PRELIMINARY ENGINEERING REPORT

RAISING OF BIG COULEE DAM

PROJECT NO. I4I8

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BISBEE

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NORTH DAKOTA

STATE WATER COMMISSION

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BIG COULEE DAM

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PRELIMINARY ENGINEERING REPORT

RAISING OF BIG COULEE DAMSl,lC PROJECT #1418

NOVEMBER, IgSi

Nont,h DakoLa State l,Iater .CommissionState 0ffice Buiì_ding

900 East BoulevardBisnarck, North Dakota 58505

neer

PREPARED BY:

GJAssÍst.ant nvestigation

SUBMITTED BY:

ID A. SPDirector of Engineering

APPROVED BY:

VERNON. FAHY E

E

Prepared for theTowner County I'IaLer Resource Board

State Enþineer"

TABI.E OF CONTENTS

page

1. TNTRODIJCTION..,.... .,.,.rr. DtscRIPTrqN OF SITE. ;... ¡ 3III. STATEMENT OF PROBLEM Ò.¡.. ¡.. i.

Baekground.:.. . ¡... g

. ¡............ r ¡.. ¡ - 11

ÏV. SYDROLOGT

1y......:.. 1q.

St.udy Results. '...1,o..e ....f .?.....i.. 16

V. AITEmûåTI\¡ES..,.....i..¡.d.. .r... !.qri .. zzAl.t.e¡native 1

Àllernat.ive Z. r,...ALt.ennat.ive 3,...

VT. SUU!..{A8T AND AECOMMENDATTÔNS.

Sumary.

Reeor¡r¡endatione. .,. . i

TABLE 1.

TARLE 2.

TÁBIE 3"

TABLE 4.

TABLE 5.

TABLES .

Routing Results, for Existing Conditions.Rout ing Resu1t.s for proposed ModÍfications. . . . . i, . .Preliminary Cost, Est.inat.e-Aj_ternative A, . .Prelini¡ra¡y Cost EetimaLe-Alternative 3.sunmary of Routing Results for proposed Art.ernat.ives...

17

19

26

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31

1

North Dakota State Water Commission900 EAST BOULEVARD . BISMARCK, ND SB50s-0187 . 17011224-2750 o FAX (701)224-3696

WÀTER DEVELOP}IENT DTVISION(701) 224-27s2

February L4, 1991

Honorable Margo HelgersonMayor of I{esthopePO Box 412Westhope, ND 58793

RE: SWC ProjecE #L267

Dear Mayor Helgerson:In considering your request for cost-sharing for the I{esthope Damproject, I have reviewed the Preliminary Engineering Reportprepared by Toman Engineering. Before t,he project can beconsidered for cost-sharing, there are several concerns whichmust be addressedÀs stated in the report, the dam, as proposed, would beclassified as a Class fIf dam under the North Dakota Dam DesignGuidelines. The freeboard requirement for a Class III dam inNorth Dakota is a 30 percent PMP flood. This means that the dammust be abl-e to pass a flood equal to 30 percent of the ProbableMaximum Precipitation without overtopping. This would beapproximately a 6 1/2-inch rainfall. The engineering reportmentioned nothing about an emergency spillvray or the performanceof the dam during floods. f should also point out that there areveLocity requirements for emergency spillways l-isted in the NorthDakota Dam Design Guidelines as wel1. An adequate emergencyspillway could vastly increase the cost of the proposed dam.

The main concern is that the preliminary engineering report besufficiently detailed to provide a good cost estimate. This costestimate is needed to determine the level of cost-share requiredfrom each entity. Once r{e are satisfied that aII requirementshave been addrelsed, your specific cost-share request wilt besubmitted io the State I{ater Commission for consideration.Sincerel Yt

s Lenn , P.E.ater Resources EngineerJL:ùncc: Toman Engineering

GOVEBNOR GEORGE A. SINNERCHAIRMAN

DAVIO A. SPRYNCZYNATYK. P.E.SECRETARY E STAIE ENGINEER

ToToToBC

MESSÀGE DTSPLAY

DaleDaveCaryJIM LENNINGTON

FTOn: JIM LENNTNGTONPostmark: Apr 30r9I 2:11 PM Delivered: Apr 30r91 2:l-1 PM

Subject: I{esthope Dam

Message:Ilesthope is considering constructing a multi-purpose reservoir to thesouth of town. They have been discussing cost sharing for thisproject with us. There is a big problem with this proposal in thatthere is a strong probability that a water use pennit applicationwould be denied. The location they are proposing for the dam is on atributary to the Souris. I discussed the possibility of transferringal1 or some of the appropriation the town currently has out of therefuge pool to the dam site with Gordon and Bob lùhite. They informedme that this would not be possible. I have a meeting scheduledtomorrow in Westhope and I'm wondering what f should teII them abouttheir proposal. Àny suggestions would be welcome.

7oo I 53 ¿S

60,000 sY

LS

59 650 LB

700 cY

1,400 cY

RÀLEIGH DAM - S.WC--P.8.A]ECT

ÀBSTRÀCT OF BIDS OPENED I:30 Pl

Dakota Dirt ÀfovingBox I3lMclaughlin, SD 57642

2 ,000.00

14,400.00

15, 260.00

84,600.00

13 ,750.00

6,840.00

29 228.5

16 800.00

.00

500.00

2,962.50

$ 290,633 .00

ITEMri- / ?<.q

I. Mobilization

2- ControL and Removal of vùater

3. Stri lopsoil

Excavation

7. Foundat ation

Reinforc Steel

lO. Rock Ri Pilter Beddi

11. Rock Riprap

L2 cel

Drawdown fnstallation LS

7.5 AC.

TOTAL

0

LS

LS

s7 . 200 .00

2,000.00

24

1.40

90

505.

6,840.00

266.OO

49

6.00

12.00

3.900-oo

q qqfì ôô

500.00

395.00

BTDDER

6. ÍIater For Compaction 2,5OO M GAL

t,t:/\t, r,r.,t,t t,til:t;¡i. l,/\t\l , .\l!(, l,l(O,Jl:(,'l ll l(t7 IAll.S'l'llA(;'l' Ol; llll)Íi Ol,t;Nt:t) 2:00 t).¡,l.,

^tltìl l, 22, l9S3 *(lot'l'r'ct crl

lll.l)r)t;R llo<¡ ¡'lrcit<l (lttn:;t rr¡r:t i o¡tl). O. llox 87tl

5 6.560I'loorllca<l

(o l(c. r'rr li 'l'irlrcr r/ rllrr r:¡ I llorrtc 2,

I ¡lc .ll<¡x 54

a cl crn ir I.f

(jc¡ttlirl l:xt'trv;rt i n¡¡f). O. llt>x l(,7,1

(.r.r

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2,144.00 6,432.00 I ,500.00 7 3() . ()0 l, I f)0. ()0

.27 52,500.00.s00. 00

.25 * 62,500.00 20 50,000.0048,000. 00 48, 000. 00 10,000.00 1 0,000. 00 30, 000 . 00 30, 000 . 00

r .77 83, 380 . 05 1 .00 7L,265.00 2 .00

.97 477 ,682.O0 .7s * 322 ,9.50 . 00 95

*r42.530.00

409,070.0095 53,960.00 7.25 71 , 000. 00 l.l(r 65,888.005B (r , (r70. 00 4.00 46,000.00 .I0 l , l5t).00

187.66 70,372.50 lB7.(r(r 70,372.50 2.55. r)0 f)5, (,25. r)()

39 25, 133..55 39 2.5,153.55 ,1.1 28,355.,srl15. B9 5,339.04 t.s . 89 5,339.04 12,5J!). (r0

57.99 5,799.00 57.99 5 , 79g. 00

37.:i5

53.0() 5,3u().0011.1.3 5,008.5t) 11.13 5,00tÌ.50 4, ()80.l)()

9.s7 3,732.30 3,732.30 .5, ()31 . ()0

7 .46 3,91(i.50 3,91(r . 50

l0.,.lt)

12.!)0

f).50 I , !)87.507!¡ .17 11,.529.20

9.s7

9.00

7 .46

(r,840.00 t 7 .2t, I3,II().()014.8(r 84,330.50 30.00 I 70, 250. 00 20.00 113,500.0(ì

