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<br />For the streams studied by approximate methods, and for the areas <br />of shallow flooding, the boundary of the 100-year shallow flood was <br />developed from normal depth calculations. Cross section data for <br />the Eagle River and the Unnamed Tributary to Gypsum Creek were <br />taken from maps at a scale of 1:12001 with a contour interval of <br />2 feet (References 9 and 10) or from U.S. Geological Survey topographic <br />maps at a scale of 1:24,000, with a contour interval of 20 feet <br />(Reference 11), as available. <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 />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations on the profiles are thus considered <br />valid only if hydraulic structures remain unobstructed, operate <br />properly, and do not fail. <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 pro- <br />grams. Each Flood Insurance Study, therefore, includes a flood boundary <br />map designed to assist communities in developing sound flood plain <br />management measures. <br /> <br />4.1 Flood Boundaries <br /> <br />In order to provide a national standard without regional discrimina- <br />tion, the lOa-year flood has been adopted by the Federal Insurance <br />Administration as the base flood for purposes of flood plain <br />management measures. The SOO-year flood is employed to indicate <br />additional 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 each <br />cross section; between cross sections, the boundaries were interpola- <br />ted using topographic maps. Boundaries for Gypsum Creek were <br />delineated on maps at a scale of 1:1200, with a contour interval <br />of 2 feet (References 9 and 10). For Eagle River, boundaries were <br />delineated on maps at a scale of 1:1200, with a contour interval of <br />2 feet (Reference 12). <br /> <br />Approximate and shallow flooding boundaries were delineated on <br />these maps and on topographic maps at a scale of 1:24,000, with a <br />contour interval of 20 feet (Reference 11). <br /> <br />In cases where the 100- and SOQ-year flood boundaries are close <br />together, only the IOO-year flood boundary has been shown. <br /> <br />7 <br />