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<br />Roughness factors (Manning's "n") used in the hydraulic computations <br />for Uncompahgre River were chosen by engineering judgment and <br />based on field observations. A roughness value of 0.05 was used <br />for the main channel of Uncompahgre River at Olathe. For the <br />overbank areas, a roughness value of 0.1 was used in the hydraulic <br />computations. <br /> <br />Starting water-surface elevations for Uncompahgre River at Olathe <br />were obtained fram the U.S. Army Corps of Engineers Montrose County <br />Flood Hazard Information report (Reference 7). <br /> <br />Flood profiles were drawn Showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1) . <br /> <br />Downstream of State Highway 348, water leaves the main channel <br />and flows down an embankment. The depth of flooding was determined <br />by hand calculations to be less than 1.0 foot. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in the study <br />are shown on the maps. <br /> <br />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations shown on the profiles are, thus, con- <br />sidered valid only if the hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />4.0 FLOOD PlAIN MANAGEMENT APPLICATIONS <br /> <br />The National Flood Insurance Program encourages State and local governments <br />to adopt sound flood plain management programs. Therefore, each Flood <br />Insurance Study includes a flood boundary map designed to assist communi- <br />ties in developing sound flood plain management measures. <br /> <br />4.1 Flood Boundaries <br /> <br />In order to provide a national standard without regional discrimina- <br />tion, the 100-year flood has been adopted by the Federal Emergency <br />Management Agency as the base flood for purposes of flood plain <br />management measures. The SOD-year flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied in detail, the boundaries of the 100- and SOD-year floods <br />have been delineated using the flood elevations determined at <br />each cross section~ between cross sections, the boundaries were <br />interpolated using topographic maps at a scale of 1:4800, with <br />a contour interval of 2 feet (Reference 10). <br /> <br />Flood boundaries for the 100- and 500-year floods are shown on <br />the Flood Boundary and Floodway Map (Exhibit 2). In cases where <br /> <br />12 <br />