Laserfiche WebLink
<br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). <br /> <br />.H.ougnness coettlcients (Manning's nn") for the Little Thompson <br />River were estimated by field inspection a The channel "n" value <br />used for the Little Thompson River is Oa03S, and the overbank IIn" <br />value is 0.040, <br /> <br />Water-surface profiles were computed for the 10-, 50-, 100-, and <br />SOO-year floods using the V,S, A<~y Corps of Engineers' HEC-2 <br />computer program (Reference 6)a <br /> <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of OaS foot for floods of the selected recurrence <br />intervals (Exhibit 1)_ <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 a <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 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 SOO-year flood is employed to indicate additional <br />areas of flood risk in the community a For each stream studied in <br />detail, the boundaries of the 100- and SOO-year floods have been <br />delineated using the flood elevations determined at each cross <br />sectioni between cross sections, the boundaries were interpolated <br />using topographic maps at a scale of 1:24,000, enlarged to a scale <br />of 1:7200, with a contour interval of 10 feet (Reference 7). <br /> <br />In cases where the 100- and SOO-year flood boundaries are close <br />together, only the lOO-year flood boundary has been shown, <br /> <br />Flood boundaries for the 100- and SOO-year floods are shown on <br />the Flood Boundary and Floodway Map (Exhibit 2). <br /> <br />Small areas within the flood boundaries may lie above the flood <br />elevations and, therefore, not be subject to flooding; owing to <br />limitations of the map scale, such areas are not shown. <br /> <br />5 <br />