ABSTRACT
ABSTRACT: HYDRUS and related software packages represent a system of numerical models for simulating variably-saturated water, heat and solute movement in the subsurface. The software packages can simulate flow and transport in one-dimensional (e.g., HYDRUS-1D, HP1, SOILCO2, and UNSATCHEM), two-dimensional (SWMS_2D, CHAIN_2D, or HYDRUS-2D), and three-dimensional (SWMS_3D or HYDRUS (2D/3D)) transport domains. While water flow in all of the models is simulated in a relatively similar manner, different solute transport modules exist in the different codes. Some models can simulate only transport of solutes independent of one another, whereas other models include biogeochemical modules simulating complex interactions between the various solutes. For example, HYDRUS-1D and UNSATCHEM models can also consider the transport of major ions and their mutual reactions, such as dissolution-precipitation, cation exchange, or aqueous complexation. The wetland module in HYDRUS (2D/3D) furthermore considers biochemical processes associated with the flow of wastewater through constructed or natural wetlands. Finally, HP1, a model resulting from coupling HYDRUS-1D and PHREEQC, accounts for a broad range of instantaneous and kinetic chemical and biological reactions, including aqueous complexation, precipitation-dissolution, cation exchange, surface complexation, and redox reactions. In this manuscript we review the various models and provide references to many of their applications.
