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<br />section; between cross sections, the boundaries were interpolated <br />using topographic maps at a scale of 1 :2400, with a contour <br />i nterva 1 of 2 feet (Reference 12). <br /> <br />In cases where the 100- and the 500-year flood boundaries are <br />close together, only the 100-year boundary has been shown, <br /> <br />Approximate flood boundaries in some portions of the study area <br />were taken from the Federal Insurance Administration's Flood <br />Hazard Boundary Map (Reference 1), <br /> <br />Flood boundaries for the 100- and 500-year floods are shown on <br />the Flood Boundary and Floodway Map. Small areas within the flood <br />boundaries may lie above the flood elevations and, therefore, not <br />be subject to flooding; owing to limitations of the map scale, <br />such areas are not shown. <br /> <br />4,2 Floodways <br /> <br />Encroachment on flood plains, such as artificial fill, reduces <br />the flood-carrying capacity, increases the flood heights. and <br />increases flood hazards in areas beyond the encroachment itself, <br />One aspect of flood plain management involves balancing the <br />economic gain from flood plain development against the resulting <br />increase in flood hazard. For purposes of the Flood Insurance <br />Program, the concept of a f100dway is used as a tool to assist <br />local communities in this aspect of flood plain management, <br />Under this concept, the area of the 100-year flood is divided <br />into a floodway and a floodway fringe. The floodway is the <br />channel of a stream, plus any adjacent flood plain areas, that <br />must be kept free of encroachment in order that the 100-Year <br />flood be carried without substantial increases in flood heights. <br />Minimum standards of FEMA limit such increases in flood heights <br />to 1,0 foot, provided that hazardous velocities ar'e not pro- <br />duced. The f100dways in this report are presented to local <br />agencies as minimum standards that can be adopted or that can <br />be used as a basis for additional studies, <br /> <br />The n'oodways presented in thi s study were computed on the <br />basis of equal conveyance reduction from each side of the flond <br />plain. The results of these computations are tabulated at <br />selected cross sections for each stream segment for which a <br />floodway was computed (Table 2). <br /> <br />As shown on the Flood Boundary and Floodway Map, the floodway <br />widths were determined at cross sections; between cross sections. <br />the boundaries were interpolated. In cases where the floodway <br />and 100-year flood are either close together or coincide, only <br />the floodway boundary has been shown. <br /> <br />8 <br />