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On that part of Eagle River studied by approximate methods, the elevation of the lOa-year flood was developed from normal depth calculations ~nd topographic maps at a scale of 1:1200, with a contour interval of 2 feet (Reference 13). For the remaining streams studied by approximate methods, the lOa-year flood eleva- tions were developed utilizing lOa-year discharges (Reference 6), field inspection, engineering judgment, and topographic maps (Reference 16). Approximate flooding in some areas was taken from the Federal Emer- gency Management Agency Flood Hazard Boundary Map (Reference 17). All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD). Elevation reference marks used in this study are shown on the maps. 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 manage- ment measures. 4.1 Flood Boundaries In order to provide a national standard without regional discrimina- tion, the lOa-year flood has been adopted by the Federal Emergency Management Agency 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- and 500-year floods have been delineated using the flood elevations determined at each cross section; between cross sections, the boundaries were inter- polated using topographic maps at scales of 1:1200 and 1:2400, with contour intervals of 2 and 5 feet (References 12, 18, and 26), and using aerial photographs at a scale of 1:1200 (Reference 14). Approximate flood boundaries on portions of Eagle River were delin- eated using COlllputed elevations on topographic maps (Reference 13). For the remaining streams studied by approximate methods, the 100- year flood boundary was delineated utilizing lOa-year discharges (Reference 6), field inspection, engineering judgment, and topographic maps (Reference 16). In cases where the 100- and 500-year flood boundaries are close together, only the lOa-year flood boundary has been shown. Approximate flood boundaries in some portions of the study area were taken from the Federal Emergency Management Agency Flood Hazard Boundary Map (Reference 17). 12