4 .02 7 ,63t\ . (')0 10.00

1,873.00 1 , 873. 0t) I , B73.00

1 !) , 00(). 00

1, tì73.00

l5

.100. 00

,9,075.00

300. 00

1 t ,20¡t.00 1 1 ,209.00 I I ,208.00 I () , l()r) . ()0 1(),200.0()

214.40

11,208.00

I0, 72(). ()() 1 50.00 7,5r)(ì. ()0 3tr ()()2 ll 800 . 00

I't't'N'

l. Clcaling lì Grubbing 3 Acrcs

2. Stri¡r fi S¡rrcad't'o¡rsoiL 25O,000 S'r'

3. Dewatcring t,S

4. Excavatic¡¡l 7J,265 CY

5 . limbankmcn t 4 30, (r00 CY

6. lrn¡r. 0l:ry llla¡tkct 5(r, ll00 CY

7 . l{ater for Compaction II,500 l'l G:r1

8 . (io¡rcrc tc 375 (:Y

I . llci¡l forcirrg Stecl 64 ,443 t.t,

10. InstalI 48" Pipe 336 t.F

ll. Dr¡ctilc Ir.on. l)ipe 100 t,t;12. l'VC Pipc 4 50 l,¡;

13. ^Cl)

- 6'r l)crforatcd 390 Llj

14. ^Clt

- 6t' No¡r-Pcrforatcd S2S Llr

15. [)r¿r i ¡r l;i I I l,lateri al 7(r0 CY

16. llock fl i ¡rrap 5 , (r75 CY

l7 . llock lì i pra¡r Fi I tcr Bcd I ,900 Cy

lB. Catc Instnllation I,S

19. llisccl lnrrcous l.lctals I,S

20 . Scccli rrg

.)1.{tll.lll.r)tll()l'¡\1,

-50 Âct'cs

ii1) lli , L),1 . l,l lil).I , 11J7, .;1)

FIOURE 1.

FÏGU8E 2.

FIGURE 3.

F'ÍGURE ¡I.

FIGURE 5.

TABLE OF CONTENTS (CONT. }

Pagje

FIGURES

GeneraL Locat.ion of Bíg eoulee Dam.,

Area CapaeÍLy Curve..... .rr.5¡¡......... 5

25-Tear. Eydrograph.. .,. . ...Proposed Alterations to Downst.ream Enbankment.. 23

J0-Fooü l{ide Chut-e.. . . ... 25

PLATES

As-Built Damsit.e Topography. 35

'Drainage Area. ...... 36

Area rnundat.ed by Reservoir for proposed ^arternatives.. 3T

area of Downstream Ennbanknlent proposed for !{odification 3g

APPENDIX

Invest.Ígation Agreement

PLATS 1.

Ptr,ATE 2.

PIATE 3.

PIATE 4.

APPENDIX A.

¡1

I. INTRODUCTION

Big Coulee Dam is a multi-purpose dam located in Towner County. It providesthe munÍcipal water supply for the City of Bisbee, North Dakota and also is a

recreational- area for the cornmunity. Since it.s init.iaL fiJ.J-ing in 1969, t,he

damsit.e has required a large amount ofl maintenance. The service spillway has arêlatively small- capaciLy, result.ing in frequent use of the emergency spii-l.,¿au.

This has caused some erosion t.o t.he emergeney spiLlway. In addit.ion t.o Lhese

problems, t.he qualit.y of the water in the reservoir has been det.eniorating.On April 30, 1980, t.he St.ate Water Commission enlered into an agreement.

with t.he Towner Count.y l'lat.er Resource Dist.rict-. The purpose of this agreement.

was to study t.he feasibil-ity of raising t.he control elevat.ion of Big Coulee Dam

in order t.o improve condit.ions for boat.ing and fishing. This involved studyingthe cost.s to buil-d a new principal- spirrway, plug t.he ord drawdown pipe, and

possibÌe modifications t.o the emergeney spillway. To improve the wat.er

quality, the Board want.ed t.he modifications to inelude a low-level (hypolimnet.ie)

wat.er qualit.y control struct.ure. A copy of the agreement. is included inAppendix A.

The hydrology of t.he waLershed was re-evaluated in order to det.ermine the

infl-ow to the reservoir. The infl-ow was flood rout.ed through several sizes ofservice spillways set. at'different. control elevat.ions. This was done t.o findthe nost feasible st-ruct.ure capable of adequately handling the infLow.

The as-built. topographic map is included in t.his repcrt. as Plat.e 1.

This reflect,s the various changes whieh happened over t.he Iife of the st.ructure.The hist.ory of t.he problems associated with t.he dam was reviewed. A descriptionof the geology.and hydrology of t.he watershed was also presented. This reportsummarizes the resuLt.s obt.ained from t.he fl-ood routing of the reservoir.

-1-

Frelininary eost. estir-{at.es r¡ere presented for the atrLernat.ives proposed. These

aLt:ernat,ives handied the design flows with a mininun of discharge over the

emergency spitiway. Final pLanq and. a &ore conlplete cost. est.irnat.e would be

pnepared after the project çouLd be aut.horÍ1ed and construetion ls imminen:t.

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II. DESCRIPTION OF SITE

Big Cou1ee Dam is located in Section 36, Township 160 North, Range 68 lvest

in Towner County. The City of Bisbee, NorLh Dakota, is approximately 3/4 milesout.hwest from t.he dam. Big Coulee Dam ls on the Big Coulee, which is a trjbu-t.ary of the Mauvais Coulee and in t.he Devils Lake Basin. Figure 1 is a map

showing Lhe general location of t.he dam and t.he surfical geology of t.he area.Big Coulee Dam is a 37-foot. high earth-fil-I dam. At. the present, cont.rol

elevat.ion of 1572 MSL, it. has a reservoir capaeity of 1,630 acre-feet whileinundat.ing an area of 195 acres. The reservoir has a maximum depth of 24 feet.and an average depLh of 8.4 feel. A'drainage area of lOB square miles suppliesinfl-ow to the reservoir. An area capacit.y curve of the resenvoir is shown inFigure 2.

The slope of t.he main channel above t.he dam is approximat.el-y Z feet. per

slile. Downst'ream the slope fl-at.tens out. to 4 feeL per mile. Ìüithin t.wo ort'hree miles downst.neam t.he topography of the land also fl-at.tens ouL. Thiscauses Big Coulee t.o become wide and sJ-uggish as it. flows in a sout.h-sout.heast.erly

di rect i on .

The very upper reaches of t.he drainage area extend t.o the eastern slopesof t'he Turtle Mount.ains near t.he town of St. John. The Turt.Ie Mountains, int.his area, have so many Floughs and ket.ttes t.hat. very little of the area

act.ually cont'ributes t.o t.he runoff collect.ed at Big Coulee Dam. Plat.e 2 depict.sBig Coulee Dam and it.s t.otal wat.enshed.

The surfical geology of t.he Basin Area is primarity of glacial origin.This area is. locat.ed in t.he centrar Lowland province (Fenneman, 1938, p.559)

and the Drift. Prairie as designated by Simpson (1929, p.4). Surfieal deposit.sin the dam site area consist entirely of glacial drift. The drift deposits arecomposed predominant.Ly of fiII and are similar in visual appearanee, but. differ

-3-

S A. S K.A T C H E W A N MAN ITI

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Fisure t- LocATloN .oF BIG COULEE DAM AND PHYSIÓGRAPHIC

(Modrlrod lTom ôloylon'J96e)

PROVINCES OF THE AREAii. :

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somewhat' in texture and composit.ion. Pierre Shal-e of the Cretaceous Age is thepredominant t.ype of bedroek in the area. The present creek oecupying Big

Coulee is a recent. st.ream wit.h a drainage area of 108 square miles above t.he

irnpoundment.

The embankment. is a zoned rolled eart.h-fill darn with a clay core. It.originally was 931 feet' Iong with a top widt.h of 12 feet. and a volune ofE2,191 c.y' The upst.ream slope was 3H:'1V while t.he downst.ream siope was 2H:1V.

A 1O-foot wide bern was added about. 12 feeL below t.he fop along the right. halfof the embanknent. on the downst.ream side. This berm has a 4H:1V slope. The

t.op of the embankment is at. an el_evat.ion of 1585.0 MSL. A 1O-floot. wide cì_ay

core trench runs t.he ent.ire lengt.h of the embankment. and ext.ends bel-ow thepermeable sands int'o a elay loam soil. Riprap covers the upst.ream slope from

elevation 1566.0 MSL to 1579.0 MSL. Plat.e 1 shows the t.opography of the entÍredamsi t.e area.

