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PageOperation with recommended gate and valvearrangement . . . . . . . . . . . . . . . . 17. . . . . . . . .ecommended stilling basin. 18Stilling basin sweep out. . . . . . . . . . . . 18Erosion of sti lling basin exit channel.. maximumflow. . . . . . * . . . . . . . . . . . . . 13Ero sion of stilling basin ex it channel- -gate andcombinations. . . . . . . . . . . . . . . . 19The Spillway . . . . . . . . . . . . . . . . . . . . 20

Pre lim ina ry Spillway. . . . . . . . . . . . . . . 20Operation of the pre lim inary 26-foot d iam ete rtunnel spillway . . . . . . . . . . . . . . . 20Modified tunnel spillway (recommended design) . 21Elliptical-shaped spillway entra nce piers. . . 21Center pier lengthened at downstream end . . . 21Tunnel enlarged to 28 feet in diameter . . . . . 21Modified spillway tunnel exi t transition . . . . 22Eros ion of downstream riverbed . . . . . . 2 3Spillway capacity. . . . . . . . . . . . . 24

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L I S T O F F I G U R E SNo .

L o c a t i o n M a p . . . . . . . . . . . . . . . . . . . . . . .Ge n e r a l P l a n and S e c t i o n . . . . . . . . . . . . . . . . . . 21 : 6 1 . 8 2 S c a l e Mo d e l . . . . . . . . . . . . . . . . . . . . 3

P r e l i mi n a ry Di v e r s i o n Ch a n n e l De t a i l s . . . . . . . . . . . 4F l o w C o n d i t i o n s i n P r e l i m i n a r y O u t l e t a n d P o w e rT u n n e l D i v e r s i o n C h a n n e l s . . . . . . . . . . . . . . . . 5F l o w C o n d i t i o n s i n P r e l i m i n a r y P o w e r T u n n e lDi v e r s i o n C h a n n e l . . . . . . . . . . . . . . . . . . . . 6Di v e r s i o n Ch a n n e l L i n i n g . . . . . . . . . . . . . . . . . ?F l o w C o n d i t i o n s i n O u t l e t D i v e r s i o n C h a n n e l a n d inP ower T unne l D ive r s i on Channe l w i th Def l ec to r Wal l I . . . 8F low Coxld i t i ons i n P ower T unne l D ive r s ion Channe lwi th D e f l e c t o r W a l l 2 . . . . . . . . . . . . . . . . . . 9F l o w C o n d i t i o n s i n P o w e r T u n n e l D i v e r s i o n C h a n n e lwi th D e f l e c t o r Wa l l 3 . . . . . . . . . . . . . . . . . . 10M a x i m u m W a t e r S u r f a c e P r o f i l e i n D i v e r s i o n C h a n n e lL i n i n g s w i t h V a r io u s D e f l e c t o r W a l l s . . . . . . . . . . . 11P re l i mi na ry O ut le t P ip in g S ys te m an d S ti ll in g B as in s . . . . . 1 2

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LIST OF FIGURES (Continued) ~No. I

Flow Conditions and Ero sio n fo r Outlet and Pow er TunnelsOperating at Discharges of 46,100 cfs and 31,600 cfs . . . . . 0b

Flow Conditions and Ero si on fo r Outlet and Bower TunnelsOperating a t Di scharg es Representing 23,480 cfa and14,700 cf s . . . . . . . . . . . . . . . . . . . . . . . . 1 .Flow Conditions in Pr eli mi na ry Spiliway Entrance andExit Channel . . . . . . . . . . . . . . . . . . . . . . . 2Spillway Inlet Structure . . . . . . . . . . . . . . . . . . . 3S n i l l w a v n n n r n t i n n w i t h R ao nm rn en A aA E?ntrsnce, 28-fo0t

I Dia meter Tunnel, and Recommended Tunnel Exit Trans itio n;48,000 cfs Discharge . . . . . . . . . . . . . . . . . . . 4 ISpillway Inlet Structure--Crest Sectfin . . . . . . . . . . . . 5Spillway Inclined S1Operation s f Recommended Spillway with Flow Through OneGate; 25,000 cfs Discha rge . . . . . . . . . . . . . . . . . 27Spillway Conduit and Outlet Channel Lining . . . . . . . . . 8Flow Conditions for Maximum Discharge Through RecommendedSpillway and Outlet Works . . . . . . . . . . . . . . . . . 9

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DEPARTMENT OF THE INTERIORBURZAU OF RECLAMATIONC ommi ssione rls Office, Denver Laboratory Report No. HYD-350Division of Engineerin g Written by: J. C. SchusterLabor atorie s Checked andHydraulic Laboratory Bra nch Reviewed by: J. W. BallHydraul ic S t r~~cturesEquip- Submitted by: H. M. Marfinment SectionDenver, ColoradoJune 22, 1 9 5 6Subject: Hydraulic model studie s of the Pal is ad es Dam Outlet Worksand Spillway- -P al isa des Project, Idaho

PURPOSEStudies to investigate the hydraulic characteristics of prelirn-ina ry designs and to a ss is t in determining any changes that would en-su re hydraulically satisfa ctory spillway and outlet works struct ures.The studies evaluated the flow conditions in the concrete-lined diversion channels, the outlet and power tunnels, the outletpiping syste m, the outlet stilling basins, the spillway entrance, thespillway tunnel, the spillway exit channel, and the downstream r iv erchannel.

