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I I I I I I I I I I I I I I I I I I I I. INTRODUCTION 4. Prepare plan and profile drawings of the Big Dry Creek drainageway showing the limits of the 100-year floodplain and the IO-year and 100-year flood profiles based upon the smdy hydrologic conditions and existing channel conditions. A. GENERAL This repon is pan of a study authorized by the Urban Drainage and Flood Control District (UD&FCD) in the agreement regarding Major Drainageway Planning and Flood Hazard Area Delineation (FHAD) for Big Dry Creek (ARAPCO) and Tributaries, dated April 10, 1995 (Agreement No. 9501.08). The study area, shown in Figure I -I, consists of the entire Big Dry Creek watershed which encompasses parts of the City of Littleton, the City of Englewood, the City of Greenwood Village, Arapahoe County and Douglas County . 5. Document the results of the study in the FHAD Repon. C. MAPPING AND SURVEYS The topographic maps for this project were prepared by Landmark Mapping under separate contract with UD&FCD. The plan maps were compiled and prepared at a scale of I" = 100' with 2-foot contour intervals. The maps were submitted in electronic format as an AutoCAD Version 12.0 drawing. The topography was compiled from aerial photographs taken on December 2, 1994. Culven and bridge diagrams were provided showing the sizes and configurations of existing drainage structures. Base mapping for the hydrologic maps consist of U.S.G.S. quadrangle maps at a scale of I" = 1000'. Soil surveys prepared by the U.S. Department of Agriculture Soil Conservation Service were used to determine soil types and hydrologic soil groups. The study is divided into three pans. The first pan (Phase A) covers the hydrological, hydraulic, and alternative evaluation aspects of the study. The second pan (Phase B) covers the preliminary design of the selected alternative. The third pan is the FHAD, for which this repon was prepared. The Hydrology Repon (Reference 16), summarized herein, was submitted for review on November 10, 1995 and was finalized on July 12, 1996. B. PURPOSE AND SCOPE The purpose of this study is to update the original master plan repon for Big Dry Creek, Major Drainageway Master Plan Big Dry Creek, dated June 1975 (Reference 10). This work includes evaluation of the bydrologic and hydraulic aspects of the storm drainage system for the Big Dry Creek (ARAPCO) watersbed to defme the runoffrates and volumes to be used in this study. A site investigation was performed to determine channel roughness values and to identify potentially sensitive environmental areas. The information gathered included channel geometry and roughness, drainage structures and photographs of the facilities and channel. D. INFORMATION PROCUREMENT The scope for the FHAD study is as follows: I. Gather and assemble available information on existing drainage facilities, comprehensive plans. land use plans, zoning and land ownership maps, and other applicable information. Maps of existing drainage facilities and previous drainage studies, where available, were provided to WRC Engineering, Inc. (WRC) by the study panicipants. During the process of this study, several agencies, organizations and individuals were contacted by WRC staff to obtain data and history regarding storm drainage within the study area. The following is a list of contributors and the peninent data obtained. 2. Determine the hydrologic aspects of the drainage area including runoff rates and volumes for various return periods of storm events. Urban Drainage and Flood Control District . Lehow Avenue Bridge Information . Aerial Photos . Big Dry Creek Photos 3. Define the floodplain and the floodway for the I DO-year flood. Douglas County . Land Ownership Maps . Detention Pond Grading Plans '-1