HYDRUS-2D is a fully interactive water, solute and heat transport, finite element solver for unsaturated and saturated porous media. The code and associated GUI is widely used by researchers and professionals to solve a broad range of vadose zone problems. It is a particularly valuable learning tool, allowing more and more complex processes and problems to be incorporated through a semester-long course in soil physics or vadose zone hydrology. The underlying transport equations are written with sufficient breadth to allow investigation of the majority of processes governing transport in unsaturated media. The code can accommodate a wide range of boundary conditions including a robust precipitation/transpiration/root uptake simulator, making it applicable to "real world" simulations.

Water flow is represented using Richards' equation, and the operator is able to specify hydraulic properties using default parameterization, neural network algorithms, or the Van Genuchten or Brooks/Corey functions. Hysteresis can be specified in both the retention and conductivity functions. Hydraulic properties can be a function of temperature via temperature dependant viscosity and surface tension relationships. The solute and heat transport portions of the code are governed by the advection-dispersion equation (solute) and convection-dispersion equation (heat). Mobile/immobile solute transport can be simulated, as can solute diffusion in the gas phase. Reactive transport is simulated using either linear or non-linear user-define isotherms.

Two dimensional finite element grids can be generated using a regular or unstructured grid generator, making the solution of complex geometries simple and efficient. The grid generator is easy to use and the mesh can be refined quickly in areas of steep moisture or solute gradients. The numerical stability of the solution algorithms is maintained through automatically adjusted time stepping, but can also be defined by the user. The code includes an inverse algorithm for estimation of hydraulic/solute/heat transport properties from observed laboratory or field data.

The graphical user interface walks the user through the necessary input steps, making the code easy to use. In addition to test cases included with the software, technical support, short courses, and a book of excellent examples of HYDRUS-2D applications are available.

Rating System
5=Excellent, 4=Very Good, 3=Good, 2=Satisfactory, 1=Poor

Ease of Use
Best Feature
General formulation of transport equations allowing a wide range of transport problems to be investigated. In addition, the available boundary conditions represent most of the commonly found "real world" conditions, also, domain generator.
Worst Feature
While the inversion algorithms are very good, the limited diagnostics and guidelines on inverse applications may frustrate some users initially.
Overall Rating

Last Update: August 2004