AN ELEGANT SOLUTION:

The Lake Brazos Labyrinth Weir

To fulfill the potential of the City

of Waco's Lake Brazos, a labyrinth

weir replaced the gated spillway on

the Brazos River. The labyrinth weir

was constructed on a flowing

river over the foundation of the

existing dam without expanding

the dam's footprint or rerouting the

river during construction-

at nearly half the cost of

earlier estimates.

By VICTOR M. VASQUEZ, P.E., M.ASCE, JOHN S. WOLFHOPE, P.E., A.M.ASCE, • AND RICKY GARRETT, P.E. ,

,

liE fcABLEI> BRAZOS RIVF.R , the longest river Rowing entirt"ly

within the state oITexas. nUlS through downtown Waco and

has played a significant role in regional history and. down­town Waco life. Spanned since 1870 by a suspension bridb>e designed by the renowned civil engineer John A. Roebling,

the designer of the Brooklyn Bridge. the river's pr('sence

underscores the tenuous dependency ofTex:lllS upon water. For Ill<lny Texas cities-indced. formany places III the Amcr­

ic:m Wcst--plentiful water is elusive. A promilll'1lt public

lake Ix:"comcs more th:1Il an aesthetic element; it t'lllbodk-s the city's claim to progressive vision and quality orlift'.

When in 1970 Waco's leaders dt-dicatt-d the g:tted

spillway fonning ukc Brazos, they were proclaiming their confidence

in and vision for the central Texas ci ty. The Brazos Ri~r, the longf!jt

Waco's leaders saw a vibrant downtown riverflowingentirelywithin that would host lakeside festivals, boating the nate of Teus, u tends

d k" .. d I th.oughdowntownwaco an waters -ling competItIons, an at ler and has played a significant

water-related events, and they foresaw role in the reg ion's history. the development of waterside parks, res- The new. ] ,000 It (914.4 m) taurants, and related businesses. How- long labyrinth weir on the

river replaces a gated spillway ever, these plans assumed dependable and an overflow embank- J lake levels, and such levels proved elusory. ment thilt had be'en plagued I Extended n.>rioosofbelow-normal water with problems, and 11 does 50

r- entirely within the footprint levels-for the most part a conscqul'nce of the previous structures.

ofmaimcn:lIlcc and operational problems I associated with the dam's gates-diminishcd tht' area's appeal. T he -

original drum gates could not maintain a constant reservoir leveL Mod- ! ifications replaced the drum gate system with leaf g:ttcs and hydraulic 8 • cylinders in 1985, but operational problems persisted and often led to f lowcr"ed lakt'levcls and unappealing rt.'SCrvoir conditions. \J

- .. Plan View

~EXISTINC STlLlINC B.t&N-""""'

Despite the problems with the lake k\'cls, signifiClut growth had taken place ~IOllgthc b.,nks of the UI';1ZOS. l>rivate devdopnK'lt along the river included apartments, waterside n"$t3urants, and fio.1ting I"l'$tallr.lllts. Baylor U ll ivel'sity expanded along the western shoreline,

;l1ld the City or Waco iilwsted in many improvcments along the

river, including parks and mik':S or prolllt!nadcs along the riverbanks. But fitced with continuing opcr .. tional problems, unreliable lake

Left Labyrinth Elevation

lewis, dallgt:rS to mainl<:n:mo: worken, and cosu

of$50,OOO to $100,000 anllually for llIaiml'n:l rlCe and n--pairs, the City of Waco t"mb.nkcd 011 a mis­sion to allcvb te the problems associated with the

dam. E.,rlU:r pI:IlIS to replace the dam hm called for the expenditure

of53O million. posed a significallt threat to the environment.., and required divC:lting the river dlJnnt'!. In 2004, at the city 's rt.'f)Ut~l,

engineers with the Anstin and Fort Worth offices ofFI'I.'CSt' and t Nichols, Inc., R'Surrected ~ pa'\Si\'C structUfC concept from ~mong l earlier assesslllcnl5.

