Hydraulic Model Studies of the Overflow Spillway of Bhakra D.'L..111, India SUMMARY

Home , Bhakra Dam

OFFI CE Fil[ COPY UNITED STATES BUREAU OF RECLAMATION DEPARTMENT OF THE INTERIOR HY DRAULI C LABORATORY BUREAU OF RECLAMATION

HYDRAULIC MODEL STUDIES OF TH E OVERFLOW SPILLWAY _.,ij ',, O F B HAKR A DAM, INDIA ' '

Hydraulic Laborator y Report No . Hyd-367

ENGINE ER.ING L ABORATORIES BRANCH

DESIGN AND CONSTRUCTION DIVISION DENVER, COLORADO

Jan 11 : 1 r y 1 !l, l 9 5 3 .

>- CONTENTS

Summary . .. . • • • • • . . . . • . • . . • • • • • • • . • • • • 1 Introduction • • • • • • ...... • • • • • • . . . • • 2 The 1:50 Model • • • • • • • • • • . .. . . • . • • • • • . • • 3 The Investigation . • • . • . . . . • . . • . • • • . • . . . • 4

Tests .on the Overflow Section • • • . • • • . • . • . • • • 4

General performance and pressures . • • • • • • . • • • . 4 Discharge calibration • . . . . . • • . • . • • . • • • . . 4

Tests on the Stilling Basin ...... • . • . . • 5 ,, .. • • • • . • Stilling Basin No. 1 . . • ...... • • • • 5 Stilling Basin No. 2 . • . . • ...... • . • . . 6 Stilling Basin No. 3 . . • . . . • • • • • • . • . . . • 6 UNITED ~TATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION

Design and Construction Division Laboratory Report No. Hyd-367 Engineering Laboratories Branch Hydraulic Laboratory Section Denver, Colorado Compiled by:· E. J. Rusho January 13, -~953 Reviewed and chec·ked by: A. J. Peterka J. N. Bradley

Subject: Hydraulic model studies of the overflow spillway of Bhakra D.'l..111, India SUMMARY

Mcxiel studies were made on the overflow spillway of Bhakra Dam, India, in connection with a redesign of the spillway to provide for -an increase in the discharge capacity. The spillway design mcxiel and studies were performed in the Denver offices of the United States Bureau of Reclamation. A sectional moo.el of the spillway, approxi mately 4 feet wide, was constructed. to a scale of 1:50 and used to study the performance of the spillway in detail.

Tests were run on the spillway shown in Figure 2 for ali ranges of spillway operating conditions. The discharge capacity of the overflow section for the entire head range was determined along with pressure measurements and water surface profiles. These studies showed that the crest shape and general dimensions of the spillway were satisfactory.

Tests on the propose? stilling basin, Basin No. 1, Figure showed 7, satisfactory performance with regard to erosion and. -wave beights, while the jump sweep-out tests indicated. that the tail water could lowered be 9 feet below normal before the jump was swept out of the basin. Two additional stilling basins, Figure 7, were tested which had more volume due to lowering of the upstream floor sections. These basins did not perform as well as the first basin. Baffle piers 20 feet high and an end sill also 20 feet high were tested with Basin No. 3, Figure 16, and they improved the perfonnance of the stilling basin. Their use, however, .cannot be recommended. without qualification of because the severe operating conditions in a structure of this size. The proposed basin, Basin No. 1, Figure 7, was considered most satisfactory-. Basin No. l would, however, provide even better performance if the entire basin, including the curved bucket, were lowered 5 to 10 feet; or, by constructing a downstream river control, the tail water could be raised an equal amount for the 290,000 cfs discharge. The additional depth of wa\er on the apron would provide additional jump stability, lower waves and surges, and a greater margin of safety against jwnp sweep-out at the higher discharges. Motion pictures of the three stilling basins were taken during the tests. A copy of these films is submitted with the report to illustrate, in motion, the action in the stilling basins.

