Program Overview
HYDRUS is 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 included to enable simulations of the 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. The program can handle flow regions delineated by irregular boundaries. The flow region itself may be composed of nonuniform soils having an arbitrary degree of local anisotropy. Flow and transport can occur in a two-dimensional vertical or horizontal plane, a three-dimensional region exhibiting radial symmetry about the vertical axis, or a fully three-dimensional domain. The two-dimensional part of this 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 the Technical Manual [Šimůnek et al., 2018].
Version 3.0 includes additional specialized add-on modules:
the DualPerm module for simulating two-dimensional variably-saturated water movement and solute transport in dual-permeability porous media, i.e., preferential and nonequilibrium water flow and solute transport [Gerke and van Genuchten, 1993a; Šimůnek et al., 2003; Šimůnek and van Genuchten, 2008], |
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The Wetland Module (for two-dimensional problems only) was developed to model biochemical transformation and degradation processes in subsurface flow constructed wetlands. In the wetland module two biokinetic model formulations can be chosen: (1) the biokinetic model as described in CW2D [Langergraber and Šimůnek, 2005, 2006, 2011] and (2) the CWM1 (Constructed Wetland Model #1) biokinetic model [Langergraber et al., 2009]. In CW2D aerobic and anoxic transformation and degradation processes for organic matter, nitrogen and phosphorus are described, whereas in CWM1 aerobic, anoxic and anaerobic processes for organic matter, nitrogen and sulphur. |
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The Major Ion Chemistry Module [UNSATCHEM; Šimůnek and Suarez, 1994] can be used instead of the standard solute transport module. Detailed description of the UNSATCHEM Module is given in the UNSATCHEM user manual [Šimůnek et al., 2012c]. More detailed description of concepts used in the UNSATCHEM module is provided in the HYDRUS-1D manual [Šimůnek et al., 2008], which provides all relevant information about the one-dimensional version of this module. |
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The C-Ride module simulates two-dimensional variably-saturated water flow, colloid transport, and colloid-facilitated solute transport in porous media. The module accounts for transient variably-saturated water flow, and for both colloid and solute movement due to advection, diffusion, and dispersion, as well as for solute movement facilitated by colloid transport. Detailed description of the C-Ride Module is given in the C-Ride user manual [Šimůnek et al., 2012b]. |
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The HP2 module is the result of coupling Hydrus (its two-dimensional part) with the PHREEQC geochemical code [Parkhurst and Appelo, 1999], and corresponds to a similar one-dimensional module HP1 [Jacques and Šimůnek, 2005, 2010; Jacques et al., 2006, 2008]. HP2 has, apart from the dimensionality (2D), the same capabilities as HP1. HP2 contains modules simulating (1) transient water flow, (2) the transport of multiple components, (3) mixed equilibrium/kinetic biogeochemical reactions, and (4) heat transport in two-dimensional variably-saturated porous media (soils). Detailed description of the HP2 Module is given in the HP2 user manual [Šimůnek et al., 2012a]. |
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The Slope Classic add-on module uses results obtained by HYDRUS (i.e., relative saturations and water fluxes) for subsequent slope-stability analyses. The module is intended mainly for stability tests of embankments, dams, earth cuts, and anchored sheeting structures. The influence of water is modeled using the distribution of pore pressure, which is imported automatically from HYDRUS runs into the SLOPE module at specified times, each of which can be analyzed separately. The slip surface in the SLOPE module is considered to be circular, and is evaluated using the Bishop, Fellenius/Petterson, Morgenstern-Price or Spencer method [Lu and Godt, 2013]. More details can be found in the user manual of this module. |
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While the Slope Classic module (added in version 2.04) is based on classical engineering soil mechanics theories and uses the effective stress approach only for saturated conditions, the new add-on module "Slope Cube" (Slope Stress and Stability) was developed to provide a unified effective stress approach for both saturated and unsaturated conditions [Lu et al., 2010]. The module is intended to predict spatially and temporally infiltration-induced landslide initiation and to carry out slope stability analyses under variably-saturated soil conditions. Transient moisture and pressure head fields are directly obtained from the HYDRUS-2D model, and subsequently used to compute the effective stress field of hillslopes [Lu and Godt, 2013]. Furthermore, instead of the methodology of one-slope for one factor safety in the classical slope stability analysis, the SLOPE Cube module computes fields of the factor of safety in the entire domain within hillslopes [Lu et al., 2012], thus allowing identification of the development of potential failure surface zones or surfaces. |
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HyPar is a parallelized version of the standard two-dimensional and three-dimensional HYDRUS computational modules (h2d_calc.exe and h3d_calc.exe). HyPar uses parallel programming tools and techniques to take advantage of multiple cores and to accelerate calculations on multi-core processor computers. HyPar currently supports only calculations in the direct mode (does not support the inverse mode), and it does not support any add-on modules (e.g., HP2, UnsatChem, Wetland, and/or C-Ride). The HyPar module is initialized on the Program Tab of the Program Options dialog window. |
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The Furrow module is a hybrid Finite Volume – Finite Element (FV-FE) model that describes the coupled surface-subsurface flow and transport processes occurring during furrow irrigation and fertigation [Brunetti et al., 2018]. The numerical approach combines a one-dimensional description of water flow and solute transport in an open channel with a two-dimensional description of water flow and solute transport in a subsurface soil domain. |
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 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 appropriate for relatively complex two-dimensional and three-dimensional domains, a small catalog of soil hydraulic properties, and the 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 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.
Technical aspects of the HYDRUS software package such as the governing equations and details about the invoked numerical techniques are documented in the Technical Manual [Šimůnek et al., 2018]. The Graphical User Interface of the HYDRUS software package is documented in a separate User Manual [Šejna et al., 2018].
The current version 3.0 significantly further expands capabilities of versions 1.0 and 2.0. See a more detailed description of New Features in Version 2.0 and New Features in Version 3.0.