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    What's New with HYDRUS Version 1.02?

    The HYDRUS Model

    HYDRUS Levels

    HYDRUS User Interface

    Automatic FE-Mesh Generation in HYDRUS

    HYDRUS Post-Processing

    Two-Dimensional HYDRUS Examples Distributed With the Model

    Three-Dimensional HYDRUS Examples Distributed with the Model

    Other Existing HYDRUS Applications

    HYDRUS System Requirements

What's New with HYDRUS Version 1.02?

• HYDRUS installation program has been optimized for Windows Vista
• Colors for graphical display of Materials, Sub-regions and Anisotropy can now be customized within the groundwater model HYDRUS
• New option for importing domain geometry from a text file in HYDRUS; there is a new key word that allows for the import of thickness variables with multiple sub-layers with variable thickness into the groundwater model

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The HYDRUS Model

HYDRUS is a Windows based modeling environment for analysis of groundwater flow and solute transport in variably saturated porous media. Computational finite element models are included in HYDRUS for simulating both 2D and 3D transport of water, heat and solutes in variably saturated media. A parameter optimization algorithm is also available in HYDRUS for inverse modeling of soil hydraulic and/or solute transport parameters. HYDRUS is also supported by an interactive graphics-based interface for data pre-processing, generation of structured and unstructured finite element mesh, and graphic presentation of the result

The HYDRUS program is a finite element model for simulating the two- and three-dimensional movement of water, heat, and multiple solutes in variably saturated media. The HYDRUS program numerically solves the Richards equation for saturated-unsaturated water flow and convection-dispersion type equations for heat and solute transport. The flow equation in HYDRUS incorporates a sink term to account for water uptake by plant roots. The heat transport equation in HYDRUS considers movement by conduction as well as convection with flowing water. The governing convection-dispersion solute transport equations in HYDRUS are written in a very general form by including provisions for nonlinear nonequilibrium reactions between the solid and liquid phases, and linear equilibrium reaction between the liquid and gaseous phases. Hence, both adsorbed and volatile solutes such as pesticides can be considered. The solute transport equations in HYDRUS also incorporate the effects of zero-order production, first-order degradation independent of other solutes, and first-order decay/production reactions that provides the required coupling between the solutes involved in the sequential first-order chain. The HYDRUS transport model also accounts for convection and dispersion in the liquid phase, as well as for diffusion in the gas phase, thus permitting one to simulate solute transport simultaneously in both the liquid and gaseous phases. HYDRUS at present considers up to fifteen solutes which can be either coupled in a unidirectional chain or may move independently of each other. Physical nonequilibrium solute transport within HYDRUS can be accounted for by assuming a two-region, dual porosity type formulation which partition the liquid phase into mobile and immobile regions. HYDRUS also includes attachment/detachment theory, including the filtration theory, to simulate transport of viruses, colloids, and/or bacteria.

HYDRUS may be used to analyze water and solute movement in unsaturated, partially saturated, or fully saturated porous media. HYDRUS can handle flow domains delineated by irregular boundaries. The flow region itself in HYDRUS may be composed of nonuniform soils having an arbitrary degree of local anisotropy. Flow and transport can occur in the vertical plane, the horizontal plane, a three-dimensional region exhibiting radial symmetry about a vertical axis, or in a three-dimensional region in HYDRUS.

The water flow part of HYDRUS can deal with (constant or time-varying) prescribed head and flux boundaries, as well as boundaries controlled by atmospheric conditions. Soil surface boundary conditions in HYDRUS may change during the simulation from prescribed flux to prescribed head type conditions (and vice versa). HYDRUS can also handle a seepage face boundary through which water leaves the saturated part of the flow domain, and free drainage boundary conditions. Nodal drains are represented in HYDRUS by a simple relationship derived from analog experiments.

For solute transport HYDRUS supports both (constant and varying) prescribed concentration (Dirichlet or first-type) and concentration flux (Cauchy or third-type) boundaries. The dispersion tensor in HYDRUS includes a term reflecting the effects of molecular diffusion and tortuosity.

