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<br />. <br /> <br />Previous Studies <br />Flood Insurance Studies have been published by FEMA for Idaho Springs, Georgetown, Silver <br />Phune, and Empire. These studies contain approximate and detailed floodplain delineations for <br />streams within those communities. Unincorporated portions of the County do not currently have <br />the benefit of detailed floodplain studies. <br /> <br />Communitv Response to the CWCB Desiroation and Approval Process <br />A letter from the CWCB was transmitted to Clear Creek County regarding the Board's proposed <br />action for designation and approval of the Clear Creek County FIRM. The County was interested <br />in discussing several issues related to the FEMA floodplain mapping for their community. A <br />meeting was held with CWCB staff, the County Floodplain Administrator, and the County <br />Emergency Manager to discuss and review mapping issues, flooded areas, floodplain regulations, <br />flood history, and the Board's designation and approval of the floodplain information. The County <br />was very interested in having updates made to the floodplain mapping as resources become <br />available from FEMA or other agencies. The County is aware that floodplain re-studies for certain <br />stream reaches are being conducted by the U.S. Army Corps of Engineers, Omaha District, under <br />contract with FEMA. Once the draft floodplain re-studies are complete, the County would like to <br />review the new floodplain delineations before they are finalized and published. The County was <br />receptive to the Board's proposed designation action, and sent an official letter requesting that the <br />CWCB designate and approve the floodplain information currently available to the community, A <br />copy of the request letter is included in the Appendix of this report. <br /> <br />. <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!ic AnaIvsis <br />Hydrologic information used for FEMA floodplain delineations in unincorporated Clear Creek <br />County is not available or was not documented by FEMA. However, acceptable hydrologic <br />information was developed by the CWCB for the previously mentioned Corps of Engineers study <br />that is under way (under contract with FEMA). The Appendix of this report contains the CWCS's <br />summary of peak flows for analyzed streams in the county. For stream reaches that were not <br />studied in the CWCS hydrology report, peak flow estimates can be obtained using a publication by <br />the U.S. Geological Survey (USGS) entitled" Analysis of the Magnitude and Frequency of Floods <br />in Colorado." The CWCS can be contacted to obtain publications and additional information <br />regarding hydrology. <br /> <br />. <br /> <br />Hvdraulic Analvsis <br />Hydraulic methods used for the approximate floodplain delineations shown on the Clear Creek <br />County FIRM panels are not available or have not been documented by FEMA. For future studies, <br />an approximate lOa-year flood elevation at a particular location on the river may be obtained by <br />using the appropriate lOa-year peak flow value (obtained from CWCS report or from the USGS <br />methodology referenced above) in conjunction with an acceptable hydraulic analysis. Hydraulic <br />analyses for determining lOa-year water surface elevations for approximate floodplains may be <br />performed using FEMA's Quick-2 computer program, the Corps of Engineers' HEC-2 computer <br />3 <br />