The city established these b'O.1ls for thl' project: 1 ; ,

• Reduce the construction costs and en"ironl1lel1l ~1 harm con- i t:;Iin!!{\ in earlier propo5.lls. J

LEFT

11-0'

'¥ NORMJoL H(AOWATER [L. 376.0 UPSfR[A\l CHANNEL

ELEVATION

CL. J77.0 IT IoISl

6.3 49' LA8rRINTH CrelE

rlOW OUTLINE OF EXISTING

OVERFLOW EMBANKMENT (SHOWN FOR'\ ....

REFERENCE ONLr)_ \ ~~ ,-

r-_D",;E~XISTlNC;

TOP..or TAYLOR .FORMAnor~ EL. 337 rT-"-ISL ±

50

, -lr-_~ --\-.- UPslR~"" SHE(TPILE/

PLATrORM CONNECTION SEE SHEET S- 28.

0"77tn,

EXISTINC CLA)' CORE

UPSTREAM DRAIt~

EXl5ntlC 5HEETPILE -

uPSTREAM SHEET PILE

I I TI III

I I DRIllED ) I

PIER U LEFT

•

,LEFT

,) ,

ICL[

' 7+00

SWI -./'­

=""

• Mainmin till' norma! pool impOlllld1l1cnr. • Maintain the existing rcgubtory (FedcrnJ Emergency Mnn­

agcment Ab't'llcy) IOO-ycnr upstJ"l'atn floodpblil. • Limit lluis;mct' inundalioll oftht: upstrc:ull rivcrsid~ prom­

enade for riwr flows ul> to the IWO-)'\'3r flood event. o Minimize disnlptiollS to lake levels during construction to

reduce tilt" effect 011 tht'. central bllSilles.~ comnlunity.

• Provide ~n :lesthetiGllly plcJsing structure tlm will rC'luire

little mnintcnance.

31 .7' 15.0' 15 .0'

The design alld constructiOLl of tile staggered labYl'inth weir

met the city 's go:lIs th rough the following:

• Studyingnnd t'VJluJting tll.:- li,Jcs of the hydmulic chalk:ngcs; • l)eveJoping:1 phased construction program using the founda,.

tion orthe t!xi~tillg dam; • I)cvcloping 3 pIau to 1I1:ulage the river dmi ngcollStl"ucrion.

TIle pha..'il-d wnstnlction plan ~nd tl Ie usc of wffcni,lll1sdiminated

the 111;tiOfl'llViIUllmerlt.ll dfectsCOllllllOl1 to dam rcpbccnlent, \Vllidl dcriVt.~ fi-onl challlld diwrsioll alld tlu.' COllSlnlction and ~itillg of a lIC\V datil. This plan ruduced tile cost ~ IlJ duration of the construction.

Research ~t Utah St:lt<! University's Umh Warer Rcst:arnl bbora­tory conducted using p;trtial- and filII-width scale models r.onfinllt:d tlwl a labyrinth weir cou ld offer sa tisfactory pcrfonmncc during subnlergcrlCl.' conditions while lnailltainillgupstTt"JllI bkl' 1<.'\'Cls. Th<.' rcst><lrth aho v.llidatt-d til{' suit:lbility of phased COll.<'(nll1:ion formini­lllizingdisnlprioll oflJkc ]r.veis ~lId divt'rting riVt.""f flows.

Fl1Istl"3tion owr thr inability to lmint:lin :\ steady lake level h~d bt!cn voicl-d loudly and rt.'peatedly, and attempts OVt.1· thc yeal"S to cor­rect Ihl' problems hJd nOI \x'ell sati9:ICtory. Valious city otlk ials ~lld the design lL~alll addressed this fi'ustrntlol1 by making pn:scnt~tiom 011 tho.' adv;)lltages of a labyrinth wcir to civic groups and to tht- Waco City Council. 11le cit.'SI!,'l1 r~m fueed qUt'SLions about CWIY Folcer of the pl"Oposcd labyrinth wl'ir fi'oln 1"I.']lrest.'111auvt'.S of the city council, the Central Te.x:tS Branch of ASCIi'S Texas Section, the Great~T Waoo

Chambt..""f ofCommercc. Kiwanis dubs, and odler groups, and the tt':lIn made numerous P\l:!s/.'lItations dl'SCribillg the n.~drch that had \x'('n carried out ocmollstr:tting th~t a bbYlinth weir could p(""fform

011 tlte site :IS proposed, that there was no nel-d to constl1lCI a dam at anoth':''l'sitc, :Iud that the blldg~'t ~Ild timetable could be met.

