Environmental Software Online, LLC / Groundwater Software

Version 1.02 - HYDRUS 2D/3D Program Software


AquaChem is a complete system for water quality data analysis, plotting, reporting and modeling! HYDRUS 2D/3D 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 2D/3D. New option for importing domain geometry from a text file in HYDRUS 2D/3D; 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.

HYDRUS 2D/3D 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 2D/3D 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 2D/3D for inverse modeling of soil hydraulic and/or solute transport parameters. HYDRUS 2D/3D 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 2D/3D 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 2D/3D 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 2D/3D incorporates a sink term to account for water uptake by plant roots. The heat transport equation in HYDRUS 2D/3D considers movement by conduction as well as convection with flowing water. The governing convection-dispersion solute transport equations in HYDRUS 2D/3D 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 2D/3D 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 2D/3D 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 2D/3D 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 2D/3D can be accounted for by assuming a two-region, dual porosity type formulation which partition the liquid phase into mobile and immobile regions. HYDRUS 2D/3D also includes attachment/detachment theory, including the filtration theory, to simulate transport of viruses, colloids, and/or bacteria.

HYDRUS 2D/3D may be used to analyze water and solute movement in unsaturated, partially saturated, or fully saturated porous media. HYDRUS 2D/3D can handle flow domains delineated by irregular boundaries. The flow region itself in HYDRUS 2D/3D 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 2D/3D.

The water flow part of HYDRUS 2D/3D 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 2D/3D may change during the simulation from prescribed flux to prescribed head type conditions (and vice versa). HYDRUS 2D/3D 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 2D/3D by a simple relationship derived from analog experiments.

For solute transport HYDRUS 2D/3D supports both (constant and varying) prescribed concentration (Dirichlet or first-type) and concentration flux (Cauchy or third-type) boundaries. The dispersion tensor in HYDRUS 2D/3D includes a term reflecting the effects of molecular diffusion and tortuosity.

The unsaturated soil hydraulic properties of HYDRUS 2D/3D are described using van Genuchten [1980], Brooks and Corey [1964], Durner [1994], Kosugi [1995], and modified van Genuchten type analytical functions. Modifications for HYDRUS 2D/3D were made to improve the description of hydraulic properties near saturation. The HYDRUS 2D/3D code incorporates hysteresis by using the empirical model introduced by Scott et al. [1983] and Kool and Parker [1987]. HYDRUS 2D/3D 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 2D/3D 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 2D/3D 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 3D are solved numerically using a Galerkin type linear finite element method applied to a network of triangular elements. Integration in time in HYDRUS 3D is achieved using an implicit (backwards) finite difference scheme for both saturated and unsaturated conditions. HYDRUS 2D/3D' 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 2D/3D' 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 2D/3D as an option for solving the transport equation. In addition, HYDRUS 2D/3D 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 2D/3D. 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 2D/3D 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 2D/3D (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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