NAME vs2di - A graphical software package for simulating fluid flow and solute or energy transport in variably saturated porous media ABSTRACT VS2DI is a graphical software package for simulating flow and transport in variably saturated porous media. This software package consists of three components: - VS2DTI, for simulating fluid flow and solute transport, - VS2DHI, for simulating fluid flow and energy (heat) transport, - a standalone postprocessor, for viewing results saved from previous simulation runs. Both VS2DTI and VS2DHI combine a graphical user interface with a numerical model to create an integrated, window-based modeling environment. Users can easily specify or change the model domain, hydraulic and transport properties, initial and boundary conditions, grid spacing, and other model parameters. Simulation results can be displayed as contours of pressure head, moisture content, saturation, concentration or temperature, and velocity or flux for each time step, thus creating a simple animation. The numerical models used for flow and transport calculations are the U.S. Geological Survey's computer models VS2DT (for solute transport) and VS2DH (for energy transport). VS2DT is a finite- difference model that solves Richard's equation for fluid flow, and the advection-dispersion equation for solute transport. The model can analyze problems in one or two dimensions using either cartesian or radial coordinate systems. Relations between pressure head, moisture content, and relative hydraulic conductivity may be represented by functions developed by van Genuchten, Brooks and Corey, Haverkamp and others, or by data points. Initial hydraulic condition can be specified as static equilibrium, specified pressure head, or specified moisture content. Boundary conditions include specified pressure or total head, specified flux, infiltration with ponding, evaporation, plant transpiration, and seepage faces. Solute transport processes include advection, dispersion, first- order decay, adsorption, and ion exchange. VS2DH is a version of VS2DT that has been modified to simulate energy transport instead of solute transport. Both VS2DT and VS2DH are written in Fortran 77. Although these models are integrated into the graphical software package, their source codes are maintained as individual Fortran programs that can be compiled and run separately from the graphical user interface. METHOD For the flow equation, spatial derivatives are approximated by central differences written about grid-block boundaries. Time derivatives are approximated by a fully implicit backward scheme. Nonlinear conductance terms, boundary conditions, and sink terms are linearized implicitly. Relative hydraulic conductivity is evaluated at cell boundaries by using full upstream weighting, the arithmetic mean, or the geometric mean of values from adjacent cells. Saturated hydraulic conductivities are evaluated at cell boundaries by using distance-weighted harmonic means. Nonlinear conductance and storage terms can be represented by algebraic equations or by tabular data. For the advection-dispersion equation, either central or backward differences may be selected for the spatial and time derivatives. In VS2DT, equilibrium adsorption can be described by either Freundlich or Langmuir isotherms; four types of ion exchange can also be simulated. In VS2DH, thermal conductivity is assumed to vary linearly with moisture content. The matrix equations produced for the flow and transport equations are solved sequentially using the strongly implicit procedure. HISTORY Version 1.1 2000/02/09 - extended to work with VS2DH; improved postprocessing capabilities. This release contains revised versions 3.0 of VS2DT and VS2DH, which allow runtime selection of hydraulic function and adsorption type. The VS2DI postprocessor has the capability to run on input files created with earlier versions of VS2DT and VS2DH. Version 1.0 1999/07/28 - Initial release DATA REQUIREMENTS A conceptual model of the geometry and boundaries of the region to be simulated is of prime importance. Initial conditions in terms of pressure heads or moisture contents for flow simulations and concentrations or temperatures for transport simulations are needed. Hydraulic and transport properties of the porous media are also required. These values can be different for different sediments. Flow simulations require values for saturated hydraulic conductivity and for relative hydraulic conductivity and moisture content as functions of pressure head. Solute transport simulations require values for dispersivity and molecular diffusion. Energy transport simulations require values for heat capacities of water and soil and thermal conductivity. Other information may be needed, depending on the program options that are selected. OUTPUT OPTIONS Simulation results can be displayed as contours of pressure head, moisture content, saturation, concentration or temperature, and velocity or flux for each time step, thus creating a simple animation. The graphical displays may be printed or saved as bitmap files. Text (or ASCII) output can be obtained for pressure head, total head, volumetric moisture content, saturations, velocities, and solute concentrations or temperatures. Time histories and spatial profiles of the data can be obtained. In addition, the user may opt to view time histories of up to 72 mass balance parameters. SYSTEM REQUIREMENTS The VS2DI software package was developed using a combination of Java, C, and Fortran programming languages. This software has run successfully on the following operating systems: Microsoft Windows 95, 98, and NT 4.0, Silicon Graphics IRIX 6.3, 6.4, and 6.5, and Sun Solaris 2.6. For other computer platforms, the usability of VS2DI depends on the availability of a Java Development Kit for that platform, and the ability to compile Fortran and C programs into dynamic or shared libraries that can be used by the Java program. Additional information on computer requirements can be found in the README file distributed with the software. The numerical models VS2DT and VS2DH may be compiled and run separately from the graphical user interface. These two models are written in Fortran 77 with the extension of using variable names longer than 6 characters. They have been used on UNIX, DOS, and Windows-based computers. DOCUMENTATION Hsieh, P.A., Wingle, William, and Healy, R.W., 2000, VS2DI--A graphical software package for simulating fluid flow and solute or energy transport in variably saturated porous media: U.S. Geological Survey Water-Resources Investigations Report 99-4130, 16 p. Healy, R.W., and Ronan, A.D., 1996, Documentation of computer program VS2DH for simulation of energy transport in variably saturated porous media--modification of the U.S. Geological Survey's computer program VS2DT: U.S. Geological Survey Water- Resources Investigations Report 96-4230, 36 p. Healy, R.W., 1990, Simulation of solute transport in variably saturated porous media with supplemental information on modifications to the U.S. Geological Survey's Computer Program VS2D: U.S. Geological Survey Water-Resources Investigations Report 90-4025, 125 p. Lappala, E.G., Healy, R.W., and Weeks, E.P., 1987, Documentation of computer program VS2D to solve the equations of fluid flow in variably saturated porous media: U.S. Geological Survey Water- Resources Investigations Report 83-4099, 184 p. REFERENCES Healy, R.W., 1987, Simulation of trickle irrigation, an extension to the U.S. Geological Survey's Computer Program VS2D: U.S. Geological Survey Water-Resources Investigations Report 87-4086, 61 p. VS2DT and VS2DH have been used by scientists at the USGS and at various universities and consulting companies. Example applications are described in: Bartolino, J.R., and Niswonger, R.G., 1999, Numerical simulation of vertical ground-water flux of the Rio Grande from ground-water temperature profiles, central New Mexico: U.S. Geological Survey Water-Resources Investigations Report 99-4212, 34 p. Mills, P.C., and Healy, R.W., 1993, Water and tritium movement through the unsaturated zone at a low-level radioactive-waste disposal site near Sheffield, Illinois, 1981-85: U.S. Geological Survey Water-Supply Paper 2386, 72 p. Halford, K.J., 1997, Effects of the unsaturated zone on aquifer test analysis in a shallow-aquifer system: Ground Water, v. 35, no.3, p. 512-522. McCord, J.T., Gotway, C.A., and Conrad, S.H., 1997, Impact of geologic heterogeneity on recharge estimation using environmental tracers: Numerical modeling investigation: Water Resources Research, v. 33, no. 6, p. 1229-1240. CONTACTS Operation and Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 firstname.lastname@example.org Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the VS2DI software can be retrieved are, respectively: http://water.usgs.gov/software/vs2di.html --and-- /pub/software/ground_water/vs2di See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications.