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<br />/"''j, <br /> <br />. ,'-Jl" .... <br /> <br />" ') <br />, .". <br />. " <br />"<_.~./ <br /> <br />2! Where the potentiometric surface was below the base of the aquifer, <br />all aquifer parameters for the cell \'/ere set at zero (0), to <br />indicate that the cell was dry. <br /> <br />3, For the Laramie-Fox Hills, where the aquifer was confined and the <br />top of the aquifer had not been coded, the top was set 286 feet <br />(average thickness from Table 1) above the base of the aquifer. In <br />Townships 1 South through 4 South, Ranges 70 West and 69 West, the <br />thickness of water yielding materials was set at 200 feet and the <br />bottom was set 309 feet below the top. <br /> <br />4. Where the thickness of water yielding materials had not been coded, <br />the aquifer thickness was computed and multipl ied by the <br />appropriate ratio n/m from Table 1 to arrive at the value for the <br />thickness of water yielding materials. <br /> <br />The above resulted in four finished arrays for each aquifer: the <br />hydraulic conductivity of water yielding materials; the elevation of the <br />base of the aquifer; the water table elevation and the thickness of water <br />yielding materials. These finished arrays are referred to'as master arrays. <br /> <br />THE HYDROLOGIC MODELS <br /> <br />Seventeen separate digital models were constructed to allow computation <br />of the depletion to stream sys.tems as a result of well pumping in the six <br />aquifers. Aquifer data required for model input was .derived from the master <br />arrays. The bedrock aquifers were modeled within designated ground water <br />basins as well as outside of designated ground water basins. <br /> <br />The areas included in the models are shown on Figures 13-18. Each area <br />is referred to as a window. Where window boundaries disect the aquifers, <br />no-flow boundaries were inserted in. the models. To insure that computed <br />stream depletion would not be affected by those no-flow boundaries, windows <br />were made to overlap and window dimensions were generally designed with the <br />no-flow boundaries away from the simulated pumping. <br /> <br />Each window was divided into a number of cells using a rectangular grid <br />system. "Input Data For and Results From the Ground Water Models" shows the <br />grid system, model input and results for each of the windO\'/s, Most cells <br />are one mile on a side. Nodes at the center of each cell define data point <br />locations as well as locations for computed water table changes. The <br />differential equation describing two-dimensional flow is approximated with a <br />finite difference equation and solved with the computer. at each node to <br />predict changes in water level and the resulting depletion to stream systems. <br /> <br />-11- <br />