HYDRUS-2D is a finite element model for simulating the two-dimensional movement of water, heat and multiple solutes in unsaturated, partially-saturated or fully-saturated media.  

The software package also includes a parameter optimization module for inverse estimation of soil hydraulic parameters and solute transport parameters.  The model is supported by an interactive graphics interface for data preprocessing and comprehensive presentation of results.  The modeling environment may optionally include a mesh generator, MESHGEN-2D, for unstructured finite element grids.

Extensive context-sensitive, online Help is part of the interface.  

Water Flow:

• The program numerically solves Richards' Equation for variably saturated water flow
• The flow equation includes a sink term to account for water uptake by plant roots
• Boundary conditions can be constant / time-varying hydraulic head or flux or boundaries controlled by atmospheric conditions.  The code can also handle seepage face boundaries and free drainage boundary conditions.

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Heat and Solute Transport:

• The program applies Fickian-base advection-dispersion equations for heat and solute transport
• Heat transport equation considers both conduction and convection
• Solute transport equations consider:
  • advective-dispersive transport in the liquid phase
  • diffusion in the gaseous phase
  • nonlinear and/or nonequilibrium reactions between the solid and liquid phases
  • linear equilibrium reactions between the liquid and gaseous phases
  • zero order production
  • two first-order degradation reactions:
    • degradation reactions independent of other solutes
    • degradation reactions which couple the solutes involved in sequential first-order decay reactions
• The solute transport code supports constant / time varying concentration and concentration flux boundary conditions

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

• Nonagricultural
  • Risk analysis of contaminant plumes
  • Tunnel design - flow around burried objects
  • Highway design - road construction - seepage
  • Stochastic theory - solute transport in heterogeneous media
  • Lake basin recharge analysis
  • Interaction between groundwater aquifers and streams
  • Environmental impacts of drawdown of shallow water tables
  • Analysis of cone permeameter and tension infiltrometer experiments

HYDRUS-2D Key Features:

Developers:  J.Simunek, M.Th. van Genuchten (U.S. Salinity Laboraty, USDA/ARS, Riverside, California)and M. Sejna (PC Progress, Prauge, Czech Republic)

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• The program can be used on its own or with the programs HYDRUS-2D and CochemFlow.  
• MESHGEN-2D enables automatic mesh generation based on Delaunay triangulation.  
• All information about a mesh can be exported to a text file in described simple format.
• The MESHGEN-2D user interface is intuitive and easy to learn.

Meshgen-2D enables the design of 2D meshes constructed from arbitrary continuous shapes bounded by poly-lines, arcs and splines.  The domain can have any number of holes, internal curves or internal points.  All geometric objects can be entered and edited graphically or numerically and coordinates of very complicated shapes can be imported from other programs. 

The mesh can be refined along any nodes or curves and meshes can be very fine, the mesh size is virtually unlimited allowing more than 2,000,000,000 triangles.

This feature enables the user to define the degree of mesh anisotropy in a general direction.  This feature is useful when a different spatial step is required in the X and Y-directions.

Several options are available to optimize mesh smoothness, default values usually yield good results but the user is given the option to change these values.

Periodical Boundary Conditions 

Boundary conditions can be defined on two parts of a boundary curve that are exactly the same and differ from each other just by a vector of translation.  The periodical condition requires a special mesh points distribution along the boundary; each point must have a corresponding ‘periodical point’ and their positions differ by the vector of periodical translation.  If the user specifies periodical conditions, the program automatically checks and corrects the mesh to satisfy these periodical conditions. 

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HYDRUS-1D is a finite element model; it numerically solves the Richards’ equation for variably saturated water flow and Fickian-based advection-dispersion equations for heat and solute transport.  The model includes a parameter optimization algorithm for inverse estimation of a variety of soil hydraulic and/or solute transport parameters.  The model is supported by an interactive graphics-based interface for data-preprocessing, discretization of the soil profile and graphic presentation of results.

Key Features:

Heat and Solute Transport:  The heat transport equation considers conduction as well as convection with flowing water.  The solute transport equations consider advective-dispersive transport in the liquid phase, and diffusion in the gaseous phase.  The transport equations also include nonlinear and/or 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.   The solute transport code supports constant and temporally variable user-defined concentration (first-type) and concentration flux (third-type) boundary conditions. 

Hysteresis:  The HYDRUS-1D code includes an empirical model which incorporates hysteresis by scaling new drying or wetting scanning curves from the main drying or wetting curve. 

Unsaturated soil hydraulic properties: The unsaturated soil hydraulic properties are described using van Genuchten, Brooks and Corey and modified van Genuchten type analytical functions. 

Hydraulic variability: The hydraulic variability within a given soil profile is approximated using a scaling procedure through a set of linear transformations which relate the individual soil hydraulic characteristics to those of a reference soil.  

Parameter Estimation:  HYDRUS-1D uses a Marquardt-Levenberg type parameter estimation technique for reverse estimation of selected soil hydraulic and/or solute transport and reaction parameters from measured transient or steady-state flow and/or transport data.  The procedure allows several unknown parameters to be estimated from observed water contents, pressure heads, concentrations and/or instantaneous or cumulative boundary fluxes  (i.e. infiltration or outflow data).

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User Interface:

·        A Microsoft Windows-based graphical user interface manages the input data required to run HYDRUS-1D, as well as for nodal discretization and editing, parameter allocation, problem execution and visualization of results.

·        All spatially distributed parameters, such as soil type, soil layer, root water uptake distribution and the initial conditions for water, heat and solute movement, are specified in a graphical environment.

·        A user can optimize the thickness of different elements by graphically editing the location of discretization nodes.

·        Both input and output can be examined using graphical tools.

·        The HYDRUS-1D shell program translates all geometric and parameter data into the HYDRUS input form. 

·        Post-processing is also carried out in the shell.  Graphical output includes:  distribution of the pressure head, water content, water and solute exchange fluxes, root water uptake, temperature and the concentration in the soil profile at predetermined times.  Output also includes variable-vs-time plots, such as actual, potential and cumulative fluxes across boundaries or leaving the root zone.

·        Observation points can be added anywhere in the profile to obtain graphical output for the water content, pressure head, temperature and/or concentration.

·        Extensive context-sensitive, online Help is part of the interface.  

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