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areas, that must be kept free of encroachment so that the lOO-year flood can be carried without substantial increases heights. Minimum Federal standards limit such increases heights to 1.0 foot, provided that hazardous velocities pruduced. in flood in flood are not The floodways for all streams studied by detailed methods were computed on the basis of equal conveyance reduction from each side of the floodplain. The results of these computations are tabulated at selected cross sections for each stream segment for which a floodway is computed (Table 2), A floodway is not because flooding River. shown for U.S. Highway 34 Levee Overflow Channel 1n this area is controlled by the South Platte No floodway was computed for the detailed study reach of the Big Thompson River. As shown on the Flood Boundary and Floodway Map, the floodway boundaries were determined at cross sections; between cross sections, the boundaries were interpolated. In cases where the floodway and 100-year flood boundaries are close together, only the floodway boundary has been shown. The area between the floodway and the boundary of the lOO-year flood is termed the floodway fringe, The floodway fringe thus encompasses the portion of the floodplain that could be completely obstructed without increasing the water-surface elevation of the 100-year flood more than 1.0 ,foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to floodplain development are shown in Figure 5. 5.0 INSURANCE APPLICATION In order to establish actuarial insurance rates, the FEMA has developed a process to transform the data from the engineering study into flood insurance criteria. This process includes the determination of reaches, Flood Hazard Factors (FHFs), and flood insurance zone designations for each flooding source studied In detail affecting the unincorporated areas of Weld County, 17