VAM2D (Variably-Saturated Analysis Model in Two (2) Dimensions) is a two-dimensional (2-D) finite-element model that simulates transient or steady-state groundwater flow and contaminant transport in porous media. VAM2D analyzes unconfined flow problems using a rigorous saturated-unsaturated modeling approach using efficient numerical techniques. Accurate mass balance is maintained even when simulating highly nonlinear soil moisture relations. Hysteresis effects in the water retention curve can also be simulated. A wide range of boundary conditions can be treated including seepage faces, water table conditions, recharge, infiltration, evapotranspiration, and pumping and injection wells. The contaminant transport option can account for advection, hydrodynamic dispersion, equilibrium sorption, and first-order degradation. Transport of a single species or multiple parent-daughter components of a decay chain can be simulated. The code can perform simulations using an areal plane, cross section, or axisymmetric configuration. An independent review of flow and transport computer codes conducted for the U.S. NRC (Kozak et al., 1989) states about VAM2D: "It is easy to use, is robust and has a wide range of numerical stability."
The saturated-unsaturated flow equation in VAM2D is solved using the Galerkin method with either Picard or Newton-Raphson iterative schemes to treat nonlinearities. The use of the upstream weighted residual finite-element method is used to solve the advective-dispersive transport equation. This circumvents numerical oscillation problems. Matrix solutions of the flow and transport problems are performed using efficient iterative solvers based on the preconditioned conjugate gradient and ORTHOMIN methods for symmetric and a nonsymmetric matrices, respectively.
Coordinate Systems and Grid Configurations
Boundary condition inputs for solute transport simulations in VAM2D may be prescribed nodal values of concentration or prescribed integrated nodal values of solute mass fluxes. Solute concentration or flux values at the boundaries can be either constant in time or variable in time with either continuous or stepwise changes. An additional option is available for modeling conditions in which source concentrations exhibit first-order decay.
VMPLOT provides postprocessing for VAM2D flow and transport simulations. Using VMPLOT, you can generate the following:
The model formulation used in VAM2D is a descendant of the formulation used in the SATURN code presented by Huyakorn et al. (1984, 1985). VAM2D has continued to be enhanced - the published algorithms and their coding to achieve greater flexibility, wider capability, and more robust numerical performances when dealing with difficult cases. The VAM2D code has been checked for numerical accuracy against several alternative analytical and numerical codes including FEMWATER/FEMWASTE and UNSAT2. The code has been applied to a wide variety of field problems (e.g., McCord et al., 1988; Kool et al., 1990) which have demonstrated its utility and versatility.
The application of VAM2D has been documented in the following studies.
Huyakorn, P.S. et al., 1984. Techniques for Making Finite Element Competitive in Modeling Flow in Variably-Saturated Porous Media, Water Resour. Res., 20, 8, 1099-1115.
Huyakorn, P.S. et al., 1985. Finite Element Matrix and Mass Balance Computational Schemes for Transport in Variably-Saturated Porous Media, Water Resour. Res., 21, 3, 346-358.
McCord, J.T. et al., 1988. Field Experiments and Numerical Simulations of Unsaturated Flow and Transport, Proc. of NATO Advanced Study Institute on Recent Advances in Modeling Hydrologic Studies, Sintra, Portugal, July 9 - 23.
Kool, J.B. et al., 1990. Model Calibration and Simulation of Flow in a Heterogeneous Soil, Proc. of Intern. Conference on Calibration and Reliability in Groundwater Modeling. IAHS Publication No. 195, pp. 321-330.
Kozak, M.W., M.S.Y. Chu, C.P. Harlan, 1989. Background Information for the Development of a Low-Level Waste Performance Assessment Methodology, U.S. Nuclear Regulatory Commission, Washington, D.C., NUREG/CR-5453, SAND89-2509, Vol. 4.
Pentium with 8 MB RAM, and HP PostScript or compatible printer for VMPLOT.
VAM2D - 2-d variably saturated groundwater analysis model - simulates transient or steady-state flow and contaminant transport in porous media
VAM2D Categories: flow models - saturated zone, flow models - unsaturated zone, solute transport models - saturated zone, solute transport models - unsaturated zone
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