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I I I I I I I I I I I I I I I I. INTRODUCTION A. GENERAL This report is part of a study authorized by the Urban Drainage and Flood Control District (UD&FCD) in the agreement regarding Outfall Systems Planning and Flood Hazard Area Delineation (FHAD) for the Plum Creek Watershed, dated October 28, 1999 (Agreement NQ 99-05_04)_ The study area, shown in Figure I-I, consists of the entire Plum Creek Watershed including West Plum Creek and Jarre Creek. The study is divided into three parts. The first part (Phase A) covers the hydrologic, hydraulic, and alternative evaluation aspects of the study. The second part (Phase B) covers the preliminary design of the selected alternative_ The third part is the FHAD, for which this report was prepared. The Hydrology Report (Reference-I), summarized herein, was submitted on May 25, 2000_ B_ PURPOSE AND SCOPE The purpose of the overall study is to prepare a master plan report and floodplain delineations for Plum Creek and select tributaries within the Plum Creek Watershed_ This work includes evaluation of the hydrologic and hydraulic aspects of the Plum CreekWatershed in order to define the runoff rates and volumes to be used in this study. The scope for the FHAD study is as follows: 1. Gather and assemble available information on existing drainage facilities, comprehensive plans, land use plans, zoning and land ownership maps, and other applicable information_ 2. 'Determine the hydrologic aspects ofthe watershed including runoff rates and volumes for various return periods of storm events_ , o. Define the water surface profiles for the 10, 50, 100, and 500-year flood events and the 0_5 foot and 1_0 foot floodways_ I I I I 4_ Prepare plan and profile drawings of the Plum Creek drainageway and select tributaries showing the limits of the 100-year floodplain and the 10-year and 100-year flood profiles based upon the study hydrologic conditions and existing channel conditions_ 5_ Document the results of the study in the FHAD Report. 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" = I 00' with 2-foot contour intervals_ The maps were submitted in electronic format as an AutoCAD Version 14_0 drawing_ The topography was compiled from aerial photographs taken in May 1999. Culvert and bridge diagrams were provided showing the sizes and configurations of existing drainage structures_ Base mapping forthe hydrologic maps consist of United States Geological Survey(USG-S) quadrangle maps at a scale of I" = 1000'. Soil surveys prepared by the U.S. Department of Agriculture Soil Conservation Service (now known as the Natural Resources Conservation Service, NRCS), were used to determine soil types and hydrologic soil groups_ A site investigation was conducted to evaluate channel roughness values and to identifY potentially sensitive environmental areas_ The information gathered included channel roughness, drainage structures, and photographs of the major facilities and channels. D. INFORM A TION PROCUREMENT Maps of existing drainage facilities and previous drainage studies, where available, were provided to WRC Engineering, Inc. (WRC) by the study participants_ During the process of this study, several agencies, organizations and individuals were contacted by WRC staffto obtain data and history regarding storm drainage within the study area_ The following is a list of contributors and the pertinent data obtained: I-I