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Show each node at 15 feet below the 1982 value. The water rights and water quality constraints were maintained at their 1982 levels. The demand for each water district was increased uniformly as a fixed percentage of its 1982 usage from the set of wells used for optimization. Table 4.5 shows the results from these applications. Table 4 .5 Parametric Solutions with Water District Demand varied Water District Demand Optimal Solution (% above 1? 82) ( 1000 Ac- ft/ vr) 0 75.25 10 75.25 20 75.25 30 75.25 40 75.22 50. 75.22 The solutions indicate that the spatial distribution of water demand is not a growth limiting factor for the system's development, if the permissible point drawdown is less than 15 feet, and a maximum increase of three times in the individual well pumpage is allowed, as long as the water district demands do not increase by more than 50% above their 1982 levels. Beyond this level, the water rights structure is likely to be critical in dictating an increase in the aquifer yield from the system. 4.3 Summary A unit response formulation for determining optimal aquifer yield, subject to constraints on drawdown, water rights, water quality and water district demand was formulated and applied to the Salt Lake County area. The unit response matrices were generated using data provided by Mr. K. M. Waddell of the Utah District Office of the USGS, and the 3- D finite difference simulation model by McDonald and Harbaugh ( 1982). Parametric applications of the model developed were performed to assess the effect of drawdown, pumping limit, and spatial demand distribution on the solution. Model results indicate that significant ( approximately double) increases in the total aquifer yield from the principal aquifer in Salt Lake County are possible, without an infringement of water rights and water quality, and with controlled drawdowns. The only areas of the aquifer where groundwater yield expansion is of concern are Sandy and White City. The other areas of the aquifer are significantly underdeveloped. Expansion of yield in these areas is possible with minimal impact on the yields for Sandy and White City. The scale of the applications was restricted to the grid spacing ( 0.7 mile x 1 mile) used by Waddell et al ( 1986). While this is adequate for assessments of yield across the system, refinements to a finer grid should be employed if applications to specifically study the water exchanges and potential well sites in the immediate vicinity of Sandy and White City. As in chapter 3, it should be possible to establish a region of influence around each well site, and then an area smaller than Salt Lake County could be defined in the neighborhood of the area ( e. g. SandyAVhite City) where the study of potential conflicts of use and yield development is of interest. Issues regarding the optimal location of wells in the above context could then be resolved by a parametric analysis of model appbcations at the finer grid scale. Corrections for relating point well drawdown to nodal drawdown, as described by Charbeneau and Street ( 1979) could also be appbed where well locations are identified within the finer grid specified. 101 |