' 6 l:i
C
TaDaL TyPE sADDLE Stptot
Fis. 13.33
(.) Ilr. creating hydrairlic jump condirions, or
* (d) 81' consrrucring friction hrocks or d,entated siils,
Volute sipbons
/olure siph.on or circular siphon is Morning Grory shaft
spillu'ay co'ered r*ith a hood. It consisrs essentially of a dome
rvith funnel placcd underneath, Ieaving ,.rnur"r spac.e
'alround, wirh a verrical pipe taken dqwn the f.rnnel to pass t-he
discharge rhrough. the dam. The parts are shorvn in ng. ts.so.
Design of circular- br .volute siphous
(/) Dtsign of domc
studies have revealed rhar for'rnaximum coefficient o[
discharge and minimum priming depth
(i) rhe height of dome : * of the' ba*el diameter.
(ii) the vertical lip is kepr equal ro rhe barrel diameter
and is srpported on the four pillars of height equar
to I c.'f barrci diamerer
(iii) rhe optimum area of depriming pipe may il ,rZ
. that of rhe barrel area. : '.
(2) Dcsign of funncl
This is veD- importanr purt and should receive ,careful
attenrion. studies have indicared rh+l the diame'rer of rhe.
top of funnc] slrould nor be less than I.5 times rhe diameter
of barrel.

55. 614 SPITLVAYS
The design of funnel should be such as ro secure a quick
formation of boil at the throat and thus to establi-.h strong
vater seal in order ro have early explusion of air from the
dome- 'arious shapes of funnels have been tried, el[iptical,
circular, parabolic, straight, stepped, slopes conlorming to.
aerated and parrially aerared nappe profiles rr'hich proved
good-
(3) Dcsign o{ barrtl
The juncrion of tire ver.tical pipe r'ith the I'unnel should, be
graduallv taperirig and smooth to preverrr the formation of
air pockets and cddies..
(4) Dtsign oJ bendi
Studies lrave shorvn that priming deptlr is minimum rvirh
sharp bends. rr'hile coefficient of discharge is greater in the case
of eas)' bends. studies reveal that the prirning depth can
also be reduced liy' giving a slight uprvard tilt to the bend.
Ol:servatiorrs also shorv that the negative pressures are greater
in sharp bends than in easv bends. Nfinimunr radius of bend
is t..5 times the barrel diameter.
(5) Dcsign of autlils
The .outler plal's an imporranr part in the design of siphon
as it is not only responsibie to priming ancl- dischaiging
qualities but also to rire dissipation of energy below ir. The
optimu:rr iength of outlet must be sucir ar rvhlch all the
6laments after being deflected ar the bend can rbgain their
straight paih to cause full bore discharge.
F-ncrgI dissipation below siphou apillwayr
i t ma,v consist o[ :
(i) Supporting rlre jer on an ogee pro{rle
. (ii) Submersion of jer .
(iii) Formation of a standing wave
(i") .Fanning out of jets rvith disperser, o.,,1 leclges.

56. :<i-X;;'i-$,.t jj
i,
DIiSIGN OF SHAFT SPILLVAY 6.15
The de*ices such as friction .blocks, and sloping apron used,
for dissiparion of high velocities jets .
below,ipt on
^."
,r"ry
much helpful in reducing the priming ciepth. They help in
forming sranding wave rin front of th* b.,tl.t rvhich aid,s in
easv formation of water seal,
;
13,12 DESIGN PRINCIPLES OF SHAFT SPILL'IYAY
. G eneral characteristics
t
A shaft or glory holc control srructure consists.of a circular
crest, either controlled or uncontrolled, over which warer
flo*'s and drops inro a vertical or inclined. shaft-rvhich finoliy
connects to a ]rorizontal or near horizontal cJosed clischarge
carricr. 'lrere the inlet is funnel shaped, rhis type of ,tr,rctui'"
iscommonl1.knorvnasa.morninggloiyhol"'pitiway.
Crest profile
This is the rnost important structure r'hich affects sub-
stantially the discharge characierisrics of the shafr spillrvay.
The u.s.B-R iras given coordinates to define fhi shape of rr,"
Iorver surface of nappe frorving over an aerated sharp crested
circular u'eir of varjous conditions of p/R, (Fig. IS.3{) rvhich
shorvs elements of nappe shaped profire for circuru, *Lir;
"r"
given in fig. 13.35.
J .
1t7tzt -rr a/ nJ 2zr. t u),t.o *t///f fr.. a/?a.l/r, w.d
Ll_
I -t.
,(
Fig. I3.34

57. 6t6 SPILLWAYS
(
..-/.1, /r.r/.? r.ylPli. ,art / €dcail,?
V{/ I Fal' lYFailrxr A4/t t.
Fig. 13.35
:
Seaign of Conduit
(.) The tunnel diameler rnust be so chosen that at fult
dircirrrge, the combined friction losses and kinetic head are
vrithin the' avaiiable gross-head.
(b) lVith a lgw dam the tunnel diameter should., if possible,
be of such size that it will always,'flow free. lVhen needed
for spillway alone it is usual to design it for B0/o depth at full
discharge. Sometimes the tunnel is used under iestricted
head to-pas, flood during. construction period and in such case
this determines tunnel diameter-
(.) For large spfl!1yay discharges, usually ftrl[ florv is
necessary" In such case, the tulrnel should be proporrioned

