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I I I I I I I I I I I I I I I I I I I 1 I SUMMARY Hydrologic and Hydraulic Analyses Detailed analyses were made of the anticipated rainfall in the Dry Gulch watershed in various rainstorms and the extents of flooding which would result from the storms were determined. Presented in this report is a conceptual Master Plan for devel- opment along the major drainageways of Dry Gulch and North Dry Gulch in the Cities of Lakewood and Denver, Colorado. The Master Plan is presented by way of plan and profile sheets depicting the recommended improvements to the channels. This Section of the report summarizes the detailed information of subsequent Sections in order to present a synopsis of the analy- ses performed and the elements of the recommendations. Development of Alternative Plans The report titled "Major Drainageway Planning for Dry Gulch, Phase A, Development of Alternative Plans," (Reference 2). presented a number of different alternatives which could be con- sidered for reducing flood damage along the channels. The Cities of Lakewood and Denver, in conjunction with the Urban Drainage District, established guidelines for the selected alter- native. The selected alternative was then evaluated in detail and a preliminary design was prepared in this report. The Study Area The Dry Gulch watershed consists of approximately 3.7 square miles lying predominantly in Lakewood. Dry Gulch is tributary to Lake- wood Gulch in the vicinity of lOth Avenue and Perry Street in Denver, and extends westward along the general alignment of Colfax Avenue to Simms Street. North Dry Gulch is tributary to Dry Gulch near l3th Avenue and Harlan Street, and also extends westward along Colfax Avenue. The watershed is essentially fully developed at present, with commercial establishments along Colfax Avenue and residential developments in the remainder. Because of the rela- tively intense urbanization, the storm runoff has increased over natural conditions, and flood damage and inconvenience has occurred frequently. The potential hazard in a lOO-year flood can be con- sidered severe, as illustrated in "Flood Hazard Area Delineation, Dry Gulch and Tributaries" (Reference l). Benefit Cost Analysis In the Phase A report, the estimated costs of construction and right-of-way acquisition were determined for each alternative. The benefits to be derived by construction of each alternative were then determined by subtracting the anticipated flood damages which would occur after construction from those which would occur before construction. In this Phase B report, the construction and right-of-way costs and the anticipated benefits have been updated and estimated in greater detail. The proposed Master Plan for Dry Gulch is estimated to cost approximately $ll,884,000.