The unsaturated soil hydraulic properties of HYDRUS are described using van Genuchten [1980], Brooks and Corey [1964], Durner [1994], Kosugi [1995], and modified van Genuchten type analytical functions. Modifications for HYDRUS were made to improve the description of hydraulic properties near saturation. The HYDRUS code incorporates hysteresis by using the empirical model introduced by Scott et al. [1983] and Kool and Parker [1987]. HYDRUS assumes that drying scanning curves are scaled from the main drying curve, and wetting scanning curves from the main wetting curve. As an alternative, HYDRUS also incorporated the hysteresis model of Lenhard et al. [1991] and Lenhard and Parker [1992] that eliminates pumping by keeping track of historical reversal points. HYDRUS also implements a scaling procedure to approximate hydraulic variability in a given soil profile by means of a set of linear scaling transformations which relate the individual soil hydraulic characteristics to those of a reference soil.

The governing equations in HYDRUS are solved numerically using a Galerkin type linear finite element method applied to a network of triangular elements. Integration in time in HYDRUS is achieved using an implicit (backwards) finite difference scheme for both saturated and unsaturated conditions. HYDRUS' resulting equations are solved in an iterative fashion, by linearization and subsequent Gaussian elimination for banded matrices, a conjugate gradient method for symmetric matrices, or the ORTHOMIN method for asymmetric matrices. Additional measures are taken to improve HYDRUS' solution efficiency in transient problems, including automatic time step adjustment and checking if the Courant and Peclet numbers do not exceed preset levels. The water content term in HYDRUS is evaluated using the mass-conservative method proposed by Celia et al. (1990). To minimize numerical oscillations upstream weighing is included in HYDRUS as an option for solving the transport equation. In addition, HYDRUS implements a Marquardt-Levenberg type parameter estimation technique for inverse estimation of selected soil hydraulic and/or solute transport and reaction parameters from measured transient or steady-state flow and/or transport data (only in 2D). The procedure permits several unknown parameters to be estimated from observed water contents, pressure heads, concentrations, and/or instantaneous or cumulative boundary fluxes (e.g., infiltration or outflow data) within HYDRUS. Additional retention or hydraulic conductivity data, as well as a penalty function for constraining the optimized parameters to remain in some feasible region (Bayesian estimation), can be optionally included in HYDRUS in the parameter estimation procedure. A new module simulating the biochemical transformation and degradation processes in subsurface-flow constructed wetlands was developed for two-dimensional applications of HYDRUS (Langergraber and Simunek, 2005). This module considers the biochemical degradation and transformation processes for three fractions of organic matter (readily- and slowly-biodegradable, and inert), four nitrogen compounds (ammonium, nitrite, nitrate, and dinitrogen), inorganic phosphorus, and heterotrophic and autotrophic micro-organisms, and dissolved oxygen.

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HYDRUS Levels

HYDRUS is distributed in five different versions (Levels) so that users are provided with the flexibility of acquiring only that segment of the software that is most appropriate for their application. Users can select software limited to general two-dimensional applications (the 2D-Standard Level, which corresponds with former HYDRUS-2D with MeshGen-2D) or for both two- and three-dimensional applications (i.e., the general two-dimensional base and layered third dimension, 3D-Standard). Users can also opt for relatively simple and more complex geometries in HYDRUS (two-dimensional rectangular geometries – 2D-Lite (which corresponds with former HYDRUS-2D without MeshGen-2D) or three-dimensional hexahedral geometries – 3D-Standard). We expect to release a version of HYDRUS in summer of 2007 that will accommodate general three-dimensional geometries (3D-Professional). Users are able to upgrade to higher HYDRUS Levels, as well as from older software (HYDRUS-2D or HYDRUS-2D/MESHGEN-2D) to any new HYDRUS Level.

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HYDRUS User Interface

A Microsoft Windows based Graphical User Interface (GUI) manages inputs required to run HYDRUS, as well as grid design and editing, parameter allocation, problem execution, and visualization of results. HYDRUS includes a set of controls that allows the user to build a flow and transport model, and to perform graphical analyses on the fly. Both input and output in HYDRUS can be examined using areal or cross-sectional views, and line graphs. 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 HYDRUS and determines which other optional tools are necessary for a particular application. The module contains a project manager and both the pre-processing and post-processing units. The pre-processing 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.

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Automatic FE-Mesh Generation in HYDRUS

Data preprocessing in HYDRUS involves specification of the two-dimensional flow region having an arbitrary continuous shape bounded by polylines, arcs and splines, discretization of domain boundaries, and subsequent generation of an unstructured finite element mesh. HYDRUS (Standard Levels) comes with an optional mesh generation program Meshgen that generates unstructured finite element mesh for two-dimensional domains. This program, based on Delaunay triangulation, is seamlessly integrated in the HYDRUS environment. In the absence of the Meshgen program, the HYDRUS GUI provides an option for automatic construction of simple, structured grids (Lite Levels). The third dimension is in both HYDRUS Lite and HYDRUS Stadard levels developed by adding specified number of layers of equal or different thicknesses.

