GENERAL33122 - Laserfiche WebLink

Home Browse Search

-35- characteristics of the overlying streams. In the Hawk's Nest mine, an inflow was encountered under the ephemeral drainage of Hawk's Nest Creek. The rates of inflow beneath this drainage fluctuated seasonally with a slight lag time in response to the flows in the overlying stream. In the Somerset mine, inflows beneath Rubbard Creek are continuous and reflect the perennial nature of this stream. Faults and fractures located outside stream valleys generally dry up with time. Those which continue to flow have flo[r rates which diminish to a relati ve trickle. Such inflows may represent the dewatering of a Lenticular sandstone unit with a limited recharge area, or may represent flow through a fracture zone extending to the surface which has a narrow recharge zone on a steep slope. Description of 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 mine plan areas are aI1 tributary to the North Fork. Figure 3 contains a location map of the tributary streams in the general area. The North Fork has an annual streamflow at Somerset of approximately 313,500 acre-feet per year (1962-1979). The flow is regulated bu the Paonia Reservoir 5 miles upstream, which became operational in 1962. Flows during that period have ranged from a high of 452,300 acre-feet per year in water year 1962 to a low of 82,270 acre-feet in water year 1977. The current Bear and Mt. Gunnison mining operations are adjacent to Sylvester Gulch and Lone Pine Gulch, which are ephemeral streams flowing directly to the North Fork. The Mt. Gunnison, life-of-mine area is drained by five tributaries to Minnesota Creek. Characteristics of the drainages are given in Table 2. No flow was observed in Lone Pine Gulch for a period of years; thus, it was omitted from the study. Sylvester Gulch is an ephemeral stream and has a drainage area of 4.25 square miles. As indicated on Table 1, the hydrologic yield of Sylvester Gulch is low compared to the other watersheds. This is due to the fact that it drains a Zo[oer elevation area with gentle slopes. Norse Creek, South Prong, Lick Creek, Dru Fork, and East Fork drain into Minnesota Creek. Their slopes are generally more steep and the watersheds are at higher elevations than those trabutary to the North Fork. Based upon streamflows Treasured in water year 1978, the water yields from these drainages are nearly an order of magnitude greater than that of Sylvester Gulch. There are numerous springs located throughout the Mt. Gunnison Life-of-mine area. Measurements indicate that spring flows generally decrease from a high in the early surrm~r to a Sow point in the fall. R number of the springs dry up in the winter, indicating that their source is most likely a small localized ground water table.