The emergency spillway is at. an elevation of 15TT.O MSL. It. is an uneon-

trolled grassed spil-Iway with 3H:1V side slopes. Although the majorit.y of t.he

emergency spillway is 200 feet. wide, t.he cont.rolling point. is'181 feet. wide.

The steepest. portion of the emergency spiJ_l_way has a slope of 3.5 percent.

A concrete drop inlet, a 54-ineh eorrugated st.eel pipe, and a concreteout.let st.ruct.ure are the components of the se¡"vice spitlway. The Ínlet.struct.ure controls the eievat.ion of t.he reservoir at. 1572.0 MSL. ÍL consistsof a reinforced concrete drop struct.ure wit.b inside dimensions of I feet by I feet.The floor of the st.ruct.une is 8 feet bel-ow t.he spillway crest.. The conduit.

consists of 109 leet of 54-inch,1O-gauge HeIicalty CorrugaLed GaLvanized SteelPipe. An open coneret.e box, 10 feet. long and 6 feet. wide, serves as the outlet.st.ruet.ure. No energy dissipat.ors are present in this structure. There is a

A-foot. cut.off wall on the outlet. end to prevent the st.ruct.ure from being

-6-

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*

undermined. A low level out.let, consisting of 156 feet. of tO-inch, lg-gaugewelded st,ee,I Fipe, disehrarges into t.he out.let. sL.ruct.ure. a gate va1ve, locat,edI feet. flio.r¡ r[he oublet., cont.rols t.he. fl<¡w through t,his pipe. Double railpi;plng and fit.tings serve as the trash raek.

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III. STATEMENT OF PROBLEM

BACKGROUND

Initial int.erest. in the construction of Big Cou1ee Dam began with a

request. for survey on Oct.ober 8, 1965. Borings were taken during mid-July of1966 and the bid opening was on JuIy 11, 1968. AI1 work, excepl for seeding,

was eompJ-et.ed on December 4, 1968. The project. was dedicat.ed on June 21, .|969.

Const.ruction of Big Coulee Dam was sponsored by the City of Bisbee, the

Towner County Park Board, the St.ate Game and Fish Department, the SbaLe Outdoor

Recreat.ion Agency, the Bureau of Outdoor Recreat.ion, and t.he StaLe l.iat.er

Commission. Actual const.ruct.ion of the dam cost. $ 107 ,693, recrealion facilit.iescost Û17,214, invest.igat.ion and design costs were $6,4t+2, and Lhe cost of land

was $27,500. Included in the t.ot.aL cost was þ32,251 allocated for cont.ract and

related cost.s incurred during the 1969 fLood damage repair.The init.ial fitling of the dam was on April 11, 1969. Water was flowing

over the emengency spillway five hours aft.er the service spillway had been

overtopped. The roar of t.he water v'/as not.iceable t.o t.he residents of Bisbee.

The flow peaked with a seven-fool head on t.he service spilì-way weir and Lwo

feet of flow over t.he emergency spillway. The maximum fl-ow over the ernergeney

spillway, which was 130 feet wide wit.h 3H:lV side slopes, was est.imated t.o be

bet.ween two and t.hree t.housand cubic feet. per second. This large discharge

caused serious erosion to t.he unseeded earthen emergeney spÍl-lway. Towner

County equipment. made emergency repairs to t.he spilrway. The spiì-lway $Jas

closed by dozing large piles of frozen malerial across t-he spillway. The

equipmenL was in operation from AprÍl 15 through April 17. After closure, t.he

service spiì-lway was able to handl-e t.he receding flow.

-8-

Foll-owing this emergency act.ion, the prime contract was extended toinclude repairing the badly seoured emergency spill-way. The bot.tom width ofLhe emergency spillway was widened.from 130 feet to 200 fleet.. (Alt.hough themain portion is 200 feet, wide, t.he controlling widt.h L¡as measured t.o be 181

feet'.) tfie slope of t.he.emergency spillway was redueed in order to lower thevelocit.y of any water flowing over it. Tot.al costs for repair and revision ofLhe ernergency spilJ-way amounted t.o 632,2j1.

Grout.ing t.he ent.ire lengt.h of t.he service spiì-J-way pipe in order t.o fitlall voids which had been created by leakage of t.he joints v,¡as recommended aft.eran inspect.ion on June 19, 1969. It was also recommended that. t.he joint.s be

sealed wít.h eit.her internal- expanding pressure bands or welding t.he joint.s.Int.ernal expanding bands were installed on the joint.s of the helical corrugat.edst.ee1 pipe in JuIy of 1969.

An inspect'ion on April 17,19TO, revealed t.hat the black dint. blanket had

sLid down t.he slope of t.he clay sub-base. The ernbankment. loeat.ion is ideal forcolÌect.ing huge snow drifts on t.he downstream sIope. The grass eover had not

obtained sufficient root depLh to st.op t.he black dirt. from sliding when

sat,urated by t.he melting drifts.It. was discovered on May 22, 19TO, t.hat. there were two cracks in t.he

headwall- of the service spillway. These L¡ere repaired Ín 19Zl by driving steelpiling along each edge o1 t.he headwall and bracing across the t.op t.o support.

and strengt.hen t.he headwall. llater had again overt.opped the emergency spi1lwayduring t.he spring of 1970.

During t.he spring of '1971, a flow of 6 inehes, or 200 cfs, was observed

over the emergency spillway. An inspection on August 18, 1971 revealed that.

the 54-ineh diameter service spillway pipe had deformed to an average size of50 inehes by 57 inches.

-9-

An inspection on May 9,1974, revealed that the Lopsoil had slid a1_ong a

150-foot. sect.ion of the downst.ream slope. l,'lat.er at a dept.h of i.5 feet had

flowed over the emergency spillway during that. spring causing scme Camage. The

eroded areas were repaired during t.hat. year-

IL was revealed that the t.opsoil on t.he downstream slope had again slidwhen an inspect.ion ulas rnade on May 6, 1976. The ND Arny National Guard

commenced repairs on t.he embanknrenl cn August. 28, 1976- They st.arted repairingt.he emergency spillway and st.abiJ-izing the downst.ream embankment. by addingmalerial to change the slope to 4H:lV. This fill extended from the right sideof t.he service spillway outl-et. t.o the right. abutment. I,lork cont-inued throughlale fal-l wit.h weekend dritls and was cont.inued t.he foLlowing year during June

and July. The compacted fill was brought. up to wit.hin 12 feet of the top oft.he embankment and lefl as a berm. The topsoiJ- was then replaced over t.he new

fiLl materÍaI.

An inspect.ion on June 14, 1977, revealed t.hat almost. all of the asphaÌtcoatÍng had peel-ed off the service spillway pipe. Corrosion was t.aking plaee

along the bot.tom 1/3 of the pipe. A Bitumastic eoat. was applied during jg7T.

!'lat.er at a dept.h of 2.5 feeL had flowed over the emergency spillway duringthe spring of 1979. This large discharge eaused a great. deal of erosion t.othe emergency spiJ-lway. Over half of the topsoil was washed away. Sevenal

pits were formed wit.hin'the emergeney spillway. Repairs Írere made at a costof $10,180.

There was a discrepancy in what was thought to be t.he elevaLions of thedifferent component.s of the dam. The correct. elevaLions and dimensions of t.he

damsite were obt.ained from a survey eonducted in August of 1980 for this re-port, An inspect.ion of t.he spillway pipe on December 2p, '1980 revealed thatt.he first. joint required addit.ional seaLer. A eoncent.rat.ion of rust was

presenL on Joint. 3.

- 10-

EXISTING AND ANTICIPATED PROBLEMS

The maintenance cost's for Big Coulee Dam have been high. In the dam,s 13year exist'ence, the emergency spiJ.lway has been used at Least. five times. Waterhas fl-owed over t.he emergency spiJ-lway Ín the spring of 1969, 1970, 1gT1, 1g7U,and 1979' The emengency spÍllway suf.eered a large amount ofl scour damage

during the 1969, 197t1, and 1979 ftoods. Even wit.h a good grass cover, the highvelocit'y of flow eaused by a large snowmeLL is eapable of eausing considerableerosi on.

