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5.1 Reach Determinations Reaches are defined as sections of flood plain that have relatively the same flood hazard, based on, the average weighted difference in water-surface elevations between the 10- and lOa-year floods. This difference may not have a variation greater than that indicated in the following table for more than 20 percent of the reach: Average Difference Betw~en 10- and lOa-Year Floods Variation Less than 2 feet 2 to 7 feet 7.1 to 12 feet More than 12 feet 0.5 foot 1.0 foot 2.0 feet 3.0 feet The locations of the reaches determined for the flooding sources of Green Mountain Falls are shoWn on the Flood Profiles (Exhibit 1) and summarized in Table 3. 5.2 Flood Hazard Factors The Flood Hazard Factor (FHF) is used to establish relationships between depth and frequency of flooding in any reaCh. This rela- tionship is then used with depth-damage relationships for various classes of structures to establ~sh actuarial insurance rate tables. The FHF for a reach is the average weighted difference between the 10- and lOa-year flood water-sutface elevations rounded to the nearest one-half foot, multipli~d by 10, and shown as a three- digit code. For example, if the difference between water-surface elevations of the 10- and lOa-year floods is 0.7 foot, the FHF is 0051 if the difference is 1.4 feet, the FHF is 0151 if the differ- ence is 5.0 feet, the FHF is 050. When the difference between the 10- and lOa-year flood water-su~face elevations is greater than 10.0 feet, it is rounded to theinearest whole foot. 5.3 Flood Insurance Zones Flood insurance zones and zone numbers are assigned based on the type of flood hazard and the FH~, respectively. A unique zone number is associated with each possible FHF, and varies from 1 for a FHF of 005 to a maximum of 30: for a FHF of 200 or greater. Zones A6 and A9: Spec~al Flood Hazard Areas inundated by the lOa-year flood 1 with base flood elevations shown, and zones subdivided according to FHFs. Zone B: Areas between the Special Flood Hazard Areas and the limits of the 500-year 12