CONCLUSIONSRiver Diversion

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1. A piping sy stem for the main outlet works us ing 2'hollow-jetvalves and 4 rectangula r slid e gate s will satisfactor ily handle the dis-charge from the outlet tunnel (Figure 14).2. Th e distribution of the di scha rge in the stilling basin chute

w i l l be sati sfa cto ry with the 8.5-foot long wal ls of the downstreamfr am es of the slide gate s made paralle l and spaced 7.5 feet apart(Figure 13B).3. Cavitation pr es su re s would occ ur in the prel imina ry constantdi am et er branch of the 2-way Y1s ups tre am of the sl ide ga tes when onegate was fully open and the oth er gate fully closed, (F ig ur es 15B and16A).4. Cavitation will not o cc ur in the constant diame ter branches up-s tr eam of the hollow-jet val ves because of the rela tive ly high pr e s su reupstream of this type valve.5. A 5-degree, 48- minute, 13-second convergin g bran ch of the2-way Y upstream of the slide gat es will prevent cavitation pr es su re sfor one or both sli de gates fully opened (Figu res 14 and 15B).6. Th e disc harg e from the fully opened valve s and gate s will bedist ribut ed 22.6 perc ent to the hollow-jet va lves and 77.4 percent tothe four slide gates.7. The u se of a coeffic ient of di sc ha rg e of 0.57 in the equation

Q = CA V@R will give the dis cha rge c apacity of the outlet works withgate s and valv es fully opened. Th is coefficient is based on the a re a ofthe 26-foot di am et er tunnel and the total head at a dis tan ce of 262 feetupstr eam of the gate exits.

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elevation is lowered 4 feet o r mo re below the computed norma l ele -vation of 5380.3 fo r a disc ha rg e of 30,550 cfs, and 6.5 feet or mor ebelow the computed normal elevztion for a discharge of 46,100 cfs.13. The exit channel of the sti lling basin can be adequately pro-tected by 3-foot dumped riprap.

Tunnel Spillway1, Good flow conditions would oc cu r in the pr eli min ar y de signspillway entr ance with the 40-foot radi us en tran ce pie rs. The designc.f the pi er s was modified during the test program to make them sm al le rand to reduce their cost.2. The recommended right- and left-hand entranc e pier s, with a

x 2section profile of an ellipse (- y2 = 1) and a 7.5-foot ra di us(3012 '(wat the upstream end w i l l be satisfactory for a ll discharges , includingthe des ign maximum of 48,400 cfs. However, the turbu lence withinthe spillway and in the fi rs t part of the tunnel is somewhat grea terthan in the preliminary design (Figure 24Ay.

3. A center pier in the spillway entrance that extends from ap-proximate ly Station 4+70 to Station 5+90 and t ape r s in the las t 60 feetfro m a th ickness of 6 feet to 3 feet will give satisfactory flow conditionsin the tunnel for disc harge s to 48,400 cfs fo rb ot hl - and 2-gate opera-tion (Figures 24, 25, and 27).

4. The 26-foot diameter tunnel of the preliminary design would

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9. A transition fro m the spillway tunnel to the exit channel thatbegins at Station 2 4 t 0 0 with a c irc ula r cr os s section; changes to ahorseshoe shape at the tunnel exit, Station 2 e t 4 6 . 3 5 ; and is the trap-ezoidal shape of the channel a t Station 25+20; w i l l provide a smoothtransition of flow from the tunnel to the exit channel (Figures 24 and10. Th e upward cu rv e of the flo or at the en d of the lined cha~nneldi re ct s the high-velocity flow upward and ov er the ro ck founda.tion.11. The maximum capacity for the spillway with a r es er vo ir ele-vation of 5621 . 0 is 48 ,400 cfs. This is indicated by the calibrationdata from the 1:61 .82 sca le model (Figure 31).

RECOMMENDATIONS. Releas e water fro m valves and gates on altern ate sid es of thebasin center line for the best energ y dissipation in the stilling basin.2 . Investigate the performance of the 7 foot 6 inch by 9 foot 0inch slide gat es by using them for regulation a t par tia l openings.Satisfactory perform ance w i l l permit symm etrica l operat ion ~f the

3. Opera te spillway ra di al gates a t equal openings to providesymmetrical flay distribution in the spillway tunnel.

ACKNOWLEDGEMENT

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Pal isades D a n and reserv oi r a r e located approximate ly 70mi le s northe ast of Pocatello, Idaho, on the sou th fo rk of the SnakeRiver (Figure 1). The dam is a rock-faced, earth-filled structurehaving a length of ap prox imate ly 2,200 feet and a height of auout 225feet above the riv er channel (Figu re 2). The re se rv oi r is used for.flood co ntrol and to supply wat er f or irrig ation and f or el ect ric power.Water rel eases from the res erv oir a r e made through the turbines ofthe powerplant, through the outlet works, o r through the tunnel spill -way; all located at the left abutment of the dam, Norm al ri ve r flowspas s through the turbines o r through two 96 -inch hollow -jet valves ofthe outlet works. Floods a r e discharged through the outlet works o rthrough the tun nel spillw ay which is approximately 200 feet to the leftof the outlet works.

Water flows fr om the re se rv oir through a bellmouth entranceinto the 26-foot ,di ame ter outlet tunnel which is lined with concretefo r approximately 692 feet of its length, and with ste el fo r the re-maining 732 feet. The tunnel bra nch es at Station 17+58 into two 16-foot diameter pipes and one 13-foot diameter pipe (Figure 14). The13-foot pipe on the tunnel cente rline b ran che s into two $-foot diam-eter pipes which terminate with 96-inch hollow-jet valves. Thetwo 16-foot pipes bra nch into two 9-foot 6-inch di am et er pipes whichtermin ate with 7-foot 6 -inch wide by 9-foot 0- inch high rec tan gul arsl ide gates . These,s l ide gates a r e discussed i n Repo rt No, Hyd-387.A maximurn discharge of approximately 33,000 cf s fr om the valvesand sli de ga tes em pti es into the left 104-foot wide sectio n of the 15C-foot wide co nc re te -b ed st il l ing basin (Figure 18).

