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<br />and drainage area-versus-depth in channel. <br />directly to get the required elevations for <br />flood boundaries. <br /> <br />These curves were used <br />the delineation of <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in this study <br />are shown on the maps; the descriptions of the marks are presented <br />in Elevation Reference Marks (Exhibit 3). <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 provides <br />100-year flood elevations and delineations of the 100- and SOD-year flood <br />plain boundaries and 100-year floodway to assist communities in developing <br />flood plain management measures. <br /> <br />4.1 Flood Plain 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 (SOO-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied by detailed methods, the 100- and SOO-year flood plain <br />boundaries have been delineated using the flood elevations determined <br />at each cross section. Between cross sections, the boundaries <br />were interpolated using a topographic map at a scale of 1:24,000, <br />enlarged to 1:12,000, with a contour interval of 40 feet (Refe- <br />rence 16). <br /> <br />The 100- and SOD-year flood plain boundaries are shown on the Flood <br />Insurance Rate Map (Exhibit 2). On this map, the 100-year flood <br />plain boundary corresponds to the boundary of the areas of special <br />flood hazards (Zones A and AE), and the SOD-year flood plain boundary <br />corresponds to the boundary of areas of moderate flood hazards. <br />In cases where the 100- and SOD-year flood plain boundaries are <br />close together, only the 100-year flood plain boundary has been <br />shown. Small areas within the flood plain boundaries may lie above <br />the flood elevations but cannot be shown due to limitations of the <br />map scale and/or lack of detailed topographic data. <br /> <br />Approximate 100-year flood plain boundaries were delinated on the <br />previously referenced topographic map (Reference 16) using eleva- <br />tions estimated by hydraulic analysis. <br /> <br />For the streams studied by approximate methods, only the 100-year <br />flood plain boundary is shown on the Flood Insurance Rate Map (EXhi- <br />bit 2). <br /> <br />9 <br />