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
h2osoft@usgs.gov
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.