FEMWATER: A Three-Dimensional Finite Element Computer Model for Simulating Density-Dependent Flow and Transport in Variably Saturated Media.

Abstract : This report presents the user's manual of FEMWATER, A Three-dimensional Finite Element Computer Model for Simulating Density-Dependent Flow and Transport The intended users of the manual will have a wide range of technical experience and have different needs that the model and documentation will fulfill. Sophisticated users will find descriptions of the numerical techniques and a complete set of governing equations that form the theoretical basis of the model. The casual users will find examples of several types of problems that will include their type of application. FEMWATER is a modern implementation of the two older models, 3DFEMWATER (flow) and 3DLEWASTE (transport). FEMWATER was formed by combining the two codes into a single coupled flow and transport model. The improvements implemented in FEMWATER are numerous. First, the entire program structure was changed to allow its integration into the Department of Defense Groundwater Modeling System (GMS). The GMS contains a state-of-the-art graphical user environmental that allows efficient model setup and visualization. Second, a series of new solvers were added to replace the previously used block iterative solver. The new solvers allow an arbitrary node numbering scheme that enables easier graphical user interface connections and still provide improved computational efficient. Their, density-driven (salinity) transport capability was added to allow salinity intrusion studies in coastal aquifers. This required the coupling of flow and transport within a common model, which is the last major improvement.