Om' important st;lkdlOldcr cOllcem- n:l.llldy, tbc pledge to maintain tlorlll:tllake levels durillg construction-was addressed through:l schedule of lake lowcrings to which 1111 parties agrct"<i. The systt'lll of cofferdams mamged both to maimain the lake dur­

ing most of the const!"ut.:tion period and to pass the Aoodw:ltl:l"S

c..xpcrienced ill M~rch 2007.

T he site of the Lake BI":!ZOS Dam prt"St'llted challenging hydr:tu­

lic conditiollS. While thr weir would eliminate the trouble­

some g:ltes and maint"Jin the nOl11lal pool impoundment, the sitt!'s r:tpidly rising t"Jilwater level cleated a SUblllt:rgellce condition

for floods lalgt.'r thall the 10-year t.:vcnt. This meant that the configu­

ration of the bbynnth weir h~d to provide optimal capacity at low hC;tds while Illaim:tilling sadSf.1CtOI), perfurlll.:JlICl' at brge hl':lds.

REJN'ORCEO COI~CRET£ ~ 5.0' 1-1 ---­ 30.0'----1

NEW ROCK RIPRAP IAi LWATER NORMAL OPERAnON PANGE

t:t [L 357 n - MSl

EXISTINC £rliOSILL (SHOWN Fi>R REFERENC£

ONLY)

I I rCL[ U

I I U

OOWNSTREAM DRAIN

JANUARl' ;!QOI) Civil E't~jl'''l'ril1.~

IMPACT SLAB EL. .355 n-MSL

OO\'/I>1'5TR[A.M SHEETPllE

n . J55 fl- MSl

RM' "HM, .. ,J g [ L. 35~ rT -MSl

j l

In addition to handling tht' taihv3tcr levels. the configuration of the labyrinth weir had to I'Cmain within the footprint of the exist­ing dam both to avoid the nced. for c.xtcnsivc riwr ch~nl1e1lllodi­fications and to facilit;l{c environmental pemlitring and reduce mitigation requin.'IT1ent.~. TO:lchicvc the i:lbyrinth length required to h:mdle the river Hows, the Iabyrimh would replace both the existing golted ~'Pi ll w;ly 3 11d the ovcrHow cmbankment.

The labyrinth weir fl!placed a gated spillway and overflow emb:lllkment on the Dr.lzOS Rivcr near Waco's downtown, elimi­nating opt.""1Oltion and maintcnance problems that had plagued the spillway gat($. The new. 3,000 ft (914.4 111) long labyrinth weir was constructed in phases within the footprint of the existing dam to conform to regulatory requirements :U1d reduce costs. The dl-sign

Ratings Curve

315.0 Chart

DI$Charge with High Tallwater

\vdth mo(iel~ /Or both dle cxist"ulgalx1 till' pmposedstnictUrL'S. FOllrtt"CJl sectional and tWO filll-wnth moods were C\'Jlu3«'f.i fOrtilC ~ ll"lt": rL'Sllks ofthe study lu\'C ix:eJ1 pllbllSbcd.

While. [he advantage of ~ labyrinth over a stra.ight weir is that it incrt'ases the discharge capacity for thc s:lllle channel w idtlJ by increasing the weir centerlille lcngth. this hydraulic benefit dtocreases as the upstream rest.'Tvoir level rises significantly above the dl'Slgn head. r"Or a large head. cross flows from adjacent weir walls mix. reducing weir efficiency. The hydrnulic capacity of the bby­rinth weir is further affected by the ra.pidly rising tailwatet" resulting from the large head. Weir efficiency progressively decreases with increasing head to the point where the dischlfge over a labyrinth weir approaches the discharge ovcra linl'ar weir with a bro~d crest.