Two 7-foot 6-inch by 9-foot 0-inch recta ngul ar slide gate sdisch arge approximately 11,500 cfs fr om the power tunnel penstock -into the r emain ing 54 fee t of basin width (F igure 18). Water fro m

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was elevati on 5378.25. Th e highest point in the power tunnel chaiulelwas 4.25 feet lower at elevation 5374.00 (Fi gur e 4, Detail C).Model flows represe nting di schar ges t o 18,500 cfs fro m eachtunnel did not s er iou sly overtop the outside o r dividing walls of thepreliminary design (Figure 5A). However, a discharge representing33 , GO0 cfs , the design maximum fo r the power tunnel, overtopped thedividing wa ll-i n quantities that would in te rf er e with construction in theadjacent outlet diversion channel (Figure 5B).Modifications to outlet tunnel diver sion channel. The walldividing .the outlet and power tunnel divers ion c hannels wa s ra is ed fr omelevation 5390.0 to 5400.0. A flow of 25,500 c fs could under ce rta incirc um stan ces be discharged through the outlet divers ion channel with-out overtopping e ith er the outside walls o r the dividing wall (Figu re5C). However, the flow direction was not stab le and the flow inte r-mittently shifted t~ the left o r right of the channel center line and ov er-topped the walls (Figures 5D and E). The flow direction was stabilized

in the basin for disc harge s up to 23,500 c fs by constructing a wedge a tthe right side of the tunnel exit (Fig ure 4, D eta il A ) .The floor of the channel down stream fr om Station 19t1 5 wasto be constructed to a parabolic shape star ting a t elevation 5378.25,and a temporary upslope was provided ahead of the parabola (Figure4, Detail B). After diver sion was completed, the slope was to be re-

I placed by a horiz ontal 15-foot long flo or that would rec eiv e the jetsdischarged f ro m the outlet work s valves. Subsequent te st s of thevalves disclosed that the flat section was not a e ~ d e d nd that the pa-rabola origin could be moved upstream 15 feet to Station 19+00. Allpre ss ur es measu red on the original chute were above atmospheric,and the prelim inary outlet channel with the c enter wall ra ised to ele -

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char ges to 26,000 cfs (F igure 6C). The discharge capacity was increasedto 32,000 cf s without overtopping the wa lls by placing a deflector p ier(Fig ure 4, Detail D) in the basin at Station 18+00 nea r the cente r of thechannel (Figure 6D).Conclusion of d ive rsi on channel investigation. Major changeswere made by the designers of the outlet diversion channel betweensta-tions 17+44 and 19+00.25 in which the wal l divergence between the tun-nel exit and the channel was made sym metr ical and mo re graduzl (Fig-

ure 7). Th e top of the dividing wall was lowered f ro m elevation 5400.0to elevatio n 5397.0 and the floo r was sloped upward t o elevation 5354.0.No model te st s were made on th is design, but it is expected that theflow will be sta ble in the sy mm et ri ca l channel with th e upward slopingfloor, and that the dividing wall will provide ample freeboard for dis -cha rge s to 26,000 cfs. Fi gu re 8A shows a flow of 26,000 cfs in a gen-erally similar channel design.A change was al so proposed f or the power tunnei diversionchannel in which the right si de wa ll star ted at Station 18+90.42 insteadof a t Stati on 18+50.00. This required a change in the temporary de-flector wall, and th ree wall angles were studied to determ ine the effecton the flow conditions in the channel. Photographs and the wa ter -su r-face profile measure ments we re obtained at model discharges r ep-rese ntin g 13,000, 18,000 and 23,000 cfs (Fig ures 8, 9, 10, and 11).The flow with the shortest wall was quite turbulent with wavesalong both walls of the channel caused by the s tr ea m fr om the powertunnel impinging on the deflector wall and on the raised portion of thechannel floor at Station 18+83.92. The inc rea se of turbulen ce ov ert ha tof the p rel imi nar y design wa s caused by the rncre ased an gle of the de-flector w all with re spe ct to the tunnel centerline.

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flect or wall was to be ma de by the con tracto r and contracting officerduring construction of the diversion channels.The res ult s of the dive rsion studies we re published in an In-te r im Report, Hyd -345, "Hydraulic Model Study of the Penstock andOutlet Diversion Channels--Palisade s D am-- Palisa des Project, " t oass is t in the diversion of the ri ve r flow during construction.

The Outlet WorksOutlet Works Piping System

Prelim inary piping syste m. The prelim inary piping syste mconsisted of two bra nch es f ro m the power penstock and two 3-way Y'swith five branches from the outlet tinne l (e ig ur e 12A). Seven 7-"1/2-foot wide by 9-112-foot high rec tangular sl ide ga te s wer e placed a t theends of thes e seven branches. The five gat es that received the ir flowfrom the outlet tunnel released the flow into the left 104-foot wide sec-tion of the stilling basin (Figur e 12B). The two gat es that receivedthe ir flow from the power penstock relea sed it into the right 54-footwide section of the stillin g basin. The planned op eratio n was that allnor ma l outlet re le as es would be made through th e five outlet tunnelgates with the gates ope rating at equal openings. The two gates on thepower penstock would be operated only when the powerplant was inop-erable.The piping sys te m for this gate arr ang eme nt appeared to besatisf actor y. However, because the gates we re a new developmentand had not been proven by field operation, the a rran geme nt was la te rchanged to r e pk c e one slide gate with two hollow-jet valves for re g-ulation of sma ll dis cha rge s. This arr ang em ent was contained in the

