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<br />flood can be carried without substantial increases in flood <br />heights. Minimum Federal standards limit such increases to 1.0 <br />foot, provided that hazardous velocities are not produced. The <br />floodways in this study are presented to local agencies as minimum <br />standards that can be adopted directly or that can be used as a <br />basis for additional floodway studies. <br /> <br />The floodways presented in this study were computed on the basis of <br />equal conveyance reduction from each side of the floodplain. The <br />results of these computations are tabulated at selected cross <br />sections for each stream segment for which a floodway is computed <br />(Table 3). <br /> <br />The floodways at the confluence of the Nissen Reservoir Channel and <br />the City Park Channel incorporate sheetflow diversion areas common <br />to both channels. The floodways were delineated through these <br />sheetflow areas after analyzing two HEC-2 computer runs: (l) wi th <br />the total flow confined to the channels, and (2) with partial flow <br />confined to the channel. If the change in water-surface elevation <br />between these computer runs was greater than allowable with <br />encroachment (i .e., greater than 1.0 feet), then the floodway was <br />shown routed through the sheetflow diversion areas. <br /> <br />As shown on the Flood Boundary and Floodway Map (Exhibit 2), the <br />floodway boundaries were computed at cross sections. Between cross <br />sections, the boundaries were interpolated. In cases where the <br />floodway and lOO-year floodplain boundaries are either close <br />together or collinear, only the floodway boundary has been shown. <br /> <br />The area between the floodway and 100-year floodplain boundaries is <br />termed the floodway fringe. The floodway fringe encompasses the <br />portion of the floodplain that could be completely obstructed <br />without increasing the water-surface elevation of the 100-year <br />flood by more than 1.0 foot at any point. Typical relationships <br />between the floodway and the floodway fringe and their significance <br />to floodplain development are shown in Figure 9. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />To establish actuarial insurance rates, data from the engineering study <br />must be transformed into flood insurance criteria. This process <br />includes the determination of reaches, Flood Hazard Factors. and flood <br />insurance zone designations for each flooding source studied by detailed <br />methods affecting the City of Broomfield. <br /> <br />5.1 Reach Determinations <br /> <br />Reaches are defined as sections of floodplain that have relatively <br />the same flood hazard. In riverine areas, reaches are based on the <br />average weighted difference in water-surface elevations between the <br />10- and 100-year floods. This difference may not have a variation <br /> <br />15 <br />