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Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway is computed (Section 4.2), selected cross section locations are also shown on the Flood Boundary and Floodway Map (Exhibit 2). . Approximate flood elevations for the Little Thompson River were determined from a u.S. Army Corps of Engineers Flood Plain Informa- tion report (Reference 28). Approximate flood elevations for the Cache La Poudre River were determined from two u.S. Army Corps of Engineers Flood Plain Information reports (References 5 and 29) . Flood profiles were drawn showing computed water-surface elevations to an accuracy of 0.5 foot for floods of the selected recurrence intervals (Exhibit 1). ~ There are no elevation reference marks provided in this study; however, elevation reference mark data can be provided by contacting the Larimer County Planning Commission. 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS ... A prime purpose of the National Flood Insurance Program is to encourage State and local governments to adopt sound flood plain management pro- grams. Each Flood Insurance Study, therefore, includes a flood boundary map designed to assist communities in developing sound flood plain management measures. 4.1 Flood Boundaries .. In order to provide a national standard without regional discrimina- tion, the laO-year flood has been adopted by the Federal Insurance Administration as the base flood for purposes of flood plain manage- ment measures. The 500-year flood is employed to indicate additional areas of flood risk in the community. For each stream studied in detail, the boundaries of the 100- and 500-year floods have been delineated using the flood elevations determined at each cross section; between cross sections, the boundaries were interpolated using topographic maps at scales of 1:2400, with a contour interval of 2 feet (References 19, 20, 21, 23, 24, and 26); 1:1200, with a contour interval of 2 feet (Reference 27); and, 1:6000, with a contour interval of 4 feet (Reference 25). In cases where the 100- and 500-year flood boundaries are close together, only the lOa-year flood boundary has been shown. . On the Little Thompson River, approximate flood boundaries were delineated using aerial photographs at a scale of 1:12,000 (Refer- ence 28). Approximate flood boundaries for the Cache La poudre River were delineated from two u.S. Army Corps of Engineers Flood Plain Information Reports (References 5 and 29). .. 17 .