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to a uniform depth ac ross the ba sin a t the beginning of thk jump. Anoptimum angle of the gate fr am e walls was determined by studying di-verging ang les of 8O, PO, oO , and a converging angle of 2 An angleof 4 0 st i l l permitted considerable jet in terference ( F i r e 13A). A sthe angle of divergence was decre ase d through 00 to 2 converging, theinterference due to the spreading of adjacent jets diminished. P r ac -tically no spreading occurred with the 2 converging walls. The bestspreading and chute flow conditions fo r the outlet tunnel gates full openwere obtained with gate frames having parallel wal ls (Figure 13B). Theparallel-walled gate fram es a r e therefo re recommended f or use on theprototype gates.Modified outlet works piping syst em with two hollow-jet valves.In an investigation of a 1:19 sca le model of the rectangula r regulatingslide gate , Hydraulic Laboratory Report No. Hyd -387, "~ydraulicModel Studies of the 7-foot 6-inch by 9-foot 0-inch Pal is ad es RegulatingSlide Gate", it was determined that a reduction in gate s ize from thepreliminary 7.5 feet by 9.5 feet dimensions to 7.5 feet by 9.0 fee t couldbe made without reducing the discharge below the requi red quantity,

Four ga te s of the sm all er s iz e and two 96-inch hollow-jet valves \:{ereincorporated in a modified outlet works piping sys tem- -the t w o h~Uowjet valves replacing the originally planned center slide gate (Figure 14).The hollow-jet valves w ere included fo r the regula tion of mod-erate flow increments because the slide gate design was a new develop-ment and had not been proven by field operation. Norm al flows fr omthe re se rv oi r through the outlet works will be controlled by the hollow-jet valves. Discharges i n ex ce ss of the capacity of the hollow -jet valves

w i l l be discharged through fully open slid e gates.P r e s s u r e s in outlet works piping sys tem . Subatmosphericpressu res occurred in the 2-way Y's of the 1~61.82 cale model near

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whereh is the pres sur e at any given piezometer,feet of waterhe is the pre ssu re in the pipe downstreamof the 2-way Y (Figure 16A)-e is the Q/A, value of the velocity in thepipe downstream of the 2-way Y

The pressu re factors w ere computed for discharge into at-mospheric pre ssur e, but the factors al so apply when the discharge iscontrolled by valves or gates. In these eases, the pr es su re s in thebranch m a y be computed if the coefficient of discharge, C, of the con-tr ol device is known. The pre ss ure at the end of the Y branch will be1 Ti!the back pre ss ur e due to the control, he = (? - 1)- lus the pipe-2gline lo sse s from the end of the Y-branch to the control. The lo ss eswould be small i f the control is attached a t o r nea r the end of the Y-branch. The value of h,may be substituted in the pre ssu re factorequation to obtain the p re ss ur e a t any given piezometer within thebranch. A s an example, f o r a dischar ge through one branch with theother closed, assume:

Q = 7,000 cfsAe = 70.9 ft 2Te = 98.8 f t per se c

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h = 0 . 9 7 ~ 51.4-k 27.5 = 173.8 feet of waterUsing the s ame method of computation it was found that cavita -tion pr es su re s would occu r in the "crotch", or c rit ica l ar ea , of the Y -branches that a r e located u pstream of the s lide ga tes which have highcapac ities and, hence, high disc harge coeffic ients. Beca use of the lowerdischarge coefficient and resulting higher back pressure from the hol-low-jet valves, the pressures in the ' cro tch" of the Y-branch u ps tre amfro m thes e valv es would be above vapor pr es su re and no cavitation wouldoccur . There fore , no change in the design of thi s 2-way Y was contem-plated (Figu re 16A). It was ne cessa ry , however, to change the 2-wayY branc hes ups trea m of the slide gates to eliminate the cavitation pr es -su res , thus the study w a s extended.Two-way Y with 900f17" conv A second 2-way Y was tested. (Figure l a b , 2-way des ign had con-verging pas sages with conic angle s of 9000'1 7". 'P re ss ur es were aboveatmospheric in a ll ar ea s except just downstream of the point where the

last conic sec tion s of the branches joined the 9.5-foot dia me ter pipes(F igure 1GB). Th is abrupt angle at the junction caused a pre ss ur e r e-duction sufficient to produce cavitation and the branch was not satisfac-tory (Area C. Figure 16B).Two-way Y with 548113" converging passages--recommendeddesi - r d 2-way Y design resulted in acceptable pres sur es (Fig-&, $%ay Y No. 3). The 5O48'13" conic angle resulted in a longerconvergent passage and a le ss abrupt change in boundary alinement

where the la st conic sec tion joined the 9.5-foot dia me ter pipe. A slightsubatmospheric pre ssu re occurred just downstream of the junction onthe inside su rf ac e of the 9.5-foot pipe. The pre ssu re was not lowenough to indicate cavitation pres su res in the prototype. Fu rth er studies

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stru ctur es that handle water at high velocities and low pressures anddo not need the tension b ar f or st ruct ural strength. (Figure 16C). Pres-su re factors for c, d, and e are applicable to la rge st ruct ures that re-quire the tension bar (Figure 16C). Pre ssu res measured on the ten-sion bar were above atmospheric for a l l flow conditions.By use of the pre ss ur e factors the head lo ss fo r the 2-way Y,without the tension bar, in terms of the exit velocity head, was deter-mined with both gates fully opened.

