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<br />One aspect of flood plain management involves balancing the economic <br />gain from flood plain development against the resulting increase <br />in flood hazard. For purposes of the NFIP, a floodway is used as <br />a tool to assist local communities in this aspect of flood plain <br />management. Under this concept, the area of the 100-year flood <br />plain is divided into a f100dway and a f100dway fringe. The f1ood- <br />way is the channel of a stream, plus any adjacent flood plain areas, <br />that must be kept free of encroachment so that the 100-year flood <br />can be carried without substantial increases in flood heights. <br />Minimum Federal standards limit such increases to 1.0 foot, pro- <br />vided that hazardous velocities are not produced. The f100dways <br />in this study are presented to local agencies as minimum standards <br />that can be adopted directly or that can be used as a basis for <br />additional f100dway studies. <br /> <br />The floodway presented in this study was computed for certain stream <br />segments on the basis of equal conveyance reduction from each side <br />of the flood plain. F100dway widths were computed at cross sections. <br />Between cross sections, the floodway boundaries were interpolated. <br />The results of the f100dway computations are tabulated at selected <br />cross sections (Table 2). In cases where the f100dway and 100- <br />year flood plain boundaries are either close together or collinear, <br />only the f100dway boundary has been shown. <br /> <br />The area between the floodway and 100-year flood plain boundaries <br />is termed the floodway fringe. The floodway fringe encompasses <br />the portion of the flood plain that could be completely obstructed <br />without increasing the water-surface elevation of the 100-year <br />flood by more than 1.0 foot at any point. Typical relationships <br />between the f100dway and the f100dway fringe and their significance <br />to flood plain development are shown in Figure 2. <br /> <br />A f100dway was computed for the South Fork Rio Grande, because <br />detailed information was not available at the time this Flood <br />Insurance Study was compiled. No floodway information was avail- <br />able for the Rio Grande near Monte Vista. <br /> <br />11 <br />