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<br />. <br /> <br />. <br /> <br />. <br /> <br />Table 1 <br />lOO-year Peak Flow Estimates for Park County <br /> <br /> lOO-year <br /> Drainage Area Mean Basin Peak Flow <br />Stream Name and Location (sq. mi.) Slope (ft/ft) (cfs) <br />Geneva Creek just upstream of its 75 .350 1,340* <br />confluence with the NF South <br />Platte River at Grant <br />Tarryall Creek downstream of its 183 .290 2,340* * <br />confluence with Jefferson Creek <br />below Jefferson <br /> <br />Notes: *USGS reported a peak flow of 1,700 cfs on June I, 1914, <br />** Peak flow from flood frequency analysis using 12 years of gage data = 2,700 cfs <br /> <br />Park County should regulate the approximate floodplains on a case-by-case basis, FEMA requires <br />that a detailed floodplain analysis must be performed by a professional engineer and submitted by <br />the developer or development proponent for development projects involving more than 5 acres or <br />more than 50 units (whichever is most restrictive). <br /> <br />Hydraulic Analvsis <br />Hydraulic methods used for the approximate floodplain delineations shown on the Park County <br />FHBM panels are not available or have not been documented by FEMA, For future studies, an <br />approximate 100'year flood elevation at a particular location on the river may be obtained by <br />computing a 100,year peak flow value (using the method as provided in this report) in conjunction <br />with an acceptable hydraulic analysis. Hydraulic analyses for determining 100-year water surface <br />elevations fur approximate floodplains may be performed using FEMA's Quick,2 computer <br />program, the Corps of Engineers' HEC,2 or HEC-RAS computer programs, Flowmaster, or other <br />acceptable hydraulic methods, Channel and floodplain cross,sections may be obtained from <br />detailed topographic mapping or from field surveys. Cross-sections obtained from USGS <br />quadrangle maps are not advised, <br /> <br />FloodDlain MaDDinl!: <br />The existing Flood Hazard Boundary Map for Park County depicts areas subject to 100'year <br />flooding based on approximate technical methods. The map does not show flood profiles, hase <br />flood elevations, or sufficient detail in order for County officials, engineers, developers, and land <br />owners to make floodplain determinations with any certainty, The Colorado Water Conservation <br />Board can be contacted to request technical assistance for approximate floodplain analyses as <br />needed. <br /> <br />4 <br />