2and5 = 0.48'7 d2g 2g;

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flowing through one branch res ult ed in a head l os s equation of

A s a res ult of the pre ss ur e investigation, it was concludedthat the 2-way Y with 5'48 ' 13" converging passages would operatesatisfactorily for all flow conditions with the high capacity sl ide g ates .The recommended tunnel outlet piping system, there fore , consistedof a 3-way Y fr om the 26-foot di am et er tunnel to the two 16-foot andone 13-foot diam et er bran ches , two 2-way Y ' s fr om the 16-foot dia m-et er pipes t o the 9.5-foot diame ter branches with slide gates a t theends, and one 2-way Y fr om the 13-foot dia me ter pipe to the 8-footdia met er branches with 96-inch hollow-jet valves at the ends (Figure14).

The high capacity slid e gate s on the 9.5-foot dia me terbranches require the 2-way Y with the 5O48'13" converging pass ag esto prevent cavitation pr es su re s in critical ar ea s. The hollow-jetvalve on the 8-foot dia met er branches cr ea te sufficient back pr es su reto perm it the use of 2-way Y' s with constant dia me ter passage s.

Capacity of outlet tunnel piping syst em. To dete rmine thelosses in the over all piping syst em, the 1 1.8 2 scal e model (Figure15A)was attached to the laboratory supply sys tem by using 8 feet of5.05-inch insid e-dia mete r plastic pipe, a 1.5-foot long 5.05- to 6-inch tran sitio n, 15 feet of 6-inch ins ide -di am ete r b r a s s pipe, and abellmouthed entra nce t o a 36-inch diam eter pre ss ur e tank. The pres -su re tank was used to provide a gr ea te r range of head and discharg ethan could be obtained with the head box of the complete mode l. Th epr es su re head ups tre am of the piping sys tem was obtained from four

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ing sys te m was ob&ined with the model gates and valves fu lly opened.The coefficient was obtained f ro m the equation C =__&A -where Q = dis cha rge in 26-foot tunnel, cubic fee t per second

A = a r e a of 26-foot tunnel, sq ua re fee tH = tot al head, pr ess ur e plus velocity head in the tun-ne l 262 fee t up str eam of the valve exits, feetC = coefficient obtained fro m model experiment sThe pres sur e head g was measured a t the piezometer r ing

-2 Vand the velocity head was computed for the measu red d ischa rges2iz

to obtain the to tal head in the model piping system . Fr om the totalhead and the discharge, the coefficiant, C, was found to be 0.57.This coefficient of 0.57 is probably slightly lower than in the proto-type because of the higher relative losses of the 1:61.82 scale model.It applies 0nJ.y to a disch arge with the four sli de ga tes and two hollow-jet valves fully opened.By computing the los ses , h , (entrance, friction, etc. ) interms of the velocity head in the 26-!foot conduit, and knowing thehead available fro m the res erv oir , the velocity in the 26-foot pipeand the disc har ge of the outlet works may be obtained.This may be accomplished in the following manner:

I b,

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was obtained during the coefficient Gs t s by a volume tric me asure mentof the di scharge. The two hollow -jet valves discharged 2 2 . 6 percent ofthe tota l flow and the sli de ga tes 77.4 percent. Th er e was no apparentdifference in the quantity c ~ fwater discharged fr om each gate.Capacity of power tunnel piping system. The capaci ty of thetwo out le ts f rom the ~ o w e runnel was determined bv the ~ r o c e d u r eused fo r the outlet syste m. The power tunnei outlgt section ofthe 1:61.82 sca le model was attached to the pipe fro m the 36-inch dia m-eter pressure tank and mea sur eme nts wer e made of the total head inthe tunnel 203 feet up str eam fr om the gate exits, and of the disc harg efrom the gates. Bott slide gates were s et for a coefficient of 0.92 tocorr espond to a fully-opened prototype gate. The coefficient of dis-charge f or the two gate s with resp ect to the tunnel was C = 0.24.A weight measur emen t with res pec t to time of the disch argefrom each gate indicated that the discharge w a s divided approxim atelyequally between the two gates. The coefficient of d ischar ge fo r a sing legate se t to represen t the full open condition, based on the tunnel ar ea,was 0.12. The dis charge capacity of the power tunnel outlets was ad-equate.

Outlet Works Stilling Basinon of pre liminary design basin. The wall which dividedg basln lnto two section s 104 and 54 fee t wide and servedto s ep ar at e the outlet tunnel and power tunnel flow during the dive rsionperiod, separa ted the flow of the two penstock gates fro m that of thefive outlet gates, to make essentially s epa rat e stilling basins. his a r -rangement was desirable because all normal rel eas es were to be madefr om the gates of the outlet tunnel, while the ga tes fr om the power gen-

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-study the spreading 6f the gate jet s showed that the 15-foot long hor-izontal section of the floor immediately downstream s f the gates wasnot essenti al for satisfactory stilling basin performance, it w a s re-moved and the basin shortened 15 feet. P r es su re s taken on th isshor ter chute showed a maximum subatmospheric p re ss ur e of 2 .8feet of water at a discharge of 31,000 cfs. Thi s pr es su re occu rredat Station 19t45 , 45 fee t downs tream of the gate fr am e exit and onthe centerline of the basin. This pr es su re was not low enough toproduce cavitation so the chute profile was considered satisfa ctory .Operation with recommended gate and valve arrangement.The gates of the prelim inary outlet works piping sy ste m were t o beequally opened and the stilling basin was sa tisf actory where the re wasapproximately equal flow per foot of width. In the ca se of the recom-mended piping sy stem the gates and valves would not be equally openfo r much of the tot al operation. It was planned tha t two hollow -jetvalves would be used f o r regulating the flow up to the point where thevalve s were fully opened. If gre ater discharges were to be passed theflow would be tr an sf er re d to one of the sl id e gates, which would be

