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<br />The IOO-year floodplain boundaries for the following streams were <br />obtained from a 1979 UDFCD report (Reference 2): <br /> <br />City Park Channel <br />City Park Channel South Tributary <br />Gay Reservoir Channel <br />Gay Reservoir Channel North Tributary <br />Nissen Reservoir Channel <br />West Lake Channel <br />West Lake Channel Tributary <br /> <br />Additional IOO-year floodplain boundaries along Gay Reservoir <br />Channel were obtained from individual consultant engineers. <br /> <br />The SOG-year floodplain boundaries for each of these streams were <br />delineated by the SC. <br /> <br />The floodplain boundaries for Big Dry Creek were obtained from the <br />FIS for Adams County (Reference 1). The floodplain boundaries for <br />Rock Creek were taken from a 1976 SCS report (Reference 8). The <br />100- and SOO-year floodplain boundaries are shown on the FBFM <br />(Exhibit 2). In cases where the 100- and SOO-year floodplain <br />boundaries are close together, only the IOO-year floodway boundary <br />bas been shown. Small areas within the floodplain boundaries may lie <br />above the flood elevations but cannot be shown because of <br />limitations of the map scale and/or lack of detailed topographic <br />data. <br /> <br />For-t"he-f'looding-s ource s-a tudi:"ed-by-approxirna"t"e-m"e"t'h~o~d.s---;-c5rf1yfne <br />100-year floodplain boundary is shown. <br /> <br />Approximate IOO-year floodplain boundaries in some portions of the <br />study were taken directly from the FIRM for the City of Broomfield <br />(Reference 9) and the FIS for Jefferson County, Colorado <br />(Reference 10). <br /> <br />1 The approximate flooding in the vicinity of the sewage disposal <br />plant was taken from the 1979 UDFCD report (Reference 2). <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, and <br />increases flood hazards in areas beyond the encroachment. One <br />aspect of floodplain management involves balancing the economic gain <br />from floodplain development against the resulting increase in' flood <br />hazard. For purposes of the NFIP, a floodway is used as a tool to <br />assist local communi ties in this aspect of floodplain management. <br />Under this concept, the area of the 100-year floodplain is divided <br />into a floodway and a floodway fringe. The floodway is the channel <br />of a stream, plus any adjacent floodplain areas, that must be kept <br />free of encroachment so that the lOO-year flood can be carried <br />without substantial increases in flood heights. Minimum Federal <br /> <br />13 <br />