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<br />Approximate flood boundaries in some portions of the <br />taken from the Federal Insurance Administration's Flo <br />Boundary Map (Reference 30). <br /> <br />tudy area were <br />d Hazard <br /> <br />The study contractor has determined that some areas s own on the <br />Federal Insurance Administration's Flood Hazard Bound ry Map (Refer- <br />ence 30) are areas of minimal flooding; therefore, th y were not <br />delineated on the maps. <br /> <br />. <br /> <br />Flood boundaries for the 100- and SOD-year floods are shown on the <br />Flood Boundary and Floodway Map (Exhibit 2). <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 show <br /> <br />4.2 Floodways <br /> <br />. <br /> <br />Encroachment on flood plains, such as artificial fill, reduces the <br />flood-carrying capacity and increases flood heights, hus increasing <br />flood hazards in areas beyond the encroachment itself One aspect <br />of flood plain management involves balancing the econ mic gain from <br />flood plain development against the resulting increas in flood <br />hazard. For purposes of the National Flood Insurance Program, the <br />concept of a floodway is used as a tool, to assist loc 1 communities <br />in this aspect of flood plain management. Under this concept, the <br />area of the 100-year flood is divided into a floodway and a floodway <br />fringe. The floodway is the channel of a stream, plu any adjacent <br />flood plain areas, that must be kept free of encroach ent in order <br />that the 100-year flood be carried without substantia increases in <br />flood heights. As minimum standards, the Federal Ins rance Admin- <br />istration limits such increases in flood heights to 1.0 foot, <br />provided that hazardous velocities are not produced. <br /> <br />The floodways for this study were divided into two ca egories based <br />upon the location of the stream. The mountain area c iteria were <br />based upon the channel of the stream plus all flood pain areas <br />where the depth of flooding was 18 inches or greater nd the floodway <br />fringe area was the area where flooding depths were 1 inches or <br />less and velocities were 3 feet per second or less (F'gure 7). The <br />plains area criteria were based upon the criteria of qual conveyance <br />reduction from each side of the flood plain with a o. -foot limita- <br />tion on flood height, provided that hazardous velocit'es are not <br />produced (Figure 8). <br /> <br />18 <br /> <br />~ <br />