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West Elk Mine 2007 Annual Hydrology Report 4 <br />• The North Fork of the Gunnison River (North Fork) and Minnesota Creek are the major surface <br />water drainages in the Project area. The U.S. Geological Survey (USGS) maintains gaging stations <br />on both of these water resources. Flows in these rivers are dominated by snowmelt from upland <br />areas. Flows in WY 2007 in both of the major drainage watersheds in the Project area were <br />generally near to slightly below the historical average (USGS, 2008a). <br />Average monthly flows for the North Fork of the Gunnison River near Somerset, CO (USGS <br />09132500) for WY 2007 ranged from 80.9 cubic feet per second (cfs) (February 2007) to 1,414 cfs <br />(May 2007) (USGS, 2008a). The historical mean monthly flows in the North Fork of the Gunnison <br />River near Somerset, CO collected from WY 1934 through WY 2006 have ranged from 66 cfs <br />(January) to 1,890 cfs (May) (USGS, 2008a). Average monthly flows in the North Fork of the <br />Gunnison River near Somerset, CO in WY 2007 were above historical means for 8 months <br />(October, November, and December 2006 and January, February, August, and September 2007). <br />Average flows were below historical means in the months of April, May, June, and July 2007 <br />(USGS, 2008a). <br />The mean annual flow for WY 2007 was 391 cfs corresponding to 86 percent of the historical <br />annual mean for the years 1934 through 2007 (453 cfs) (USGS, 2008b). Historical mean annual <br />• flows have ranged from 114 cfs in 1977 to 829 cfs in 1984 (USGS, 2008b). The peak flow in the <br />North Fork of the Gunnison River in WY 2007 was 2,300 cfs on May 15, 2007, compared to the <br />maximum peak flow of 9,220 cfs in 1978 (USGS, 2008b). A summary of the average monthly <br />stream flow data for the North Fork of the Gunnison near Somerset, CO including historical and <br />WY 2007 data is graphically presented in Figure 6. <br />Figure 6. Stream Flow Data for the N Fork of the Gunnison River near Somerset, CO <br />(USGS 01932500) <br />• <br />North Fork of the Gunnison <br />2000 <br />1500 <br />3 -?-Average Flow <br />1000 WYs 1934-2006 <br />E -Average Flow <br />500- <br />0- WY 2007 <br />oG?o0o, ??e??????Ja PQ?\ <br />? o?c? <br />5 <br />Adapted from USGS (2008a) <br />June 2008 <br />HydroGeo, Inc.