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S.l Reach Determinations Reaches are defined as lengths of watercourses having relatively the same flood hazard, based on the average weighted difference in water-surface elevations between the 10- and 100-year floods.- This difference does not have a variation greater than that indicated in the following table for more than 20 percent of the reach. Average Difference Between 10- and 100-year Floods Variation Less than 2 feet 2 to 7 feet 7.1 to 12 feet 0.5 foot 1.0 foot 2.0 feet Twelve reaches meeting the above criteria were required for the flooding sources in Las Animas County. These included two reaches for Reilly Canyon Arroyo, three reaches for Raton Creek, three reaches for Powell Arroyo, and four reaches for the Purgatoire River. 5.2 Flood Hazard Factors The Flood Hazard Factor (FHF) is the Federal Insurance Administration device used to correlate flood information with insurance rate tables. Correlations between property damage from floods and their FHF are used to set actuarial insurance premium rate tables based on FHFs from 005 to 200. The FHF for a reach is the average weighted difference between the 10- and lOa-year flood water-surface eleva- tions expressed to the nearest one-half foot, and shown as a three-digit code. For example, if the difference between water-surface elevations of the 10- and 100-year floods is 0.7 foot, the FHF is 005; if the difference is 1.4 feet, the FHF is 015; if the difference is 5.0 feet, the FHF is 050. When the difference between the 10- and 100-year water- surface elevations is greater than 10.0 feet, accuracy for the FHF is the nearest foot. 5.3 Flood Insurance Zones After the determination of reaches and their respective Flood Hazard Factors, the entire unincorporated areas of Las Animas County were divided into zones, each having a specific flood potential or hazard. Each zone was assigned one of the following flood insurance zone designations: 29