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<br />Starting water-surface elevations were obtained at points of conflu- <br />ence. <br /> <br />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations shown on the profiles are thus considered <br />valid only if hydraulic structures remain unobstructed, operate <br />properly, and do not fail. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in this <br />study are shown on the maps. <br /> <br />, <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 <br />by FEMA as the base flood for flood plain management purposes. <br />The 0.2 percent annual chance (SOO-year) flood is employed to <br />indicate additional areas of flood risk in the community. For <br />each stream studied in detail, 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 orthophotogrammetric maps at a scale of <br />1:4,800, with a contour interval of 2 feet (Reference 9). <br /> <br />The 100- and SOO-year flood plain boundaries are shown on the <br />Flood Boundary and Floodway Map (Exhibit 2). In cases where the <br />100- and SOO-year flood plain boundaries are close together, only <br />the 100-year flood plain boundary has been shown. Small areas <br />within the flood plain boundaries may lie above the flood elevations <br />but cannot be shown due to limitations of the map scale and/or <br />lack of detailed topographic data. <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 />100-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 />tions for the studied streams; therefore, no floodway has been <br />computed. Computed 100-year regulatory elevations at selected <br />cross sections are shown in Table 2. <br /> <br />11 <br />