Any design for the Lake Drazos D~m had 10 :.ddress this situation, and the tealll had to demonstrate tllat the dt'.Vgu lvou ld provIde opti­llIal cap3Cityat low heads while per­forming SltJSf.1ctorily at large heads with tailwilter submcrgenct'.

The physical model sllldy assl.\l.oo in determining the following:

OIsc:narge with Low Tallwater • Suirable labyrinth cydeclill1cn­siolls and wall crest shape; Normal Pool

. . · f ·

370.0

. . . ..

DIKha.ge with Gatl!$ Fully LDwered

• Sequcn~e of construction effects on rivt.'Tflows:

• Effi.oet oftempomrycoiTerd"ulls; UpstrC'am ch~n n el

~ configur:llions; D ownstream 1 c hannel

Gilted Spillway I contigur:Jtions.

labyrinth Weir 1 The sectiol1~ 111todds made it

,.,. o 10,000 20,000 ",000 40,000 50,000 60.000

Flowicbl

incorponltcs all upstream shift across the bbyrimh ncar midstream. The left labyrinth ha~ 13.5 cyelt.'S with walls 12 ft (3.66 m) high extending 307 ft (93.57 Ill) to the channel midpoint lnd ft'St'; 011

drilled piers within the art";! ortht' overflow embankllll'l1t. The right bbyrinth h .. 1~ II cyck:s ,vith \v,dls 20.5 It (6.25 Ill) high e_'l:tt'"nding 240 ft a). IS Ill) to the channel midpoint and rests directly upon a portion of the exi~ngsti lling basin. ConStructiOiI was perfunned in twO phases cOITCSponding to the left and right bbyrinth sections to eliminate c~dy fiver divt.."TSions ,md to manage normal rivcr flows and potential flooding. T he fuul ronstnlctioll COS! WlS $16.373,502, aud construction was completed in 706 days.

Placemencofthe labyrinth on the ellloonkment area resulted in an upsu ealll shift across the labyrHlth Ilear midstre~m. Bea.U5e of this shin. the bbyrinth 'VlS considered unorthodox. ami this Iv.lS

,Ill import.lIlt n:asoll for developing the hydraulic model study. Studies to :l5SCM the hydraulicperfurnuncc of the hbyrinth spillway

included ck."\·doping a refin ... -d hydrnulic model of the Hmos R.ivcr t.hrough Waco alx\ physic:ll n lodt:ling of tht- labyrinth weir, including cooditionsduringconstruction. First, the team developed a 1l1.1dlClll.lti­Cll hydraulic riv(:r model. ID euimare raihvatt."r lcvcls below die l.2ke .. . Brazos Dam and to asst"S.'! the efrect of dlC labyrinth weir 011 up$tream water b-cls. Theil pltySICll mocldingy,'a'; perfonned at the Urah WatJ:r Research Labor.lIory. Physical modd testil Lg includt'tf st:ctional and fulI-

5'

I 70.000 80,000

J 90.000

possible to tC!St variations ofindivid­ual labyrinth \veir cycle geometry. Such par:ulletl'r:l as \V":lll angle, wall

width, cycle width. cycle depth, apex dupe, and crest shape Wl'I'C evalu.1tcd, and in eneh C.IS(: the effects ofrailw:ttcr SublllL'TgCnCe on disch~f"bre capacity wen: considered. Ultimately. the selected cycle configuration consists of a compact cycle with a wall :Ingle of 8 degrees and rounded apexes. TIle cyd .... wall has a thickness of2 fi (O.61 111) and is (OptX'd with an agee-type.- crest.

One adv.lllt;l!,'C of the sl'iected configuration is that t h~ COlll­

pact cycle with small w:l1l angles provides a significlIll amount of effective weir length in a relatively slllall -area. This made it possible [0 reuse the existing dam footprint while mainftlining signifi­cant discharge capacity. A second advanf:lge is Ihat the ogee-type c~St provides increased discharge over cOlll'emiolial crest shapes, providing the bctter perfonnancc al low flows needed to limit upstreallllluiS:lllce inundation during nOl"mal river flows.

