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Roughness factors (Manning's On") used in the hydraulic computations Were chosen by engineering judgment and based on field observations of the streams and flood plain areas. Channel roughness values used for the Roaring Fork River ranged from 0.04 to 0.045, while the overbank values ranged from 0.08 to 0.1. The channel roughness value used for Castle Creek was 0.045, while the overbank values ranged from 0.08 to 0.1. For Maroon Creek, the channel roughness value used was 0.045 and the overbank roughness value used was 0.08. " . Starting water-surface elevations for the Roaring Fork River were taken from the Flood Insurance Study for adjoining areas of Pitkin County (Reference 9). Starting water-surface elevations for Castle and Maroon Creeks were taken from the Roaring Fork River flood elevations. 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 (500-year) flood is employed to indicate additional areas of flood risk in the community. For each stream studied 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 1:600 and 1:1,200, with a contour interval of 2 feet (Reference 7). The 100- and 500-year flood plain boundaries are shown on the Flood Boundary and Floodway Map (Exhibit 2). In caSes where th~ 100- and 500-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 7