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I , I I I I I I I I I I I . I I I I I SOUTH BOULDER CREEK FLOOD HAZARD AREA DELINEATION - AUTHORIZATION - information and conducted a preliminary hydraulic analysis of the study reach. The information developed by the COE was utilized to complete this Flood Hazard Area Delineation Report. The following is a brief summary of the scope of work for this project. This report was authorized and contracted through the Urban Drainage and Flood Control District (UDFCD) as part of a program of identifying floodprone areas within the District's jurisdiction. The study was jointly funded by the UDFCD and Boulder County. 1. Calculation of water surface profiles for the 10-, 50-, 100-, and 500-year flood events; 2. Delineation of the 100-year floodplain boundary on Flood Hazard Area Maps; 3, Development of discharge profiles indicating the relative magnitudes of the 10-, 50-, 100-, and 500-year flood events; 4. Determination of floodways based on encroachment resulting in a maximum increase in the energy grade line of 0.5 feet and 1.0 feet; 5. Preparation of a report describing characteristics of the study area, flood history of South Boulder Creek, various hazards associated with areas in or near the 100-year floodplain, tabulations indicating pertinent floodplain and floodway information, and reduced copies of floodplain maps and flood profiles. This study identifies floodprone areas along South Boulder Creek within portions .of the City of Boulder and unincorporated Boulder County. The study reach extends from the Colorado and Southern Railroad (C&S R.R.) crossing, located approximately 1100 feet north of Arapahoe Road, upstream to the town of Eldorado Springs, Colorado. The floodplain information included in this report is provided by the Urban Drainage and Flood Control District to enable Boulder County to adopt and administer comprehensive floodplain management regulations. Upon acceptance of this report by the Urban Drainage and Flood Control District and designation of the flood hazard areas by the Colorado Water Conservation Board, this study can be used by Boulder County to regulate future floodplain construction, to guide future drainageway improvements and to plan flood protection measures along the channel and floodplain of South Boulder Creek. - PURPOSE AND SCOPE - With the exception of planned improvements to the South Boulder Road crossing of South Boulder Creek, which were incorporated in this study, the flood profiles and floodplain delineations presented in this report are based on existing flood- plain and channel conditions. Flood elevations and the corresponding floodplain are often altered by road and bridge construction, floodplain development, flood control improvements, or natural processes. Prior to utilization of this report for planning or design purposes, the user is advised to contact the Urban Drainage and Flood Control District or Boulder County to determi ne if the information in this report has been amended. This report was prepared to guide county officials in planning the use and regulation of the 100-year floodplain. The report includes information on past floods and the nature and extent of probable future floods along an 8.4 mile study reach of South Boulder Creek. - ACKNOWLEDGEMENTS - Hydrologic analysis of the South Boulder Creek basin was completed by the Omaha District, U.S. Army Corps of Engineers (COE). The COE also compiled hydraulic This report was prepared by Greenhorne and O'Mara, Inc., Consulting Engineers of Denver, Colorado, under contract with the Urban Drainage and Flood Control District (Agreement No.84-l2.02). 1