Modelling particle mobilization and leaching in macroporous soil

The migration of colloidal particles in the unsaturated zone may enhance le aching of sorbing contaminants to surface waters and groundwaters. This pap er describes a simple model of particle leaching and translocation based on the dual-porosity model MACRO. The model includes descriptions of processe s such as 'source-limited' particle detachment due to the kinetic energy of rain, replenishment of the depleted store of particles up to a maximum val ue determined by the amount of dispersible clay in the soil, and convective transport of particles in macropores subject to a filter sink term varying as a function of pore water velocity. Estimates of model parameter values are obtained by comparing simulations with measurements of particle concent rations in the discharge from tile drains made in a silty clay soil in sout hwest Sweden. Calibrated in this way, the model is shown to reproduce satis factorily the observations. A sensitivity analysis suggests that the critic al parameters in the model are those related to particle filtering during v ertical transport in soil macropores.