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-20- <br />precipitation increases with elevation, reaching approximately 40 <br />inches per year on the summit of Mt. Gunnison. The May-September <br />precipitation is 5 inches for the lowlands and 13 inches for the <br />mountain peaks. This indicates that snowfall patterns play an <br />important part in determining the hydrology of the area. <br />Temperature extremes at Paonia have ranged from -28oF in January to <br />100°F during Julyo and August. The average annual temperature is <br />approximately 49 F. Snow fall averages 58 inches per year. <br />The North Fork of the Gunnison River is the major drainage for .the mine <br />site. Streams on the northern portion of the permit area drain <br />directly into the North Fork near Somerset. Minnesota Creek drains the <br />remaining areas to the south which are outside the five year permit <br />boundary. It enters the North Fork near Paonia. <br />The North Fork has an annual streamflow at Somerset of approximately <br />313,200 acre feet per year (1933-1982). The flow is regulated by the <br />Paonia Reservoir 5 miles upstream, which became operational in 1962. <br />Flows during that period have ranged from a high of 451,300 acre-feet <br />per year in Water Year 1962 to a low of 82,270 acre-feet in Water Year <br />1977. <br />A number of separate drainages have their headwaters in the mine <br />environmental study area. Sylvester Gulch and Lone Pine Gulch are <br />ephemeral streams which drain the northern portion of the area. They <br />flow directly into the North Fork. There are five tributaries which <br />drain into the main flow of Minnesota Creek. Characteristics of the <br />drainages are given in .Table 1. No flow was observed in Lone Pine <br />Gulch for a period of years thus, it was omitted from the ,study. <br />Sylvester Gulch is an ephemeral stream and has a drainage area of 4.25 <br />square miles. It is important to note that the major portion of the <br />surface facilities will be located near this drainage in the valley <br />adjacent to the North Fork. The hydrologic yield of Sylvester Gulch is <br />low compared to the other watersheds. This is due to the fact that it <br />drains a lower elevation area with more gentle slopes. <br />Horse Creek, South Prong, Lick Creek, Dry Fork, and East Fork drain <br />into Minnesota Creek. Their slopes are generally more steep and the . <br />watersheds are at higher elevations than those tributary to the North <br />Fork. Based upon streamflows measured in water year 1978, the water <br />yields from these drainages are nearly an order of magnitude .greater <br />than that of Sylvester Gulch. <br />There are numerous springs located throughout the permit and life of <br />mine area. Measurements indicate that spring flows generally decrease <br />from a high in the early summer to a low point in the fall. A number <br />of the springs dry up in the winter, indicating that their source is <br />most likely a small localized ground water table. <br />-- ;..~ <br />