INTRODUCTION

Bhakra Dam is located on the Sutlej River in the eastern section of the State of East Punjab, India, Figure 1. It is under construction by the Punjab Irrigation Department. The dam is a con crete gravity type, about 680 feet high with a maximum reservoir ca pacity of 7,600,000 acre feet. The drainage area upstream from the dam involves 21,950 square miles. The project 'Wi.li provide flood control, hydroelectric power, and irrigation for the whole of the Province of East Punjab and Delhi. The design of Bhakra Dam, prepared in 1949 by the InternatiQnal Engineering Company, Incorporated, was investigated by hydraulic models. 1/ Two spillways were provided for the major flood flows passing the dam--one a centrally located overflow, or main spill way controlled by two drum gates, and the other ·a tunnel spillway con trolled by two radial gates. In addition, 24 river outlets were provided which passed through the main spillway and discharged onto the spillway face. The combined discharge of this system was sufficient to acconmodate the probably ma.xi.mum flood of 400,000 cfs. Under these plans, the upper 5 feet of reservoir storage or surcharge was reserved as a safety factor. In a recent review by the Bhakra Control Board the 5 feet of reservoir surcharge was utilized in routing the flood of 400,000 cfs through the re.servoir. This procedure resulted in reducing the maximum flood to be passed to 290,000 cfs. The reduction of 110,000 cfs in flow made it possible to eliminate the tunnel spillway on the left, provided 'the center overflow spillway was modified to provide for 290,000 cfs. Thus it was necessary that a redesign of the spillway be made. The new spillway design and accompanying hydraulic model studies were.undertaken by the United States Bureau of Reclamation, Denver, Colorado, in an agreement with the Central Water and Power Conmission, India.

1f Hydraulic Model Studies of Bhakra Dain-Colorado A&M College, November 1949.

2 'nle overnov·spillvaJ" as first designed ant tested is ehOND in Figure 2. 'nle over-all width of the.spill~ is 260 feet, and it is dirlded into two sections by- a wall 10 teet wide rmming the length ot the spillway frQR the em of the spilllllV' pier to the domst.1"8811 em ot the stilling basin. The max:iDJID capacit1' or the cwerfiow section is 210,000 crs, ard the crest is controlled by' tour radial gates each 57.5 f'eet in length by' 37.4 ·feet '1fgb. '!be riTer outlets discharging dom the race of the spill'lfq baTe a capacity or 8>,000 cts vbieb results in a maxin111 now tbroagb the. stiJ Jing basin or 290,000 cfs. ·

. Since the outlets -.ere not constructed in the sectional a:xle1, it was necessary vben making stilling basin tests above 210,000 cts to pass the water. which voold ordinarily be discharged through the out lets, over the spillway crest. 'the cwer-:-all quantity of water entering the. stilling basin was therefore correct, the total ·energy- entering the basin was very nearly correct, ant the direction of the now entering the basin vas·correct. fllerefore, the stilling basin st.mies are believed to be as accurate as though tbe outlets bad been axieled ant operated.

'fflE 1:50 111m.

To constnict a :model or the entire spillway an:i adjacent area to a scale sut.ficient to make a detail.ed study of the spillway- and stilling basin would have required special and costly modifications to the laboratory- equipaent. Instead of.this ccnpl.ete JDOdel, it was dec.ideq to build a sectional. IIIDdel which VOllld give just as reliable results for crest an:l stilling basin studies at less cost.

'nle model was constructed in the penaanent laboratory fiume, an:l the upstream walls 111ere raised 4 feet in order to build the model to a scale of 1: 50. 'nle nwae width of 47.6 inches was equiYalent to a prototype spillway width or 198 f~. 'ffms 198 of the total OYer-al.1 width or 26o feet was represe'°nt.ed. Use. or the laboratory .tlune provided not only ·the advantages or a large IIIDdel; but the now in the stilling basin could be observed throogh the glass wa.1..1 on the right side or the flume. '!he maximum now or 1,160 crs per foot or stillir.ag basin width, for 198 feet of width, . was. ... represented by 13.0J crs in the model.

The model as installed in the filllle is shown in Figure 3. 'nle overnow section, made of sheet 11etal, was placed above a steel bulkhead which acted as the upstream face of the dam. The spiD.va;y su.rface am stilling basin sections were made of sheet metal screwed to wooden frames cut to the shape of the spillllaT profile. 'ftrl.s portion of the-model was made of several separate units to facilitate changes in the model. A movable riverbed of gravel averaging about 1/4 inch . . . in

3 diameter was placed downstream from the stilling basin. Water was supplied to the model from the permanent laboratory supply lines con nected to fixed pumps and venturi meters for measuring the discharge. A tailgate was used to control the elevation of the tail water which was read from a scale on a glass manometer connected to a piezometer in the side of the flume. The reservoir elevation was read using a point gage in a stilling-well connected to the side of the head box •

