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I I Floodways ~ere not computed for Horizon Drive Channel and Leach Creek for t~e following reasons. First, some areas along Leach Creek and Hprizon Drive Channel are shallow flooding, and floodways are not established. The remaining flooding from these two streams is contained in the channels; therefore, floodways were not computed. However, no encroachment should be allowed within the stream channel, as it would obstruct flow and cause an increase in the water-surface elevations. 5.0 INSURANCE APPLICATION In order to establish actuarial insurance rates, the Federal Insurance Administration ~as developed a process to transform the data from the engineering study into flood insurance criteria. This process includes the determinatibn of reaches, Flood Hazard Factors, and flood insurance zone designatio~s for each flooding source studied in detail affecting the county. , 5.1 Reach Dete~minations , Reaches are defined as lengths of watercourses having relatively the same flood hazard, based on the average weighted difference in water-surface elevations between the 10- and lOa-year floods. This difference Idoes not have a variation greater than that indicated in the follow~ng table for more than 20 percent of t.he reach. I Average Difference Between 10- and 100-year Floods variation Less than 2 feet 2 to 7 feet 0.5 foot l. 0 foot Thirteen r$aches meeting the above criteria were required for the flooding s0urces studied by detailed methods. These included one reach on tfue Colorado River, two for West Creek, and five each for , Leach Cree~ and Horizon Drive Channel. The locat:ions of the reaches are shown on the Flood Profiles (Exhibit 1). I 5.2 Flood Hazard Factors The Flood Hazard Factor (FHF) is the Federal Insurance Administra- tion devic~ used to correlate flood information with insurance rate tables. Correlations between property damage from floods and their FHF a~e used to set actuarial insurance premium rate tables based on FHFs fr0m 005 to 200. The FHF for a reach is the average weighted difference between the lQ- and 100-year flood water-surface elevations expressed to the nearest on~-half foot, and shown as a three-digit: code. For example, if the difference between water-surface elevations of the 10- and 24 -.- L~.~ -"'~~