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<br />Starting water-surface elevations were determined using the slope- <br />area method. <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 />The approximate 100-year flood elevations for Tongue Creek, and <br />for the segments of Cedar Run studied by approximate methods, <br />were determined by normal-depth calculations of typical sections <br />based on field observation. <br /> <br />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations shown on the flood profiles are, thus, <br />considered valid only if the hydraulic structures assumed to stay <br />in place remain unobstructed, operate 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 the study <br />are shown on the maps. <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />A prime purpose of the National Flood Insurance Program is to encourage <br />State and local governments to adopt sound flood plain management programs. <br />Each Flood Insurance Study, therefore, includes a flood boundary map <br />designed to assist communities in developing sound flood plain manage- <br />ment 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 Insurance <br />Administration as the base flood for purposes of flood plain manage- <br />ment measures. The SOD-year flood is employed to indicate addi- <br />tional 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 1:2400, with <br />a limited contour interval (Reference 11). <br /> <br />Approximate flood boundaries in some portions of the study area <br />were taken from the Federal Insurance Administration's Flood Hazard <br />Boundary Map (Reference 12). <br /> <br />8 <br />