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Water-surface profiles for floods along Cherry Creek utilized in this stUdy were obtained from a 1976 COE Flood Plain Information report (Reference 10). The water-surface profiles for 10-, 50-, 100-, and 500-year floods on Cherry Creek were developed using the COE HEC-2 step-backwater computer program (Reference 21). The computations were based on channel and flood plain conditions as represented by the survey data gathered in April 1975 and as supplemented by later field investigations. The methods used in estimating elevations of streams studied by approximate methods include direct use of drainage area-discharge curves from a USGS report (Reference 22), direct use of UDFCD information where available, and calculation of normal depth from field cross sections and estimation of topwidth. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the profiles are thus con- sidered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD). Elevation reference marks used in this study are shown on the maps; the descriptions of the marks are presented in Elevation Reference Marks (Exhibit 3). 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound flood plain management programs. Therefore, each Flood Insurance Study pro- vides lOa-year flood elevations and delineations of the 100- and 500- year flood plain boundaries and laO-year floodway to assist communities in developing flood plain management measures. 4.1 Flood Plain Boundaries To provide a national standard without regional discrimination, the 1 percent annual chance (IOO-year) flood has been adopted by FEMA as the base flood for flood plain management purposes. The 0.2 percent annual chance (500-year) flood is employed to indicate additional areas of flood risk in the community. For each stream studied by detailed methOds, the 100- and 500-year flood plain boundaries have heen delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:24,000, with a contour interval of 20 feet (Reference 23). 13