~.% ! . . . . " ' " : _ ~:BUR.!~,U:0FRE~LAM,,~ [ O N '~" ~,'~ BYDRAULI C DABOB A'I'0}]Y

I~0T/TO. ~ BE ~BE~OVED FROM F~7~ ~. • , <%

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UNITED STATES DEPARTMENT OF THE INTERIOR

Bb'REAU DF ~qECLA~TION

]:k~ ./i" I :": Memor

~BAC~C~;ATER ",INVEST!GAT!ONS

~COLUM~IA~RI~ RES~VOIE

W° M. BOP&/~ID, ~'.~SOCIATE N ' I ~ I N ~

* .R. -A ~GOODPASTURE, ASSISTANT :.~IGI]~E~

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Denver, ,:Colorado, ~ 1940. ~May 2~,

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PREFACE /~02' ~ 0 ' ~ " - .... 'l'OI~y

E f~VOVl~D t , "

The investigations on.the backwater effects of the Grand Coulee Dam were made by the Bureau of Reclamation at i Grar" Coulee, Washington, and'Denver, Colorado. ~The backwater were made under the direction :of D. C. McConaughy,/Senior ~.-:i, neer, by W. M. Borland, Associate !:Engineer. The hydraulic ~model of the Little Dalles was constructed and~tested under !the super- vision of R, A. Goodpasture, :Assistant Engineer, bydirection of J. E. Warnock, Engineer.

These investigations were made under the general ~ supervision of d. L. Savage, Chief;Designing Enjineer. All engineerinz vmrk of the Bureau of l{eclamat~on is under the direction Of i R, FF, • Walter, Chief:Eng'ineer, and all activities;of the Bureau are un- der the direction of J. C. Page, Commissioner.

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Denver, Colorado, May24,,1940.

MEL[OR'~DUM ~ TO ~THE CHIEF DESIGNING ::ENGIN~X~ (W. M.:Borland and :R. A. Geodpasture)

Subject . Inves t iga t ions of: back~'~ater :Sf: : the Cblumbi~ iRiver Reservoir.

i. Introduction. ated on :the Columbia River •about ~ iSO miles ~::dovaustream :, from ,the:Canadian boundary will, When Completed, ~formT~a~:vast ~lake which may rise as: high as elevatio: elevations, a small r- national Boundary. i The:'investigations i presented in'this ,~report were made to determine.the, backw, ater c. Onditions :along ~ the. Upper

channel :im- reaches:of~the:reservoir and develop somepiano" = " provement to relieve the excessive:bac~,~ater.-, along the~railroad . ...... ' and at the International Boundary.

!2,,, ~:Field::data. Major=observation:stations ~were established a • c~ itlcal points where: water surface elevations have bee., ~ oossrved, especi~ at flood.stages,~since:~/arch~i1930. ~ These obserVations were made by: the Geolo ~ icai'Surve . and Cor "Of: ~ineer , , ~ . y, p~ Eng s, ~In.19S2 - the Domlnlon ,Water .-and ~ Power :Bureau ~ cooperated ::withi the Geological :Survey !in: taking observations and this! program!, has =beenilcOntinued to the present time. i~In ~19S5, S~veral additional obser~tion ,sta- tions were established,by~thei Bureau,~of "Reclamation a ~to- tal:! of 17 stat ions:: betwecn Kettle~ F~S ,:and i ~ the ibou ig~re il).. ~i S°undi~__g: of various : river '-cross i':sections were ~ mado::by , the

additional: soD/q~lat i, the Little. Dallcs:and at '~the International Boundary, A! total:of,'41 river~: cross :soctions~ are available along ~,.the!:upper,, and of: the~ reservoir:where they: ,~'erc :most ~ needed ::in ~the backwater Computations. -

.~ser% the Lmajor::ob-

_ . .... : ~-- - --- .......... o .................. arges ~!ranging

on ~ the Columbia ?River. The tributaries ~of the Col~nbia-.~iver be- tween the mouth of the Kettle River ::and • the Clark :~ Fork ::River :are

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o . . . . . . . . . . ' i' il . . . . . . . . .

all very small and do~ not materiallyaffect the flow: so that the discharge obtained in the above manner is applicable throu~h- out~ the, reach~being~studied. This dlscharge'was checked by add' ing~ the flow of the i Columbia~River ias determined: abiTrail, British ~ Columbia, to ~the~flow of the ~C]

S. Analysis'of!field!data. With~ surface elevations, c~id'the~ river cross~ roughness coefficie: ed between observation

roughness coeffiC±, face elevation,~for observation ~statioz feet. These~curve~ with :-the r.id ofl.me~ mated, as 650,000~.s~ to vary v,~t~ eat- er them :400, disch~2'e cu ~vere in ~re of~n ~as usually ~ " ~: . . . . . . . ~'~ ~ " ' zound ...to ~decreasc~~,~th an: ~ncrease ~u'.the dis- chm'~c or stage of~tho r~vcr. ~ With-c~y b~cl~vater~s~age~a~ new: ~ n for ~z~r reach is determined iTrom the n versus average~'~ater sur- face elevation curve. ~This coefficient ~is designated as ,~the ~ back- water n ~wh~le the coefficient obtained, [ assuming variation only with the-discharge, was ~ designated~as-the natural n.

