1. General Model Information

Name: the Vadose Zone Flow and Transport Model

Acronym: VADOFT


Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: ecosystem
Type of model: partial differential equations (finite elements,1D), ordinary differential equations
Main application:
Keywords: soil, unsaturated, water transport, solute transport, pesticide transport, root zone, adsorption, degradation, Richards equation, convection-dispersion equation, finite element numerics

Contact:

Center for Exposure Assessment Modeling (CEAM) (EPA)Center for Exposure Assessment Modeling (CEAM)
National Exposure Research Laboratory - Ecosystems Research Division
Office of Research and Development (ORD)
U.S. Environmental Protection Agency (U.S. EPA)
960 College Station Road
Athens, Georgia (GA) 30605-2700

phone: 706/355-8400
Fax: 706/355-8302
e-mail:ceam@epamail.epa.gov

Author(s):

Huyakorn, P.S., T.D. Wadsworth, H.O. White Jr., and J.E. Buckley

Abstract:

VADOFT is a finite-element code that simulates one-dimensional, single-phase moisture and solute transport in unconfined, variably saturated porous media. Transport processes include hydrodynamic dispersion, advection, linear equilibrium sorption, and first-order decay. VADOFT employs the Galerkin finite-element technique to approximate the governing equations for flow and transport and allows for a wide range of nonlinear flow conditions. Boundary conditions of the variably saturated flow problems may be specified in terms of prescribed pressure head or prescribed volumetric water flux per unit area. Boundary conditions of the solute transport problem may be specified in terms of prescribed concentrations of prescribed solute mass flux per unit area. All boundary conditions may be time dependent. An important feature of the algorithm is the use of constitutive relationships for soil water characteristic curves based on soil texture.

Limitations:
Hysteresis effects in the constitutive relationships are assumed to be negligible. Sorption and decay of the solute are described by a linear equilibrium isotherm and a lumped first-order decay constant. The code considers only single porosity soil media and does not simulate flow or transport in fractured porous media or structured soils.

Validation:
Three sets of benchmark problems were used to test the VADOFT code; numerical results from VADOFT were compared with analytical solutions and results using two other finite-element codes (MULLINS et al. 1993).

Source of the Abstract:

Mullins, J.A., R.F. Carsel, J.E. Scarbrough, A.M. Ivery. 1993


II. Technical Information

II.1 Executables:

Operating System(s): DOS, uses XMS-memory VADOFT is included in US-EPA's PRZM2 Model system as a submodel. Note that this version does not run independantly. The self-extracting file INSTALP2.EXE contains executables, source-code, an extensive manual, and some example data.Europe:INSTALP2.EXE

II.2 Source-code:

Programming Language(s): FORTRAN 77 FORTRAN Source code of VADOFT is included in INSTALP2.EXE (File: /source/rsvado.for)

II.3 Manuals:

See Executables

II.4 Data:



III. Mathematical Information


III.1 Mathematics


III.2 Quantities


III.2.1 Input

III.2.2 Output


IV. References

Mullins, J.A., R.F. Carsel, J.E. Scarbrough, A.M. Ivery. 1993. PRZM-2, A Model for Predicting Pesticide Fate in the Crop Root and Unsaturated Soil Zones: Users Manual for Release 2.0. U.S. Environmental Protection Agency, Environmental Research Laboratory, Athens, GA.



V. Further information in the World-Wide-Web



VI. Additional remarks


Last review of this document by: T. Gabele: 17. 07. 1997 -
Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:51 CEST 2002

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