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West Elk Mine <br />per year on average, and during November, the probability of any mean daily flow falling below the <br />minimum is nearly 25 percent. <br />• <br />Estimates of peak flood flows for various recurrence intervals for the North Fork were provided <br />by the USGS using a Log-Pearson Type III distribution and Water Resources Council guidelines. <br />The estimates were based on historic streamflow data from the USGS gaging station on the <br />North Fork near Somerset. At the time of analysis, this station was located at the access bridge <br />to Bear Mine. Since the Paonia Reservoir Dam, located a few miles upstream from the gaging <br />station, was completed in 1961, the period of record from 1934 to 1960 only was used in the <br />analyses by the USGS. Estimated discharges for various recurrence intervals and the <br />probabilities of exceeding those estimated discharges are presented in Table 13 and shown <br />graphically in Exhibit 20. <br />Table 13 <br />Flood Frequency Estimates for Various Recurrence Intervals <br />North Fork Gunnison River Near Somerset, Colorado' <br />Exceedance <br />Probability Recurrence Interval <br />(years) Expected Discharge <br />(cubic feettsecond <br />0.995 1 910 <br />0.500 2 3,520 <br />0.200 5 4,970 <br />0.100 10 5,910 <br />0.040 25 - 7,060 <br />0.020 50 7,940 <br />0.010 100 8,770 <br />0.005 200 9,630 <br />0.002 500 10,770 <br />Notes: <br />1. Estimated using a Log-Pearson Type III Distribution by USGS using Water Resources Council Guidelines Period <br />of record 1934-1960. <br />2. Recurrence interval = 1/exceedance probability. <br />Minnesota Creek <br />Baseline characterization of streamflow conditions for Minnesota Creek was developed from the <br />USGS/MCC Gage (09134000) 4.5 miles east of Paonia. Discharge volumes average 16,100 <br />acre-feet per year based on water years 1937 through 1947, and 1986 to 2000 monitoring records. <br />The annual mean discharge is 22.2 cfs for the 41.3 -mil drainage basin. The lowest daily mean <br />flow was 1.0 cfs on November 14, 1936, and the lowest 7-day minimum was 1.4 cfs on January <br />16, 1990 and February 179 1999. Flow at this site is influenced by two small reservoirs, <br />Minnesota Reservoir and Beaver Reservoir and a trans-basin diversion from the Coal Creek basin <br />(Little Gunnison Creek) into Mimiesota Creek via Dry Fork. <br />• <br />2.04-97 <br />Revised NoveMber 2009 PRIG; Rev. Apri1 2006 PRI G; Sep. 2007 PR12; Feb. 2008 PR12