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<br />The 100-year floodplain boundary is shown on the FIRM <br />(Exhibit 2). On this FIRM, the 100-year floodplain boundary <br />corresponds to the boundary of the area of special fluod hazards <br />(Zone AE and A). Small areal within the floodplain boundaries <br />may lie above the flood elevations but cannot be shown due to <br />limitations of the map scale and/or lack of detailed topographic <br />data. <br /> <br />For the streams studied by approximate methods, only the lOO-year <br />floodplain boundary is shown. Initially, approximate lOO-year <br />floodplain boundaries in some portions of the study area were <br />taken from the Flood Hazard Boundary Map (FHBM) (Reference 7), <br />but through correspondence with the Colorado Water Conservation <br />Board thp~e houndaries were modi fied to account for changes in <br />topography since publication of the ~HBM in December 1975. The <br />topographic map published for the modified boundaries was <br />prepared at a scale of 1:2400, with contour intervals of 2 feet <br />(Reference 8) and was used as an aid in establishment of the 100- <br />year approximate floodplain boundaries. <br /> <br />4.2 Floodways <br /> <br />Encroachment on floodplains, such as structures and fill, reduces <br />flood-carrying capacity, increases flood heights and velocities, <br />and increases flood hazards in areas beyond the encroachment. <br />One aspect of floodplain management involves balancing the <br />economic gain from floodplain development with the resulting <br />potentiaL increase in flood hazard. For purposes of the NFIP, a <br />floodway is used as a tool to assist local communities in this <br />aspect of floodplain management. Under this concept, the area of <br />the 100-year floodplain is divided into a floodway and a floodway <br />fringe. The floodway is the channel of a stream, plus any <br />adjacent floodplain areas that must be kept free of encroachment <br />so that the 100-year flood can be carried without any substantial <br />increase in flood height. Minimum federal standards limit such <br />increases to 1.0 foot, provided that hazardous v~Locities are "not <br />produced. <br /> <br />Floodways were not computed for this study. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />For flood insurance rating purposes, flood insurance zone designations <br />are assigned to a community based on the results of the engineering <br />analyses. These zones are as follows: <br /> <br />Zone AE <br /> <br />Zone AE is the flood insurance rate zone that corresponds to the <br />lOO-year floodplains that are determined in the Flood Insurance <br />Study by detailed methods. In most instances, whole-foot base <br />flood elevations (BFEs) derived from the detailed hydraulic <br />analyses are shown at selected intervals within this zone. <br /> <br />7 <br />