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Elevation of 100-Year Flood South Boulder Creek A B C 6,500 7,080 7,650 5,220.1 5,225.4 5,230.5 Flood boundaries along the streams studied through approximate methods were obtained from the Wright- McLaughlin reports (Reference 1). Information on flood limits in areas subject to sheet flooding was furnished by the City Flood Control Engineer. 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 programs. Each Flood Insurance Study, there- fore, includes a flood boundary map designed to assist com- munities in developing sound flood plain management measures. 4.1 Flood Boundaries In order to provide a national standard without regional discrimination, the 100-year flood has been adopted by the Federal Insurance Administration as the base flood for purposes of flood plain management 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-year and the 500- year flood have been delineated using the flood eleva- tions determined at each cross section; between cross sections, the boundaries were interpolated using topo- . graphic maps at a ..scale of 1: 24 ,000 wi th contour . intervals of 10 feet (Reference 4). In cases where the 100-year and the 500-year flood boundaries are close together, only the 100-year boundary has been shown. Although flood boundaries are ordinarily shown on the Flood Boundary and Floodway Maps, in this study, a map showing flood insurance zones (Exhibit 2) has been used to indicate the flood boundaries. On the map, the 100- year flood boundary coincides with the boundary of the areas of special flood hazards (Zones A, A4, A7, AlO, A12, and A14); and the 500-year flood boundary coincides with the boundary of areas of moderate flood hazards (Zone B). 6