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As shown on the FIRM, the floodway boundaries were computed at cross sections. Between cross sections, the boundaries were interpolated. In cases where the floodway and I-percent-annual-chance floodplain boundaries are close together or collinear, only the floodway boundary has been shown. Floodways were not computed for the flooding sources studied in Georgetown. Downstream of Interstate 70 at Silver Plume, no floodway encroachments were made because of high flow velocities. The area between the floodway and I-percent-annual-chance floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be completely obstructed without increasing the water surface elevation of the base flood more than 1 foot at any point. Typical relationships between the flood way and the floodway fringe and their significance to floodplain development are shown in Figure 1. I- 1-PERCENT -ANNUAL-CHANCE FLOODPLAIN FLOOOWAY 1- FRINGE -, FLOOOWA Y LOODWAY FRINGE STREAM CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FLOOOWAY ENCROACHMENT AREA OF FLOODPLAIN THAT COULD BE USED FOR DEVELOPMENT BY RAiSING GROUND LINE AS IS THE fLOOD ELEVATION BEFORE ENCROACHMENT. LINE CO IS THE FLOOD ELEVATION AFTER ENCROACHMENT. .SURCHARGE IS NOT TO EXCEED 1.0 FOOT (FIA REQUIREMENT) OR LESSER AMOUNT If SPECifIED BY STATE. Figure 1, "Floodway Schematic" 5.0 INSURANCE APPLICATIONS For flood insurance rating purposes, flood insurance zone designations are assigned to a community based on the results of the engineering analyses. These zones are as follows: Zone A Zone A is the flood insurance rate zone that corresponds to the I-percent-annual-chance floodplains that are determined in the FIS report by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no base (l-percent-annual- chance) flood elevations (BFEs) or depths are shown within this zone. 20