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3.1.6 Recharge to the Ground-Water System <br /> The primary recharge mechanism for the bedrock aquifers in the mountains north of Silver-ton <br /> is infiltration of rain and snownielt. The average annual precipitation in the upper reaches of <br /> Cement Creek and Eureka Creek between 1921 and 1950 was approximately 45 inches, of which <br /> approximately 30 inches occurred as snow (Iorns, et al., 1964). A simple water balance can be <br /> performed to estimate the amount of annual recharge to the bedrock aquifer by subtracting <br /> runoff, sublimation, and evapotranspiration values from the precipitation. The United States <br /> Geological Survey has estimated the annual runoff from the high mountain basins north of <br /> Silverton at between 10 inches (Longbein, et al., 1949) and 20 inches (Gebert, 1987). The total <br /> losses from an alpine snowpack above timberline (via evaporation, sublimination, and wind <br /> transport) are approximately 50 to 60% (Meiman and Grant, 1974). Therefore, the total <br /> remaining precipitation contributed by snowfall on an average annual basis (1921-1950) is <br /> between 12 and 15 inches. Considering the short growing season at high altitude, the average <br /> evapotranspiration rate for alpine meadow is expected to be low. <br /> Taking the average of the range of values for precipitation, losses to snowpack, and runoff, the <br /> amount of annual precipitation available for recharge to the ground-water system is estimated <br /> at 8.5 inches. Using minimum values results in an estimate of only 2 inches of recharge per <br /> year. <br /> sanjuan\sunny\110361\mt91.R,t 27 <br /> n N snon Hrann=aao mcH <br />