Water and solute movement in a coarse-textured water-repellent field soil

Unstable water flow in water-repellent unsaturated soils can significantly affect the processes of infiltration and soil water redistribution. A field experiment was carried out to study the effect of water-repellency on water and bromide movement in a coarse-textured soil in the southwestern part of The Netherlands. The field data were analyzed using a relatively simple numerical model based on the standard Richards' equation for unsaturated water flow and the Fickian-based convection-dispersion equation for solute transport. Water-repellency was accounted for by multiplying the water content and the unsaturated hydraulic conductivity of the soil with F, a factor equal to the volumetric fraction of soil occupied by preferential flow paths resulting from the unstable flow process. The good comparison of simulated and measured bromide concentrations suggests that the model provides a viable method for simulating unstable water flow in water-repellent soils.