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West Elk Mine 2014 Annual Hydrology Report 6 2.2 Stream Flow Data The North Fork of the Gunnison River (North Fork) and Minnesota Creek are the major surface water resources in the MCC permit area. The U.S. Geological Survey (USGS) maintains a gaging station on the North Fork (USGS 09132500). The USGS maintained a gaging station at Minnesota Creek (USGS 09134000) until April 2, 2014, when the station was decommissioned. In mid-April 2014, the Colorado Division of Water Resources (CDWR) installed a new staff gage and strip chart stream depth recorder at the same location. A continuous stream depth recorder was also installed by HydroGeo in June 2014. A flow rating curve has not yet been developed for the new Lower Minnesota Creek staff gage (CDWR, 2015). Flows in the North Fork and Minnesota Creek are dominated by snowmelt from upland areas, but are affected by small upstream diversions for irrigation, and by storage and releases from upstream reservoirs (USGS, 2015c, 2015d). The average daily flows in the North Fork in WY 2014 were slightly above historical averages (USGS, 2015a). 2.2.1 Flows in the North Fork of the Gunnison River A summary of the average daily stream flow data for the North Fork near Somerset, CO (USGS 09132500; Hydrologic Unit 14020004), including historical and WY 2014 data, is graphically presented in Figure 6. Average daily flows for the North Fork for WY 2014 ranged from 64 cubic feet per second (cfs) (January 12, 2014) to 3,040 cfs (June 2, 2014) (USGS, 2015a). The historical mean daily flows in the North Fork collected from WY 1934 through WY 2013 have ranged from 63 cfs (9 days in January) to 2,170 cfs (May 22) (USGS, 2015a). The average daily flows measured at the North Fork gaging station in WY 2014 were nearly equal to historical means from October through March, variable from April through July, and slightly above historical means in August and September (USGS, 2015a) (Figure 6). The mean annual flow at the North Fork near Somerset (USGS 09132500) in WY 2014 was about 458 cfs, corresponding to 101% of the historical annual mean of about 451 cfs for WYs 1934 through 2013 (USGS, 2015a). The historical mean annual flows in the North Fork have ranged from 114 cfs in 1977 to 829 cfs in 1984 (USGS, 2015a). The highest daily mean flow for the North Fork WY 2014 was 3,040 cfs on June 2, 2014 and the maximum recorded peak flow in WY 2014 was 3,750 cfs, also on June 2, 2014 (USGS, 2015a, 2015c). Flows in the North Fork can be influenced by upstream releases and storage in the Overland and Paonia reservoirs (since February 1962), small diversions for irrigation in nearby drainage areas, and irrigation of about 3,000 acres upstream from station 09132500 (USGS, 2015c). June 2015 HydroGeo, Inc.