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Channel improvements along Weir Gulch have been constructed from West Alameda Avenue to the confluence with the South Platte River (References 26-30), Improvements include the regrading of Barnum Lake and the construction of an additional outlet culvert under West 6th Avenue (U.S, Highway 6), designed to reduce the extent of 100- and 500-year flooding below Barnum Lake. .' Channel improvements along Weir Gulch have been constructed from -just downstream of West Alameda Avenue to Sheridan Boulevard, Improvements included the construction of an approximately 4,200 foot long channel designed to convey the 100-year flood, five bridges, and three drop structures, designed to convey the flows beneath the four roadways it crosses (Reference 31). Weir Gulch Dakota Avenue Tributarv .. The Weir Gulch Dakota Avenue Tributary project, which extends from the confluence at Weir Gulch upstream to South Sheridan Boulevard, is comprised of a new culvert system which supplements the capacity of an existing adjacent storm sewer system (Reference 32), The culvert system was designed to convey the 100-year flood, Sand Creek Levees are located along Sand Creek in the vicinity of Havana Street; however, these levees have no effect on the 100-'and 500- year floods. Marston Lake North The Marston Lake North drainageway improvements extend from Vaile Lake upstream to the corporate limits. These improvements include construction of an energy dissipation plunge pool basin and a golf cart crossing in a portion of the existing Vaile Lake; installation of two 5-foot high by 10-foot wide reinforced-concrete box culverts under Quincy Avenue; construction of a grass-lined channel from South Wadsworth Boulevard to just upstream of Quincy Avenue; the addition of two 72-inch steel pipes under Highway 121; construction of a 40-foot transition structure directly upstream of Highway 121; addition of 1,532 linear feet of 8'x7' twin barrel box culvert, and 520 feet of open channel; and construction of an 8.4 acre-feet sedimentation control basin with 85 linear feet of drainage channel which connects to the existing channel (References 33 and 34). The channel and culvert improvements convey the 100-year recurrence interval flood, wi th the exception of some overland flow at South Wadsworth Boulevard. 3,0 ENGINEERING METHODS For the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study, Flood events of a magnitude that are expected to be equaled or exceeded once on the average during any 15