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I I I I I I I I I I I I I I I I I I I ABSTRACT This report was prepared for the Urban Drainage and Flood Control District, Colorado Water Conservation Board, the City of Littleton, and Arapahoe County, and describes the areas that would be inundated by a flood with a return frequency of 100-years. Lee Gulch has a well defined natural channel and, with a few exceptions, the 100-year flood is contained within its banks. Windermere Street, Elati Street, Broadway, Mineral Avenue, and COunty Line Road will be flooded where they cross the Gulch. Little Creek varies from an improved channel to one that has been completely encroached upon by development. Downtown Little- ton is subject to flooding along Low Street. The improved portion of Little Creek is paralled by Sterne Parkway with numerous streets crossing the channel. All of these crossings and Sterne Parkway will be subjected to flooding. Two agricultural canals, the City Ditch and the Highline Canal intercept the storm flow. Upstream of the llighline Canal the streets that generally follow the Historic channel will be flooded. A. B. C. I . INTRODUCTION SCOPE OF WORK On December 27, 1976 Agreement No. 76-10.5 "Major Drainage- way Planning and Flood Hazard Area Delineation for Lee Gulch and Little Creek" was executed by the Urban Drainage and Flood Control District, Arapahoe County, the City of Little- ton, and KKBNA. Although the District has the authority to regulate flood plains, it has chosen to leave such regulation responsibility to the local governing authority. This report describes the areas that would be inundated by a flood with a frequency of return of 100 years. This informa- tion can be used by the City and County officials in the adoption of any desired land use or other regulatory devices to guide flood plain management. It must be noted that flood depths and topographical boundaries may be altered by both public and private construction, as well as natural processes. Therefore, the use of this report for planning or regulation purposes should be coordinated with the Urban Drainage and Flood Control District for possible amendments. COORDINATION Topographic mapping and cross-sections were provided by Bell Mapping Company under a separate contract with the Urban Drainage and Flood Control District. Biweekly meetings were held with representatives of the District, County, and City. Additional coordination was made with the U.S. Army Corps of Engineers, Soil Conservation Service, Federal Insurance Ad- ministration, U.S. Geological Survey, State Geologist, Denver Water Board, Regional Transportation District, Littleton Historical Society, Division of Highways, and others. METHODOLOGY The basic mapping was made at 1" = 1 00' with 2 I contour in- tervals. Following several field investigations, all perti- nent land use data and drainage facilities in place were ob- tained from local authorities. Six sub-basins for each of -2-