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Title: The HYDRUS Software Package for Simulating Two- and Three-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, User Manual, Version 1.0

Author
item SIMUNEK, JIRKA
item SEJNA, M
item Van Genuchten, Martinus

Submitted to: University of California-Riverside Research Reports
Publication Type: Other
Publication Acceptance Date: 2/16/2006
Publication Date: 3/24/2006
Citation: Simunek, J., Sejna, M., Van Genuchten, M.T. 2006. The HYDRUS Software Package for Simulating Two- and Three-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, User Manual, Version 1.0. University of California-Riverside Research Reports. 161 pp.

Interpretive Summary: Computer models are now increasingly used to predict the fate and transport of a range of agricultural and other chemicals (salts, nutrients, pesticides, pathogenic micro-organisms, fertilizers, heavy metals) in the subsurface, and to study alternative soil and water management practices aimed at reducing groundwater pollution. This report documents version 1.0 of the Graphical User Interface of HYDRUS, a software package for simulating two- and three-dimensional water, heat, and solute movement in the subsurface. The code is especially suited for simulating transport processes in the unsaturated (vadose zone) between the soil surface and the groundwater table. It considers such processes water uptake by plant roots, transpiration by a crop, evaporation from the soil surface, nonlinear or nonequilibrium solute adsorption onto the solid phase, transport of solutes involved in consecutive decay chains (e.g., for nitrification-denitrification), and colloid and virus transport. The software package consists of a computational computer program, and an interactive graphics-based user interface (GUI). Details of the various processes and features included in HYDRUS are provided in a separate Technical Manual. The main program unit of the GUI defines the overall computational environment of the system. This main module controls execution of the program and determines which other optional modules are necessary for a particular application. The main module contains a project manager and both the pre-processing and post-processing units. The preprocessing unit includes specification of all necessary parameters to successfully run the HYDRUS Fortran codes, grid generators for relatively simple rectangular and hexahedral transport domains, a grid generator for unstructured finite element meshes for complex two-dimensional domains, and catalogs for generating the soil hydraulic properties. The post-processing unit provides such output as distributions versus time of a particular variable at selected observation points, and actual or cumulative water and solute fluxes across boundaries of a particular type. The post-processing unit also includes options to present results of a particular simulation by means of contour maps, isolines, spectral maps, and velocity vectors, and/or animation. This report serves as a User Manual and reference document of the Graphical User Interface of HYDRUS. The model provides theoretical and applied scientists and engineers with a much-needed tool for predicting water and chemical transport in the subsurface.

Technical Abstract: This report documents version 1.0 of the Graphical User Interface of HYDRUS, a software package for simulating water, heat, and solute movement in two- and three- dimensional variably saturated media. The software package consists of a computational computer program, and an interactive graphics-based user interface. The HYDRUS program numerically solves the Richards equation for variably saturated water flow and advection-dispersion equations for both heat and solute transport. The flow equation incorporates a sink term to account for water uptake by plant roots. The heat transport equation considers transport due to conduction and convection with flowing water. The solute transport equations consider advective-dispersive transport in the liquid phase, as well as diffusion in the gaseous phase. The transport equations also include provisions for nonlinear nonequilibrium reactions between the solid and liquid phases, linear equilibrium reactions between the liquid and gaseous phases, zero-order production, and two first-order degradation reactions. In addition, physical nonequilibrium solute transport can be accounted for by assuming a two-region, dual-porosity type formulation which partitions the liquid phase into mobile and immobile regions. Attachment/detachment theory, including filtration theory, is additionally considered to enable simulations of the transport of viruses, colloids, and/or bacteria. The two-dimensional part of the program also includes a Marquardt-Levenberg type parameter optimization algorithm for inverse estimation of soil hydraulic and/or solute transport and reaction parameters from measured transient or steady-state data for two dimensional problems. Details of the various processes and features included in HYDRUS are provided in a separate Technical Manual. The main program unit of the HYDRUS Graphical User Interface (GUI) defines the overall computational environment of the system. This main module controls execution of the program and determines which other optional modules are necessary for a particular application. The module contains a project manager and both the pre-processing and post-processing units. The preprocessing unit includes specification of all necessary parameters to successfully run the HYDRUS FORTRAN codes, grid generators for relatively simple rectangular and hexahedral transport domains, a grid generator for unstructured finite element meshes for complex two-dimensional domains, a small catalog of soil hydraulic properties, and a Rosetta Lite program for generating soil hydraulic properties from soil textural data. The post-processing unit consists of simple x-y graphics for graphical presentation of soil hydraulic properties, as well as such output as distributions versus time of a particular variable at selected observation points, and actual or cumulative water and solute fluxes across boundaries of a particular type. The post-processing unit also includes options to present results of a particular simulation by means of contour maps, isolines, spectral maps, and velocity vectors, and/or by animation using both contour and spectral maps. This report serves as a User Manual and reference document of the Graphical User Interface of the HYDRUS software package. Technical aspects such as governing equations and details about the invoked numerical techniques are documented in a separate Technical Manual.