opened fully, and the valves would be throttled t o re le as e the pro peraddi tional r a te of flow. If the valves again reached their capacity, asecond slide gate would be opened. If neces sary, thi s would be re -peated until al l four s lid e gates and both hollow-jet valves were open.Thi s operation would impose seve re conditions of ene rgy concent rationand flow distribution in the basin. Studies were there for e made to de-ter mine the adequacy of the basin.The dividing wall between the outlet and power tunnel basin

was removed to determine the need of the wall. The jump in the still-ing basin w a s deflected to the le ft by an eddy that fo rmed a t the rightside of the basin (Figur e 17A). This action prevented effective use ofthe full stilling bas in width. The w a l l was replaced and the top eleva-

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was s epa rat ed into th re e se ction s by two dividirig walls on the chute(Figure 18). Th e elevation of the top of the ma in dividing wal l down-st re am fr om Station 19+38.25, and of the two inte rmed iate walls , wa s,cr' t 5378.5. T o reduce the cos t of the wal ls, the downstream endswere sloped to elevation 5355.0 (10 feet above the basin floo r). Chuteand floor blocks were provided in the stillin g basin to in cr ea se its ef-fectiveness in dissipating energy. The chute blocks, 6.75 fe et high and5 feet wide, were located a t the junction of the c l~ ut e nd floo r of thestilling basin. The upstream ends of the 8-foot high by 5-foot widestreamlined floor blocks were located 69.5 feet down stre am of the chuteblocks.

Ea ch s ecti on of the divided chute tended to ac t a s a separatestilling basin for a p air of gate s o r valves, and the eddy that formedin the down stream end of the basin wa s reduced i n siz e and intensity,and confined t o the region ne ar the ex it of the basin (Fi gur e 19). Theindividual se cti ons wer e l arg e enough to handle the dis char ge 3rompairs of gates o r valves and also s m al l enough to fo rm a good jumpwith the discharge frorn only one gate or valve.Th e per for mance of the divided basi n wa s satisfactory witheffective ene rgy dissipatio n for all combinations of gates and valves.Water splastred ove r the walls between adjacent sections, but only inrelatively small quantities.Stilling basin sweep out. The revised tail-water curve, basedupon th er e being mate r ia l removed f rom a borrow a re a in the r iv erbank, is shown-h F ig ur e 31. When the tail water was lowered 4 feet

below the computed normal elevation of 5380.3, with a di sc ha rg e of I '.30,550 c fs fr om the equally opened outlet gate s and valves, the fro nt~ of the jump moved fr om a point ov er the chute blocks to the u ps tr ea m

. +

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proximately 300 feet prototype, w a s used to locate ex it channel con-tours and the riprap.Opera tion of the combined outlet tunnel and power tunnel still-ing basin for 4 hours at a discharge representing 46,100 cfs and atail -wat er elevation of 5382.1 resulted in practically no erosion (F igures20A and B). An eddy that fo rmed between the basin di sch arg e and theri ve r bank, and rotated in a clockwise direction, w a s of low velocityand did not appe ar t o affect the powerplant tail water. A smallamountof sand was deposited dow nstream of the end of the right train ing wallalong the boundary of the eddy and the outlet works flow. This sandhad been washed f ra m beneath the r ip ra p and ca rrie d downstream bythe water for a distance equal. to approxima tely two-th irds the lengthof the ri pr ap . A slight decre ase in the riverbed elevation occu rredi m-mediate ly downstream of the end of the ripra p. The ma te ri al fro mthis a r e a moved downstream and formed a low sand bar which did notimpede the flow. The extent and depth of ri pra p w a s believed sufficientand the exit channel protection was considered satisfactory for themaximum combined discha rge of the outlet and the power tunnels.Ero sio n of stilling basin exit channel-gate and valve combina-tions. Additional erosion te st s we re made fo r various combinations ofE a t e s and valves. Opera tion of the outlet basin a t a disc harg e of31,600 cf s with no rma l ta il wate r 5380.4 produced only slight eFosionof the riverbed and formed a low sand bar downstream of the ri>rap(Figures 20C and D) . The exit channel protection wa s satis fact ory for

- outlet works operation at maximum discharge.Ero sion res ulting fro m the operation of two s lide g ates andtwo hollow-jet valves at the left of the basin was essentiallv the sa mea s fo r the two slide gate s alone. F o r both operating cond?k)c+ns, hejet tended to flow close to the left tra ining wa ll and t o dive.:qc:. at th e

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-;--

Pre limi nary SpillwayOperation of the preliminary 26-foot diameter tunnel spill-way. When the model of the preliminary spillway was placed in op-er at io n the en tran ce flow conditions we re found to be sat isfacto ry,but three othe r prob lems w ere encountered: (1) the capacity of the26-foot dia mete r tunnel was sma lle r than that requ ired f or the designdis ch arg e of 48,000 cfs, (2 ) the center pier s eparatin g the radial gatesneeded lengthening and streamlining, and (3) the abrupt transit ion from

the tunnel to the exit channel lining caused the water to overtop thelining (Fi gure 22).At a di sc ha rg e of 43,000 cfs, the tunnel exit and then the en-t i r e tunnel and it s en tran ce transition filled to subm erge the overflowsection and to limit the capacity of the spillway to 46,800 cfs a t themaximum re se rv o ir elevation of 5621.0. Operation of the spillway ina submerged condition is shown on Figure 22C. The rest r ic ted capac-ity of 46,800 cf s was not much le ss tha n th e de si re d capacity of 48,400

