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<br />hazar~ ~ purpOEe5 of the National Flood Insurance Program. tha <br />concept of a floodway is used as a tool to assist local communities <br />in this aspect of flood plain management. Under this concept, the <br />area of the lOa-year flood is divided into a floodway and a floodway <br />fringe. The floodway is the channel of a stream, plus any adjacent <br />flood plain areas, that must be kept free of encroachment in order <br />that the lOa-year flood be carried without substantial increases in <br />flood heights. As minimum standards, the Federal Insurance Adminis- <br />tration limits such increases in flood heights to 1.0 foot, provided <br />that hazardous velocities are not produced. <br /> <br />The floodway for this study was computed on the basis of equal <br />conveyance reduction from each side of the flood plain. The results <br />of these computations are tabulated at selected cross sections for <br />each stream segment for which a floodway is computed (Table 2). <br /> <br />As shown on the Flood Boundary and Floodway Map (Exhibit 2), the <br />floodway bOundaries were determined at cross sections; between cross <br />sections, the boundaries were interpolated. In cases where the <br />floodway and lOa-year flood boundaries are close together, only the <br />floodway boundary has been shown. <br /> <br />The area between the floodway and the boundary of the lOa-year flood <br />is termed the floodway fringe. The floodway fringe thus encompasses <br />the portion of the flood plain that could be ~ompletely obstructed <br />without increasing the water-surface elevation of the IOO-year floOd <br />more than 1.0 foot at any point. Typical relationships between the <br />floodway and the floodway fringe and their significance to flood <br />plain development are shown in Figure 3. <br /> <br />7 <br />