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Coal Creek, Dutch Creek, Bear Creek, Porcupine Creek, and <br /> ✓''• Oilwell Creek. These drainages are in Hydrologic Area 5 and <br /> Flood Frequency Region A (Pattersen & Somers , 1966) . It <br /> should be understood that the flood discharges are estimates <br /> based on regional surface runoff gauging records and should <br /> not be used for design purposes . The calculations provide a <br /> method of comparison for the various drainages and a basis <br /> for estimation of flood peaks . <br /> A 100-year flood occurred on July 24 , 1977 , <br /> on Coal Creek. A description of this event is given in <br /> Appendix C to Appendix III-E-1 . The same storm event <br /> produced a peak flow of 1730 . cfs at the stream gauging <br /> station on the Crystal River above Avalanche Creek . The <br /> \`• base flow on the Crystal at Placita on the 24th was 117 . <br /> cfs . <br /> Base flow calculations were extrapolated to <br /> Coal Creek using #9-0815 . 5 and #9-0816 USGS continuous <br /> Crystal River USGS gauging records . The minimum inflow <br /> between the gauges represents an average base flow ranging <br /> from approximately 10 to 12 cfs . The analysis was cal- <br /> culated for the months of November - March flow records <br /> because little or no runoff occurs because water is stored <br /> in snowbanks . Table III-E-4 summarizes difference in mean <br /> flows and volume on a year by year basis for the drainage <br /> D <br /> areas between the Crystal gauging stations . Base flows for <br /> perennial streams within the Coal Creek Basin were calculated <br /> and extrapolated using the data presented in Table III-E-3 <br /> and III-E-4 and are presented in Figure III-E-4 . <br /> 27 <br />