On the basis of 5eCtionailllodcl remits, the team ultimately scb:ted a 25-cydc labyrinth dC1ign that would maintain the Federa.l EllwrgCl1CY M:tnab>enlem Agency l1pstre~ 1Jl inundation levels. The Jeft labyrinth has 13.5 cycles within the fooq)rim of the OYfiAow embanknu.. .. llt, and the right st.'Ction has 11.5 cycles within the [001-print of the gated spillway.

The full-width llIodei confi rmed h)"(irauJic results from the sectional mode.ls, including sublllcrgt'nce effects. and made it possibk to evaluate:. the offiet between tht: labyrinth sections. The

I

• full-width modd also assisted in evaluating hydr.\ul ic requirements

immediately upstream and downstream of the bbyrinth weir. The physiol model proved critical in assessing the projcct approach

and provided important information on the performance of the labyrinth weir during construction, panicubrly beouse the 3,000 fe (914.4 Ill) long weir was constructed within the existing dam's fOot­print. The team planned the work in such a \Yay that the conSlmction would be performed in phases and thM coffi:rd:ullS would be used to accommod.,tc river flows and maintain a filII reservoir during COI1-

stnlction. As a result of the hydraulic studies, the construction docu­ments cIIlph:LSizcd strict toler.lllces for the bbyrinth w.1.11 profile lnd finish during construction and provided for risk sharing between the

T he construct ion schedule for the Lake Brazos Dam

specified three phases for constructi ng twO distinct sec­

tions-the left and right labyrinth weirs and a il\unber of miscellaneous i'rnprovernents. The phased construction w.as

developed to accommodate the city's requirements to mainuin

lake levels :md Illanab<e river flows.

As the project design evolved it became app:m:nt that p4ssing

on all risks associated with managing the river to the contrac­

tor would resllit in much higher construction bids. Contractors

would have to cover the unknowm with inflated bids in order to

111:1nage the known risk of working in the river. The design tealll

wotked c10sdy with the city and developed a program for shar­

oWllcr,u1<! the contractor in the , .. vem ofAoodillg at the construction site.

Key arc:as of the construction phase evaluated

with the full-width model were as follows:

• Sequence of construction effects on river

Rows and discharge rating: CUf\'t.'S for temporary

conditions;

The hydr<luli( studie5 conducted for the project included physic<ll

modeling performed by Ut<lh Stilte University's Ut<lh Wilter Rese<lrch

L<lbor<ltory. The modeling 5howed

ing the risk. The city purchased special insur­

ance through the contractor to insure the work

against flood damage :md to mitigate risk costs.

The key features of the risk sharing incorpor:ned

into [he project documents were as follows:

• Effect of temporary coffenbms;

thilt the lilbyrir'lth weir could provide optim<ll cap<lcity <It low

heads white m<linlaining s<ltidu­tory perfOrmiln(e <It high huds ilnd

• Colkrdam: A minimum elevatiOIl was speci­fled for the cofferdam, and the top elevation was left to the disortion of tllC contr.lctor.

• Up!!trcam channel excav:uion and grading; <llso yielded iroform<ltion used in

determining the weir design. • Lost time: The contractor was respon-

• i)ownsueal1l ch;mnei configurations.

On the b.uis of theSt' numerous evaluations,

the team deveiopt."(\ the following appro.lch :md

St'(lul'l'lCt: to minimize cost and IlUIUgc the river:

• The left labyrinth would be constructed

first.

• The left labyrinth would be constructed

upon a II('W concrete pbtform occupying the

footprim of the oVt'rflow embankment.

• The sheet- Ilile cutoff at the left bbyrinth

could b" extcncfed and used as a coffe1'(bm if

desired by the contractor.

• The existing hydraulic gates would remain

operable (luring conSl:nlroon oftl'll' left labyrinth.

• An upstream scour protection concn:te slab

would be constructed on the south end of the left labyrinth to address scour issues brought to light

during the hydraulic modeling.

