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the lO-year 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. A.verage Difference Between 10- and 100-year Floods Variation Less than 2 feet 2 to 7 feet 0.5 foot 1. 0 foot Eight reaches meeting the above criteria were required for the flooding sources in the City of Longmont. These included two reaches for Dry Creek, one reach for Left Hand Creek, three reaches for Spring Gulch; and two reaches for the St. Vrain Creek. ;, .. The locations of the reaches are shown on the Flood Pro- files (Exhibit 1). 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 100-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 flood 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 to the nearest foot. 5.3 Flood Insurance Zones After the determination of reaches and their respective Flood Hazard Factors, the entire incorporated and Prime Urbanized Areas of the City of Longmont were divided into zones, each having a specific flood potential and hazard. Each zone was assigned one of the following flood insurance zone designations: Zone AD: Special flood hazard areas inun- dated by types of shallow flood- ing where depths are between 1.0 26