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Colorado and Southern Railroad Culvert Impravement~ Improvements at Stuart street consist of installing five 9- foot wide by 5-faot high box culverts. Stover Street improvements are five 9-foot wide by 6-foot high box culverts. Bridges with an equivalent opening can be constructed in lieu of the proposed culverts. Existing street elevations ore 3"""umed to be approximately maintained. The existing 13-Coot wide by lO-foot high box culvert under the C & S Railroad restricts flow such that approximately 180 cfs overtops the tracks with an estimated -/':> cfs also crosGing Timberline Road. In order to eliminate this situation and provide adequate freeboard, a 66-inch culvert will be in.<;talIE,d adjacAnt to the existing box. Installation of the culvert will require jacking. Inlet and outlet modificat:ion to t_he existing culvprt will be required in addition to transition grading of the channel both up and downstream of the crossing. Welch Street Bridqe Improvements I I I I Channel improvements between stuart street and Stover street consist of widening the channel while maintaining the existing low flow section as well as its riparian habitat. Consequently, the improved Creek channel will have a varied cross section. Channel improvements downstream of Stover Street and upstream of Stuart Street will consist of several hUndred feet of channeli~ation and excavation tor the necessary transition between the new street crossings and the existing Creek. Bike path improvemenh; along this route are included in the preliminary design. The existing Welch Street bridge with double 5-foot high by 10-foot wide openings has a capacity of approximat_ely 1300 cfs before overtopping of Welch street occurs. An opening of 24-foot wide by a-Coot high is required, given the residual conditions design flow of 2100 cis and WelCh Stt.eot maintained at its approximate current elevation. I.mProvements between Colll;'S!LA,,---e_llue_3n_dj\t".thur-'- s_Dit!='h_ stuart ~et and Stover Street Imorovements 8ridQe dQU Ch1;J..'1!:llU The key elements in this reach "-re new culverts under the railroad and a channel d('signE'd to ['''SS ,'ppro><imat..ly 175(1 cf.. p"''1k dischi'lrge from the npw culvE'rt" "'<1st to the College AvenuE' bridg"'. The existing culvert will be restrlcted to " 27-ind, diilmeter opening, allowing 60 cfs to pass through the storm sewer under the mobile home park. Thus, the total maximum out.flo'" from the pond will be 1810 cfs. The culvert crossing, whiCh acts as the primary pond outlet, has been preliminarily sized a" two 84-inch diameter pipes and One 78-inch diameter pipe. In order to maintain existing flows downstream, th.. 78-inch pipp will hp m<>np inpff",,-,tjvp until The existing bridges at stuart street and Stover Street have capacities of approximately 1000 <lnd 2000 ofs, respectively. The restrictions caused by the Stuart Street bridqc combined with the limited channel capacity bet",een and adjacent to the bridges create a SE'riOllS flaadin'] potpntint, with nllm<>r(l11S "'Iji\,-",,,,nt stru"t."n's located in the 100-year floodplilin. The Stover street bridge, Which is margini'llly adequate hydrdul ied 11y, ha" struetulCdl deficiencies and consequently is being recommended for r<'placement at the City's direction. Design now at this locath1l1 of Spring Creek is appro><imately 19JO cfs. the ponding elevation reaches 4989.0. This '~'ill be done by constructing a 25-foot long weir, with a crest elevi'ltion of 4939.0, around the inlet of the pipe. The pipe will beco",,, fully effective when ponding occurs abov"" elevation 499l. O. When and if the optional detention pond improvements described <'I section"> are built, the weir can be removed and the entin; I-'i"e lit.i.li.~ecl. " ,