Aeconding t'o it's history, the service spill-way for Big Coutee Dam cannothandle anything great'er than a 3-year snor¡melt. without the emergency spÍrlwaybeing used. At' the present. elevation of the service spirrway, t.he emergeneyspiJ'l-way is used too frequentJ-y. Simply raising the lever of t.he exist.ingservice spilJ-way woul-d eause water t.o flow oven the emergency spÍl1way morefrequent'ly, endangering Lhe dam. rf t.he cont.rol elevat.ion of Lhe reservoirwere t'o be raised, a complete new service spillway woul-d have t.o be const.ruct.ed.It should be designed so that. t.he emergency spill.way is not used durjng t.he

Z5-year snowmelt'- For largen runoffs, t.he velocity of fl-ow over the emergeneyspillway should be kept. smarr in order i.o p"euent. scouring.

The downstream embankment was originatty const.ructed with a ZH:1V slope.The right' hal-f of this enbankment suffered an annuar sroughing probrem untilcorrecLive measures were t.aken in l9T6 and 1977. The embankment has apparentlybeen stabilized by t.hese efforts. RaisÍng t.he control elevation of the reser-voir could cause t.he port.ion of t.he embankment. t.hat. js still at. a 2H:lv slopet'o become unstabLe. Att.hough minor seepage exists currentry, t.he increasedwater pressure may eause greater seepage through t.he dam.

The service spillway consists of an 8-foot. by 8-foot weir wit.h a 54-inchCMP leading from iL. The pipe, set. at a st.eep slope of 13.6T percent., cannotmaint.ain full pipe flow for any length of t.ime. llhen flowing under partiarly

-11-

full- condit.ions, hígh vel-ocities are obtained due to t.he steepness of the pipe.This hígh veloeity causes the wat.er t.o entrain air, thus swelì.ing in vol-ume

and filì-ing the pipe. The increased wetted perimet.er creales greater frictionalresist.ance and reduces t-he ilow rat.e. This causes the air t.o become separated

from the wat.er. The flow then returns to a partially fulI condition. Thisprocess' called slugging, is repeated cont.inuously. It. is t.he cause of fhe

l-oud roar occasionally heard by Bisbee resident.s. The slugging effect. causes alarge pnessure differenLial wit.hin the pipe. Strong vibrations ane produced,

which ean jan t-he pipe fnom its posit.ion.

There has been some deteriorat.ion of t.he met.al spilJ-way pipe. Rust.ing has

been evident on the bott.om 1/3 of t.he pipe and at the joints. The Bitumasticcoating appears to be retarding t.his process at. the present time. There has

been some leakage at t.he joinls which could eause the soil support.ing the pipeto be washed away. Due to t.he weight of t.he soil above it, t.he pipe has deformed

t.o an average size of 50 inches by 57 inches. This pipe will probably have t.o

be replaeed in the fulure.The low level drawdown pipe also present.s a problem. The gate valve is

located near t.he out-Iet. end of the dam. This allows t.he pipe, whieh extends

below Lhe dam, t.o eontain water under pressune. There is the pot.ential fort'his pipe t.o rust. out and cause a large amount. of seepage. This could easilyeome to t.he surface and cause exlensive erosion or failure of the st.ructure.

The Cit.y of Bisbee has receÍved poor qualÍty wat.er fnom the reservoir.This is due Lo eutrophicaLion and the strat.ifieat.ion of t.he wat.er in t.he

reservoir- St.agnant wat.er concentrates on t.he bott.om while the fresher wat.er

stays on t.op and is discharged downstream t.hrough t.he spilJ.way. A low Level(hypolimnetic) wat.er quality cont.rol struct.ure could be const.ructed to helpalleviate this problem. This struet.ure would discharge the stagnant water from

-12-

t.lre bs1.tsn, allowing t.he reservoln t.o be fi'eshened by inflows. .The ¡¡ater

. quality of the neservoir woutrd improve, due to an lncrease in the dissolve.d

oxygen and a decrease in nutrients which cause.algae

At. the present el-evat.ion of t.he reset'voir, pleasure boat.ing ls only

possible in t.he area of t.he original coulee. Thè average depth at present is8.4 feel. .Thís would be inereased to 8.9 f,eet .if lhe cont.roÏ elevat.ion ¡¡ere

raised 2 fe,et,. An average depth o.f 9.7 feet.'¡ouLd be obtaÍned ifl Lhe reservoir

"$rere raised 4 feet. Tbere çrould still be a J.arge amounl of shallow âFêâs.

However, the area accessible to boaLing t¡ouÌd ínerease.

Und'en t.he reservoirrs present..condiLions, many of t.he fish do Rot survive

through the wint.er. The poor qualit"y of the water nay be as big ä eon:tribl¡tór

to this problem as t.he shallow dept.h is.

î

- 13-

IV. HYDROLOGY

DISCUSSION OF THE STUDY

The hydrology of the ent.ire Big coulee wat.ershed was analyzed using theTR-20 comput'er prograrn which was developed by the u.s. conservat.icn service-rt r¡as used to deternine the peak erevat-ions, peak infllow, and peak dischargesof various frequency storms. The program forrnulates a mat.hematieal, hydroì_o3iemodel ol the walershed. This is based on t,he forlowing daLa: t.he amount. ofrainfarl-, rainfatl distribution, soiì_ type, land use, and the hydrauriceharacterist.ics of t-he st.ream channers and drainage area.

The Big couree watershed ext-ends from the dan nort.hwestward to incl_ude theeastern sropes of the Turt.le Mountains near t.he t.own of sainL John. rt ineludes108 square niles of drainage area. rn order to obt.ain mone accurate data t.oinput int'o the TR-20 program, t.he watershed was divided into 22 sub-basins-Each of these sub-basins has it.s own distinct drainage boundaries exeept forfour divisions wit-hin t'he TurLle Mountains. These regions r^rere separated fromt'he remaining sub-basins beeause of the differences in topography. They arecomprised of sevenar sloughs and ket.t.les which are capable of storing most oft'he runoff' For t'he input on t.he TR-20 program, a reduct.ion in the effeet.iverunoff r^¡as made in order to aceount. for this storage capacit.y.

Cross sect'ions F¡ere,taken at. several point.s along t.he main channel of Bigcoulee' The surface roughness and type of vegeLative growt.h was not.ed for eachcross-sect.ion in order to obtain a roughness eoeffieient (n). The slope, n_value,and the dimensions of the channel for each cross-sect.ion were Ínput- int.oan open channel program utilizing Manning's formula. The output from Lhisprogram provided the area and discharge at 1/2 foot int.ervars fon each cross-seet.ion.This was put int.o the TR-20 pnogram.

- 14-

No special allowances were made for point.s where t.he ereek crossed roads

utilizing culvert.s for drainage. These erossings do not impede t.he flow t.o any

measurabl-e degree because t,he water can easily overtop t.he road. The onlycrossing t.haL could back up t.he flow an apprecÍabl-e amount is t.he t.wo 7-foot.diamet-er culverLs under the railroad tracks in Section 1, Township 161 North,Range 69 Ítest. The rat.e of ftow through t-hese culvert.s was t.aken into accounlon t-he TR-20 program.

A general land use deseript.ion of t.he v¿at.ershed, wit.h t.he except.ion of t.he

Turtle Mountain Sub-basins, is as follows:Past.ure 41í

Small Grain 39?l

FaIIow 18í

Farmst.eads and Roads 2fThe divisions wit.hin the Turt.le Mountains are predominant.ly woods and past.ure

land. About. 4O% of the area is sloughs and kelt.les.The rat.e of flow over t.he emergeney spillway was det.ermined by inputting an

n-valve and'the dimensions int.o an emergency spiJ-Iway rat.ing curve program.

The discharge through t.he service spillway was deLermined by using forrnulas forweir flow, orifice flow, and full pipe flow.

