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<br />segments for which a floodway was computed (Section 4.2), selected <br />cross section locations are also shown on the Flood Boundary and <br />Floodway Map (Exhibit 2). <br /> <br />The hydraulic analyses for this study were based on unobstructed <br />flow. The flood elevations shown on the profiles are thus <br />considered valid only if hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFl? encourages state and local governments to adopt sound floodplain <br />management programs. Therefore, each Flood Insurance Study produces maps <br />designed to assist communities in developing floodplain management <br />measures. <br /> <br />4.1 Flood Plain Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the 1 percent annua 1 chance (lOO-year) flood has been adopted by <br />FEMA as the base flood for floodplain management purposes. The <br />0.2 percent annual chance (SOO-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied by detailed methods, the 100- and SOO-year floodplain <br />boundaries have been delineated using the flood elevations <br />determined at each cross section. Between cross sections, the <br />boundaries were interpolated using topographic maps. <br /> <br />Floodplain boundaries have been <br />information shown on topographic <br />reports referenced in Section 6.0 <br /> <br />revl sed to <br />workmaps <br /> <br />include <br />i ncl uded <br /> <br />boundary <br />wi th the <br /> <br />The 100- and SOO-year floodplain boundaries are shown on the Flood <br />Boundary and Floodway Map (Exhibit 2). In cases where the 100- <br />and SOO-year floodplain boundaries are close together, only the <br />100-year floodplain boundary has been shown. Small areas within <br />the floodplain boundaries may lie above the flood elevations but <br />cannot be shown due to limitations of the map scale and/or lack of <br />detailed topographic data. <br /> <br />For the streams studied by approximate methods, only the 100-year <br />floodplain boundary is shown. <br /> <br />4.2 Floodways <br /> <br />Encroachment of floodplains, such as structures and fill, reduces <br />flood-carrying capacity, increases flood heights and velocities, <br />and increases flood hazards in areas beyond the encroachment <br />itself. One aspect of floodplain management involves balancing <br />the economic gain from floodplain development against the <br />resulting increase in flood hazard. For purposes of the NFl?, a <br />floodway is used as a tool to assist local communities in this <br />aspect of floodplain management. Under this concept, the area of <br /> <br />14 <br />