HYDRUS is a Microsoft Windows based modeling environment for the analysis of water flow and solute transport in variably saturated porous media. The software package includes computational finite element models for simulating the one-, two-, and three-dimensional movement of water, heat, and multiple solutes in variably saturated media. The model includes a parameter optimization algorithm for inverse estimation of a variety of soil hydraulic and/or solute transport parameters (only for the standard modules). The model is supported by an interactive graphics-based interface for data-preprocessing, generation of structured and unstructured finite element mesh, and graphic presentation of the results. The program can be extended with a number of special add-on modules. HYDRUS version 5 was released in April 2022 and it merges two previously independent software packages HYDRUS-1D (version 4, for one-dimensional applications) and HYDRUS (2D/3D) (version 3, for two- and three-dimensional applications).
HYDRUS Editions / Levels
HYDRUS is distributed in multiple different versions (Editions / Levels) so that users may acquire only that segment of the software that is most appropriate for their application.
Users can select software limited to one-dimensional applications (the 1D-Standard Level), 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., 3D-Standard or 3D-Professional).
Users can also opt for relatively simple (two-dimensional rectangular geometries – 2D-Lite [which corresponds with former Hydrus-2D without MeshGen-2D] or three-dimensional hexahedral geometries – 3D-Lite) or more complex geometries (i.e., 2D-Standard for general two-dimensional geometries, 3D-Standard for problems that can be defined using the general two-dimensional base and a layered third dimension, or 3D-Professional for applications with general three-dimensional geometries). Users may upgrade to higher Levels from lower Levels, as well as from lower versions (e.g., version 1.x) to higher versions (e.g., version 2 (and higher - in the future)).
HYDRUS Editions and Their Features
| Feature Description | 1D Standard | 2D Lite | 2D Standard | 3D Lite | 3D Standard | 3D Professional |
|---|---|---|---|---|---|---|
| 1D Simple Domain | Yes | Yes | Yes | Yes | Yes | Yes |
| 2D Simple Domain, Structured FE-Mesh | No | Yes | Yes | Yes | Yes | Yes |
| 2D General Domain, Unstructured FE-Mesh | No | No | Yes | Yes | Yes | Yes |
| 3D Simple Domain, Structured FE-Mesh | No | No | No | Yes | Yes | Yes |
| 3D Layered Domain and FE-Mesh | No | No | No | No | Yes | Yes |
| 3D General Domain, Unstructured FE-Mesh | No | No | No | No | No | Yes |
Simple Domain 1D/2D/3D
The transport domain is defined using the one-dimensional profile or relatively simple two-dimensional rectangular or three-dimensional hexahedral objects. Dimensions and other parameters of the transport domain are specified numerically in the Domain Definition dialog window. In all these cases the transport domain is discretized into a structured finite element mesh.
In the Rectangular or Hexahedral Domain Definition dialog windows, users need to specify the vertical and horizontal dimensions of the transport domain, as well as a possible slope of the base of the domain in different directions. Nodes along the upper boundary may have variable z-coordinates. However, the lower boundary must always be horizontal (or have a specified slope), while the left and right boundary lines (sides) must be vertical.
2D General Domain
General Two-Dimensional Domains can be formed using one or more Surfaces that can touch each other, but cannot overlap. Each of the Surfaces is defined by a set of Boundary Curves that enclose the transport domain. All surfaces must lie in the same plane. Surfaces can contain openings, internal points, or internal curves. It is also possible to create an opening in a surface and then enter another surface into it.
An unstructured Finite Element Mesh is used to discretized 2D-General Domains. The very flexible unstructured finite element generator (MeshGen2D) can be used for virtually any type of complicated domain. The generator attempts to generate finite elements with the size defined using the parameter Targeted FE Size. This FE size can be further modified in different parts of the domain using various tools, such as Stretching in different directions to make the mesh anisotropic, specifying the Maximum and Minimum Numbers of Nodes on a Boundary Curve, or using Finite Element Mesh Refinement, that can be defined around Points, and for Lines and Surfaces.
3D Layered Domain
3D-Layered Domains are defined using a Base Surface (a General Two-Dimensional Domain, see the text above) and one or more Thickness Vectors. Thickness vectors do not have to be perpendicular to the Base Surface. The Domain can be divided into one or more Layers, which subdivide the domain into multiple, usually horizontal, Subdomains. These Layers can be used, for example, to keep constant thicknesses of selected horizons or constant discretization close to the soil surface. Relatively general three-dimensional domains, fulfilling the needs of most HYDRUS users, can be defined using the 3D-Layered Domains.
However, 3D-Layered Domains still have certain limitations. For example, Layers have to be continuous and some shapes cannot be directly considered (e.g., spheres). All these limitations are overcome in the most general option (Level) of HYDRUS, i.e., in 3D-General Domains (3D-Professional).