58. SHAFT SPILLVAY
such that the pressuic
stages.
(d) oullct rnd hqs ro be 6xed rvirh respccr to rail rvater
level- The main considerarion in. fi..ring rhe invert level at the
outlct cncl is effccrivc L,ss clf crc'g),.,rf fi,>rr. It is also d.ri;^;i;
to keep inverr Ievel of the.tunnel above taii water for irupec-
tion and for avoiding submer.gence of tunnel.
5[?
conditions are developed in the early
. oEcE:ruttttto rtoi)
CONOtflON !. CAr.57 COtrlpOZ
(-,
*-:Ei:qF
L- j:l[ Y'4
"t'i?o^'
.-orrrtcE coNTrt2 ?)Lftr? or 7-.ytr?rorJ
-2,'-PYDRau.n n-.Orr-r-
- --li-}-
-:l -:---.---- :
ii *:
7ra ur?rr .lr ,
B
L
r
h
tJ
I
s
t
t
I
i
i
s
o
Q]
ri
tt
.. I
l
a',
7u., oi ortrEt co,,rypo1.,e.rr4L laorr-.ro))'
cotrollroP 3, FULL P,PT FLOI,V
,rrt C ot rreat, et ft (+ - 4 ), c or.afitot
l>Ot^rt O, CMrrAt ,2O, Oarrra,
-Corr7,ol fr-rlri rto4-
J-
,C
,
o
Dtt ct{.,raa
NATU.qf cF Ftoly ./No otsctrtci.r canpttrr*rrnci
F 1 .t+O,+Ntrte . rStoRy
"rrrrOrV.
Fig. 13.36
i'a
+T= -
t t.rrtr
_a_ r)__,<a_a ^
J1//L|l
iFl- 7r)Hstrrcx 7ur!
Qfi'*o,' or r*<.irtrto, tL,..
,r*rortrrr4,-;
Ftov -N-
corrDtTto$ 2.TUAE q oa/Flc€ €ott.l?ot

59. 6t8
Rtsislal,u,z in conduits and bcnds
SPI LLVAYS
Tlre ratc
formula.'
o[ loss of ]rcad ma}" lle calctrlated b1']Ianning's
t
D*chargc charactcristics
' Tlpicai flot, conditions and discharge characterisrics o[ a
shaft or glory [ole or a drop inler spillrvay are shorvn in 6gure
13.36. Crest ccintrol rvill prevail fo'r heads betrveen the
ordinates of 'a'and'g': orifice or tube c<-:trtrol !'ill goverrr lor
heads betrveen the ordinates of 'g' and 'h'; and tfte spillrtav
conduit rvill florv full for heads above the ordinate of h' Vith
a thange in tlie proPortional size of the different Parts o[ the
giorv hole spiilway, florv cltaracterisrics wil[ var] and the
position oI points 'g' artd 'h' rvill charlge'
V orttx lfornruiion
,_ . r,orte- foirnations lrave been obser(jed in slrafi
r vo t pe"', -;:::':,:"i:"?:"
: rvrrose motion
spillrr'avs. Tlie important is 3' single vorte]
embraces the phole colttmn of 'eter .in tlle spillrvay shafr
and conduir. r vortex of this tvpe is formed rvhen rhe he+d
ovcr (lle crest reac[es a .critical v'4l1te, so tlrat thc discharge,
having risen ro a rflaximum, drops abruptl,v to a much Iorver
fig.,rr". This is dangerous rvhen floods are passing dorvn the
,pill.u"t, as this vortex fOrmation rvilI increas€ Yater level'
Alternatively, snrail internrittent vottices may apPear singlv or'
in pairs. Thev are less easv to control. bur tfteir effect on
cii5charging capacitv is Irot scri()us'
Tlrc singlc v()rtcx call bc avoidcd b-v :
(r) Proportioning the spillrvav st) tlrat thc des'ircd nrexillrunl
disclrarge is reaChed at. a ItCad rvell l>clor'v tl'te "critical" head'
(lr) Bv prer,enting rhe developlrrent of rorational moti'jrr in
rhe follorvir:g rvaYs :
(i) Picrs arc provided to brcak vortex : For uncontrolled
.r.lr,u the pi.,', ,.a made cr['Iesser lreighr as tlte suppression of
--.-t-'..heiglrtkeepsthenappealsofriefromVortex..
"il,T ";':'::H':i";:;il;* *; b" .o,,,,..,.1.a ro di'ide
t lrc ltell-n'rorrtlr n'trli'lttlc,' into (tvrl halves l() f'reveIlt nlass
rotation. ' :