. The TR-20 program produced out.put. of t.he infiow into the resenvoir. Thisinflow was flood rout,ed t-hrough several shapes of service spillways set atdifferent cont.rol elevat-ions. This was done t.o find the most- feasiblestructure t-hat. wilI meet Lhe recommended guidelines. These result.s showed t.he

peak elevat.ions and discharges for eaeh sit.uation_

-15-

r:L, i:.{, i r3. ùr:,v+sìr.i#.tuìiÉ-É jú-jilÀ*rirájae

STUDY RESULTS

The TR-20 eomput.en program showed that. all floods due t.o spring snowmeltswere greater than t'hose due to rainfall. These result.s are supported by thefact' that' aLl the larger fl-oods at Big Coulee Dam have oecurred during t.he

snowmelt period- The eomput.er results also confirm t.hat t.he t.wo 7-foot diamet.ereulverts in Sect.ion 1, Township 161 North, Range 69 West cause wat.er t.o back upbehind them' The dischange raLe from the drainage area upstream from Lhis point.is eont'rolled by t.he fl-ow¡"ate t.hrough these culvert.s. This control poinl causesthe peak inflow at Big Coulee Dam t.o be reduced.

TabLe 1 shows t'he peak inflow to t-he reservoir for various frequency sno!¡me1t,s

as obtained from Lhe Tn-20 model, The peak reservoir elevat.ion and peak dis-charges through the service spillway and emengeney spillway are arso shown fort'he present condit.ions af Big Coulee Dam. The veloeit.y of flow over the emer-gency spillway is also shown in order t.o see if scouring would occur. The

result's obtained from the computer program appear to cl-osely coineide wit.h t.he

act.ual condit.ions experienced at Big Coul_ee Dam.

Any revisions made t.o t.he service spiltway at. Bíg Coulee Dam should neet.

cert.ain design requirements in order t.o ensure the safety of the dam. No flowshould be allowed to pass over the emergeney spillway during a 25-year snowmel.t.

For events larger t.han t.he 25-year snou¡meit., t.he velocit.y of flow over t.he

emergency spillway should be limit.ed so that scouring does not oceur. The

velocity at which seouring occurs is dependent on t.he t.ype of soil- and grasscover. For the conditions at Big CouLee Dam, scouring will- occur when thevefocit'y is in the range of 4 feet.per second t.o 6 feet per second. The velocÍt.yof flow should not. be allowed to exceed t.his range. The present. weir and conduitare not eapable of meeting t.hese requirements. An ent.irely new service spillwaywould have to be const.ructed if the reservoir elevation were t.o be raised.

- 16-

TABLE 1

NOUTING RESULTS FOR EXISTING CONDITIONS

Cont.noL Etrevation Frequency of Snowmelt. Inflow(cfs )

Elevat lon ofReservolr

1578.8

1 579.0

1579.5

1580,1

Diseharge ofServjce Spillway

(cfs )

561

565

654

740

Discharge ofEnergency Splllway

(ofs )

960

1 ,17A

1'' 700

2,480

VeLoci t.y 1nEmergency

8pi 1i¡¡ay ( f ps ì.

6. lt

7.0

8. r

9.4

10

25

50

100

year

year

yeâr

yeãn

11622

1,822

2,436

3, 143

sno¡¡melt,

snowmelt

snowmelt.

snowmeLt.

I{I

1572 MSL

All values shown are t.he peak values for fhat. frequeney snowmelt,.

Emengency spillway at an elevat.ion of 1577.0 MSL.

A service spiì-lway, aL eaeh proposed control efevat,ion, vJas found thatwould meet the suggested requirements. The resuLt.s obtained by rout.ing t.he

inflow of t.he reservoir t.hrough each service spiltway showed whet.her iL coul_d

adequately handle t.he flow. These result.s are shown in Table 2. A cost esLÍmat.e

was completed for the construct.ion of a service spillway at. each cont.rol eleva-tion. ft. was found that. t.here would be a relat.ively smal1 difference in Lhe

cost of const'ruct.ing a service spillway which woutd raise t.he contrcl eievaLionof the reservoir by 1 foot or 2 feet.- Therefore, t.he 1 foot rÍse was disnegarded.

Addit-ional land would have to be aequired if t.he cont.rol el-evation $rere

raised more than 2 feet. Pl-afe 3 shows t.he boundaries of the land that. have been

acquired around the reservoir. It also shows the land inundat.ed under t,he

present. condit.ions and with a Lwo foot, and four foot rise in the reservoirelevat.ion. The emergeney spiJ-Iway would al-so have Lo be raised in order tocont'rol the amount. of water flowing over it.. This would increase t.he ehance ofwater overLopping its banks in the Nl'¡ 1/4 of Sect.ion 3'l , Township ,¡60 Nort.h,

Range 67 vlest. This water could spread over a large area. A smal-t dike couldbe built at the low area to prevent. t.his from happening. The sane sit.uationexists whet'her t.he reservoir were raised 3 feet. or 4 feet, Therefore, raisingt.he reservoir 3 feet will not. be Iist.ed as an alt.ernat.ive.

Figure 3 is a hydrograph of the inflow int.o Big Coulee Dam for the 25-yearsno¡¡melt'. The dischargeà under current. eondit.ions and wi th a 2 foot. and 4 foot.rise in the reservoir elevat.ion are also shown in t.he hydrograph. The out.flowrates l¡Iere nearly ident.ical- whet.her the reservoir hras raised 2 feet or 4 feet.One line represents bot.h discharges on the hydrograph.

A dam is considered unsafe if it cannot pass one-hal-f of t.he probable

Maximum Flood (PMF) wit.hout overt.opping occurrÍng. About. ?5 percent. of t,he pMF

passes before overtopping occurs under the eurrent condit.ions of t.he dam. A

- 18-

TABLE 2

NOUTINb RESI]ITS FON PFOPOSED MODIFTCATTONS

Cont.nol Elevat.lon Frequeney of Snowmelt,

year

year

year

year

snowmeLt.

snowrnel t:

sno¡melt,

snowmelt

Inflow(cfs)

1 ,622.

1r82?

2,u36

3 , '!l{3

1,622

'1,822

2,436

3,143

Elevat,lon of,Reservofr

1576.9

1577 .1

1577 .6

1578.2

1578.9

1579.1

1579,6

1580.0

Discharge ofServi ce SpiJ.Iway

o

1 ,600

1,7TO

?,230

2,540

1,580

1,735

2 1200

2,667

Dlsoharge ofBmergency Splllway

(cfs)

0

30

1'60

u75

0

3o

160

353

Velocity inEmergency

Spi tl-way ( f ee ).

0

x.?

3.24.E

0

1.7

3.2

4,4

t5?4 MSL1

10

25

50

100

at 10 year sno¡¡melt

25 yaar snoüflmelt

50 year snohtmelt

100 year snohmelt

15?6 MSr2

AlI values shown are t.he peak values f,or that frequency'snowmeLt.1Émergency spÍIlway aL an elevat,lon af 157V.0 MSL.

2E ""genoy spillway at an elevatl.on ot 1579.0 MSt.

ii I il 1 ïI

II

I

I

Tv

-l#t--i ,il

-t-I

-l...1

1

IF+$

tl'.l-l-

-l-+

:]l

{t

cHU

-t

I I_ll

asTr looJ tfpue asTr looJ ¿ e L{1Tû1 a8;eqoslq

suoT? Ipuoc luesa.rd Japun a8;eqoslq

¡4oïJuï

I

t--t.

I

I

l

-lI

l-l-it

NVC g!1n0C ÐIg

HdvuÐouoÃH uvgà 9z

E sunÐrJ

i.H

TJ è,81Õ c:ttt Y t rì ll l(v* o1 H:lfilìll v I I1 lllly-¡l tl¡/t . t{tl . Í)I I1r\l

üaxÍmun ol 0.85 feet, oventops the dar¡ upon oeeurrence of ttre pMF. I¡aler ç¡ould

fLow over the top of. the dam fon 11.2 bours. The'FMF ¡¡as rout.ed t.hrough theserviee spillways proposed for construction Íf t,he re,servojr was rajsed 2 feeLor 4 feet above the exist.ing cont.rol elevat.ions. I,laLer did noL flo+¡ over t,he

lop of t.he daln for eit:her of these situaLjons.

-?1-

:a< r - :@!-r4< ¿: @\rtffi j,tì-1ô::.¡siÉijÀSJr¿.rtåb-Þ

V. ALTERNATIVES

AlI the possible combinations of spillways have been narrowed down to t.he

t.hree most. feasible solutions. These alternatives are dependent on t.he el-evation

of t.he reservoir. The Towner Count.y tlat.er Resource Distriet. has the oplion ofdoing nothing at.the present. t.ime, inst,all a service spillway which would raisethe elevat.ion of the reservoir by 2 feet., or to conslruct a spillway with a

conLrol- elevat.ion 4 feet. higher i.han Lhe current. el_evaLion.