cfs, but the tunnel was not intended to ope rate under pre ssu re, andstudie s were subsequently made on a tunnel of lar ge r d iamete r to in-c r e a s e the capac ity s uc h that the tunnel flow would have a f re e watersurface.Water entered the tunnel spillway in a tranquil manner through-out the range of discharge. Some turbulence occur red a s the waterflowed past th e slo pe on the left-hand si de of the a pproa ch channel.This turbulence passed through the overflow section without apparent

effect on the capacity. Water enter ed fro m the right si de around the40-foot rad ius end pier with only slight turbulence. For dischargesto approxim ately 30,000 c f s a ridge of water with a width of approxi-mately 10 percen t of th e tunnel di am ete r formed in the horizontal tun-

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Elliptical-shaped spillway entran ce pi ers . An economy wasaffected in the design of the spillway entrance ap proa ch by revis ing thesha pe of the right and left entr ance piers. The amount of ver t ica l wallrequire d for the 40-foot radius of the prelimi nary pi ers was costlyand field exploration showed that it would b e difficult and e xpensi ve toprovide suitab le support fo r the right-hand wall. Both walls wer e re-vised f ro m the pre l iminary 40-foot radius c w v e to the e l l ip tica l curve-2 + y2 = 1, with the right wall being completed with a 7-foot 6-( 3 0 ) ~ (12.512inch radi us around the outside of the pier (Figure 23). The width of theright pi er wa s reduced from 80 feet to 20 feet with a corresponding r e -duction in wall length and in foundat ion requirem ent. The elliptical curv eof the lef t pie r continued until it intercepted a tangent a t r ight ang les tothe spillway center line and thi s tangent was extended into th e hillside.

The flow conditions in the modified spillway entra nce w er esatisfactory, although th er e wa; a slight in crea se in the turbulence offlow (Figure 24A). The flow contraction along the righ t pier increa sedwith discharg e and formed a standing wave within the inlet st ruc tur e.The flow contraction along the lef t pier was less pronounced and nostanding wave appeare d. The waves a t the entrance t o the tunnel wer edissipated rap idly a s the flow acc eler ate d in the shaft. No unsatisfac-to ry flow conditions result ed fr om the use of the ellipt ical entran cepiers, and they wer e corisidered satisf actory .

Center pier lengthened a t downst ream end. An i n rease inthe length of the cent er pie r a t the downstream en ds er ve d two purposes.The modified 120-foot long pi er (Fi gu re 25) extended 40 feet far th er in-to the inclined shaft to add support to the tunnel transition, and to r e -

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nel was approximately 0.019 i n both thep rel imi na ry and modifiedtunnels .

Operation of t he spil lway with the ell iptical en tran ce piers,the longer center p ier , and the 28-foot d iam ete r tunnel disclosed s at is -factor y operation and that the tunnel would flow with a f re e water s u r -face a t maximum re se rvo ir e levation of 5621.0 , and with the de sir edmaximum discha rge of 48,400 cf s (Fig ure 24).The average water surf ace prof i le a long the s id es of the tun-

nel inlet transit ion and shaft indicated a rat he r uniform acce leratio n ofthe flow fr om the cr es t to the bend JFigur e 24B). The centerl ine depthwas gen erally lower than the depth at ei the r side. A fin of wat er oc-cu rr ed in th e horizo ntal tunnel downs tream of th e lower bend. With thedischarge increased above 15,000 cfs the f in decreased and disappeared.Flow conditions we re s atis fact ory in the inclined shaft .The water sur fac e through th e tunnel had no undue waves orfluctuations downs tream of the bend. Sur face waves of a s m al l choppy

nature which we re attr ibuted t o wall disturb ance and turbulence fro mthe inclined shaft appea red throughout the tunnel. The wave amplit uderemained essent ia l ly constant for all discharges .The tunnel operated with a f r ee water sur face to a maximum of48,400 cf s at a re se rv oi r elevation 5621.0. The water su rfa ce touchedthe top of t he tunnel a t maximum di sc har ge in the a r e a of Station 22+66,180 feet u pst rea m of the tunnel exit. When the flow was slightly re-st ri ct ed a t the tunnel exit, the tunnel would flow full fr om the exit to

the tunnel bend. When the re str ict io n was removed, the tunnel re -turned to fr ee sur fac e flow. An incr eas e in tail-water elevation to5400.0, 14 feet above norm al for the maximum design discharge, didnot affect the flow in the exit channel and tunnel. Operat ion of t he tun-

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without overtopping the wall: at any dis char ge (Fig ure 2 4 ~ ) . "Flowconditions over the deflector at the channel exit were satisfactory withthe water flowing upward and travel ling a consid erable dis tanc e beforefalling back to the riv er surface.Another design change was t r i ed in which the slo pe nf the tun-nel w a s increased by lowering the exit channel fro m elevation 5370.0to 5360.0. The tunnel flowed fre ely to an overload disc ha rge of 50,000cfs with a res er vo ir elevation of 5622.0, but freeboard above the tun-nel water surf ace was ve ry limited and a prototype tunnel res ist anc egr ea te r than that re prese nted by the model might cause the tunnel torun full at flows near the maximum. The channel floor was returnedto elevation 5370.0 to red uce water pondage within it t o a minimum,thus offering gr eat er protection against winter ice formation.Ero sion of downstream riverbed . The excavated exit channelsof the powerplant, outlet works, and spl%way we re repr ese nt ed in themodel with sand, with a protectiv e layer of grave l ripr ap, accordi ngto the gen eral plan of Fig ur e 2. The model was operated 4 hours with

