New Hydrus Modules for Simulating Preferential Flow, Colloid-Facilitated Contaminant Transport, and Various Biogeochemical Processes in Soils.

The capabilities of the HYDRUS (2D/3D) software package have been substantially expanded by new modules accounting for processes not available in the standard HYDRUS version. These new modules include the DualPerm, C-Ride, HP2, Wetland, and Unsatchem. All these modules simulate flow and transport processes in two-dimensional transport domains and are fully supported by the HYDRUS graphical user interface. Additionally, the DualPerm module implements the dual-permeability modeling approach of Gerke and van Genuchten [1993] simulating preferential flow and transport. The C- Ride module implements colloid transport and colloid-facilitated solute transport [Šimùnek et al., 2006], the latter often observed for many contaminants, such as heavy metals, radionuclides, pharmaceuticals, pesticides, and explosives. HP2 is a two-dimensional alternative of the HP1 module [Jacques and Šimùnek, 2005], currently available with HYDRUS-1D, that couples HYDRUS flow and transport routines with the PHREEQC geochemical model of Parkhurst and Appelo [1999]. The Wetland module includes two alternative approaches (CW2D of Langergraber and Šimùnek [2005] and CWM1 of Langergraber et al. [2009]) for modeling aerobic, anaerobic, and anoxic biogeochemical processes in natural and constructed wetlands. Finally, the Unsatchem module simulates the transport and reactions of major ions in a soil profile. A brief description and several demonstrative applications of each module will be presented. Further development of these modules, as well as of several other new modules (such as Overland. Slope Stability, and Meteo/Freezing), is still envisioned. Continued feedback from the research community is encouraged.