FE-Mesh in 3D Layered Domains
The Base Surface of the 3D-Layered Domains is discretized first using, as above for 2D-General Domains, the unstructured finite element mesh generator MeshGen2D. The same options as for 2D-General Domains, i.e., Targeted FE Size, Stretching, FE-Mesh Refinement (see the text with Figure 3 above), can be used when discretizing the Base Surface as well.
Discretization in the vertical (perpendicular to the Base Surface) direction follows Layers defined at Thickness Vectors. Users can specify the number of horizontal FE-Layers to discretize the Domain in the vertical direction. Users have high flexibility in defining the vertical spacing of FE-Layers, by specifying, for example, the relative sizes of elements at the top and the bottom, with element sizes then proportionally distributed.
3D General Domain
In the 3D-Professional version, the 3D General Domains (general three-dimensional domains) can be formed from three-dimensional objects (Solids) of general shapes. Three-dimensional objects (Solids) are formed using Boundary Surfaces, which can be either Planar Surfaces or Curved Surfaces (Quadrangle, Rotary, Pipe, B-Spline). Boundary Surfaces of a Solid must enclose a closed space and cannot intersect each other.
In more complicated cases it is also possible to use Intersections of Surfaces and Solids to create, in this way, openings in solids or to carry out with Solids various logical operations. Internal Solids, Cavities, and Integrated Objects can be defined as well.
FE-Mesh in 3D-General Domains
The mesh generator Genex/T3D is used to generate three-dimensional FE meshes for the 3D-General Domains. The generated unstructured FE-Mesh is composed from either only tetrahedrals or from elements of different shapes (e.g., tetrahedrals, triangular prisms, and others). Similar options as in MeshGen2D, i.e., FE-Mesh Refinements at Points, on Curves, Surfaces, and Solids, and FE-Mesh Stretching, are available in Genex/T3D as well.
Modules
HYDRUS Add-on Modules
Add-on modules can be purchased for an existing HYDRUS license either individually or as part of a cost-effective package
| Module Name | Dimension | Flow, Transport, and Reaction Simulations |
|---|---|---|
| HP1, HP2 | 1D, 2D | The HP1 and HP2 modules are the result of coupling Hydrus (its one- and two-dimensional parts) 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., 2012]. |
| UnsatChem | 1D, 2D, 3D | 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 manuals [Šimůnek et al., 2012, 2022]. More detailed description of concepts used in the UNSATCHEM module is provided in the HYDRUS-1D technical manual Šimůnek et al., 2022], which provides all relevant information about the one-dimensional version of this module. |
| Wetland | 2D | 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. |
| C-Ride | 1D, 2D | The C-Ride module simulates one- and 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 manuals [Šimůnek et al., 2012, 2022]. |
| DualPerm | 1D, 2D | 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, 1993; Šimůnek et al., 2003; Šimůnek and van Genuchten, 2008]. |
| Furrow | 2D | 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. |
| PFAS | 1D, 2D, 3D | The PFAS module includes options to consider sorption to the air-water interface and the concentration effects on surface tension and viscosity Silva et al., 2020]. |
| Particle Tracking | 1D | The Particle Tracking algorithm from Šimůnek [1991] was implemented into HYDRUS Zhou et al., 2021]. The results of this module can be used to calculate soil water travel times and water age for different locations in the soil profile. |
| COSMIC | 1D | The COSMIC module developed by Brunetti et al. [2019] calculates above ground neutron fluxes used the physically-based COsmic-ray Soil Moisture Interaction Code (COSMIC) of Shuttleworth et al. [2013]. |
| DPU | 1D, 2D | The Dynamic Plant Uptake (DPU) module developed by Brunetti et al. 2019, 2021, 2022] simulates the translocation and transformation of neutral compounds in the soil-plant domain. |
| Fumigant | 1D, 2D, 3D | The Fumigant module includes options required to simulate the fate and transport of fumigants in soils (e.g., removal of a tarp, temperature-dependent tarp properties, an additional injection of fumigant) Spurlock et al., 2013]. |
| Module Name | Dimension | One-dimensional Applications |
|---|---|---|
| H1D Pro | 1D | This add-on package expands the capabilities of one-dimensional applications with the following add-on modules: hydrus-modules Cosmic, DPU, C-Ride and PFAS (see the description of these modules below). These modules can only be used with the 1D-Standard edition or with the H1D add-on module. |
| Module Name | Dimension | Program Performance |
|---|---|---|
| HyPar | 2D, 3D | 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. |
| Module Name | Dimension | Slope Stress and Stability |
|---|---|---|
| Slope Cube | 2D, 3D | The 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 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. |
| Slope Classic | 2D | The "Slope Classic" add-on module is intended to be used mainly for stability checks 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 the HYDRUS results for specified times. Each time step of water distribution can be analyzed separately. |
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