THE INVESTIGATION

Te·sts on the Overflow Section General performance and pressures. Two bays 57.5 feet wide with gates and piers were represented in the model which was one-half the overflow section of the spillway. The maximum discharge was 105,000 cfs for the two bays which was represented by 5.94 cfs in the model. The shape of the overflow section and gates are ·shown in Figure 2. The model was operated at various discharges including the maximum and the appearance of the now was ~bserved. The contractions or the now occurring at the upstream end of the piers was not considered excessive even at the maximum discharge, Figure 4A. The disturbance caused by ·the piers is reflected in the water surface down stream from the crest, Figure 4B. A fin of water, caused by the inter section of the now from the two bays, originated. at the tail of the center pier. At the maximum discharge the fin rose several feet above the face of the spillway, but it was not considered a harmful flow condition. Piers gradually tapered in the downstream dire·ction might help to reduce this fin, but they were not tested.

Pressures and water surface profiles were taken on the over flow section for various conditions of now, Figure 5. The discharges shown in the figure represent the total discharge with four gates operated equally. Pressure variations were small between the various flow conditions except f9r the region upstream-fran the gate. Since the lowest pressure was only J.5 feet of water prototype below atmos pheric, the overflow section was considered satisfactory. The water surface profiles shown in the figure al.so indicate uniform and satis factory now com.itions. Discharge calibration. The overflow section was calibrated with f'ree now over the crest and with the gates at fixed openings. Although the.tests were made using two 57.5-foot radial gates the dis charge capacity curves_, Figure 6, were made by- doubling the model results

4 to obtain the total discharge for the complete spillway with four gates operated. symmetrically. The total head over the crest was J8.50 feet for the maximum discharge of 210,000 cfs which resulted in a coefficient of discharge C of 3.82 in the equation c·l'II _g___ The studies made on . . LJW2" the overfiow section did not show any favorable hydraulic ·conditions, and no modifications to the proposed. design were considered necessary. Tests on the Stilling Basin Stilling Basin No. 1. The stilling basin first-tested in the model had a relatively short horizontal floor 165 feet long at elevation 1095, Figure 7A, and the upstream floor section had a slope of 10:1. In the prototype the stilling basin is divided into two sections, 125 feet wide, by a center wall, but this wall was not used in the sectional model. The performance of the stilling basin was observed for various discharges. The appearance of the flow as seen through the glass wall is shown in Figure 8, for discharges of 200,000 ~ 290,000 cfs. The operation is better illustrated-by the motion pictures ta.ken through the glass panel. At the ma.xi.mum discharge the waves downstream from the basin in the river channel had an amplitude, or maximum variation in water surface, of 8.3 feet, Figure 9. The waves heights were measured and recorded electronically and give an accurate value for the maximum waves in the channel. , The lowering of the tail-water elevation 9 feet below normal for maximum disch~ge caused the jump to sweep out of the basin as shown by the sweep-out curve A in Figure 10. The amount the tail water had to be lowered to·cause sweep-out increased for lower discharges. The perfonnance of the basin with normal tail water was better for all discharges less than 200,000 cfs than for discharges above 200,000 cfs. Thus, the operation below 200,000 cfs ·may be called excel lent and that above 200,000 cfs satisfactory. The average water surface profile at a discharge of 290,000 cfs is shown in Figure llA with normal tail-water elevation. To determine the erosion in the riverbed, the model was o~rated for 1 hour at the maximum discharge with normal tail-water elevation. The lowest riverbed elevation was 1086 which was 9 feet lower than the horizontal floor of the stilling basin, Figure 12A. The material moved by the flow is represented by the area between the original bed and eroded bed. After the studies on Basin No. 1, it was decided to increase the volume of the basin by extending the horizontal floor upstream to determine whether the performance could be improved.

5 Stilling Basin No. 2. For Basin No. 2, Figure 7B, the horizontal length of floor was extended upstream 117.5 feet and a slope of 5:1 was used for the upstream floor. The operation of the basin for discharges of 200,000 and 290,000 cfs was in most respects similar to the previous basin and is shown in Figure lJ. The surging action was more pronounced with Basin No. 2, however. This action can observed.by comparing the operation as shown in the motion pictures. The amplitude of the waves at the maximum discharge was 17.5 feet, Figure 9, or about twice the value for Basin No. 1. The sweep-Ol1,t curve was unchanged from Basin No. 1, Figure 10, . because the downstream end of the basin, which controls the sweep-out, was the same for the two basins. The average water surface profile, Figure llB, showed the depths at corresponding sections to be very similar to those for Basin No. 1. In other words, lowering the floor of th~ basin caused a lowering of the water surface elevation. Pres sure6 were measured on the portions of the floor sections shown by the piezometer locations in Figure 14A. The results shown in the figure · indicate a similarity between the press~es and the depth of water over the floor.

