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Calculation of normal estimation of top width study areas. ! . depth from fleld was used to plot cross section and the flooding for approximate 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and loca~ governments to adopt sound floodplain management programs. Therefore, each Flood Insurance Study provides 100-year flood elevations and d~lineations of the 100- and 500- year floodplain boundaries and lOO-year! floodway to assist communities in developing floodplain management measures. 4.1 Floodplain Boundaries , To provide a national standard without regional discrimination, the I-percent annual chance (lOO-year) i flood has been adopted by FEMA as the base flood for floodplain: management purposes. The 0.2- percent annual chance (500-year) if100d is employed to indicate additional areas of flood risk in! the community. For Sulphur and Tallman Gulches, 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 1:24,000, with a contour interval of 10 feet (Reference 20). Floodplain boundaries for Cherry Creek were taken from the previously referenced COE Floodp1ai:n Information report for Cherry Creek-Cherry Creek Lake through Franktown, Colorado, (Reference 12). That study was also used to !determine the boundaries at the confluences with the Cherry Creek tributaries included in this study. The 100- and 500-year floodplain boundaries are shown on the FIRM (Exhibit 2). On this map, the, lOO-year floodplain boundary corresponds to the boundary of the: areas of special flood hazards (Zone(s) A and AE), and the 500-year floodplain boundary corresponds to the boundary of are~s of moderate flood hazards. In cases where the 100- and 500-year ifloodp1ain boundaries are close together, only the lOO-year floodplain boundary has been shown. Small areas wi thin 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 topog~aphic data. Approximate lOO-year floodplain boJndaries were delineated on the previously referenced topographic m~ps (Reference 20). For the streams studied by approxit/late methods, only the lOO-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, increa~es flood heights and velocities, 10