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corresponds to the boundary of areas of moderate flood hazards (Zone B). 4.2 Floodways The floodway is the channel of a stream, plus any adjacent flood plain areas, that IDUst be kept free of encroachment so that the 100-year flood can be carr1ed without substantial increases in flood he1ghts. Jefferson County has a Floodplain Zoning Ordinance with floodway and high-hazard-area regulations more restrictive than the minimum FEMA standards; therefore, no floodways were defined for this Flood Insurance Study. 5.0 INSURANCE APPLICATION To establish actuarial insurance rates, data from the engineering study must be transformed into flood insurance criteria. This process includes the determ1nation of reachea, Flood Hazard Factors, and flood insurance zone designations for each flooding source studied in detail affecting the unincorporated areas of Jefferson County, Colorado. 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 100- 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 Between 10- and 100-Year Floods VariaC10n 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 Jefferson County are shown on the Flood Profiles (Exhibit 1) and summarized in Table 4. 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 establish actuarial insurance rate tables. 27