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sections, the boundaries were interpolated. In cases where the floodway and 100-year flood plain boundaries are either close together or collinear, only the floodway boundary has been shown. The area between the floodway and 100-year flood plain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the flood plain that could be completely obstructed without increasing the water-surface elevation of the 100-year flood by more than 1.0 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to flood plain development are shown in Figure 2. I- 1 aD-YEAR FLOOD PLAIN ) I F LOODWA Y FRINGE FLOOD ELEVATION WHEN CONFINED WITHIN FLOODWAY AREA OF FLOOD PLAIN THAT COULD BE USED FOR DEVELOPMENT BY RAISING GROUND F LOOOWA Y FLOODWAY FRINGE STREAM CHANNEL o fLOOlJ ELEVATION BEFOREENCRO^CHMENT ON FLOOD PLAIN LINE AS IS THE FLOOD ELEVATION BEFORE ENCROACHMENT LINE CD IS THE FLOOD ELEVATION AFTER ENCROACHMENT 'SURCHARGE ISNOTTOEXCEED 1.0 fOOT (FEMA REQUIREMENT} OR LESSER AMOUNT IF SPECIFIED BY STATE. Figure 2. Floodway Schematic 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 determination of reaches, Flood Hazard Factors, and flood insurance zone designations for each flooding source studied in detail affecting the unincorporated areas of Garfield County. 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 32