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convert the point precipitation values to average precipitation over the watershed area. The studies were conducted using runoff computa- tions based on information regarding type and location of existing and planned land use provided by the Boulder County Planning Depart- ment (Reference 5). Hydrologic soil cover complexes and associated Runoff Curve Numbers were extracted from a U.S. Soil Conservation service report (Reference 5) and field checked. Values of 10-, 50-, 100-, and SOO-year peak discharges were obtained using U.S, Soil Conservation Service computer programs, WSP2 and TR20 (Reference 6 and 7, respectively), Peak discharge-drainage area relationships for Coal Creek are shown in Table L 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of streams in the commu- nity were r.arried out to provide estimates of the elevations of floods of the selected recurrence intervals along each stream studied in the community. Cross section data were taken from 1974 photography and mapping of the study area (Reference 2), All bridges and culverts were surveyed to obtain their elevation and size. The normal openings of the bridges and culverts were used to determine flood data at road crossings. Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments Lor which a floodway is computed (Section 4.2), selected cross section locations are also shown on the Flood Boundary and Floodway Map (Exhibit 2). Typical Manning's "n" values for the channel and overbanks ranGed from 0.085 to 0.120 (Reference 2). Starting water-surface elevations were determined by the U.S, Soil Conservation Service (Reference 6). Using stream slope at a starting valley section, water-surface profiles for the 10-, 50-, 100-, and SOO-year floods were developed using the u.S. Soil Conservation Service WSP2 and TR20 computer programs (References 6 and 7, respec- tively) , Flood profiles were qrawn showing computed water-surface elevations to an accuracy of 0,5 foot for floods of the selected recurrence intervals (Exhibit 1). All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD), Elevation reference marks used in the study are shown on the maps. 6 1 '"II .' . ,'~t I ',;..~ A" ,! r ..... " , .,.