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For Tongue Creek and for the segments of Cedar Run studied by approximate methods, approximate 100-year boundaries were delineated using topographic maps at a scale of 1:24,000, with contour intervals of 20 feet and 40 feet, in conjunction with previously determined elevations (Reference 13). Segments of the approximate flood plain of Cedar Run are less than 200 feet in width and are areas of minimal flooding. In accordance with the Federal Insurance Administration guidelines, these approximate areas of minimal flooding are not shown in this study. Flood boundaries for the 100- and SOO-year floods are shown on the Flood Boundary and Floodway Map (Exhibit 2). In cases where the 100- and SOO-year flood boundaries are close together, only the 100-year flood boundary has been shown. Small areas within the flood boundaries may lie above the flood elevations and, there- fore, not be subject to flooding; owing to limitations of the map scale, such areas are not shown. 4.2 Floodways Encroachment on flood plains, such as artificial fill, reduces the flood-carrying capacity and increases flood heights, thus increasing flood hazards in areas beyond the encroachment itself. One aspect of flood plain management involves balancing the economic gain from flood plain development against the resulting increase in flood hazard. For purposes of the National Flood Insurance Program, the concept of a floodway is used as a tool to assist local communities in this aspect of flood plain management. Under this concept, the area of the 100-year flood is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent flood plain areas, that must be kept free of encroachment in order that the 100-year flood be carried without substantial increases in flood heights. As minimum standards, the Federal Insurance Administration limits such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. The floodways in this study were computed on the basis of equal- conveyance reduction from each side of the flood plain. The results of these computations are tabulated at selected cross sections for each stream segment for which a floodway is computed (Table 2). As shown on the Flood Boundary and Floodway Map (Exhibit 2), the floodway boundaries were determined at cross sections; between cross sections, the boundaries were interpolated. In cases where the floodway and 100-year flood boundaries are close together, only the floodway boundary has been shown. 9