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4.0 . e . I I FLOOD PLAIN MANAGEMENT APPLICATIONS I I The National Blood Insurance Program encourages state and local governments to adopt soun~ flood plain management programs. Therefore, each Flood Insurance stu9Y includes a flood boundary map designed to assist communi- ties in develqping sound flood plain management measures. I 4.l Flood Bdundaries 4.2 I In ordet to provide a national standard without regional discrimina- tion, t~e 100-year flood has been adopted by the Federal Emergency Managem~nt Agency as the base flood for purposes of flood plain managem nt measures. The 500-year flood is employed to indicate additio al areas of flood risk in the community. For each stream studied lin detail, the boundaries of the 100- and 500-year floods have besn delineated using the flood elevations determined at each crgss section; between cross sections, the boundaries were interpo~ated using topographic maps at a scale of 1:l,200, with contour lintervals of 4 and 20 feet (Reference 9). I I The apprloximate 100-year flood boundaries for the flows along Sutherldnd Creek downstream of cross section A were delineated using t~pographic maps as referenced above. The apprloXimate flood boundar ies for Suther land Creek upstream of crossl section M were taken from the El Paso County Flood Hazard BoundarY1 Map (Reference lO). I I The lOO-lyear flood boundar ies for the remaining streams studied by apprdximate methods were delineated using topographic maps enlarge~ to a scale of l:4,800, with a contour interval of 40 feet (Re1ference 11). Flood bdundaries for the 100- and 500-year floods are shown on the Flodd Boundary and Floodway Map (Exhibit 2). In cases where the 100-1 and 500-year flood boundaries are close together, only the lOO-~ear flood boundary has been shown. small areas within the floo~ boundaries may lie above the flood elevations and, there- fore, ndt be subject to flooding; owing to limitations of the I map scal~, such areas are not shown. I I Floodwayls I Encroach~ent on flood plains, such as artificial fill, reduces the floop-carrying capacity, increases the flood heights of streams, and incr~ases flood hazards in areas beyond the encroachment itself. One aspept of flood plain management involves balancing the economic gain fro~ flood plain development against the resulting increase in flood: hazard. For purposes of the National Flood Insurance Program,: the concept of a floodway is used as a tool to assist local cOfnmunities in this aspect of flood plain management. Under l3