Several changes should be made if a serviee spillway is constructed. The

port.ion of t.he downsLream embankment. which is currenlly at a 2H:1V slope should

be changed to a 3H:'lV slope in order t.o ensure t.he st.abiJ-it.y of t.he embankment..

Plat.e 4 shows t-he area of t-he embankment. where the slopes are Lo be changed.

Figure 4 shows the changes t,haL shoutd be made for t.he different condit.ions ofthe downstream embanl:nent.. The 54-inch CMP and the low level- drain should be

removed. A low level (hypolimnetic) wat.er qualit.y control slruet.ure could'be

const.ruct.ed. A Saint. Ant.hony Fall-s (SAF) st.iì-ling basÍn, complet.e wit.h energy

dissipat.ors, should be const.ructed for t.he out.Iet. st.ruct.ure.

ALTERNATIVE 1

The first. choice available to t-he Board is t.o do nothÍng at. t.he presenL

t.ime. Alt.hough t.here are no init.ial cost,s, t.he costs to maint.ain the dam ingood eondition could becpme veny high. The service spillway pipe has been de-

t.eriorating. It will most. likely have to be replaced in t.he fut.ure. The energency

spillway is vulnerable to seouring damage due t.o t.he high velocit.y of s¡at.er

frequent.ly flowing over it..Raising t.he conLrol elevat.ion of t.he reservoir by inst.all-ing flashboards

on t.he serviee spillway, would jeopardize the safet.y of t.he dam. this procedure

would increase t.he frequeney that the emergency spillway would be used. The

velocit.y of flow, and chance of scouring occurring on it., would also be increased.

-22-

UPSTREAM

UPSTREAM

5

2 \l3 New Embonkment

Exlstlng Embonkment

TYPICAL CROSS-SECT|ON BETWEEN STA. O+OO AND STA. 6+gO

New Embonkment

DOWNSTR EAM

5

DOWNSTREAM

N-2 7Erlstlng Embankment 4

TYPICAL CROSS - SECTION BETWEEN STA. 5+OO AND STA. 9+3I

Flgure 4

Therefore, the likelihood ol the da;o being washed out would inerease.

åLTERNATIVE 2

A 30 foot by 3o foot. weir with a 3O-foot wÍde chute coul-d be constructed at.

a cont.rol elevation of l5Z4 MSL. This chut.e Ís shown in Figure 5. This woul_d

const.itut'e a 2 foot rise in t.he eLevalion of the reservoir. The area Lhat thewat.er inundat.es would increase fron 195 acres Lo 226 aeres while the storagecapaeity wourd change from 11630 acre-feeL t.o 1r99g aere-feet.. This wouldincrease the average dept.h of the reservoir from 8.4 feeL t.o g.9 feet.. The peak

elevat'ion of the reservoir and peak discharge through t,he serviee spillway and

emergeney spillway for different- frequeney st.orms are shown in Table 2.This alLernat.ive is estimaled io eosL $3ZO,0OO. The breakdown of these

costs are shown in Table 3. The cost. of acquirÍng land is not. Íneluded in thisest.imat.e- TiLle woul-d have t.o be acquired for an addit.ional 17.33 acres. A

flood easement. is currently in effect. for t.his land. lJat.er would permanently

cover Lhis area if the spillway were const.ruct.ed at an elevaLion of t5Z4 MSL. A

flood easement should be obtained for land which would be temporariJ_y inundat.ed

by the '100 year snowmelt. Approxinat.eì-y 50 acres is bel-ow this elevation of1578.2 MSL. As shown in Plate l, the najority of t,his Land is located along theupper reaches of the reservoir, alt-hough there are severat smal1 areas whieh

extend beyond Lhe boundaries of the land originall,y acquired for t.he resenvoir.

ALTERNATIVE 3

A 30 foot. by 30 foot' weir with a 3O-foot. wide chut,e could al-so be installedat. an elevat.ion of 1576 MSL. This would allow a 4 foot. rise in t.he elevation oft.he reservoÍr. A 2 foot rise Ín the emergency spil1way, t.o l5Z9 MSL, would be

required in order t.o meet. the reeornmended guidelines for t.his project. The

-24-

elr Chute

Steel plpe

Top of Chute

24'

S.A.F. Stllllng Bosin-+

Er. t574.O

=G@ ìfEÐpìE= E Elr r= = ÈB =, = =¡ =:E =,=: =,= :Erhilng tO,':.: :,:,: -_:: I El. 1548.0

ELEVATION

30

Hypollmneilc Struclurc

Flgure 5 - 30 FOOT WIDE CHUTE

o 8.5' 32' 32r]_

PLAN

-

Llne5

ttrtrltrtItrEE¡¡tl

Scqle: l";30'

TABLE 3

PRELIMINARY COST ESTIMATE - ALTERNATTVE 2

2 FOOT RISE ]N THE CONTROL ELEVAT]ON OF BIG COULEE DAM

QUANTITY UNIT UNIT PRICE TOTAL

L. S. 5,000 .00

3

4

ITE},I

1. Drainage

Si t.e Preparat i on andRes i.oraii on

Coffer Dam 8,OOO

Salvaging and SpreadingTopsoil 1 Z,OOO

Earthwork (pipe recovery &chut.e preparation) 3,500

Earthwork (achieve 3:1 slopes) 4,OOO

Concnet.e (sidewall-s) 3OO

Concret.e (base slab) 3OO

Rest.eel 84 , OOO

Sheet. PilÍng 300

Structural PilingRock Riprap 400

Rock Fiprap Filt.er Material 150

Low Level Drawdown Syst.em

Underdrai nage

Seeding z

Sodding 3OO

I'Iat er 2OO

Demolition and Removal

2

6.

7.

8.

9.'t0.

11.

12.

13.

14.

't5.

16-

17.

18.

19.

L. S. 4,000 .00

c.Y. r .50

S.Y. o.20

$ 5,ooo

4 ,000

1 2,000

2 ,400

7 ,000

6,ooo

90,0oo

75,ooo

42 ,000

6 ,0oo

7,000

8,000

I ,500

I,0oo

ó ,000

300

2,400

600

2,5OO

5c.Y. 2.00

c.Y. 1.50

c.Y. 300.00

c.ï. 250.00

Lbs 0.50

L. F. 20.00

L. S. 7,000.00

c.Y. 20.00

c.Y. 10.00

L.S. 8,000.00

L. S. 6,000. oo

Acres 150.00

s.Y. 8.00

1 ,000 Ga1. 3.00

L. S. 2,500.00

Subt.ot al 9285 ,200Cont.ingeneies 2T,3OOConst.ruet.ion Inspect.ion 28,¡OOCont.ract. Admini st.rat ion 28,500TOTAL $37O|OO0Does not include cost. of acquiring land

-26-

st.eepest. slope ofl the emergency spil-Iway should not. be Íncreased when the fillis added. A steepen slope on the emergency spillway would allow the velocity offLow to increase. The area inundat.ed by t.he reservoir woul-d increase from'195 acres l.o 25T acres whire the capaeity would increase from 1630 acre_feet. to2Ll8l acre-feet. This aÌLe¡ native woul-d increase the average depth of t.he

reservoir from 8.4 feet. to 9.7 feeL. Table 2 shows the results obtained from

nouting the inflow of various frequeney snowmelts through t.his sLrucLure.A low area exists in t.he lir¡i 1/\ of Sect.ion 3i, Township 160 Nort.h, Range 6Z

t'lest. (See Plat'e 3)' l,Iat.er could overtop t.his area when t.he reservoir reachesit's peak elevat.ion during fhe annual snoumelt.. This water would t,hen spread

across the count.ryside. Apparenlly there was no problem wit.h wat.er overt.opping

t.his point. during t.he 1979 snowmelt. Wat,er was flowing over the emergeney

spillway at. a depth of 2.5 feet during that spring. Therefore, no overt.opping

should oecur aL this l-ow area below an elevalion of 1579.5 MSL. Írrit.h thisalLernative in operation, the 1O0-year snowmelt would produce a peak reservoirelevat.ion of 1580 MSL. A snall dike could be built. to prevent any high wat.er

from flowing over t.his area.