• Work would start on the right bbyrinth

o nly when the left labyrinth was completed and

river flows could be passed over it.

• T he hydraulic gates could be blocked and

flashboards added to serve as a cofferdam for work on the right

labyrinth if the contractor determined that this was preferable.

• The right labyrinth would be constructed upon the existing

rollcr-comp;icted concrete foundation of the gaRod structure.

• Very tight construction tolerances would be required on the

entire labyrinth to ensure that it performed as intended.

• CitY-3pproved lake lowerings would be accommodated ;1.(

certain times to facilitate specified work items.

T he Illodel studies yielded information for the final parameters

nece~S3ry fot the development of the project construction docu­

ments. The modeling indicated that the river could be lll3i1aged in

stages consistent with the two distinct segments of wall anticipated

for the construction of tile left and right labyrinth \veirs. Modeling

also highlighted the need for temporary upstream scour prote<:tion

to handle flows created by blocking half the river.

JANUARY ZOO9 Cillil ElIgiHt'f'rilt~

sible for construction delays attributed to river flows below

20,000 cfs (566 m'/5), the two-year flood having a rate of

25,000 cfs (708 m '/s). For nows at or above 20,000 cfs

(566 m'/s) but less than the lO-ycar nood (42,400 cfs [1,201 Ill'/S]), time and money allowances were allocated in

the contract to assist the contractor with delays associated with these more significant flood events. For events beyond the

10-yea r flood, the contractor was responsible for lost time.

• S("ructuf:ll damage: The contractor was responsible for any

structural damage from flooding at or below the IO-year flood

(42,400 cis [1,201 Ill'/S]). For damab'C associated with larger flood

events, the insurance policy would cover the cost and the city was

to pay a significant portion of the insurance deductible.

The construction contract was aw:mled to Archer Westem Con­

tractors, of Arlington, Texas. The project duration was specified as

53

6CX) calcndar days, and thc c.xIX'Ctt-d final comple­

tion date was St!ptember 24, 2007.

Constructing the labyrinth crest to thc very tight

tok'r.llicessctforth in the projectdoculllcnts required

int<.~lsc effort and field wrific:uion. Thccolitrad doc­ummts called for the as-built crest: profile to match

the drawing profile within I/S in. (3 Illlll) when

A~ the proje<t neilred comple­tion, flooding o<curred on the Brilzos River after record rilins.

WilCO receive d 3.37 in. (B5.6 mm) in ju~t one day. ilnd m/my nearby ilreas Hooded. The labyrinth weir

system fur tlle lcfi labyrinth weir. As part of the l"lIVI- II ronmcnt:\l control plan, environmental boom lilies

wcn' inS(:Ilk'(\ around the work areas, an(1 all waste

colb.:ted during l"OnSCnJction \vas t:lketl to 1:lIldfills

orappro\"(.'(\ disposal sites. J performed ilS designed.

With hke levels back to nor111al pool by e;lrly J

measured nonnal to the surface. The as-built crest: clevation had to be

within 1/4 in. (6.4 mm) of the dcvation showll in the plans.

Numerous discussions imrclving the contractor and thc d(.'Sign

team focu sed on thesc tolcrances, includi ng considerations of

entrapped air, which could cause a vuggy surface without proper

attcntion. It was also realized tim setting the forms properly would

require carefill stlfVt.'Ying. Archer Western elected to usc Illetal forms

with removablc lOp crc..'SI forms for the walls. In a test placeillenr of a

wall crest section, Archcr Westcrn dcmonstrated its propost.-d form­

ing and finishing tcchniqut.'S. The tcst section was a success, and the

firm de .... cloped a quality control plan to adlie\"e the specified wk-r­

ances for the wall and crest construction.

