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<br />In cases where the 100- and SOO-year flood boundaries are close <br />together, only the lOO-year flood boundary has been shown. <br /> <br />Small areas within the flood boundaries may lie above the flood <br />elevations and, therefore, not be subject to flooding; owing to <br />limitations of the map scale, such areas are not shown. <br /> <br />4.2 Floodways <br /> <br />Encroachment on flood plains, such as artificial fill, reduces the <br />flood-carrying capacity and increases flood heights, thus increasing <br />flood hazards in areas beyond the encroachment itself. One aspect of <br />flood plain management involves balancing the economic gain from <br />flood plain development against the resulting increase in flood hazard. <br />For purposes of the National Flood Insurance Program, the concept of <br />a floodway is used as a tool to assist local communities in this <br />aspect of flood plain management. Under this concept, the area of <br />the 100-year flood is divided into a floodway and a floodway fringe. <br />The floodway is the channel of a stream, plus any adjacent flood <br />plain areas, that must be kept free of encroachment in order that the <br />IOO-year flood be carried without substantial increases in flood <br />heights. As minimum standards, the Federal Insurance Administration <br />limits such increases in flood heights to 1.0 foot, provided that <br />hazardous velocities are not producedw <br /> <br />The floodway for the Los Pinos River was computed on the basis of <br />equal conveyance reduction from each side of the flood plain. The <br />results of these computations are tabulated at selected cross sections <br />for each stream segment for which a floodway is computed (Table 2) <br /> <br />As shown on the Floodway Map (Exhibit 2), the floodway boundaries <br />were determined at cross sections; between cross sections, the boun- <br />daries were interpolated. <br /> <br />The area between the floodway and the boundary of the 100-year flood <br />is termed the floodway fringe. The floodway fringe thus encompasses <br />the portion of the flood plain that could be completely obstructed <br />without increasing the water-surface elevation of the lOO-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 2. <br /> <br />7 <br />