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Flood depths for approximate atudies were computed from nomographs contained in Technical Manual No.1: Manual for Estimatinl!; Flood Characteristics of Natural-Flow Streams in Colorado, prepared by the CWCB and the USGS (Reference 42). The hydraullc 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 Datum of 1929 study are shown are referenced to the National Geodetic (NGVD). Elevation reference marks used on the maps. Vert ica 1 in this 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound plaln management programs. Therefore, each Flood Insurance produces maps designed to assist communitles in developing flood management measures. flood Study plain 4.1 Flood Boundaries To provide a national standard without regional discrimination, the 1 percent annual chance (lOO-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 studled in detail, the 100- and 500-year flood plain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were inter- polated using topographic maps at scales of 1:1,200, 1:2,400, 1:4,800, and 1:24,000, with contour intervals of 1, 2, 10, and 40 feet (References 22-39). The above-referenced topographic maps were also used to delineate approximate flood boundaries. For the streams studied by approximate methods, only the 100-year flood plain boundary is shown. Approximate 100-year flood plain boundaries in some portions of the study area were taken directly from the Flood Hazard Boundary Map (FHBM) (Reference 43). Flood plain boundaries are indicated on the Flood Insurance Rate Map (Exhlbit 2). On this map, the 100-year flood plain boundary corresponds to the boundary of the areas of special flood hazards (Zones A1-A16, Al8, and A21); and the 500-year flood plain boundary 26