Laserfiche WebLink
<br />considered valid only if hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />All elevations are referenced to the National Ceodetic Vertical <br />Datum of 1929 (NGVD). <br /> <br />4.0 FLOODPLAIN MANAGEMENT I~PLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound <br />floodplain management programs. Therefore, each Flood Insurance Study <br />provides lOO-year flood elevations and delineations of the 100- and 500- <br />year floodplain boundaries and lOO-year floodway to assist communities <br />in developing floodplain management measures. <br /> <br />4.l Floodplain Boundaries <br /> <br />To provide a national standard without regional discrimination, the <br />1 percent annual chance (lOO-year) flood has been adopted by FEMA <br />as the base flood for floodplain management purposes. The 0.2 <br />percent annual chance (SOD-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied by detailed methods, the lOO- and 500-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 at a scale of <br />l:2,400, with a contour interval of 2 feet (Reference 2). <br /> <br />The lOO- and 500-year floodplain boundaries are shown on the Flood <br />Insurance Rate Map (Exhibit 2). On this map, the lOO-year <br />floodplain boundary corresponds to the boundary of the areas of <br />special flood hazards (Zone AE); and the 500-year floodplain <br />boundary corresponds to the boundary of areas of moderate flood <br />hazards. In cases where the lOO- and 500-year floodplain <br />boundaries are close together, only the lOO-year floodplain <br />boundary has been shown. Small areas within the floodplain <br />boundaries may lie above the flood elevations but cannot be shown <br />due to limitations of the map scale and/or lack of detailed <br />topographic data. <br /> <br />For the streams studied <br />floodplain boundary is <br />(Exhibit 2). <br /> <br />by approximate methods, only the lOO-year <br />shown on the Flood Insurance Rate Map <br /> <br />4.2 Floodways <br /> <br />Encroachment on floodplains, such as structures and fi 11, 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 the <br />economic gain from floodplain development against the resulting <br />increase in flood hazard. For purposes of the NFIP, a floodway is <br />used as a tool to assist local communities in this aspect of <br />floodplain management. Under this concept, the area of the 100- <br /> <br />8 <br />