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Average Difference Between 10- and lOa-year Floods Variation Less than 2 feet 0.5 foot One reach meeting the above criterion was required for the Rio Grande in Alamosa. The location of the reach is shown on the Flood Profiles. 5.2 Flood Hazard Factors The Flood Hazard Factor (FHF) is the Federal Emergency Management Ag~ncy device used to correlate f,lQQd 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 elevations 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 lOa-year ~loods 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 lOa-year water-surface elevations is greater than 10.0 feet, accuracy for the FHF is to the nearest foot. 5.3 Flood Insurance Zones After the determination of reaches and their respective Flood Hazard Factors, the entire incorporated area of the City of Alamosa was divided into zones, each having a specific flood potential or hazard. Each zone was assigned one of the following flood insurance zone designations: Zone AO: Special flood hazard areas inundated by types of shallow flooding where depths are between 1.0 and 3.0 feet and the product of the depth (in feet) and velocity (in feet per second) is less than 15; no Flood Hazard Factors determined. Zone A4: Special flood hazard areas inundated by the lOa-year flood, determined by detailed methods; base flood elevations shown, and zones subdivided according to Flood Hazard Factors. 14