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HYDRUS Post-Processing

Output graphics in HYDRUS include 2D contours (isolines or color spectra) in areal or cross-sectional view for heads, water contents, velocities, concentrations, and temperatures. HYDRUS output also includes velocity vector plots, color edges, color points, animation of graphic displays for sequential time-steps, and line-graphs for selected boundary or internal sections. The post-processing unit of HYDRUS also includes 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. Areas of interest can be zoomed into, and vertical scale can be enlarged for cross-sectional views. The HYDRUS mesh can be displayed with boundaries, and numbering of triangles, edges and points. Observation points can be added anywhere in the grid. Viewing of grid and/or spatially distributed results from HYDRUS (pressure head, water content, velocity, or concentration) is facilitated using high resolution color or gray scales. Extensive context-sensitive, online HYDRUS Help is part of the interface.

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Two-Dimensional HYDRUS Examples Distributed With the Model

• Column infiltration test
• Water flow and solute Transport in a field soil profile under grass - seasonal simulation
• Two-dimension unidirectional solute transport - comparison with analytical solution
• One-dimensional solute transport with nitrification chain - comparison with analytical solution
• One-dimensional solute transport with nonlinear cation adsorption - Data from Selim et al. (1987)
• One-dimensional solute transport with non-equilibrium cation adsorption
• Axisymetrical three-dimensional water and solute infiltration test
• One-dimensional water flow with multiple hysteretic loops, data from Lenhard et al. (1991)
• Water flow and solute transport from furrow to a drain
• Three wetland examples

• Parameter estimation from a cone penetrometer experiment (Gribb et al., 1987) Parameter estimation from a tension disc infiltrometer experiment (Simunek et al., 1998)

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Three-Dimensional HYDRUS Examples Distributed with the Model

• Column infiltration test
• Water flow and solute Transport in a field soil profile under grass - seasonal simulation
• Three-dimension unidirectional solute transport - comparison with analytical solution
• One-dimensional solute transport with nitrification chain - comparison with analytical solution
• One-dimensional solute transport with nonlinear cation adsorption - Data from Selim et al. (1987)
• One-dimensional solute transport with non-equilibrium cation adsorption
• One-dimensional solute transport with first-order attachment
• One-dimensional water flow with multiple hysteretic loops, data from Lenhard et al. (1991)
• Three-dimensional contaminant transport from a waste disposal site
• Three-dimensional flow and transport through a dike with a seepage face and root water uptake

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Other Existing HYDRUS Applications

• Irrigation management
• Drip irrigation design
• Sprinkler irrigation design
• Tile drainage design - flow to a drainage system
• Crop grow models, i.e., cotton model
• Salinization and reclamation processes, salt leaching
• Movement of pesticides; nonpoint source pollution
• Seasonal simulation of water flow and plant response

• Deep percolation beneath final closure cap designs for radioactive waste management sites at the Nevada test site
• Flow around nuclear subsidence craters at the Nevada test site
• Capillary barrier at the Texas low-level radioactive waste disposal site
• Evaluation of approximate analytical analysis of capillary barriers
• Landfill covers with and without vegetation
• Risk analysis of contaminant plume from landfills
• Seepage of wastewater from land treatment systems
• Tunnel design - flow around buried objects
• Highway design - road construction - seepage
• Stochastic theory - solute transport in heterogeneous media
• Lake basin recharge analysis
• Interaction between groundwater aquifers and streams
• Environmental impact of the drawdown of shallow water tables
• Analysis of cone permeameter and tension infiltrometer experiments

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HYDRUS System Requirements

• Operating System Windows NT 4.0 (SP3 or higher) / 2000 / XP
• X86 CPU with 1 GHz
• 512 MB RAM
• 10 GB total hard disk capacity with about 500 MB reserved for installation
• Graphic card with a resolution of 1024 x 768 pixels

To use HYDRUS comfortably for calculation of 3D models, we recommend the following system requirements:

• Operating System Windows 2000 / XP
• X86 CPU (Intel or AMD) with 3 GHz
• 1,024 MB memory
• 80 GB hard disk capacity
• Graphic card with OpenGL hardware acceleration

HYDRUS runs on these systems but we do not guarantee error-free functionality of the program on these OS.

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HYDRUS Summary

HYDRUS New Features