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I I I I I I I I I I I I I I I , I I I I I floodplain, HEC-2 input/output for the split flow model, the original right overbank and the as-built right overbank are included in Appendix 2, Multiple profile runs have been provided using the 10-, 50-, 100- and 500-year discharge quantities listed in Table 1, 4.0 FLOODPI,AIN MANAGEMF.NT APPLICATIONS 4.1 FlooQplain Boundaries Floodplain boundaries were determined using the U, S, Army Corps of Engineers HEC-2 computer program, Flood elevations and cross section geometries were determined using 1 foot contour topographic maps and channel design information, The maps were prepared at 50 scale and 1 foot contour intervals using national mapping standards. The date of the aerial photography used to prepare this mapping is December 5, 1988. The lOa-year floodplain boundaries are contained in the wetlands area of the UCBRP (see construction drawings), Floodplain boundaries and flood profiles have been tied to existing boundaries upstream and downstream of the study reach. Flood profiles for Boulder Creek are included in this report (Figures 2 through 4, a and b), 4,2 Floodway There is currently no FEMA accepted floodway for Boulder Creek, As discussed in Section 3,2,5, the wetlands area of this project will convey the lOa-year flood flows which spill from Boulder Creek, It is recommended that this area be defined as the floodway (channel right) for regulatory purposes, Note that while encroachment on this area from channel right will be independent of flows in the main channel, encroachment of the floodplain from the left, i,e" Arapahoe Avenue, will affect the performance of the design, 7,0 OTHER STUDIES The information contained in this study is intended as a revision to the existing flood insurance study (Ref, B), The existing published information shall be used to regulate the floodplain until such time as the an official map revision is issued, Love & Associates, Inc. Page 13