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<br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />A prime purpose of the National Flood Insurance Program is <br />to encourage state and local governments to adopt sound <br />flood plain management progra~s. This Flood Insurance Study, <br />therefore, includes a flood boundary map designed to assist <br />the community in developing sound flood plain management <br />measures. <br /> <br />4.1 Flood Boundaries <br /> <br />In order to provide a national standard without regional <br />discrimination, the 100-year flood has been adopted by <br />the Federal Insurance Administration as the base flood <br />for purposes of flood plain management measures. The <br />500-year flood is employed to indicate additional areas <br />of flood risk in the community. For each stream studied <br />in detail, the boundaries' of the lOO-year and the <br />SOO-year flood have been delineated using the flood <br />elevations determined at ~ach cross section; between <br />cross sections, the boundaries were interpolated using <br />topographic maps at a scale of 1:24,000, with a contour <br />interval of 20 feet. (Reference 6). In cases where the <br />lOO-year and the 500-year: flood boundaries are close <br />together, only the 100-ye~r boundary has been shown. <br /> <br />. <br /> <br />Small areas within the flood boundaries may lie above the <br />flood elevations and, therefore, not be subject to flood- <br />ing; owing to limitations of the map scale, such areas <br />are not shown. <br /> <br />4.2 Floodways <br /> <br />Encroachment on flood plains, such as artificial fill, <br />reduces the flood-carrying capacity and increases flood <br />heights, thus increasing flood hazards in areas beyond <br />the encroachment itself. 'One aspect of flood plain <br />management involves balancing the economic gain from <br />flood plain development against the resulting increase <br />in flood hazard. For purposes of the Flood Insurance <br />Program, the concept of aifloodway is used as a tool to <br />assist local communities in this aspect of flood plain <br />management. Under this concept, the area of the 100- <br />year flood is divided into a floodway and a floodway <br />fringe. The floodway is the channel of a stream, plus <br />any adjacent flood plain areas, that must be kept free <br />of encroachment in order that the lOO-year flood be <br />carried without substantial increases in flood heights. <br />Criteria adopted by the Federal Insurance Administration <br />limit such increases in flood heights to 1.0 foot, <br /> <br />10 <br />