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<br />4.2 Floodways <br /> <br />The floodway is the channel of a stream, plus any adjacent flood <br />plain areas, that must be kept free of encroachment so that the <br />100-year flood can be carried without substantial increases in <br />flood heights. <br /> <br />No floodways were computed in the Flood Plain Information Report <br />for Wray (Reference 1). Therefore, no floodways are shown in <br />this study. Regulatory elevations computed at selected cross <br />sections used in the hydraulic analyses are shown in Table 3. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />To establish actuarial insurance rates, data from the engineering study <br />must be transformed into flood insurance criteria. This process includes <br />the determination of reaches, Flood Hazard Factors, and flood insurance <br />zone designations for each flooding source studied in detail affecting <br />the City of Wray, Colorado. <br /> <br />5.1 Reach Determinations <br /> <br />Reaches are defined as sections of flood plain that have relatively <br />the same flood hazard, based on the average weighted difference <br />in water-surface elevations between the 10- and 100-year floods. <br />This difference may not have a variation greater than that indicated <br />in the following table for more than 20 percent of the reach: <br /> <br />Average Difference Between <br />10- and 100-Year Floods <br /> <br />Variation <br /> <br />Less than 2 feet <br />2 to 7 feet <br />7.1 to 12 feet <br />More than 12 feet <br /> <br />0.5 foot <br />1.0 foot <br />2.0 feet <br />3.0 feet <br /> <br />The locations of the reaches determined for the flooding sources <br />of Wray are shown on the Flood Profiles (Exhibit 1) and summarized <br />in Table 4. <br /> <br />5.2 Flood Hazard Factors <br /> <br />The Flood Hazard Factor (FHF) is used to establish relationships <br />between depth and frequency of flooding in any reach. This rela- <br />tionship is then used with depth-damage relationships for various <br />classes of structures to establish actuarial insurance rate tables. <br /> <br />The FHF for a reach is the average weighted difference between <br />the 10- and 100-year flood water-surface elevations rounded to <br />the nearest one-half foot, multiplied by 10, and shown as a three- <br />digit code. For example, if the difference between water-surface <br /> <br />12 <br />