THE HYDRUS-1D SOFTWARE PACKAGE FOR SIMULATING THE ONE-DIMENSIONAL MOVEMENT OF WATER, HEAT, AND MULTIPLE SOLUTES IN VARIABLY-SATURATED MEDIA

Authors: SIMUNEK, JIRKA - UC RIVERSIDE, CA; Van Genuchten, Martinus; SEJNA, M - UC RIVERSIDE, CA

Submitted to: University of California-Riverside Research Reports
Publication Type: Other
Publication Acceptance Date: 3/1/2005
Publication Date: 4/1/2005
Citation: Simunek, J., Van Genuchten, M.T., Sejna, M. 2005. The HYDRUS-1D software package for simulating the one-dimensional movement of water, heat, and multiple solutes in variably-saturated media. University of California-Riverside Research Reports. pp. 240.

Interpretive Summary: There is growing concern about the fate and transport of agricultural chemicals (salts, pesticides, pathogenic micro-organisms, fertilizers, heavy metals) in soil and groundwater systems. Computer models are now increasingly used to predict the future behavior of these chemicals, and to study alternative soil and water management practices aimed at reducing groundwater pollution while optimizing crop yield. This report documents version 3.0 of HYDRUS-lD, a software package for simulating water, heat and solute movement in the unsaturated zone between the soil surface and the groundwater table. The software consists of the modified HYDRUS computer program, and the HYDRUS 1 D interactive graphics-based user interface. HYDRUS numerically solves the governing equations for water, heat and solute movement. The program considers water uptake by plant roots, transpiration by a crop, evaporation from the soil surface, solute adsorption by the soil's solid phase, and solute degradation, among many other features. One new feature of the current version 3.0 is the possible simulation of preferential flow by means of a two-region (or dual-porosity) type formulation which partitions the liquid phase into mobile and immobile regions. Alternatively, the transport equations can also include provisions for kinetic attachment/detachment of solute to the solid phase, and as such can be used to simulate the transport of viruses, colloids, or bacteria. The HYDRUS software package further includes modules for simulating carbon dioxide and major ion solute transport. HYDRUS additionally includes a parameter optimization algorithm for inverse estimation of soil hydraulic and/or solute transport and reaction parameters from measured transient or steady-state flow and/or transport data. This publication serves as both a user manual and reference document. Detailed instructions are given for data input preparation. The graphics-based user interface, HYDRUS-lD, facilitates easy data preparation and output display in the MS Windows environment. 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 3.0 of HYDRUS-lD, a software package for simulating water, heat and solute movement in one-dimensional variably saturated media. The software consists of the HYDRUS computer program, and the HYDRUS ID interactive graphics-based user interface. The HYDRUS program numerically solves the Richards equation for variably saturated water flow and convection-dispersion type equations for heat and solute transport. The flow equation incorporates a sink term to account for water uptake by plant roots. The flow equation may also consider dual-porosity-type flow with a fraction of the water content being mobile, and a fraction being immobile. The heat transport equation considers transport due to conduction and convection with flowing water. The solute transport equations consider convective 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: one which is independent of other solutes, and one which provides the coupling between solutes involved in sequential first-order decay reactions. In addition, physical nonequilibrium solute transport can be accounted for by assuming a two-region, dual-porosity type formulation which partition the liquid phase into mobile and immobile regions. Alternatively, the transport equations include provisions for kinetic attachment/detachment of solute to the solid phase and thus can be used to simulate the transport of viruses, colloids, or bacteria. The HYDRUS software package also includes modules for simulating carbon dioxide and major ion solute movement. The major ion chemical module accounts for equilibrium chemical reactions such as complexation, cation exchange and precipitation-dissolution. Precipitation-dissolution of calcite and dissolution of dolomite are simulated using either equilibrium or multicomponent kinetic expressions. The program may be used to analyze water and solute movement in unsaturated, partially saturated, or fully saturated porous media. The flow region may be composed of nonuniform soils. Flow and transport can occur in the vertical, horizontal, or a generally inclined direction. The water flow part of the model can deal with prescribed head and flux boundaries, boundaries controlled by atmospheric conditions, as well as free drainage boundary conditions. The governing flow and transport equations are solved numerically using Galerkin-type linear finite element schemes. HYDRUS 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 flow and/or transport data. This report serves as both a user manual and reference document. Detailed instructions are given for data input preparation. A graphical user interface, HYDRUSID, for easy data preparation and output display in the MS Windows environment is described in the second part of the manual.