a discharge representing 46, 100 cfs from the outlet works and a dis-charge of 48,400 cfs from the spillway (Figure 29). This total dis-charge was used because the outlet works will reach maximum capacityand then the spillway will be operated. Water flowed from ri ght to leftjust downstream of the outlet works stilling basin and toward the flowfro m the spillway channel. This gen eral flow was a pa rt of a la rgeeddy rotating about a center.locat ed som e distance downstream of thepowerplant. Water fro m the spillway channel was deflected slight ly tothe left, but in general , flowed on the spillway centerline . Flow con-ditions in the r iver channel appeare d good with no undue su rf ac e rough -ness, but a 70-foot deep hole that extended appro xim atel y 600 feet waseroded downstream of the spillway channel exit (F igu re 30). In addi-tion, the le ft bank was eroded and the walls and tile ass um ed founda-tion ro ck at the do wnstream end of the spillway exit channel were ex-

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31 a r e foF the recommended spillway using the ellibtical en tranc epie rs, the lengthened cen ter pier , and the 28-foot dia met er tunnel.The plot includes capacity cur ves for the ra dial gates a t various open-ings, and the tail-water cu rve used in concluding phases of the modelstudy. The capacity of the spillway at the maximum re se rv oi r eleva-tion of 5621.0 was 48,400 cfs.

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REPORT HYD. 350

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Figure 3Repor t Hgd-350

A . Spillway and tunnel entrances in model head box

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A. Preliminary outlet and power tunnel chan-nels - Discharge 18,500 cfs per channel

C. Outlet tunnel diver sion - Symmetrical flowthrough cente r of channel - Discharge25,500 cfs

E. Outlet tunnel flow deflected to right sid e ofchannel by eddy on left sid e - Discharge

B. Power tunnel diversion channel - Dis-charg e 33,000 c fs

D. Outlet tunnel flow defle cted to left side ofchannel by eddy on right s ide - Dischargerepresenting 25,500 c fs

PALISADES DAM p?3 2FLOW CONDITIONS IN PRELIMINARY OUTLET AND zfiPOWER TUNNEL DIVERSION CHANNELS x"'1:61.82 Sca le Model YaWVI0

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A. Pre l i mina r y channe lwith chute f loor el e-vat ion 5374 - Dis -c h a r g e 26,000 c f sB. Fl oo r e leva t ion5378.25 with pro-f i l e s a m e a s o u tl etchannel - Discharge27, 700 c f s

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Figure 8Report Hyd-350

A . Outlet tunnel diversion - Dis-charge 26,000 cfsB. Power tunnel diversion -Discharge 13,000 cfs

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'igurLepo~

A . Discharge of 13,000 cfs B . Discharge of 18 ,000 cfs

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Figure 10Report Hyd-350

A . Discharge of 13,000 cf s B . Discharge of 18,000 cfs

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Figure 12Report Hyd-350

A . Preliminary piping sys tem

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Figure 1 3Report Hyd-350

A . Total discharge 50,000 c fs (33,000 cfsthrough outlet tunnel) - 4' div erg enc e ongate frames - Tailwater elevation 5383.0

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A. F o u r gates and two valvesdischarging 31,CQOcfs- T ai l -water e leva t ion 5382.0 Dividingwall removed

B. Two valves discharg -in g 8000 cf s - Tail-water elevation 5377.0 C. Two valves and out erleft gate discharging15,500 cfs - Tailwaterelevation 5379.0

D. Two valves and adjacentleft gate discharging15,500 cf s - Tailwaterelevation 5379.0

E. Two valves and two F. Two valves and adjacentleft gates discharging right -hand left gates dis -23,400 cfs - Tailwater charging 23,400 cf s -elevation 5380.0 Tailwater elevation 5380.0 3PALISADES DAM

FLOW CONDITIONS IN PRELIMWARY OUTLET WORKS STILLINGBASIN WITH KECOlMMl3NDEDOUTLET PIPING

1:61.82 s c a h m o d el

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A . Two valves discharg-ing 8000 cfs - Tailwaterelevation 5377B. Two valves and outerleft gate discharging15,500 cfs - Tailwaterelevation 5379

C. Two valves and ad-jacent left gate dis -charging 15,500 cfs -'railwater elevatian5379

D. Two valves and ad-jacent right and leftgates discharging23,400 cfs - Tailwaterelevatio n 5380.0E. Two valves,two leftgates, and adjacentright gate discharging28,000 cfs - Tailwaterelevation 5381.0

. F. Two valves an d fourgates discharging31,600 cfs - Tailwater !arelevation 5382 4sFXcoPALISADESDAM

FLOW CONDITIONS IN RECOMMENDED O U T ~ TORKS STILLLNGBASIN WITH RECQMWNDED O U T U T PIPING1:61.82 sc ale model

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A . 2 left slide g ates and 2hollow jet valves of out-let tunnel syst em opera-ting at 23,100 cfs - Tail-water elevation 5379.1B. Riverbed after 3 hoursmodel operation at 14,700cfs released through 2left outlet works slidegates - Tailwate r elevation

5377.2

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B. P r e l i m i n a r y d e s i g n s p i l l -w a y e x i t c h a n ne l

. P r e l i m i n a r y d e s i g n s p i ll w a y e n t r a n c e

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Figure 24

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Report Hyd-350

A . Recommended spillway entrance withelliptical piers - Both gates full open

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A . Spillway entrance - F l ow through right-lnandgate - Recommended elliptical piers

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F&sre 29Report Hyd-350

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