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are shown on the maps; the descriptions of the marks are presented in Elevation Reference Marks (Exhibit 3). 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. Therefore, each Flood Insurance Study provides 100-year flood elevations and delineations of the 100- and 500- year floodplain boundaries and 100-year floodway to assist communities in developing sound floodplain management measures. 4.1 Floodplain Boundaries To provide a national standard without regional discrimination, the I-percent annual chance (lOO-year) flood has been adopted by FEMA as the base flood for floodplain management purposes. The 0.2- percent annual chance (500-year) flood is employed to indicate additional areas of flood risk in the community. For each stream studied in detail, the 100- and 500-year floodplain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were interpolated using topographic maps at a scale of 1:1,200 and 1:2,400, with a contour interval of 2 feet (References 11 and 12). Shallow flooding boundaries were at a scale of 1:1,200, with (Reference 11), and using methods delineated using topographic a contour interval of 2 described in Section 3.2. maps feet The 100- and 500-year floodplain boundaries are shown on the Flood Insurance Rate Map (Exhibit 2). On this map, the laO-year floodplain boundary corresponds to the boundary of the areas of special flood hazards (Zones A and AE), and the 500-year floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In cases where the 100- and 500-year floodplain boundaries are close together, only the laO-year floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevations but cannot be shown due to limitations of the map scale and/or lack of detailed topographic data. For the streams studied floodplain boundary is (Exhibit 2). by approximate methods, only the laO-year shown on the Flood Insurance Rate Map 4.2 F100dways Encroachment on floodplains, such as structures and fill, reduces the flood-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain development against the resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as a tool to assist local communities in this 11