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<br />3
<br />
<br />and brldge deck on both bridges could not sustaln without damage. This is
<br />based on the Frontal OragForceandKydrostatlcForce. Tne extent of the
<br />damage would be difflcult to determine due to the addltional impact forces
<br />applied by the flood force and debris dam that would build up on the front
<br />part of the bridges.
<br />The forces indicated by Existing Bridge, Additional Structure and Channel
<br />Improvement, as sho\~n in the tab] e could be sus ta; ned by the ex; sti n9 bridge
<br />with improvements made to the bridge such as. additlonal tie-downs and
<br />anchorage at the bearing areas, provision for trapped air ;n the girders
<br />to be released to prevent uplift. Also, additional connections at diaphragms
<br />and deck could be made in order to transfer load to the other girder units
<br />in the bridge deck.
<br />The forces shown in the table under Existing Bridge with Shaping, Additional
<br />Structure and Channel Improyementscould be sustained bytheexi sting bridge
<br />structure but would also require sope additional tie-down improvements at
<br />the bear;~gs, a release for trapped air to prevent uplift, diaphragm ties and
<br />deck ties.
<br />
<br />Recommendations
<br />I~nediate action would require additional tie-down anchorage at the bearing .
<br />area for the single stemmed units on the upstrea~ side of the bridge, ~onnectlons
<br />at the diaphragm and additional connections at the top flange of the Slngle
<br />stemmed units on the bridge deck. Proper venting would be required to prevent
<br />uplift. Shaping of the upstream beam face of the firs~ prestressed girder
<br />would be an additional safety factor if funds were eyal1able.
<br />The only positive way to eliminate the forces 00 the existing b~id~es is to
<br />raise the bridge deck above the 100 year water surfa~e. The eXI stlng
<br />abutrneots dnd roadway could be rlOdified and a newbndgedeck install ed
<br />along with the other improvements. This would enteil removal of the old
<br />bridge aeCk. bridge giroers and a new superstructure constructea.
<br />
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<br />WRIGHT,MCLAUGHLiN ENG'NEERS
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<br />Iktober5,1981
<br />
<br />~. Bill DeGroot
<br />Chief. noodpl~in Manag~,ent
<br />Urban Drainage and Flood Control District
<br />Suite156-B,248DW.26thAve.
<br />Oenver, Colorado 80211
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<br />Re; Purch~se Oraer No. 00358
<br />Upper Clear Creek
<br />Fl oodpl ain AA~lysi s
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<br />DearSi11;
<br />We h~ye completed the ~nalysjs of the JOO-yea~ flOOdplain for IJppe~ C)ea~
<br />C~eek bet~en Ford street ~nd Washin9ton ~,venue. A discuss10n of the
<br />results follows and supporting calcul ations ~re includetl in the ~p~ndix.
<br />Ford Street Area
<br />
<br />Initially, computer backwater runs ~re :!lade for flows varying from 5,1)00
<br />cfs to 9,000 cfs to determine the bar.k full channel capacity. TheChanne1
<br />just dO>ll1stre~ of Ford Street was found to have a capacity of 6,500 cf, to
<br />7,000 cfs. Based on dn assOJT1E'd flow s~l it of 5.000 cfs weir flo~' and 7,000
<br />cf~ bridge flow, a backwater run was made start i n9 wi th the full 1 DO-ye ar
<br />flow of 13,470 cfs at the b~ewery ared downstream and dtCcreasing to 10,000
<br />cfs at the fabridNn aM 7,000 cfs dOW"1strea-r of Fowd Str~~t.
<br />
<br />The 7,000 cfs water surface r!o""streOl:' of Ford Street was used as thE
<br />t<ilw,tt>r e1~Hti('~ for ha~d calcu1dti~rs to ~eter:ri~~ the hcad"'i;ter surface
<br />eleyationupstrearcofFordStreet.
<br />Sta~dard cul vert h)l1raul ic anal ysis was fjrst applied to the Fore: Street
<br />structure, but subseQuent appl ication of the ,"Hydraul ics of p,r i~S~
<br />OIaterways" methodology yielded more satishcto~y results ..+:en combined with
<br />tile calculations for weir flow around the bridge. M eleYdtion of 5657.8
<br />was determined to be the 100-year water surface upstream of Ford Street.
<br />resulting in a flew of 7,000 cfs through the bridge and 5.000 cfs weir
<br />flow.
<br />
<br />In order to determine the direction d~d extent of overbank flooding.
<br />Sepdrdte overbank backwater ca1culdtions were done starting in the brewery
<br />parking lot and proceeding UpHre~ to Ford Street. Thl' results of this
<br />an~lysis jndic~tes that appro. imat!'ly 3,550 cfs of the 5,000 cfs weir flo~'
<br />will rejoin the channel flow in the area of the agr1cultural ditch hear!gate
<br />and diversion ch~nnel downstre~ of Ford Street. The r€'l1dining 1,~50 cfs
<br />flows to the south of the Coor s We 11 ness Center down 12th Street ~nd th~o LJQ h
<br />the brewery parking lot at an average depth ofO.S foot to 1.0 foot. Tr.ls
<br />overb~n~ flow is not connectea to the main Channel flow until it reaches the
<br />brewery (Xlwer building ~ere ~n auto bridge creates a significant back~'ater.
<br />Th/' o"erbank flow decreases as it trdyelsthroughthe parking lotto wardtne
<br />power bui 1 d i og ~s flow spills over the curb and into the malo channel.
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