Recent Progress in Modelling Water Flow and Chemical Transport in the Unsaturated Zone

This introductory paper reviews alternative approaches for modelling water and solute movement in the unsaturated (vadose) zone of field soils. A large number of analytical and numerical models are now available to predict unsaturated water flow and solute transport. The most popular models remain the classical Richards' equations for unsaturated flow and the convection-dispersion equation for solute transport. While deterministic solutions of these equations are important tools in research and management, their utility for predicting actual fieldscale processes is increasingly being questioned. Problems caused by soil heterogeneity at a variety of spatial scales, and a lack of progress in improving our field measurement technology, have contributed to some disappointment with the classical models. Alternative deterministic and stochastic approaches have been developed to better deal with field-scale heterogeneity. This paper briefly reviews these models, and outlines several areas of research in need of further investigation.

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