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<br />economic gain from floodplain development against the resulting increase in flood hazard. <br />For purposes of the NFIP, a floodway is used as a tool to assist local communities in this <br />aspect of floodplain management. Under this concept, the area of the IOO-year floodplain <br />is divided into a floodway and a floodway fringe. The floodway is the channel of a <br />stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that <br />the IOO-year flood can be carried without substantial increases in flood heights. Minimwn <br />Federal standards limit such increases to 1 foot, provided that hazardous velocities are not <br />produced. The floodways in this study are presented to local agencies as minimum <br />standards that can be adopted directly or that can be used as a basis for additional f100dway <br />studies. <br /> <br />The floodways presented in this study were computed for certain stream segments on the <br />basis of equal-conveyance reduction from each side of the floodplain. F100dway widths <br />were computed at cross sections. Between cross sections, the floodway boundaries were <br />interpolated. The results of the floodway computations are tabulated for selected cross <br />sections (see Table 2, "F1oodway Data"). In cases where the floodway and IOO-year <br />floodplain boundaries are either close together or collinear, only the floodway boundary <br />is shown. <br /> <br />The area between the floodway and 1000year floodplain boundaries is termed the floodway <br />fringe. The floodway fringe encompasses the portion of the floodplain that could be <br />completely obstructed without increasing the water-surface elevation of the 1000year flood <br />more than I foot at any point. Typical relationships between the floodway and the <br />floodway fringe and their significance to floodplain development are shown in Figure 1. <br /> <br />I, <br /> <br />loo.Yt:AII:Fl.OOOPl.AIN <br /> <br />ROODWAY 1- R.OOOW4Y <br />FRINGE <br />'YMAM <br />CHANNEL <br /> <br />,1 <br /> <br /><.OOOW4Y <br />fRINGE <br /> <br />FLOOOELEVATlONWI-IEN <br />CONFINED WITHIN FLOODWAY <br /> <br /> <br />R.OOD ELEVATION BEFORE <br />ENCIl:OACHMOIT ON FlOOOPlAlN <br /> <br />UN&: AllIS THE R.OOO EUVATlON BEFORE ENCItOACHMENT. <br />UNE CO IS T1fE FLOOD EUVATION AFTERE~MENT. <br />.SURCHARGE IS NOT TO EXCEED 1.0 FOOT (FIA. REQUIJIlEMENl) OR LiSSER AMOUr(f IF mOFIED BY U....TE. <br /> <br />Figure 1. F100dway Schematic <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />For flood insurance rating purposes, flood insurance zone designations are assigned to a <br />community based on the results of the engineering analyses. These zones are as follows: <br /> <br />8 <br />