• • Bac~vaten ~caiculations, ~Two ~:types of • baci~ater: curves were calculated, one assuming n to ~vary only v~ith the discharge (natural: n), , stage (bac~'~'at er n) s ~ ~

j,-

baclo';ator conditions ~ is w h e n ~, • quiteilarge ' I

average v~ater~ surface elevation curve. I~ correct bac~,Tator curve should lia bct~eez with natural ~Lnd~back~iater coefficients. ~In~:tho~inter~st~of con- serw..tism, the bac~;'ater . . . . . curves for~ the :upper :ond~of ~eservoir were com~,uted by usinA" n~ u~..1 coeffic ~t ~ ;ienbs, a n d l a r e as~the basis Tor~ future comparisons, i

Kutter!s formula for computing~ the value of~C~in the Chezy formula has: en30yed v~der nse-th~u }Lm~ningts ana, was used for the ,bacl~ater comput~.tions, except • below the Little Dalles, v;here,

i I • i/ "i ~ ~i ~.

- due to, the /~radiont, - ener serv

the! fro~ and with

~th ~'l)

~nergy rearer

3-

Q

where the :railr0a8 • suffer ~additional at i~ the ~ boundary ~ for hi

u ~ . . . . . . . . . . . . . . . . .

if of a distance ~,of ~2~500/feeti feet withthe reservoir water surface: at :elevation 129000: ~there ~-~uld be:a ]~head i 10ss of 15,5 :feet • through these.~rapids ,!(flgure ,~S), Chann@l ~ improvement at ithis location ~would bel effective ~in .... reducing energy losses at~ both natural:~ and ~back~'~-ater ~flow Con- :~ all%ions, beLittle Dalles Is shovn~ in:'figura 4. ~ ~

6. Nodel studies :of the~ Little D~

.4-~4-,~,a•~ 4-,. " ~ ' ~ " ~ L ~ 4 ~ I ~ A

that iwhen: natural-flow i conditions ~were ,reProduced at the the Little D~_lles, ~the~ npstream~ tea ....... j well'~ ~v, ith those iobtained~! from th ~6).

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,Aft er~the model ~h flow+.Condi~ions, ~+bac~ at + elevation +1290- 0 ,we rating ++curve as ~comput end of. the iLittle .~ D/ll. resul~ing ~+water ~surfac~ Dall~s +were, observe'd + (~ the Little ~Dalles -, !using bac~vater +~coef .......

+.

~ ive~ Slightly +~lower m~watez O0; 000s e cond-fe et i.than'. dis charges, ,the' ~i~model ~,ga~ one The ~'dis c greater than! 5 Da fa

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justified.+~ ~ ~++

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complished }above low-v~ater ~I¢ excava~1on+nou~ ~+'int ~ ~he "reservoir'~reach

£ • + - +

- + The • charmel improveme lydraulic mddel ~.were +~the simul+~ted rock • made. in steps + by. removi~

t h a t :. n o t i c e a b l y ~ d i s t n r b e d . f low condi t

was :made' with ~ the ~large + rock ~iSland - Dalles ~removed +.~o no additionalimp ~ation 1250~0~ .+~A

• +,:~

• + V . plan ~restored ~ natural-flow condltlons ~abo e ~tl s e c ona,i eet +for ~ r es erv( a disch.~rge ofi597,000 L+

Above + a,:discharze !of 400,000~ second-feet, %he + lower ~ than. with natural • channel flow~ ~.

• 7. Analys~s :.o£ ~,excavation~studies. ::After :+a ::satisfactory e ..... -+~ ~ , +,had'been +evolved '~-iit ~ e wheth-

er additional :excavation ,would~be jus %he amount ~of <excavation ~ for each ~excavatl _ ageinst

= ~ + , + the ~corres~ndi~_~ ~ischarge at ~which nat'Jral ~+conditions +were ~re-. . ,+

stored upstremm ~and by ~loga- ~

rithmic ~ PlotZing ..~fi ~natural rating curve at ~gage ~ll ~with <the ~backwater ~rAting~ctu-ve ~at gage 13~ (fa~e 7~)~shows !that .no ~amount i bf-excavation ~v~ould~restore ~ natural conditions

approz/mat ely e? o~ 000 ~ cubib .~'yards of ' addi~ional~!excavation would be ire~Uiredlto ~eproduce !natural,~con~itions.'.at a~discharge ~of 350,000 ~second-feet ~ iPlan ' 5 :is ~:ac~c . . . . : :,

8, Bac~.~ater ~with .improved ~ch that ~hile ~the .. recommended : channel impr ovement ~wo~ld ~res~ore ~natural- flow~ conditions at i the hsad Of the LitZle ~:~Dalles ~or ;a discharge "of 1400,000 second-feet, som~ .~ined for all '~larger ~floods, Th- Little ~Dalles, but' ~ou'id S

S,~ :fiA~re ?ii. ~These ~comou

this curve no ! back~;'at follo~ing ~.

face ~at elevation 1290;0. • / !D • ."

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BACKV;AT~FV~R ELEVATIONS AT ~INT~d~ATION~/L

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Figu~.e~in'.:parent-heses iindicates ba( ff iminus.

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tude wfl face ~is atthe~b for ;rose present:

9~, (Conclusions~ -

(a) ,Th t .International flow ito about

ed: . ;:.

there .;,~ll exist:at.the .!!.

'hoodof!4OO.,.OOO-secon~-feet•, d.~age,.:~he~back;~ater..surface ~illbeabo~t at.the's"/meele~ation as thenatural:su~-face for 'lO0,O00.second-feet less..di:

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(C ~) That for~.dischal-ges les~ ~h~n ,~n_noo ~o~a,~÷. '~+ .~.~..

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(d) /-That -bY channel ~mnprovement ~at equiring':i'i ~

tions atGSO,O00 second.~feet.

.(e'~) ' That y uhis !npr ovement ~the water surf~ce ~lo~ the -r~il- road.w~ll be no hiEl~er ~ith-~n under ~-present conditions '.for "" s ..charge of .400,000 :second.feet...and.wAll be lower .th'~u :under present Conditions :for gr eater, dis charges by . amounts .~up to abou t/ll...f eet.

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