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<br />, . <br /> <br />very simplest of hydrologic systems.. Therefore, approximation methods for <br />so 1 ving systems of simultaneous 1 inear algebra ic difference equations are <br />used. The accepted method of S.I.P.' (Strongly Implicit Procedure) of <br />Weinstein, Stone and Kwan (2) was utilized to solve for head distribution. <br />Head distribution is then used to compute stream depletion (q) after 100 <br />years of pumping. <br /> <br />The finite difference model utilizes rectilinear parallel piped cells <br />whose dimensions are specified by the user. Finite difference equations are <br />formulated at the beginning of each iteration. The system of simultaneous <br />equations is then approximately solved for the head distribution and <br />compared to the head distribution at the previous iteration. If the <br />comparison results in a head difference greater than a user specified "head <br />closure criteria", the finite difference equations are again formulated and <br />solved. Iterations proceed untiJ.ptSlosure is met. The Denver Basin Models <br />used head closure criteria oT/\U.OOl or 0.0001 feet. The method of <br />approximate solution for ground water models is generally accepted because <br />even if an exact solution to the system of simultaneous ground water flow <br />equations could be obtained, it would still only be an approximation of true <br />field conditions. <br /> <br />Options Used in the Ground Water Model <br /> <br />"":J The USGS Finite Difference Ground Water Model. has different options for <br />simulating hydrologic . conditions and specifying output. The reader is <br />referred to "Input Data For and Results From the Ground Water Models" which <br />specifically details input data and options selected for each aquifer <br />modeled. <br /> <br />The optional packages selected for this study were the Well Package, <br />River Package, and General Head Boundary Package. The River Package is used <br />to simulate induced ground water flow from the stream systems to the aquifer <br />as a result of pumping. The well package is used to specify pumping. The <br />Genera 1 Head Boundary Package simulates flow between aquifer layers in the <br />vertical direction. <br /> <br />Output <br /> <br />The output from the USGS Ground Water Model includes the stream <br />depletion rate (q). The value of (q) during the 100th year of pumping, as <br />provided by the final time step budget of the model was used as the <br />numerator of the ratio of q/Q. <br /> <br />-2- <br /> <br />, )"",\ <br />. .. . <br />...j.' <br />...;.J'" <br />