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<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 />DOS: if the difference is 1.4 feet, the FHF is 015: 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 <br />approximate methods: no base flood <br />elevations shown or FHFs determined. <br /> <br />Zone AD: <br /> <br />Special Flood Hazard Areas inundated by <br />types of 100-year shallow flooding where <br />depths are between 1.0 and 3.0 feet: <br />depths are shown, but no FHFs are deter- <br />mined. <br /> <br />Zones A2, A3, A4, AS, <br />AlO, and AlS: <br /> <br />Special Flood Hazard Areas inundated by <br />the 100-year flood: with base flood <br />elevations shown, and zones subdivided <br />according to FHFs. <br /> <br />Zone B: <br /> <br />Areas between the Special Flood Hazard <br />Areas and the limits of the SOD-year <br />flood: areas that are protected from <br />the 100- or 500-year floods by dike, <br />levee, or other local water-control <br />structure; areas subject to certain <br />types of 100-year shallow flooding where <br />depths are less than 1.0 foot: and areas <br />subject to 100-year flooding from sources <br />with drainage areas less than 1 square <br />mile. Zone B is not subdivided. <br /> <br />16 <br />