AN IMPROVED DUAL-POROSITY MODEL FOR CHEMICAL-TRANSPORT IN MACROPOROUSSOILS

The often observed processes involved in preferential water flow and c hemical transport in porous media appear to be realistically described using a dual-continuum (dual-porosity) approach. In this approach, th e porous medium is conceptualized as two coexistent continua, one repr esenting 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, oscillator y behavior (overshoot problems in the macropore region) of the transpo rt equation was observed fur high values of the advective solute flux relative to the diffusive solute flux between the two regions, To circ umvent this oscillatory behavior, the fluid coupling term in the trans port equations was treated as an element-averaged, rather than a nodal property. The model was extended to two space dimensions for evaluati ng the impact of agricultural practices on solute leaching, A linear k inetic sorption module in the transport equations and a simple plant r oot extraction routine in the flow equations were also added. Although the simulation results show promise, additional work will be needed t o determine realistic model parameter values.