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-31- Description of Hydrologic Environment - Surface Water Regime (Cont'dJ Two reservoirs are located within tl~e Minnesota Creek drainage. Pinnesota Reservoir is located on Dry Fork. It has a decreed capacity of 1,285 acre-feet. The actual capacity may be closer to 500 acre-feet, however. Beaver Reservoir is located on the East Fork of Minnesota Creek and has an absolute decreed capacity of 1,620 acre-feet and a conditional decree of 522 acre-feet. Both reservoirs store water for irrigation purposes and are filled during spring runoff. They are usually drained by late August or early September. Water quality data has been collected at several sites throughout the Minnesota Creek drainage. The data indicate that these waters are of a calcium bicarbonate type with relatively low total dissolved solids concentrations. There are over 100 springs located throughout the Mt. Gunnison life-of-mine area. Measurements indicate that spring flows generally decrease from a high in the early summer to a low point in the fall. A number of the springs are ephemeral, indicating that their source is most likely a small localized ground water table. There are a total of 13 decreed spring water rights on or near the Mt. Gunnison permit area. Precipitation and Runoff Only two precipitation stations exist for the watershed; one at Paonia and one at Wilcox Ranch. Since these are located near the North Fork of the Gunnison River, they may not be representative of the total watershed. Isohyetal lines can be used to show average precipitation that falls on the watershed. Figure 5 represents Wean annual precipitation and Figure 6 illustrates lfay to September precipitation of the years 193I to 1960. A11 values were obtained from maps drawn by the U.S. weather Bureau. Table 6 summarizes precipitation data for both the north and south sections of the watershed. Comparing these isohyetal maps with Figure 7 shows that precipitation patterns are strongly influenced by topography. During the period May through September, the amount of precipitation which falls upon the watersheds is Less than the potential amount of water Lost to evapo- transpiration (PET), In other words, the native vegetation will use most of the precipitation and also will remove water from the soil profile. For those areas where cash crops such as apples, peaches, and the like are grown, irrigation water is removed from the North Fork of the Gunnison River and applied on such lands. Surface water in the general area is dominated by the North Fork of the Gunnison River. Flow records exist for a USGS Gaging Station near Somerset. Data from this station (Table 2) show inflows to the area and releases From Paonia Reservoir. Outflow from the basin is not as easily determined. For example, the nearest station to Paonia is located on the Gunnison River near Lazear, Colorado, 11 miles southwest of Paonia. Such a station is too far from the study area to be acceptable for this analysis since many inflows and outflows occur between Paonia and Lazear. However, a review of past U.S. Geological Survey (USGS) records indicates that for the years 1922 through 1932, a gaging station existed on the north of the Gunnison River near Paonia. Also, for the years 1932 through 1950, a gaging station existed in Somerset. These two stations are important since Paonia Reservoir was not yet constructed and, thus, did not affect inflows to the basin. Use of these stations allows determination of approximate inflows to the North Fork of the Gunnison River contributed by the study watershed boundary located on