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<br />gain from flood plain development against the resulting increase <br />in flood hazard. For purposes of the Flood Insurance Program, the <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 100-year flood is'divided into a proposed floodway <br />and a floodway fringe. The floodway is the channel of a stream <br />plus any adjacent flood plain areas that must be kept free of <br />encroachment in order that the 100-year flood be carried with- <br />out substantial increases in flood heights. Criteria adopted by <br />the Federal Insurance Administration I imit such increases in <br />flood heights to 1.0 foot, provided that hazardous velocities <br />are not produced. The floodways in this report are proposed to <br />local agencies as minimum standards that can be adopted or that <br />can be used as a basis for additional studies. <br /> <br />The floodway proposed for this study was computed on the basis <br />of equal conveyance reduction from each side of the flood plain <br />or encroachment to the stream banks. The results of these com- <br />putations are tabulated at selected cross sections for each stream <br />studied (Tables I & 2). As shown on the Flood Boundary and <br />Floodway Map (Exhibit 2), the floodway boundaries were determined <br />at cross sections; between cross sections the boundaries were <br />extrapolated. <br /> <br />The area between the floodway and the boundary of the 100-year <br />flood is termed the floodway fringe. The floodway fringe thus <br />encompasses the portion of the flood plain that could be com- <br />pletely obstructed without increasing the water surface elevation <br />of the 100-year flood more than one foot at any point. Typical <br />relationships between the floodway and the floodway fringe and <br />their significance to flood plain development are shown in <br />Figure 3. <br /> <br />II <br />