Laserfiche WebLink
<br />4.2 Floodways <br /> <br />Encroachment on floodplains, such as structures and fill, reduces <br />flood-carrying capac i ty, increases flood he ight sand veloc it ies, <br />and increases flood hazards in areas beyond the encroachment. <br />Floodplain managers must balance the economic gain from floodplain <br />development against the resul ting increase in flood hazard. For <br />purposes of the NFIP, a flood~ay is used as a tool :0 assist local <br />communities in thi s aspect of floodplain management. Under this <br />concept, the area of the IOO-year floodplain is divided into a <br />stream, plus any adjacent floodplain areas, that must be kept free <br />of encroachment so that the IOO-year flood can cen be carried <br />without substantial increases in flood heights. Minimum Federal <br />standards limit such lncreases to 1.0 foot, provided that hazardous <br />velocities are not produced. The floodways in this city are <br />presented to local agencies and are minimum standards that can be <br />adopted directly or that can be used as a basis for additional <br />floodway studies. <br /> <br />The floodways presented in this study were computed for certain <br />stream segments on the basis of equal conveyance reduction from <br />each side of the floodplain. Floodway widths were computed at <br />cross sections. Between cross sections, the floodway boundaries <br />were interpolated. The results of the floodway computations are <br />tabulated at selected cross sections (Table 2). In cases where the <br />floodway and IOO-year floodplain boundaries are either close <br />together or collinear, only the floodway boundary has been shown. <br /> <br />The area between the floodway and IOO-year floodplain boundaries is <br />termed the floodway fringe. The floodway fringe encompasses the <br />portion of the floodplain that could be completely obstructed <br />without increasing the water-surface elevation of the IOO-year <br />flood more than 1.0 foot at any point. Typical relationships <br />between the floodway and the floodway fringe and their significance <br />to floodplain development are shown in Figure 6. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />For flood insurance rating purposes, flood insurance zone designations <br />are assigned to a community based on the results of the engineering <br />analyses. These zones are as follows: <br /> <br />Zone A <br /> <br />Zone A is the flood insurance rate zone that corresponds to the <br />IOO-year floodplains determined in the Flood Insurance Study by <br />approximate methods. Because detai led hydraul ic analyses are not <br />performed for such areas, no base flood elevations (BFEs) or depths <br />are shown within this zone. <br /> <br />14 <br />