Laserfiche WebLink
<br />aspect of floodplain management. Under this concept, the area of <br />the laO-year floodplain is divided into a floodway and a floodway <br />fringe. The floodway is the channel of a stream, plus any adjacent <br />floodplain areas, that must be kept free of encroachment so that <br />the 100-year flood can be carried without substantial increases in <br />flood heights. Minimum FEMA standards limit such increases to 1.0 <br />foot, provided that hazardous velocities are not produced. The <br />floodways in this report are presented to local agencies as minimum <br />standards that can be adopted or that can be used as a basis for <br />additional studies. <br /> <br />The f100dways presented in this study were computed on the basis of <br />equal-conveyance reduction from each side of the floodplain. <br />Floodway widths were computed at cross sections. Between cross <br />sections, the floodway boundaries were interpolated. The resul t 5 <br />of these computations are tabulated at selected cross sections <br />(Table 2). In cases where the floodway and lOa-year floodplain <br />boundaries are either close together or collinear, only the <br />floodway boundary has been shown. <br /> <br />The area between the floodway and the laO-year floodplain <br />boundaries is termed the floodway fringe. The floodway fringe <br />encompasses the portion of the floodplain that could be completely <br />obstructed without increasing the water-surface elevation of the <br />laO-year flood more than 1.0 foot at any point. Typical <br />relationships between the f100dway and the f100dway fringe and <br />their significance to floodplain development are shown in Figure 2. <br /> <br />I" <br /> <br />IOO-YEAR FLOODPLAIN <br /> <br />.1 <br /> <br />.......-- FL 00 DW A Y ---.. I( <br />FRINGE <br /> <br />FLOODWAY <br /> <br />FLOODWAY <br />FRINGE <br /> <br />STREAM <br />CHANNEL <br /> <br />- <br /> <br /> <br />FLOOD ELEVATION WHEN <br />CONFINED WITHIN FLOODWAY <br /> <br /> <br />....... ~~~.R~A.~~.M.~N.T........1\ <br /> <br />ENCROACHMENT <br /> <br />AREA OF FLOODPLAIN THAT COULD BE USED FOR <br />DEVELOPMENT BY RAISING GROUND <br /> <br /> <br /> <br />FLOOD ELEVATION BEFORE <br />ENCROACHMENT ON FLOODPLAIN <br /> <br />LINE AS IS THE FLOOD ELEVATION BEFORE ENCROACHMENT. <br />LINE CD IS THE FLOOD ELEVATION AFTER ENCROACHMENT <br />'SURCHARGE IS NOnO EXCEED 1.0 FOOT (FIA REQUIREMENT) OR LESSER AMOUNT IF SPECIFIED BY STATE. <br /> <br />Figure 2. Floodway Schematic <br /> <br />12 <br />