SOLUTION OF GROUND-WATER FLOW PROBLEMS WITH GENERAL-PURPOSE AND SPECIAL-PURPOSE COMPUTER CODES

Increasingly, ground water hydrologists and engineers must solve satur ated/unsaturated flow and transport problems. The unsaturated componen t of flow is especially important when considering transport of contam inants that originate from surface or nearsurface sources such as wast e spill sites, landfills, and hazardous waste storage sites. Numerical solution of such problems has been accomplished with special purpose computer programs developed for solution of unsaturated flow problems. However, general purpose partial differential equation (PDE) solvers also exist, which often provide greater model flexibility. In this pap er, the performance of PDE2D, a general PDE solver, and SWMS_2D, a spe cial purpose program, are compared for solution of unsaturated flow an d transport problems. Both programs accurately calculated changes In w ater volume in the flow domain for four examples, but PDE2D did not ca lculate boundary fluxes as well as SWMS_2D, resulting in high mass bal ance errors. However, PDE2D yielded a smoother solution of the example solute transport problem, despite a large mass balance error. SWMS_2D offers ease of use and excellent mass balances while PDE2D offers the user greater flexibility in terms of the types of problems solved, an d a grid generator that ensures that the element size and distribution of elements are appropriate for a given problem.