An erosion test was run for 1 hour with maximum discharge and normal tail-water elevation. The shape of the riverbed resulting from this test is shown in Figure 12B and was very similar to that obtained with Basin No. 1. One additional modification to the basin floor was believed desirable in the study of the stilling basin. Stilling Basin No. 3. Additional volume was given.Basin No. J, Figure 7C, by using a full length horizontal floor which required lowering of the curve connecting the spillway face and the floor. The appearance of the.flow in the stilling basin for a discharge of 200,000 and 290,000 cfs is shown.in Figure 15. · The performance and. surging action was similar to that of Basin No. 2 which can be seen by observing the motion pictures taken through the glass panel. The amplitude of th~ waves at the maximum discharge was 15.0 feet, Figure 9, or about the same as measured with the second ~asin. The sweep-out- curve, Figure 10, was the same as found for Stilling Basin No. 1 and No. 2. The average water surface profile, Figure 11, showed a similarity of depth to.the two previous basins. Pressures were measured at the six piezometer locations shown in Figure 14B. The pressures were greater at higher discharges, and there was a drop in pressure at the two do~stream piezometers. The reason is not known. To increase the effectiveness of the basin a row of 20-foot baffle piers and a 20-foot end sill were installed as shown in Figure 16A.

6 The performance was impro~ed as indicated by the appearance of the flow for a discharge of 290,000 cfs, Figure 16B. The amplitude of the waves in the channel downstream from the basin was reduced to 6.9 feet for the maximum discharge, Figure 9. Although exact measurements were not taken the erosion close to the end sill was not as deep as occurred with the other basins. The sweep-out tests showed a greater margin of safety, Figure 10, requiring 17 feet of tail water reduction before the jump was swept out at the maximum discharge. The water surface profile in the stilling basin with the 20-foot baffle piers and sill is shown by the dotted line in Figure llC.

A piezometer was installed on the side of one of the baffle piers as shown in Figure 16A. Tests on other models had indicated that the lowest pressure to be expected on a baffle pier of this type occurred in this general location. Pressures obtained for three discharges are also shown in the figure and were all well above atmos pheric. The velocity of the water impinging on the face of the piers · was measured and found to be as high as 135 feet per second at the maximum discharge. While these additions to the basin improved the performance, the life of the baffle piers would be limited under such severe conditionn, and their installation is not considered good practice. Although the limited tests made to measure pressures shoi.red cavit~tion-free pressures, it is possible that local conditions in the prototype might produce local.cavitation with resultant pitting. With the high velocitjes present on th~ apron, ordinary abrasive action might cause severe damage since the baffle piers might direct the flow into the apron itself. The hydraulic performance of Basin No. l was considered to be the most satisfactory of the three basins tested.

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•

• • •

•

---

•

·290,000

•

Baffle

•

e.lev.

··:·o·-·.··.··.··.·o·:.·.···'?·::.·.-c:,::.-;;:

....

• .

7+13

•

·,,;

piers

a·

·.·-

profiles·

Sta

!:~o

• • • • •

••• _9

Sta.8+~5.00,

...

1_0

.....

baffle.

NO.

W.S.

+ailwater

•

NO.

·,··

• • • • •

20'

-\-~.·.·.·.·.··

~1._

discharge

,.,,,-s

•

and

•

N N

...

Note:

• •

With

10:J-

•,

,-,,,

·::·:o::.·

•

------

---

•,

A S

·.o.

BASIN

•.•.

• • •

S:J

·.-.-....

••

•

C-

A-

.•...

· · ·

·e>.·

·o.·.·.·.

o.·.~

Q;-"

...

Sta.f>+I0.45---<:-.;:.·.···p·-:·.:-

Q:-"

">"

._Q: ...

t;-

Cr)"

Sta.5+14.22--,

PROFILES

MO_DE.L

DAM

BASIN

3+54.94

SCALE.

''-Sta.3+71.41

SURFACE

---Sta.

