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maps designed to assist communities in developing flood plain management measures. 4.1 Flood Boundaries To provide a national standard without regional discrimination, the 1 percent annual chance (lOO-year) flood has been adopted by FEMA as the base flood for flood plain 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 flood plain boundaries 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 1:2,400 and 1:4,800, with a contour interval of 2 feet (References 11, 12, and 13). The 100- and 500-year flood plain boundaries are shown on the Flood Boundary and Floodway Map (Exhibit 2), In cases where the 100- and 500-year flood plain boundaries are close together, only the 100-year flood plain boundary has been shown. Small areas within the flood plain 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. Approximate flood plain boundaries in some portions of the study area were taken from the Flood Hazard Boundary Map (Reference 14), 4.2 Floodways Encroachment on flood plains, such as structures and fill, reduces flOOd-carrying capacity, increases flood heights and velocities, and increases flood hazards in areas beyond the encroachment itself. One nspect of flood plain management involves balancing the economic gain from flood plain 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 aspect of flood plain management. Under this concept, the area of the 100-year flood plain is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent flood plain aeeas, that must be kept free of encroachment so that the 100-year flood can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1.0 foot, provided that hazardous velocities are not produced. The floodwajs in this study are presented to local agencies as minimum standards that can be adopted directly or that can be used as a basis for additional floodway studies, The floodways presented in this study were computed on the basis of equal conveyance reduction from each side of the flood plain. The results of these computations are tabulated at selected cross sections for each stream segment for which a floodway is computed (Table 2). 8