The increased cont-rol elevation of the reservoir would cause t.he beach and

boat launching ramp at Lhe recreaLional site t.o be inunda[ed by the normal poot.

The wat.er level would be nean the edge of the parking area. Modificat.ion couldbe made at an est.inat.ed .cost. of $41000.

ThÍs alt.ernative is estimated t.o cost $390,000. The costs are broken down

int'o individual items in Table 4. The eost. of acquiring land and modifying thebeach area are not, included in this est.imale. At. t.his stage of planning, theonly difference in cost betr¿een the const.ruction of alternative 2 and 3 is due

t.o the earthwork involved in raising the elevation of the emergency spillway and

construct.ing the dike. The higher control elevation also requires more land to

_27 _

TABLE 4

PRELIMINARY COST ESTIMATE - ALTERNATIVE 3

4 FOOT RISE IN THE CONTROL ELEVATION OF BIG COULEE DAM

QUANTITY UNIT UNIT PRTCE TOTAL

2

ITEM

Drai nage

Sit.e Preparat.ion andRestor aLion

Coffen Dam 8,ooo

Salvaging and SpreadingTopsoi I 1 7 ,000

Eart.hwork (pÍpe recovery andchute preparat.ion) 3,500

Eanthwork (achieve 3:1 slopes,dike, emergencyspillway revision) i0,000

L.S 5,000.00 $ 5,ooo

L.S

3

4

c. Y.

S.Y.

c. Y.

c. Y.

c. Y.

c. Y.

Lbs.

L.F

L.S

c. Y.

c. Y.

L. S.

L. S.

Acres

S. Y.

1,000 GaI.

4 ,0oo - oo

1 .50

1 .50

300.00

250.00

0.50

20.00

7,000 . oo

20.00

10.00

8,ooo.0o

6,000.00

150.00

8.00

3. oo

4 ,000

1 2,000

0.20 3, 400

2.00 7 ,0005

6

7.

8.

9,

10.

11.

'12.

13.

14.

15.

16.

17.

18.

19.

Concret.e (sidewalts)

Concret.e (base slab)

Rest.eeI

Sheet PilingSt.ructural PiIingRock Riprap

Rock Riprap FiIt.er Material

Low Level Drawdown System

Underdrâi nage

Seedi ng

Soddi ng

I'lat.er

Demolition and Removal

84,

300

300

000

300

I 5,000

90 , ooo

75 ,0oo

42 ,000

6 ,000

7,ooo't4 ,000

2,500

8,o0o

6,ooo

600

2 ,4oo

ç'00

700

250

4

300

300

L. S. 2 ,500 . 00 2 ,50oSubt.ot.al $303,300Cont.ingenci es Z6 ,iOOConstruction Inspection 30,000Cont ract. Admi ni st.rat i on__39r999TOTAL $390,000

Does not include cost. of acquiring land

-tA-

be purehased'. As shor¿n in PLat.e 3, the reservoÍr elevat.ion of 1576 l,,lSL ¡¡ould

exfend beyond t'he bsundaries of the Land originally purchased fo:¡" Lhe reservoÍr.ApproxÍmatel-¡¡ l$ acres of la¡ld r¿ill have io be aeguii.ed a-t varjous poinis along

the neservQír. eurrenLJ.y, 17.33 aeres of thÍs a¡nouRt is included Ín flsodeasemen¿. Flood easenent.s should be obtained for any other land surrounding t.he

reservoir which is o-eLor.¡ an etrevation of 1580 MSL. This is t,he- elevation that. a

100-yean snomnelt would at.t.ain. Eighty acres of lanC are included in Lhisdesignation. The najority of this aereage is in t.he upper port.ions of thereservoi r.

-29-

VI. SUMMARY AND RECOMMENDATIONS

SUMMARY

Big Coulee Dam provides t.he municipal water supply for the City of Bisbee.

The qualily of the water has been poor. The reservoir al-so serves as a

recreat.ional area for the community. Reeently some problerns have arisen- Lccalresident.s have compl-ained t.hat, pleasure boat.ing is only possible in t.he area ofthe original coulee. Ì"lany of the flish do not survive t.hrough the wint-er- The

54-inch metaL spillway pipe has been deteriorat.ing. It has deformed due t.o theweight of the soil above it.. Rust. is evident on the bot.t.om 1/3 of t.he pipe.A dangerous situat.ion exists because t.he val-ve fon t.he dnawdown pipe is on t.he

downstream side of the structure. It. could cause severe damage if it. breaks.The emergency spillway is suscept,ible to scouring since wat.er frequent.l_y flowsover it at high velocities during the spring snowmelL.

The inflow for various frequency snowmel-ts was obLained with t.he use of t.he

TR-20 comput.er program. Fl-ows from a Z5-year snounnel-t. were routed t.hrough

several combinat.ions of serviee spillways set. at. different. cont.rol elevations.This was done in order t.o find t.he nost feasible st.ruet.ure which could adequatelyhandl-e the inflow while allowing an increase in the normal reservoir elevation.Tabl-e 5 summarizes the results oblained for the three alt.ernatives.

Three alt.ernat.ives !'tere looked at. in lhis sludy. The first alt.ernat.iveinvolves doing nothing aT t.he present. time. This may resul-t in high maint.enance

costs in t.he fuLure due to erosion on t.he emergency spiJ-Iway. The servicespillway pipe has been det.eriorat.ing and may have t.o be replaced in the future.Similar1y constructed spiltways in t.he St.ate have expenienced problems and have

had to be replaced.

The second alt.ernative would raise the control elevat.ion two feet to an

elevation of 1574 MSL' In onder to raise the cont.nol el-evation of t.he reservoir,

-30-

. ji: . 1..qil4rtuÈtt1+1

TAELE 5

SI'I,IMARY OF ROUT'ING RESULTS FON PROPOSED ATTERNATIVES

Frequency of Snowmelt Besenvoir Elevat.lonDiilcharge lnEmergeney Spillway

(cfs )

1'1?0

2 , tl8CI

3o

[tt5'

' Velocit.y inErnengency Splllway

?.0

9.4

1.7

4.8

1,7

4.4

Alternat.ive 11

.lAlt.ennat i ve 2'

25 year

1O0 year

25 year

100 year

25 year.l00 year

1579.0

1580. 1

1517.1

1578.2

1,579 .1

IwI

Allernatlve 321 580.0

All t¡alues shown are the peak values f,on t.hat frequeney sno!ümelt..

lEhergency sp11.Lway at. an elevation of 1577.0 MSL.

2Emergency spillway at an elevaLion of 1579.0 MSL.

30

353

a complet'ely new service spilrway wil-l have t,o be const.ruct.ed. A 30 foot by 3ofoot weir wit'h a 3o-foot. wide chut.e was found t.o be t.he best spitrway for thissit'uation' Average depth of the reservoir would increase from 8.4 feet to g.9feet' The increased elevation of the reservoir wouLd require thaf 17.33 acres,'currently únder flood easement, be bought.. A fl-ood easement shoutd be obtainedfor 50 acres of l_and belors t.he 1OO_year flood elevat.jon of .15Tg.2. This alt.ernat.iveis est.imat.ed to cost $3Z0,OOO, not including land cost.s.

Art'ernat'ive I consist.s of eonstruct.ing the same lo foot. by 30 foot. weir and3O-foot wide chut.e at. a cont.rol elevat.ion of 1526 MSL. This would provide anaverage dept'h of 9'7 feet'- The emergency spilrway would have to be raised2 feet' t'o an el-evat.ion of 1579 MSL. A smart dike wourd have t.o be eonstruct.edin the Nl'l 1/4 of section 31, Township 160 North, Range 6z !,lest. prat.e 3 showsthe locat'ion of t'his low area. l,IiLhout a dike, water could overt.op t.his regÍonand spread out' over a large area of land during the 100-year snowmel-t. Thirt.y-sixacres of l-and wirl have t'o be purchased to accommodate t.he rarger reservoirarea. A flood easemenL is currently in effect for 12.33 acres of this. Fl_oodeasements shourd be obt'ained for 80 acres of tand below t.he loo-year frooderevalion of 1580. The est.imated cosl for this alt.ernative, not including thecost of obtaining 1and, is $39O,OOO.

rncluded in the costs for alt-ernat'ive 2 and I are sevenal ehanges whichshould be made if a new service spillway is constructed. The 54-inch CMp andlow level drain should be removed. Inst.al'at.ion of low

'eve' (hypolimnetic)

water quarit'y cont'ror strueture would help improve Lhe water quarity by removingst.agnant water fnom the bot.tom of the reservoin.st.illing basin, complet.e with energy dissipat.ons,

A Saint Ant.hony Fatls (SAF)

should be const.ructed for theout.Iet. st.ruct,ure. The port,ion of the downstream embankment. which is current.ryat a 2H:1v slope should be nodified so the sropes are 3H:lv t.o ensure thestability of t.he embankment.

