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Fm-ev-i99s es: se Frame ~w ~toN a rinm TO ~91303g930213 P.10 section; between cross sections, the boundaries were interpolated using topographic maps at a scale of ]:2400, with a contour interval of 2 feet {Reference 12). In cases where the i00- and the 500-year flood boundaries are close together, only the 100-year boundary has been shown. Approximate flood boundaries in Some portions of the study area were taken from the Federal Insurance Administration's Flood Hazard Boundary Map (Reference 1). Fiood boundaries for the lOD- and 500-year floods are Shown on the Flood Boundary and Floodway Map. Small areas within the flood boundartes may lie above the flood elevations and, therefore, not be subject to flooding; owing to limitations of the map scale, such areas are not shown. 4.2 Floodways Encroachmenfi on flood piains, such as artificial fill, reduces the flood-carrying capacity, increases the flood heights, and increases flood hazards in areas beyond the encroachment itself, One aspect of flood plain management involves balancing Lhe economic gain from flood plain development against the resulting increase in flood hazard. For purposes of the Flood Insurance Program, the concept of a floodway is used as a tool LO assist local conmunities in this aspect of fiood plain management. Under this concept, the area of the i00-year flood is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any aejacent flood plain areas, that must be kept free of encroachment in order that Lhe ]00-year flood be carried without substantiai increases in flood heights. Minimum standards of FftiA limit such increases in flood heights to 1.0 foot, provided that hazardous velocities are not pro- duced, The floodways in this report are presented to total agencies as minimum standards that can be adapted or that can be used as a basis for additional studies. The floodways presented 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 was computed (Table 2). A5 shown on the Flood Boundary and Floodx~ay Map, the floodway widths were determined at cross sections; between cross sections, the boundaries were interpolated. In cases where the floodway and 100-year flood are either close together or coincide, only the floodway boundary has been shown.