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-47- From Table 0, it becomes evident that during the time period of May through September, the amount of precipitation which falls upon the watershed is less than the amount of water required for PET. Therefore, for this time period (May - September), the actual evapotranspiration (AET) will be less than 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. It is expected that those areas would have an AET which is nearly equivalent to the value predicted by PET. However, since the majority of the watershed has native vegetation, it will be assumed that the value for AET for the May to September period will be equivalent to the May through September precipitation value. Therefore, for the entire year, the value of AET will be represented by approximately 159,000 acre-feet (AF). Another inflow parameter to a mass balance study involves how much water is entering the watershed via the North Fork of the Gunnison River. Ideally, it would be desirable to have a gaging station at the downstream location of the watershed illustrated in Figure 1. However, such is not the case. A station presently exists near Somerset, Colorado, as illustrated in Table 8. By use of this particular station, we are able to approximate the inflow into the basin via the North Fork of the Gunnison River 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. Such a station is not acceptable for this analysis since many inflows and outflows occur between Paonia and Lazear. However, a review of past U.S. Geological Survey (USCS) records indicates that for the years 1922 through 1932, a gaging station existed on the North Fork 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 watershed located within the boundaries of Figure_l. The average monthly flows are illustrated on Table 8, along with the inflows to the North Fork of the Gunnison River from Minnesota Creek. These figures were utilized to determine the amount of outflow via the North Fork of the Gunnison River from the basin. Obviously, such predictions are not entirely correct. For example, Less than 3 years of data existed for Minnesota Creek and 1 year (1977) included drought conditions. However, for purposes of this analysis, such figures provide the basis for determining the impact of development by the Mt. Gunnison mine which as can be seen in Figure la and Ib, has a substantial portion of it's lease area located in the Minnesota Creek drainage basin. Note that column 5 of Table 8 gives the net drainage to the North Fork of the Gunnison River between Somerset and Paonia. As more data is available, these values will become more accurate. The consumptive use of water by the mines within the North Fork Drainage basin constitutes a minor outflow component in the mass balance. The consumptive use is discussed below on a mine by mine basis.