An improved dual porosity model for chemical transport in macroporous soils

The often observed processes involved in preferential water flow and chemical transport in porous media appear to be realistically described using a dual-continuum (dual-porosity) approach. In this approach, the porous medium is conceptualized as two coexistent continua, one representing the bulk matrix and the other the macropore region. Fluid and solute mass transfer between the two regions in the conceptual model occurs under pressure and concentration gradients. However, oscillatory behavior (overshoot problems in the macropore region) of the transport equation was observed for high values of the advective solute flux relative to the diffusive solute flux between the two regions. To circumvent this oscillatory behavior, the fluid coupling term in the transport equations was treated as an element-averaged, rather than a nodal property. The model was extended to two space dimensions for evaluating the impact of agricultural practices on solute leaching. A linear kinetic sorption module in the transport equations and a simple plant root extraction routine in the flow equations were also added. Although the simulation results show promise additional work will be needed to determine realistic model parameter values.