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I I I I I I I I I I I I I I I I I I I I. MAJOR DRAINAGEWAY PLANNING LITTLE DRY CREEK Introdllction Northwest of Denver, in Jefferson and Adams Counties, Little Dry Creek rises at the eastern edge of the foothills and flows southeastward to its confluence with Clear Creek. Topography of the Little Dry Creek basin is dominated by the bordering hills and ridges. The upstream region in Jefferson County and Arvada has a narrow floodplain. The downstream lowlands, in Adams County and Westminster, are fairly level and wide. While no serious flood damage has been recorded on this stream, the Cities of Westminster and Arvada have experienced rapid growth in recent years and the trend is toward fully developed conditions within a few years causing increased runoff potential in all reaches of Little Dry Creek. Industrial and residential developments already exist in the floodplain along the lower reaches of the stream and without regulation, anticipated future growth could spread urbanization to agricultural areas located in probable flood zones. It is impossible to predict when a flood will. occur on Little Dry Creek. In its present condition, a flood of even minor magnitude has the potential to cause extensive damage to homes, businesses, streets and utilities. In view of the foregoing, the Urban Drainage and Flood Control District together with the City of Arvada, the City of Westminster, Adams County and Jefferson County have contracted with Merrick and Company, Consulting Engineers, to compile information, evaluate, study and to recommend design solutions to the drainage problems on Little Dry Creek which are in the best interest of the involved parties and agencies. The results of the study are published in three separate reports: I. Flood Hazard Area Delineation - Little Dry Creek n. Major Drainageway Planning - Phase "A", Little Dry Creek III. Major Drainageway Planning - Phase "B", Little Dry Creek The necessary field work, compilation of data, the development and consistent evaluation of alternative flood control plans were completed and the results were presented in the Phase "A" Report. Upon reviewing the study findings and recommendations, the Urban Drainage District, City of Arvada, City of Westminster, Adams County and Jefferson County, selected an alternative plan for implementation which most satisfies local interests and is consistent with their planning endeavors. I - I This final report presents the selected plan for flood control and culminates the Little Dry Creek Master Plan Study. It includes a description of final hydrologic and hydraulic studies conducted during the preliminary design, and defines the 100-year flood plain for existing and improved channel conditions, presented on the Plan and Profile Maps at a scale of 1"=200'. A narrative description of the proposed improvements and a final cost estimate are also inciuded on a sheet by sheet basis. Exis ting- Flood Hazards For the purposes of this study, the Little Dry Creek channel has been divided into the following reaches: Reach 1 - Confluence with Clear Creek to Federal Boulevard; Adams County Reach 2A - Federal Boulevard to West 69th Avenue; Adams County Reach 2B - West 69th Avenue to West 72nd Avenue; Westminster Reach 3 - West 72nd to West 75th Avenue; Westminster Reach 4 - Sheridan Boulevard to Wadsworth Boulevard; Arvada Reach 5 - Wadsworth Boulevard to the upstream study limit; Arvada and Jefferson County Reach AlA - Shaw Heights Tributary - West 75th Avenue to West 80th Avenue; Westminster Reach AIC - C & S Railroad to Detention Dam; Westminster Reach AID - Detention Dam to upstream study limits; Westminster Tributary B Influence with mainstem west of Sheridan Boulevard, through Lake Arbor, to upstream study limits; Arvada Tributary C- Lake Arbor to upstream study limits; Arvada The Little Dry Creek Floodplain is presently utilized for residential, commercial, and industrial purposes. While some reaches are capable of conveying all or part of the design floods, Ii ttle provision has been made in the lower reaches for passing flood flows and the hydraulic analysis revealed that the potential flood-induced damages and hazards are significant. With the exception of some culverts beneath city streets, the entire channel in Reaches 1, 2, 3 and the Shaw Heights Tributary is on private property. Few easements have been provided in Westminster and Adams County for maintenance, and those provided are very narrow at best. The channel is neglected. Flood hazards in these reaches originate from inadequate culverts and a historic lack of regulation of development in the floodplain.