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Por streams studied by approximate methods, the bound- ary of the 100-year flood was taken from the Wright- IlcLaughlin reports (References 1 and 2). Small areas within the flood noundaries may lie above the flood elevations, and therefore, not be subject to flooding; owing to limitations of the map scale, such areas are not shown. , 5.0 INSVRANCE APPLICATION In order to establish actuarial insurance rates, the Federal Insurance Administration has developed a process to trans- form the data from the engineering study into flood insurance criteria. ~his process includes the determination of reaches, Flood H~zard Factors, and flood insurance zone designations for each flooding source studied in detail affecting Boulder. 5.1 Reach Determinations Reaches are defined as lengths of watercourses having relatively the same flood hazard, based on the average I"eighted difference in ,.,ater-surface elevations between the 10- 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. Average Difference Between 10- and 100-year Ploods Variation Less than 2 feet 2 to 7 feet 0.5 foot 1. 0 foot Six reaches meeting the above criteria were required for the flooding sources studied in detail in the City of Boulder. These included four on Boulder Creek and two on South Boulder Creek. ~he locations of these reaches are shown in Exhibit 1). 5.2 Plood Hazard Factors " The Flood Hazard Factor (FHF) is the Federal Insurance Administration device used to correlate flood informa- tion with insurance rate tables. Correlations between property damage from floods and their FHF are used to set actuarial insurance premium rate tanles based on FHFs from 005 to 200. The PHF 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 shovm 7