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Calculation of normal depth from field cross section and the estimation of top width was used to plot flooding for approximate study areas. '~ i I 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local ~overnments to adopt sound floodplain management programs. Therefore, each Flood Insurance Study provides lOa-year flood elevations and delineations of the 100- and 500-year floodplain boundaries and lOa-year floodway to assist communities in developing floodplain management measures. 4.1 Floodplain Boundaries To provide a national standard without regional discrimination, the l-percent annual chance (lOa-year) nood 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 ri sk in the communi ty. For Sul phur and Tallman Gulches, the 100- and 50 a-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 1:24,000, with a contour interval of 10 feet (Reference 20). Floodplain boundaries for Cherry ,Creek were taken from the previously referenced COE Floodplain Information report for Cherry Creek-Cherry Creek Lake through Franktown, Colorado, (Reference 12). That study was al so used to determine the boundaries at the confluences with the Cherry Creek tributaries included in this study. The 100- and 500-year floodplain bOljndaries are shown on the FIRM (Exhibit 2). On this map, the ~OO-year floodplain boundary corresponds to the boundary of the ~reas of special flood hazards (Zone(s) A and AE), and the 500-year floodplain boundary corresponds to the boundary of areasi of moderate flood hazards. In cases where the 100- and 500-year floodplain boundaries are close together, only the lOa-year floodplain boundary has been shown. Small areas within the floodplain boundaries may lie above the flood elevat ions but cannot be shown due to limi tations of the map scale and/or lack of detailed topographic data. , Approximate lOa-year floodplain boundaries were delineated on the previously referenced topographic maps (Reference 20). For the streams studied by approximate methods, only the lOa-year floodplain boundary is shown on the FIRM (Exhibit 2.) 4.2 Floodways Encroachment on flOOdplains, such as structures and fill, reduces flood-carrying capacity, increases ,flood heights and veloci ties, La