-32-

RECOMMENDATIONS

The three alternatives pnesent.ed in t.his report. are al-l viable, alt.houghsome may be more desirable Lhan ot,hers. Several problems current,ly exist wiLhthe water quaLit.y and t.he operat.ion of t.he Big Coulee reservoir. Therefore,alternat.ive 1, do noLhing, wouLd be of no val_ue_

Alternafive 2, the two foot increase, would improve t.he waLer quaì-ity ofthe reservoir- The peak water Ìevel-s, due t.o runoff, would be l-ess than t.hosefor the exist'ing condiLions since t.he capaciLy of fhe spillway wourd be iner^eased.In additÍon, use of t.he emergency spiÌlway would be redueed and t.he velocit.yof fl-ow over it' woutd be reduced during t,he larger snovmerts. Tne greaterreservoir dept,h would increase the area avairabre t.o boat.ing.

ALternative 3, the four foot increase, wouJ-d arso improve the water quaì.it.yof t'he reservoir' rt' would provide a langen area for boating t.han alt.ernative2' The average dept'h of the reservoir wourd arso increase. use of theemergency spillway and t.he veiocity of flow over it. during the larger snow-nelts would be reduced t.o the same revel as obLained in alternat.ive Z. Ex-cluding t'he cost of acquiring land, this alt-ernative woul-d cost abouL sixpercent. more than al_t.ernat,ive 2.

Al-though alt'ernative 3 appears t,o be the best choice, a pnoblem exisLsdue Lo the higher water level. The normäl poor wourd complet.ely inundat.e thebeach and boat' launch area. The water revel woutd extend crose to the bathhouses and parking lot (see Prate 3). The peak wat.er revels wouLd be aboutthe same as for the exist.ing eondit.ions. A port.ion of t.he parking lot. nay beinundat'ed during t'he peak level- The remainder of the recreation area shourdnot. be affeet'ed. Possibly, t.he beach could be ext.ended t.o a highen erevationor moved to a different' loeation. This modificat.ion ü¡as est.imat.ed to cost$4,ooo.

-33-

the ?ou¡ner County ïlate¡'Resounce Board must. deaide ç¡Aåt alternat.ive i.ü

deens the nsst. feasible. Det.eriorat.ion may cause sorne spiì"lway improvemenL to

be required in t.he near fuLure. Therefore, the first. al[ernalive ls.notrecommended; Al.though alternati"ve J is the ¡nosL costly, it ie neeommended as

fhe þreferred a.lternative. The Boa¡'d nust. weigh t,he value of inproving the

.. depth of the reservoir while losing part, of the exist.fng recreation area.

-3ll-

-47 t

aèl- -

a]

o'f

EIIERGENCYSPILL WAY

I/

P.O If

856

o+oo\as r

E

z.=No¡

uø

t3{ 428

Þ

o\f2e

i*EoxlnletWa¡r

oo

,530

t&t qo

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la!

a7.a

tO-

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g.a

tl.6

t>a

t

tll

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ft.o75.ã

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fz.tt

78.alls

so7a.t

st

ff.z

709

so

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la

ù,ó

PLÂTE I

NORTH DAKOTASTATE WATER COMMISSIOHittHAtct. ioRt¡ oAxoÌa

PROJECT tlo. l4lS

BIG COULEE DAM

SITE TOPOGRAPHY- AS EUILT

DÄ18 A-7-¡OÊñrßtY lowNFFStc. 36, Twp. 160 N., Rgc.6E W.

tt.õ

rltt578

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o

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llolh Racapiäc ra

z

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PARKIN6. ÂRÉA

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XÔtgo ì.1qt6¿¡'q I ¿¡tl

6tsbcc) N [_t.k. â016 Ae.

'x^x./Il

g

RECREATION AREA * Iscers t". loo'

¡¡¡"1 f Morris CårisloPhørsonþiebca; N. Þck

l. I ec.Ac.

sw,4 N \^,'J4

l-L r ^oo"Allc,¡ ë

-i. t60 l,l

30õ<è

^r"u.t ... co..

CONTROL ELEVATION 1572.0 MSL

CONTROL ELEVATION 7574.0 MSL

- 'ï t60 N. R. ø8W

CONTROL ELEVATION 7576.0 MSL

].OO YEAR FLOOD EASEMENT EL. 1580.0 MSL (T'OR CONTROL EL. 7576)

1OO YEAR FLOOD EASEMENT EL. 1578.2 IT,ISI (FOR CONTROL EL. 7574)-

I

PROPO$EDóJ5I

I

¡

II

II

II

I

K+

I

I

I)

G'

StN )z+_oB

:R CEeK ÉL t5=6.É-

W./t 7 /59 i{.R. 67 r^l

wa -t

4 .!a-a¡

7 t59 ü-R.. €8 w'

LI-r- Isvl)t+

I

I

iiI

,aI"nl t ot *.:t

oEcx EL 1585 5

-- eFEEK Bo.ÍroM EL ta7t.o

¡fuÐ s

A.A3 Ac

3EX

^ffÁ GAPACITY TABLE

;'úP taU L at +

sbce, N Da I

fz- È ôt Ro&

-1, -=- àetzo l1 eoeI

2sI

,4e

I

/t=

_=

A¿-

NE/+

R66Uf R.6r W

3c-Y4

I

IIL or nwy . * 2--íI

PRESENT CONDITIONS:TOÎAL ACREAGE ACÔUIRTD 326,Itì ACRESTOTAL ÀCR¿À6E PERMÀ}'EI{T EASEMEMT 1.35ACRE9TOTAL ACFIEÄGE FLOOO EÀsEJ'4ËNT 17.33 ACRES

PLATE 5

PAêæSEO ÐA É 5'7ÉÞ

DECK EL. ''5A,I

-

q4x ær7aM Ê1. ¡547.1

ur{oER DF-CÍ eL r!84 o -

2ô' ,vúIOE

f ¡æE

'C. t6t

Locnt¡oN M¡e

--(2f,

B R lD6¡ No. 2-NO SCAL€.

¡

I

|-L ÆBE:

25 t-\l!7Ð'.5'.3Ì562r5t81554ì;90.548

275.8it'7.5lo3.b67.1lo.6I

la

o

I ,998. 2

ó59.0107.6lll.22r.i

ù

NORTH OAKOTASTAÏE WATER COMMISSION

ErsrÁFûx- trôÂli oa<of^

PRoJãcr Ho. 14lBBIG OOULEE DAM

AREA INUNDATED BY RESERVO]RoarE 12-13-65¿r,u*rv iÍlwl¡F R

DAAWrñ(i NO.

cHEcts¿D aY:Df 9r6l.tc af:

): WJDE

ôR I DGE iuo INê gc'ALÊ

t' . ¿ M¡L¿s

-47 )

Gt

Jf .f

EXÉ,ßGENCYSPILLWAY

II

P.O f.C

85.6

o+oo

t¡{

a

aÛt

s'7

FT

57.6

PROPOSED 3H:1V SLopE

. fz.a

8o¡hþ1ì¡.if

rtl' dú

fù

30 FOOT W]DE CHUTE 1¡.2

ü-d

"""t*

t+o-

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I

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flt

PLATE 4ãf

A.a----'¿'iotfx olfo

NORÍH DAKOTASTATE WATER COMMISSION

PRoJ€CT llo. l4t8BIG COULEE DAM

AREA OF DOIIINSTREAM EMBANKMENTPROPOSED FOR MODIFICAT]ON

-23HO, 9 t4src. 36, ÎrP. 160 N., Rgc.68 W

fta

tja ,57e

7+a ,à16'

nl

r.c no6

aa! ato156e