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<br />. <br /> <br />. <br /> <br />. <br /> <br />Previous Studies <br />The initial flood hazards in Park County were identified by the Federal Insurance Administration <br />and published on November 22, 1977. The Flood Insurance Rate Map became effective, by letter <br />from FEMA, on April 1, 1987, There have been no revisions to the Flood Insurance Rate Map <br />since that time. The Town of Fairplay has its own floodplain information map in addition to the <br />published information for unincorporated Park County, <br /> <br />Community Response to the CWCB Desilmation and Approval Process <br />A letter from the CWCB was transmitted to Park County regarding the Board's proposed action for <br />designation and approval of the Park County FHBM, A meeting was also held between CWCB <br />staff and the County's Planning and Zoning staff to discuss technical issues and the floodplain <br />designation process. Floodplain mapping needs are generally limited to the areas receiving <br />development pressure along the natural drainage courses. The County is interested in receiving <br />technical assistance from FEMA or the CWCB to update and revise floodplain information for <br />select streams, The County was also receptive to the Board's proposed designation action, and sent <br />an official letter requesting that the CWCB designate and approve the floodplain information <br />currently available to the community, A copy of the request letter is included in the Appendix of <br />this report <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!ic Analvsis <br />Hydrologic information used for the FEMA floodplain delineations in Park County is not available <br />or was not documented by FEMA, However, acceptable hydrologic information can be developed <br />by the CWCB using a methodology for computing 100-year flood,flow values. The method <br />involves the use of a publication by the U,S, Geological Survey entitled "Analysis of the Magnitude <br />and Frequency of Floods in Colorado," The 100-year flow for two streams in the county were <br />estimated by utilizing the regional regression equation for the Mountains Region. The Mountains <br />Region equation is used for streams having drainage watershed areas above an elevation of 7,500 <br />feet The USGS regression equation is: <br /> <br />Q100 =39.5(At'06 (S+1.0)1.<77 (For 55<A<988 and 0,081 <8<0562) <br /> <br />The Q100 is the 100-year peak flow in cubic feet per second, A is the upstream (contributing) <br />drainage area in square miles, and S is the mean drainage basin slope in feet per feet The regression <br />equation is only valid for streams with drainage areas between 5,5 and 988 square miles, and mean <br />basin slopes between 0.081 and 0562 feet per feet <br /> <br />Table I presents 100,year flow estimates, as computed using the regional regression equation, for 2 <br />locations in the county, <br /> <br />3 <br />