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A4ovnrain Coo! Comporry 1997 Annual Hydrology Report Wesr E!k Mine <br />average conditions. Snow depths at Overland Reservoir were 148 percent of average during <br />• WY97. April snowpack was 133 percent of average at McClure Pass and 131 percent of average <br />at Overland Reservoir. The fact that May and June had below average snow depths indicates <br />that snowmelt occurred earlier than normal in WY97. Figures 1 through 3 show the monthly <br />distribution of the precipitation measured at each of these three stations. <br />Hydrological Data <br />In addition to the climatological data, a water yeaz can be chazacterized by streamflow. The <br />significant drainage basins in the vicinity of the West Elk Mine are the North Fork of the <br />Gunnison River (North Fork) and Minnesota Creek. The U.S. Geological Survey (USGS) has <br />gaging stations on both of these streams. Both of these watersheds are large and the annual flow <br />is dominated by snowmelt from the higher elevations. The North Fork flow regime is also <br />affected by Paonia Reservoir. <br />To facilitate comparison of the WY97 streamflow data to the period of record, Figures 4 and 5 <br />were prepared. These graphs indicate that both drainages experienced higher than average <br />runoff, which is substantiated by the snow station data. Annual runoff in the North Fork <br />drainage was 144 percent of the long-term average, and in the Minnesota Creek drainage, runoff <br />was 146 percent of the long-term annual average. An instantaneous peak discharge of 3,590 <br />cubic feet per second (cfs) was recorded on the North Fork on May 15 for WY97, and an <br />instantaneous peak discharge of 290 cfs was recorded on Minnesota Creek on May 25 for WY97. <br />• Since the North Fork is the primary water supply for the West Elk Mine, these flows are the most <br />relevant. The heavy snowpack maintained higher than average flows throughout the summer. <br />The average annual discharge for the North Fork was 673 cfs in WY97, whereas the average <br />annual discharge for the period of record is 465 cfs. As a result of the above average flows in the <br />North Fork during the summer months, a water rights "call" was not placed on the stream during <br />WY97. <br />r1 <br />I-03 .450 age rig [ a[er ng~neers <br />