TIle wall constmction process involved setting the VcrtiC3l \va ll

forms to specifil-d li nt.'$, grndc5.. and devations_ TIle crest fonns were

then bolted on top of the wall fonllS. TIle concrete plaCCllK'Ilt pro­ceedcd through the 5 in. (127 mm) wide continuolls slot" in the crest

fonllS. After fining the forms, the crest concrete \vas givetl approx­

imately t\\tO to four hours to set, aftt-or which the CI"(.'SI: fonllS were

removed from the green concret!!. Concrete finishers rubbed and

Aooted the green concrete to the specifil-d profile. This climinat<.-d all

the 'lugs fiom entrapped air and providt.-d a tight, smooth finish, thus

CltSUrillg proper hydraul ic perfonnance.

ConstnJction work on tile left labyrinth wcir began on January 2,

2006, aftt.oran iniriallake lowt.'fingschoouled to last four months. TIl ls

Im.vering made itpossible to constnict tile temporary p>fiCrdam syst:(.~11

and to make upstrealll channel improvcmt."llts. During this illitiallake

lowering, the contr:Jctor \vas also able to complete thc foundation

54

May 2006, cOllstnlction continued on the relhain- ~

ing dements of the Idi labyrinth \vei r, including the platform slab,

the labyrinth walls, the acc('SS driveway, the downstream impact

sbb, and the downstream riprap. Construction of the left bby­

rinth weir was substantially complete in early October 2006, th ree

months ahead of the next spt.'C.ified lake lowering.

Given the early completion of till' left labyrinth, the intenllttdiate

lake lowering, which \vas originally scheduled fOr Janu:try 2007, took

place during the first two weeks of October 2<XX>. The intel"llll-di:lte

b ke lowering fucilit:ltL-d the removal of temporary coffi.'f(lam5 0 11 ti lt:

left labyrinth \veir and the installation of temporary coffenbms for

construction ofclleright labyrinth weir. With removal ofits tempof;\ry

cotrerrla.m systems, the It'li labyrinth weir was put into service. TIIC first

spill over clle lefi bbyrinth \V\.;roccurred on October 31, 2006.

C onstruction work on the r ight labyrimh weir began as its cof­

ferdam system W:lS installed during the intermt.-diate lake 1o\Vl.."ring.

Right labyrinth weir COI\S[flIction reached an :tdvanced s[a~,'c by

J~nuary 2007, when significa nt work on tht'. right outlet works

beb>:ln. T he r ight bbyrinth wcir was substantially COlllpJctl.' by

e:t rly March 2007, and substantial completion of the right outlet

works was expected by the middle of the following 1lI0mh. As of

early March, the project [ellll was expecting final project comple­

tion in May 2007. However, riVl.."rconditiOlls changed dramallcally

in late March, significantly altering project completion.

During most of the project construction thc Or-IZOS Ri .... e r

experienced low Aow conditions owing to a statewidc drought.

Except on rainy d:tys and days whcn the tempt:raturc was below freezing, the construction carril'(\ out between January 2006 ali(I

Civil ElIgilltTrillg J ,o\.NUMIY lOO<)

Co

'I

, 1 I t I

March 2007 had few interruptions. Then, as work 011 the right omiN works was nC;lringcompiction, river conditions changed. On March 29, heav), r:tins increased Rows in the river fro111 4,000 cfs (113.3 ml/s) to 3--lAOO rfs (974 ml/s) illjust 12 hours. R ain pcrsislL'<i in the area for the next few months and upstream reservoirs filled. The river flows at the site rcmailLL-d high owing to flood control rdcaSl:S 011 " ."sefvoirs upstream of the site, slowing construction. Work cominucd, but at a fl.-dueed pace.

During dll"SC days of high flows the rid: managcmL'u clauses in the contract dOCUIllL'IltS ix.'CIIllC applicable. DL"Spitc the lost rime, the colltrnctor \\';IS able to rt."CO\"cT 50IllC of the 1Il00lL'tary losses thanks to

thl' vandby lime conditions spt:cifil-d in the contract. It \\~\S 1101 until carly August 2007 that riveT flow'S (iL-crca5(-d suffi­

cit.,uly for work to resume at its nonnal pace. Givcnthe cxtt:nded Sl. ... er\· \\"t:ath~r conditions :md high riR'"!" flO\\'S, a projt"<:t dur.ltion eXh:nsion was grantL"CI nne:! nppro\\."CI in :lCCOI"d.mce with commet docUllklltS. and subsranna! ("ompktion \v:lS delayed lIntil Octobcr 2007.

