NUMERICAL MODELING OF VADOSE ZONE PROCESSES (WITH FOCUS ON THE LATEST HYDRUS SOFTWARE PACKAGES)

Modern human society uses an unprecedented number of chemicals, such as in plant and animal production, making agriculture one of the most important sources for non-point source pollution. Many mathematical numerical models evaluating the fate and transport of these chemicals were developed over the last three or four decades, and these models are now readily available and widely used. In this presentation I will first briefly review different types of mathematical models that can be used to evaluate fate and transport of various chemicals in the environment, with a special focus on numerical models. Then I will review various versions of the HYDRUS models modeling water flow, chemical movement, and heat transport through variably-saturated soils. I will also discuss various specialized HYDRUS modules intended to simulate processes not available in the standard HYDRUS versions, such as the transport of multiple interacting solutes (the HP1/HP2 and UnsatChem modules), preferential flow (the DualPerm module), colloid-facilitated solute transport (the C-Ride module), the processes in wetlands (the Wetland module), and transport of fumigants.