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Backwater flooding from Yampa River in unincorporated Moffat County affects two small areas of Craig; the vicinity east of Barker Street near its intersection with Second Street, and the area immediately south of where Pine Ridge Gulch leaves the corporate limits. The lOO-year flood elevation is 6,167 feet. The approximate 100-year flood elevations for Tributaries 1 and 2 were determined by normal-depth calculations of typical sections based on field observation, 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. 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 produces maps designed to assist communities in developing flood plain management measures. 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 (SOD-year) flood is employed to indicate additional areas of flood risk in the community. For each stream stJdied 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 interpolated using topographic maps at scales of 1:2,400 and 1:4,800, with a contour interval of 2 feet (Reference 8). For Tributaries 1 and 2, the lOO-year flood boundaries were determined by normal-depth computations using field observations and U.S. Geological Survey topographic maps (Reference 9). The 100- and SOO-year flood plain boundaries are shown on the Flood Boundary and Floodway Map (Exhibit 2). In cases where the 100- and SOD-year flood plain boundaries are close together, only the 100-year flood plain boundary has been shown. Small areas within the flood plain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. 12