Three‐dimensional modeling of groundwater flow systems

Practical aspects of three‐dimensional (3‐D) modeling of groundwater flow systems are closely examined. A Galerkin finite element model is designed with a view to providing flexibility, user convenience, and a high degree of efficiency, qualities which are critical to the success of 3‐D modeling of real systems. The model is based on the general saturated‐unsaturated continuity equation. Several integration schemes and matrix solvers are compared, and relative costs are expressed as functions of grid size. Examples presented include a hypothetical system and a real system. Simulation costs are generally found to be reasonable for grids of the size encountered with real systems. It is found that a remaining obstacle to the unified treatment of saturated‐unsaturated systems is that the optimum element sizes required for saturated and unsaturated flow are not always compatible because of constraints arising from the physical properties of the materials. In general, however, it appears that with presently available tools, 3‐D analysis is a practical option.