GENERAL44240 - Laserfiche WebLink

Home Browse Search

-25- Description of the Surface Water Regime The North Fork of the Gunnison River is the major drainage for the general area. Smaller streams in or adjacent to the life-of-mine areas are all tributary to the North Fork (Figure 1). Figure 4 contains the drainage map of the study area with the locations of streams and reservoirs which are described in the following discussion. The North Fork has an annual streamflow at Somerset of approximately 313,500 acre-feet per year (1962-1979). The flow is regulated by the Paonia Reservoir on Muddy Creek 5 miles upstream of the town of Somerset, which became operational in 1962. River yields during that period have ranged from a high of 451,300 acre-feet per year in water year 1962 to a low of 82,270 acre-feet in water year 1977. Flow records for the North Fork of the Gunnison River near Somerset are given in Table 2. Water quality parameters for the North Fork are given in Table 3. As indicated, waters in the North Fork are a calcium bicarbonate type. There are moderate levels of sulfate. Salinity averages less than 100 mg/1. Just below Paonia Reservoir, Muddy Creek and Anthracite Creek join to form the North Fork of the Gunnison River. Anthracite Creek contributes about two-thirds of the flow to the North Fork. Anthracite Creek is a perennial stream with an average annual yield of 157,313 acre-feet for the period of record between July, 1977 to October, 1980 (U.S.G.S., Water Research Data). This corresponds to an average flow rate of 217 cfs. The highest discharge recorded was 4,200 cfs on May 27, 1979. Low flows of 12 cfs have been recorded several times during the period of record. The water of Anthracite Creek is an alkaline, moderately hard, calcium-bicarbonate type water with an average total dissolved solids concentration of 71.6 mg/1, average pH is 7.8. Total suspended solids average approximately 25 mg/1. Dissolved metal concentrations are low throughout the year, and total metal concentrations are directly related to the total suspended solids concentrations. The Hawk's Nest life-of-mine area is drained by nine ephemeral streams for which no flow records exist. Two of the gulches have had two water samples collected during 1980; once when they were flowing during snowmelt and once during a thunderstorm event. The water is alkaline with an average total dissolved solids concentration of 121 mg/1. Total suspended solids concentrations are low. There are a total of eleven springs and seeps within or adjacent to the Hawk's Nest Mines, three are perennial. The maximum total flow from all springs during the summer of 1982 was 16.085 gpm. The Somerset Mine has mine workings below the surface facilities along both Elk and Bear Creeks. These streams are ephemeral and intermittent respectively, and drain directly to the North Fork. Bear Creek is perennial below the Somerset Mine's discharge point, where the stream flow is sustained by the mine discharge.