VS2DT (Variably-Saturated Two-Dimensional Flow and Transport)

Computer program VS2DT solves problems of water and solute movement in variably saturated porous media.

watersolutemovementvariably saturated porous media



Initial contribute: 2021-01-17


U.S. Geological Survey
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Detailed Description

English {{currentDetailLanguage}} English

Quoted from: https://water.usgs.gov/cgi-bin/man_wrdapp?vs2dt 


       Computer program VS2DT solves problems of water and solute movement

       in variably saturated porous media.  The finite difference method is

       used to approximate the flow equation, which is developed by

       combining the law of conservation of fluid mass with a nonlinear

       form of Darcy's equation, and the advection-dispersion equation.

       The model can analyze problems in one and two dimensions with planar

       or cylindrical geometries.  There are several options for using

       boundary conditions that are specific to flow under unsaturated

       conditions: infiltration with ponding, evaporation, plant

       transpiration, and seepage faces.  Solute transport options include

       first-order decay, adsorption, and ion exchange.  The program is

       written in standard Fortran 77.  Extensive use of subroutines and

       functions subprograms provides a modular code that can be easily

       modified for particular applications.



       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.

       Equilibrium adsorption can be described by either Freundlich or

       Langmuir isotherms.  Four types of ion exchange can be simulated.

       The matrix equations produced for both the flow and transport

       equations are solved using the strongly implicit procedure.



       Version 2.5 1996/09/11 - Added interactive file name designation

          procedure.  Hard-coded file unit numbers were replaced with

          common block variables.


       1996/04/09 - Uses Freundlich solution of slope of sorption isotherm

          instead of Langmuir solution and incorporates several bug fixes.


       1991/09/01 - Supersedes VS2D and allows simulation of solute



       1986/10/10 - Original VS2D release.


       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 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.  Transport simulations require values for dispersivity and

       molecular diffusion.  Other information may be needed, depending on

       the program options that are selected.



       Simulation results can be output in terms of pressure head, total

       head, volumetric moisture content, saturations, velocities, and

       solute concentrations.  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.



       VS2DT is written in Fortran 77 with the following extensions:  use

       of include files and variable names longer than 6 characters.

       Generally, the program is easily installed on most computer systems.

       The code has been used on UNIX-based computers and DOS-based 386 or

       greater computers having a math coprocessor and 4 mb of memory.



       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.



       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 is being used by personnel in several districts, as well as by

       scientists at various universities and consulting companies.  An

       application is described in:


       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.



       Advanced Modeling of Subsurface Flow and Transport (GW3086TC), USGS

       National Training Center.



       Operation and Distribution:

          U.S. Geological Survey

          Hydrologic Analysis Software Support Program

          437 National Center

          Reston, VA 20192




       Official versions of U.S. Geological Survey water-resources analysis

       software are available for electronic retrieval via the World Wide

       Web (WWW) at:




       and via anonymous File Transfer Protocol (FTP) from:


                  water.usgs.gov (path: /pub/software).


       The WWW page and anonymous FTP directory from which the VS2DT

       software can be retrieved are, respectively:







       moc(1) - Two-dimensional method-of-characteristics

                ground-water flow and transport model

       modfe(1) - Modular Finite-element Model for areal and

                  axisymmetric ground-water flow problems

       modflow(1) - Modular three-dimensional ground-water flow


       Modflowp(1) - Parameter-Estimation Version of the Modular Model

       sutra(1) - Saturated and (or) unsaturated, constant or

                  variable-density fluid flow, and solute or energy

                  transport (2-dimensional finite-element code)




VS2DT team (2021). VS2DT (Variably-Saturated Two-Dimensional Flow and Transport), Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/376cb04e-6c26-44ac-a48d-28e810e9ef41


Initial contribute : 2021-01-17



U.S. Geological Survey
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