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Title: THE SWMS_3D CODE FOR SIMULATING WATER FLOW AND SOLUTE TRANSPORT IN THREE- DIMENSIONAL VARIABILITY SATURATED MEDIA. VERSION 1.2 USSL RESEARCH REPORT NO. 139

Author
item SIMUNEK, J - U.C. RIVERSIDE
item HUANG, K - U.C. RIVERSIDE
item Van Genuchten, Martinus

Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 7/25/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Interest in the unsaturated zone has dramatically increased in recent years because of growing concern that the quality of the subsurface environment is being adversely affected by agricultural, industrial and municipal activities. Fertilizers and pesticides applied to agricultural lands inevitably move below the soil root zone and may contaminate underlying groundwater reservoirs. Chemicals migrating from municipal and industrial disposal sites also represent environmental hazards. The same is true for radionuclides emanating from energy water disposal facilities. This report documents a new model, called SWMS_3D, for simulating the three-dimensional movement of water and dissolved chemicals in the unsaturated zone between the soil surface and the groundwater table. The models considers several physical and chemical processes, such as diffusion, adsorption/desorption, and water uptake by plant roots. This report serves as both a user manual and reference document. Detailed instructions are given for data input preparation. Example input and selected output files are also provided.

Technical Abstract: In this report we developed a version 1.0 of a computer program SWMS_3D for simulating water and solute movement in three-dimensional variably saturated media. The program numerically solves the Richards' equation for saturated-unsaturated water flow and the convection-dispersion equation for solute transport. The flow equation incorporates a sink term to account for water uptake by plant roots. The transport equation includes provisions for linear equilibrium adsorption, zero-order production, and first-order degradation. The program may be used to analyze water and solute movement in unsaturated, partially saturated, or fully saturated porous media. SWMS_3D can handle flow regions delineated by irregular boundaries. The flow region itself may be composed of nonuniform soils having an arbitrary degree of local anisotropy. The water flow part of the model can deal with prescribed head and flux boundaries, as well as boundaries controlled by atmospheric conditions. The governing flow and transport equations are solved numerically using Galerkin-type linear finite element schemes. Depending upon the size of the problem, the matrix equations resulting from discretization of the governing equations are solved using either Gaussian elimination for banded matrices, or a conjugate gradient method for symmetric matrices and the ORTHOMIN method for asymmetric matrices.