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<br />5.1 Reach Determinations <br /> <br />Reaches are defined as leng~hs of watercourses having relatively the <br />same flood hazara, based on the average weighted difference in <br />water-surface elevations between the 10- and IOO-year floods. This <br />difference does 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-yea!:_ Floods <br /> <br />Var ia tion <br /> <br />2 to 7 feet <br /> <br />0.5 foot <br /> <br />One reach meeting the above criterion was required for Dry Creek, <br />the only flooding source of Hayden. The location of the reach is <br />shown on the Flood Profiles (Exhibit 1). <br /> <br />5.2 Flood Hazard Factors <br /> <br />The Flood Hazard Factor (FHF) is the Federal Insurance Administration <br />device used to correlate flood information with insurance rate <br />tables. Correlations between property damage from floods and their <br />FHF are used to set actuarial insurance premium rate tables based on <br />FHFs from 005 to 200. <br /> <br />The FHF for a reach is the average weighted difference between the <br />10- and lOO-year flood water-surface elevations expressed to the <br />nearest one-half foot, and shown as a three-digit code. For example, <br />if the difference between water-surface elevations of the 10- and <br />100-year floods is 0.7 foot, the FHF is 005; if the difference is <br />1.4 feet, the FHF is 015; if the difference is 5.0 feet, the FHF is <br />050. When the difference between the 10- and lOa-year water-surface <br />elevations is greater than 10.0 feet, accuracy for the FHF is to the <br />nearest foot. <br /> <br />5,3 Flood Insurance Zones <br /> <br />After the determination of reaches and their respective Flood Hazard <br />Factors, the entire incorporated area of Hayden was divided into <br />zones, each having a specific flood potential or hazard. Each zone <br />was assigned one of the following flood insurance zone designations: <br /> <br />Zone A: <br /> <br />Special flood hazard areas inundated by <br />the lOa-year flood, determined by <br />approximate methods; no base flood <br />elevations or Flood Hazard Factors <br />determined. <br /> <br />Zone AS: <br /> <br />Special flood hazard areas inundated by <br />the 100-year flood, determined by <br />detailed methods; base flood elevations <br />shown, and zones subdivided according <br />to Flood Hazard Factors. <br /> <br />11 <br />