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Show d. Reservoir management. The appropriation of ground water has been patterned after that of surface water, and each well has a priority determined by the date of first use or application for use of water from the well. It is important to note, however, that grpiind water occurs in reservoirs, and that the control of ground water should therefore be analogous to that of streams in which the flow can be effectively regulated by reservoirs. It is fundamental in reservoir operation that the reservoir be filled in times of surplus and drawn down to meet the needs for beneficial use during periods of low inflow o Under these conditions, it is possible to provide a firm supply of water perennially to a number of water users. For determining how much water can be perennially withdrawn from a groundwater reservoir ( the " safe yield"), an administrator would need to know the capacity of the reservoir, which might include " dead storage" below the economic pumping lift; seasonal changes in storage, as shown by water levels in index wells; long- term average recharge to the reservoir, and cyclic deviations from that average; and the discharge from that reservoir by wells, evapotranspiration, and effluent seepage. Complete information on these questions is not available for any ground- water basin in Utah. In some basins there is good evidence that present development is not even close to the " safe yield," and detailed scientific studies can logically be put off for awhile. In several basins, however, present rates of pumping are believed to be close to the " safe yield" and may have gone beyond it. In such basins the need for intensive study becomes more urgent every year. e. Interference among wells. Many of the most ticklish problems in ground- water administration arise in areas where there demonstrably is unappropriated water, but where new wells in trying to intercept this water along its course toward natural discharge, also affects the yields of previously appropriated well, spring, or stream supplies„ Such interference is commonplace in increasing development, and because of it the early appropriators - 16- |
