IMPROVING A COMPLEX FINITE-DIFFERENCE GROUND-WATER FLOW MODEL THROUGHTHE USE OF AN ANALYTIC ELEMENT SCREENING MODEL

This paper demonstrates that analytic element models have potential as powerful screening tools that can facilitate or improve calibration o f more complicated finite-difference and finite-element models. We dem onstrate how a two-dimensional analytic element model was used to iden tify errors in a complex three-dimensional finite difference model cau sed by incorrect specification of boundary conditions. An improved fin ite-difference model was developed using boundary conditions developed from a far-field analytic element model. Calibration of a revised fin ite-difference model was achieved using fewer zones of hydraulic condu ctivity and lake bed conductance than the original finite-difference m odel, Calibration statistics were also improved in that simulated base -flows were much closer to measured values. The improved calibration i s due mainly to improved specification of the boundary conditions made possible by first solving the far-field problem with an analytic elem ent model.