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estimation of topwidth, and direct' use of drainage area versus discharge and drainage area versus, depth in channel curves from USGS Technical Manual No. 1 (Reference 13). The hydraulic analyses for this st~dy 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 Datum of 1929 (NGVD). Elevation study are shown on the maps; the presented in Elevation Reference the National Geodetic Vertical reference marks used in this d~scription of the marks are Marks (Exhibit 3). , ' 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound flood plain management programs. Therefore, e~ch FIS provides lOa-year flood elevations and delineations of the 100- ~nd SO a-year flood plain boundaries and lOa-year floodway to assi~t 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 (lOa-year) flood has been adopted by FEMA as the base flood for flood plain management purposes. The 0.2 percent annual chance (SOO-yea~) flood is employed to indicate additional areas of flood risk in ~he community. For each stream studied by detailed methods, the lpO- and SOO-year flood plain boundaries have been delineated using the flood elevations deter- mined at each cross section. Betw~en cross sections, the bound- aries were interpolated using topographic maps at a scale of 1:24,000, with contour intervals of 10, 20, and 40 feet (References 29, 30, and 31, respectively). Flood plain boundaries for Cherry Creek were determined by a COE report entitled Flood Plain Inform~tion, Cherry Creek-Cherry Creek Lake through Franktown, Colorado (~eference 14). This report was also' used to determine the boundaries at the confluences with Cherry Creek tributaries included in this study. The 100- and SOO-year flood plain boundaries are shown on the Flood Insurance Rate Map (Exhibit 2). On this map, the lOa-year flood plain boundary corresponds t$ the boundary of the areas of special flood hazards (Zones A andiAE); and the SOO-year flood plain boundary corresponds to the ~undary of areas of moderate flood hazards. In cases where the! 100- and SO a-year flood plain boundaries are close together, only the lOa-year flood plain boundary has been shown. Small areas within the flood plain 26