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<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 (500-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 500-year flood plain boundaries <br />have been delineated using the flood elevations determined at each <br />cross section. Between cross sections, the boundaries were inter- <br />polated using topographic maps at a scale of 1:2,400, with a contour <br />interval of 5 feet (Reference 10). <br /> <br />Because of the scope of work for the original report, no 500-year <br />flood boundaries were delineated in this study. <br /> <br />The 100- and 500-year flood plain boundaries are shown on the Flood <br />Boundary and Floodway Map (Exhibit 2). In cases where the 100- <br />and 500-year flood plain boundaries are close together, only the <br />100-year flood plain boundary has been shown. Small areas within <br />the flood plain boundaries may lie above the flood elevations but <br />cannot be shown due to limitations of the map scale and/or lack of <br />detailed topographic data. <br /> <br />For the streams studied by approximate methods, only the 100-year <br />flood plain boundary is shown. <br /> <br />Approximate flood boundaries in some portions of the study area <br />were taken from a previous Flood Insurance Rate Map published by <br />FEMA (Reference 11). <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 />lOa-year flood can be carried without substantial increases in <br />flood heights. <br /> <br />The scope of work for this study did not include floodway determina- <br />tion for Uncompahgre River. <br /> <br />Cross sections and regulatory figures for Uncompahgre River are <br />shown in Table 2. <br /> <br />8 <br />