Water repellent soil and surface layers exhibit a complex flow and transport mechanism. Knowledge of the underlying principles is essential, for instance, to simulate water availability for crops and to estimate leaching potentials of agrichemicals. The present study aims to introduce and apply a new modelling approach to simulate preferential flow and transport in water repellent porous media, and to test the model on basis of an extensive field tracer experiment.

The process of preferential flow and transport has been incorporated in the well-known SWAP model and applied to field data of tracer transport through a water repellent sandy soil in the Netherlands. Flow concept and model structure have been outlined, and simulation results presented. Results indicated early arrival times of bromide tracer in the subsoil in the case where preferential flow has been taken into account in the model. Comparison of measured and computed bromide concentration profiles and bromide recovery rates show close resemblances.

Several strategies to alleviate soil water repellency and prevent the occurrence of preferential flow and transport processes are highlighted, such as irrigation scheduling, clay additions, and application of surfactants.