The Aoodsexperu:ncL-d L1tl' in the project providL-d a fu ll-scale to..'Sf:

offlll'left bbyrinth pt.·rform:mce and v:llie:!mL-d the hydraulic Illodcl­in~ eXpL"<:tmions for the projL'Ct during the construction phase. The right bbyrinth weirwithsfood the high rivcr flows with nostmctural

dal11a~l" ~n(1 the left labyrinth weir lJI..'lfornlL-d as expected. TIll' Lake Brazos Dam construction phase was very boor

intensive, cOloprising 104.395 work hours. However, the con­struction safety pl'rforlllance for the project was excellent, and no tillK' was lo~t l)Cc;\u~l' of accidel1t5. T he s"fety progr.Hll included (biIY:llld wl'l'kly activitil'S. The crews performed daily (Jsk haz­

the contractor began preparing for project complet ion. A final 13ke lowering was scheduled for mid-October so tim [he right

labyrinth weir cofferdams could be removed and final work items could be completed. T he entire labyrintl{ weir \v:lS d;clared subst:lllt ially completl' on October 31, 2007. The first spill over the entire labyri nth weir occurred on November 7, 2007. The project was decbred officially complete on January 8, 2008, twO yc~rs after th~ notice to proceed and with an ~c tual duration of 706 days.

The (b m was dl'd ica!ed on November 13, 2007, • Virt,>r 1\1. Vl1$qua, !'.E., M.,HCl!, ;5 1111 11$$,>(;(11(' if Fm'SI' <lllil Nidwls, hlr., (llId $em'll <IS I/u: profra lead mId rf5idrlll rl!'.!.ill('('r (HI fill." 'abl'rill,h lI'firprojw;)olill S. I 1'o!f1wpc, J'.l!., A.M-ASCI;, is a pn·llcip(li <!fFIL"fsrlllul Nidw/s dllIl served as 'he PIly«tlll/uII!I.,<,roll rill' projl."a; (llId Rick), Gmt'lI,

/>.E., is 'he IIlllN" IIlililies dircf/(Jr./ilf the Cit)' 'f W(I(O, Tcx(lS('.

P.O ... CT C •• DIT. Owner : City of Waco, Texas En gineer: Frc~'SC aud Nichols, Inc .. Fort Worth. Texas Prillle contraClor: Archer Western ContrnclOTS, Arlington, Texas Geotcc h nical investigation and quali ty control tcsting: Klcillfcld~r, W:l(;O, Tex:ls Topographic survey: All Count ySl\fvcying, Inc., T ("mple, Texas Corrosio n evaluation : Corrpro Comp;mies, IIIC., Houston Pccr rcviews: Eric H. Kol lgaanl, r. E., ConcQnl. C1lifomia; Henry T. Falwy & Associates, Inc" Conif("r, Color.ado:John A. Focht,Jr., I'.E., HOllstou: and Tullis Engineering Consu ltants. Lo~,'a ll , Utah Quali ty assurance testing: Fogro Consult:lnts, til, Waco, Texas

ard ~nalyse~, and the contractor's project !ll~Il ­agcll}em tC;II11 completed weekly s,1fety ~udits.

s'1fety 3SIX.'Cts wen' considered ill e\'("fY task per­formed by CT("W IlIcl1luers.

With riwr flows back 10 Ill~nageable levels,

The left ~t;on of the ~byrinth has 13.5 (ydes within the footprint of the overflow embankment, and the right se«ion, bPJow, hilS 11.5 cydes within the footprint of the gated spillway.

Bathymetric survey: Hydrographic Consul­tJIltS, Ltd .. Bellaire, Texas Aeri a l mapping:

Surdex Corporation, C llestcrfic1d , M issouri Physical 1110 delin g: Utah Water R esearch Labor:llOry, UI:lh State University, LOb>"3ll

4055 International Plaza, Suite 200 Fort Worth, Texas 76109

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