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4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound flood plain management programs. Therefore, each Flood Insurance Study pro- duces maps designed to assist communities in developing flood plain management measures. 4.1 Flood Boundaries To provide a national standard without regional discriminationr 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 (SOO-year) flood is employed to indicate additional areas of flood risk in the community. For each stream studied in detail, the 100- and SOO-year flood plain boundaries have been delineated using the flood elevations determined at each cross section. Between cross sections, the boundaries were inter- polated using topographic maps at a scale of 1:2,400, with a con- tour interval of 2 feet (Reference 11). The 100- and SOO-year flood plain boundaries are shown on the Flood Boundary and Floodway Map (Exhibit 2). In cases where the 100- and SOO-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. For the streams studied by approximate methods, only the 100-year flood plain boundary is shown. The approximate flood boundaries for this study were taken from the Flood Hazard Boundary Map for Otero County (Reference 12). 4.2 Floodways Encroachment on flood plainsr such as structures and fill, reduces flood-carrying capacity, increases flood heights and velocitiesr and increases flood hazards in areas beyond the encroachment itself. One aspect of flood plain management involves balancing the economic gain from flood plain development against the resulting increase in flood hazard. For purposes of the NFIPr 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 flood- way is the channel of a stream, plus any adjacent flood plain areas, 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 footr pro- vided that hazardous velocities are not produced. The floodways in this study are presented to local agencies as minimum standards 9