BHAKRA

STILLING

WATER

2.0J FIGURE. 12

Note:.. f:>ischarge 290,000 c.f.s. for one hour, ta i I water elevation 1206.

EL.. 1090

" I 1981

PLAN

Original, bed El. I 139 :-:-i

0 0 ODO 0000 oo 0000 000 0 0

0 0 0 0 00 0 0 0 " 0 0 0 Cl O O :

0 0 D O 0 0 0 00 0 0 0 0 0 0 0 0 0 0 ~ «;. o: o oo oo • o o o o o" o •o o o o o o o o • o O " o c I c o o II o O o o o, a o - o o o _o o ------G5 Q ------Od: 00 0 0 0 0 0: 0 0 D IP O O O O O O O O O O 0

SECTION ON ·

I 198'

PLAN Original bed-:.. 0 • 0. 0 0 0 .. 0 0 ·o 0 0 D 0 0 " D 0 0 • 0 0 • 0 0 " 0 0 0 0 • O O o

SECTION ON ~ B BASIN NO. 2

BHAKRA DAM STILLING BASIN E.ROSION TE.STS 1,.01 1:50 SCALE. MODEL Figure 13

A. Discharge 200,000 cfs

B. Discharge 290, 000 cfs

SPILLWAY STILLING BASIN NO. 2 BHAKRA DAM - 1:50 MODEL FIGURE 14

E.X PLANATION Discharge 100 000 c:f.s., taih1·~01ter El. 1184 Discharge 2.00 000 c:f.s., tailwc:1ter El. 1197 Discharge 290000c:f.s.,+ailwater El.1206

100

,ILi 80. _. cl 0 VJ I- 40 en w Ww I cl LL -- Sta. 17+13.57 20 0. Sta.10+10, ~

Pl EZOM ETERS

A· - BAS l N NO. 2

100 w 80 <{....I°' I.LI IJ I- ,,..- en w --~ Ww 20 0.°' Lr.. sta.10+00-, / I ~ ~

. . · ·o.. ·. I ·. ·0 •• • • •• • •• • • • • • • • • ;, • • • • • • • • • • • • • • ·o • • • • • • · • • • • • • • • • :. • •• • •• • • • • • • • • • • • • •• ·· •. o. 0····,2· --~,0,4·0·5·0·6· ·····o .·"?·. ·o·o··"'···.·--c:· . • . • . • . o . • • • . • . • .. C: • • . .' . • .0. .. : .. : .. o .. ? • • 0: Pl E.ZOME.TE.RS

B - BAS I N N 0. 3

BHAKRA DAM FLOOR PRESSURES IN STILLING BASIN J:SO SCALE. MODEL 2.01 Figure 15

A. Discharge 200, 000 cfs

B. Discharge 290, 000 cfs

SPILLWAY STILLING BASIN NO. 3 BHAKRA DAM - 1:50 MODEL FIGURE 16 - - ~ c"' I ~-J I L_ - I I I \ I I I I I I 't 1 I<--- -- 40 --1--> 10' f<.- piers I 20' 1 >-Baffle I I ~ 101 I<.- / I I I I I •• 62.51 I I I . I 20 1 ------66 ------> I I Si II I ,---ctrI ' I I •• t---- I 12 51 , .... Piezometer I .:,· ~-Training wall v

PLAN PIEZOMETER PRESSURES H>S feet of water at 100 000 c:f.s. discharge +E,7 feet of water at 200 000 c:f.s. discharge +5'2. feet of water at 290 000 c:f.s. discharge ->I k:- I I i i , ,,-,- Piezometer y------~-:--:-r--- 3,-- . ~-· --~ 'j\ • .·o··.· ,::-- .. ·o : I • c, • • • • 1 •• : ;, •••• o. -- I •• o.·, • 201 20 ~ • • • • • I ...... · O· · o ·. 10 1 ·o· · . · · El. 1095 -, I : • : ~ •. 'o, I O • . o. -.-.-.- • ._,.- ..... • • • • • • • • • • • • ·o • • • • o • · • • • · • • · • ·O· .o.. _.., .. o. -:o:.··?· s·E·c-rt'o'N ·.o:.~· ·.~.

A- DETAIL OF BAFFLE PIERS & SILL

B- DISCHARGE zqo,ooo C.F.S.-NORMAL TAILWATER

BHAKRA DAM STILLING BASIN N0.3 WITH BAFFLE P1£RS AND 2.0' SILL 1:50 SCALE MODEL 2.01