Conservative Eulerian-Lagrangian Methods and Mixed Finite Element Methods for Modeling of Groundwater Flow and Transport

Abstract : New, improved computational methods for modeling of groundwater flow and transport have been formulated and implemented, with the intention of incorporating them as user options into the DoD Groundwater Modeling System under development at the Waterways Experiment Station. These methods, which are specifically designed to treat the difficulties of subsurface flows in porous media, yield greater accuracy with coarser spatial grids and longer time steps, making possible more detailed three-dimensional (3D) simulations than would otherwise be practical. For 3D solute transport, the methods have been implemented and perform as expected on representative test problems. Theoretical analysis that substantiates this performance has also been carried out. The method for flow equations leads to linear algebraic equations that are difficult to solve, and an efficient 3D solver that overcomes these problems has been analyzed theoretically, implemented, and shown to perform well on model problems. The 3D flow code has been extended to distorted grids, the 3D transport code has been incorporated into the USGS MOC3D codes, and the two codes are being coupled together into a flow and transport code for solute.