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<br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound flood <br />plain management programs. Therefore, each Flood Insurance Study produces <br />maps designed to assist communities in developing flood plain management <br />measures.. <br /> <br />4.1 Flood Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the 1 percent annual chance (lOO-year) flood has been adopted by <br />FEMA as the base flood for flood plain management purposes. The <br />0.2 percent annual chance (SOD-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied in detail, the 100- and SOD-year flood plain boundaries <br />have been delineated using the flood elevations determined at "each <br />cross section. Between cross sections, the boundaries were <br />interpolated using topographic maps at a scale of 1:2,400, with a <br />contour interval of 1 foot (Reference 6). <br /> <br />Due to the scope of work for the original report, no SOO-year flood <br />boundaries were delineated in this study. <br /> <br />The lOO-year flood plain boundary is shown on the Flood Boundary <br />and Floodway Map (Exhibit 2). In cases where the 100- and 500- <br />year flood plain boundaries are close together, only the lOO-year <br />flood plain boundary has been shown. Small areas within the flood <br />plain boundaries may lie above the flood elevations but cannot be <br />shown due to limitations of the map scale and/or lack of detailed <br />topographic data. <br /> <br />For the streams studied by approximate methods, only the lOa-year <br />flood plain boundary is shown. <br /> <br />4.2 Floodways <br /> <br />The floodway is the channel of a stream, plus any adjacent flood <br />plain areas, that must be kept free of encroachment so that the <br />IOO-year flood can be carried without substantial increases in <br />flood heights. <br /> <br />No floodway was computed for the Uncompahgre River as part of this <br />study. WOrk submitted by the study contractor did not meet FEMA's <br />requirements for establishing a floodway. <br /> <br />Regulatory elevations computed at selected cross sections used in <br />the hydraulic analyses (Section 3.2) are shown in Table 2. <br /> <br />10 <br />