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<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 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 lOa-year Floods <br /> <br />variation <br /> <br />Less than 2 feet <br /> <br />0.5 foot <br /> <br />Four reaches meeting the above criterion were required for the <br />flooding sources of Idaho Springs. These included one each on <br />Clear Creek, Chicago Creek, Soda Creek, and Virginia Canyon. The <br />locations of the reaches are 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 <br />on FHFs from 005 to 200. <br /> <br />The FHF for a reach is the average weighted difference between the <br />10- and lOa-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 />lOa-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- <br />surface elevations is greater than 10.0 feet, accuracy for the FHF <br />is to the nearest foot. <br /> <br />5.3 Flood Insurance Zones <br /> <br />After the determination of reaches and their respective Flood <br />Hazard Factors, the entire incorporated area of the City of Idaho <br />Springs was divided into zones, each having a specific flood potential <br />or hazard. Each zone was assigned one of the following flood <br />insurance zone designations: <br /> <br />Zones AI, A2, and A3: <br /> <br />Special Flood Hazard Areas inundated by <br />the lOa-year flood, determined by <br />detailed methods; base flood elevations <br />shown, and zones subdivided according <br />to Flood Hazard Factors. <br /> <br />14 <br />