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<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 in <br />water-surface elevations between the 10- and 100-year floods. This <br />difference may not have a variation greater than that indicated in <br />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 Yuma County are shown on the Flood Profiles (Exhibit 1) and <br />summarized 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 the <br />10- and 100-year flood water-surface elevations rounded to the <br />nearest one-half foot, multiplied by 10, and shown as a three- <br />digit code. For example, if the difference between water-surface <br />elevations of the 10- and 100-year floods is 0.7 foot, the FHF is <br />0051 if the difference is 1.4 feet, the FHF is 0151 if the differ- <br />ence is 5.0 feet, the FHF is 050. When the difference between the <br />10- and 100-year flood water-surface elevations is greater than <br />10.0 feet, it is rounded to the nearest whole foot. <br /> <br />5.3 Flood Insurance Zones <br /> <br />Flood insurance zones and zone numbers are assigned based on the <br />type of flood hazard and the FHF, respectively. A unique zone <br />number is associated with each possible FHF, and varies from 1 for <br />a FHF of 005 to a maximum of 30 for a FHF of 200 or greater. <br /> <br />Zone A: <br /> <br />Special Flood Hazard Areas inundated by <br />the 100-year flood, determined by approxi- <br />mate methods 1 no base flood elevations <br />shown or FHFs determined. <br /> <br />Zones A4, A6, <br />and A7: <br /> <br />Special Flood Hazard Areas inundated by <br />the 100-year flood 1 with base flood <br />elevations shown, and zones subdivided <br />according to FHFs. <br /> <br />17 <br />