Hydrus is a suite of Windows-based modeling software that can be used for analysis of water flow, heat and solute transport in variably saturated porous media (e.g., soils).

HYDRUS suite of software is supported by an interactive graphics-based interface for data-preprocessing, discretization of the soil profile, and graphic presentation of the results.

UNSAT was a finite element model simulating water flow in two-dimensional variably-saturated domains as described with the Richards equation.

This last version of UNSAT formed the basis of the SWMII model developed by Vogel (1987) during his stay at Wageningen University, the Netherlands.

The code simulated variably-saturated water flow in two-dimensional transport domains, implemented the van Genuchten soil hydraulic functions (van Genuchten, 1980[12]) and modifications thereof, considered root water uptake by taking advantage of some of the features of the SWATRE model (Feddes et al., 1978[13]), and included scaling factors to enable simulations of flow in heterogeneous soils.

These included solution of the mixed form of the Richards equation as suggested by Celia et al. (1990),[16] thus providing excellent mass balances in the water flow calculations.

This model greatly expanded upon the capabilities of SWMS_2D by including, among other things, sequential first-order solute decay chains and heat transport.

A unique feature of HYDRUS-2D was that it used a Microsoft Windows-based Graphics User Interface (GUI) to manage the input data required to run the program, as well as for nodal discretization and editing, parameter allocation, problem execution, and visualization of results.

In addition to features and processes available in HYDRUS-2D and SWMS_3D, the new computational modules of HYDRUS (2D/3D) consider (a) water flow and solute transport in a dual-porosity system, thus allowing for preferential flow in fractures or macropores while storing water in the matrix, (b) root water uptake with compensation, (c) the spatial root distribution functions, (d) the soil hydraulic property models of Kosugi and Durner, (e) the transport of viruses, colloids, and/or bacteria using an attachment/detachment model, filtration theory, and blocking functions, (f) a constructed wetland module (only in 2D), (g) the new hysteresis model to eliminate pumping by keeping track of historical reversal points, and many other options.

Both HYDRUS models may be used to simulate movement of water, heat, and multiple solutes in variably saturated media.

In addition, physical non-equilibrium 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.

The HYDRUS packages use a Microsoft Windows-based graphical user interface (GUI) to manage the input data required to run the program, as well as for nodal discretization and editing, parameter allocation, problem execution, and visualization of results.

Also included is a small catalog of unsaturated soil hydraulic properties, as well as pedotransfer functions based on neural networks.

CWs are popular systems which efficiently treat various types of polluted water and are therefore sustainable, environmentally friendly solutions.