1. General Model Information

Name: Estimating transport parameters from laboratory or field tracer experiments

Acronym: CXTFIT

Main medium: terrestrial
Main subject: hydrology
Organization level: ecosystems
Type of model: partial differential equations (1D)
Main application:
Keywords: parameter estimation, parameter identification, transport parameters, solute transport, tracer, nonlinear least-squares optimisation, inverse problem, inverse modeling, convection-dispersion equation, analytical solution, nonequilibrium transport, stochastic transport, stream tube model,Levenberg-Marquardt-algorithm


N. Toride
U. S. Salinity Laboratory, USDA, ARS
450 West Big Springs Road
Riverside, CA 92507-4617
Tel.: (909)369-4850
Fax.. (909)342-4964
email: titan@citrus.ucr.edu
Walter Russell
U.S. Salinity Laboratory
450 West Big Springs Road
Riverside, CA 92507-4716Tel: 909-369-4850
FAX: 909-342-4964
email: wrussell@ussl.ars.usda.gov


Toride, N., Leij, F.J., Parker, J.C., van Genuchten M.ThUSDA, ARS, Riverside, CA


Successful predictions of the fate and transport of solutes in the subsurface hinges on the availability of accurate transport parameters. CXTFIT 2.0 is a update and extension of the CXTFIT code of Parker and van Genuchten (1984) for estimating solute transport parameters using a nonlinear least-squares parameter optimization method. The program may be used to solve the inverse problem by fitting mathematical solutions of theoretical transport models, based upon the the convection-dispersion equation (CDE), to experimental results. This approach allows parameters in the transport models to be quantified. The program may also be used to solve the direct or forward problem to determine the concentration as a function of time and /or position.
Three different one-dimensional transport models are included: (i) the conventional CDE; (ii) the chemical and physical nonequilibrium CDE; and (iii) a stochastic stream tube model based upon the local-scale CDE with equilibrium or nonequilibrium adsorption. The two independent stochastic parameters in the stream-tube model are the pore water velocity, and either the dispersion coefficient, the distribution coefficient, or the nonequilibrium rate parameter. These pairs of stochastic parameters are described with a bivariate lognormal probability density function (pdf).

II. Technical Information

II.1 Executables:

Operating System(s):

II.2 Source-code:

Programming Language(s): ANSI standard FORTRAN 77 The source code is available upon request from the authors, please email:jsimunek@ussl.ars.usda.gov or : wrussell@ussl.ars.usda.gov The program comes with a user manual giving adetailed description of the computer program, including the subroutines used toevaluate the analytical solutions for optimizing model parameters. Input andoutput files for all major problems are also included in the manual.

II.3 Manuals:

(see Source-code)

II.4 Data:

(see Source-code)

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

Toride, N., Leij, F.J., van Genuchten M.Th., 1995.The CXTFIT code for estimating transport parameters from laboratory or field tracer experiments, Version 2.0. Research Report No. 137, 121 p., U.S. Salinity Laboratory, USDA, ARS, Riverside, California.
Parker, J.C., van Genuchten M.Th., 1984.Determining transport parameters from laboratory or field tracer experiments, Bull. 84-3, Va. Agric.Exp.St., Blacksburg.

V. Further information in the World-Wide-Web

VI. Additional remarks

Last review of this document by: T. Gabele : 7. 7. 1997 -
Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:41 CEST 2002

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