Laserfiche WebLink
<br />stream, plus any adjacent floodplain areas, that must be kept <br />free of encroachment in order that the lOa-year flood be carried <br />without substantial increases in flood heights. As minimum <br />standards, the Federal Insurance Administration limits such <br />increases in flood heights to 1.0 foot, provided that hazardous <br />velocities are not produced. <br /> <br />The floodway for this study was computed on the basis of equal <br />conveyance reduction from each side of the floodplain for Sand <br />Creek. The floodway for the South Platte River was developed by <br />setting the limits along the levees. The results of these <br />computations are tabulated at selected cross sections for each <br />stream segment for which a floodway is computed (Table 2). <br /> <br />As shown on the Floodway Map (Exhibit 2), the floodway boundaries <br />were determined at cross sections; between cross sections, the <br />boundaries were interpolated. <br /> <br />In cases where the floodway and lOa-year flood boundary are close <br />together, only the floodway has been shown. In some areas, part <br />of the floodway lies outside the corporate limits. <br /> <br />The area between the floodway and the boundary of the lOa-year <br />flood is termed the floodway fringe. The floodway fringe thus <br />encompasses the portion of the floodplain that could be <br />completely obstructed without increasing the water-surface <br />elevation of the lOa-year flood more than 1.0 foot at any point. <br />Typical relationships between the floodway and the floodway <br />fringe and their significance to floodplain development are shown <br />in Figure 10. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />In order to establish actuarial insurance rates, the Federal Insurance <br />Administration has developed a process to transform the data from the <br />engineering study into flood insurance criteria. This process <br />includes the determination of reaches, Flood Hazard Factors, and flood <br />insurance zone designations for each flooding source studied in detail <br />affecting the City of Commerce City. <br /> <br />5.1 Reach Determinations <br /> <br />Reaches are defined as lengths of watercourses having relatively <br />the same flood hazard, based on the average weighted difference <br />in water-surface elevations between the 10- and lOa-year floods. <br />This difference does not have a variation greater than that <br />indicated in the following table for more than 20 percent of the <br />reach. <br /> <br />13 <br />