Modelling the fate of pollutant in overland flow

A physically based numerical model is developed to simulate pollutant dissolution and transport in overland flow with infiltration effects. The numerical simulation of the complete process requires the solution of the unsteady, two-dimensional St. Venant equation, an equation for the infiltration process and the pollutant transport equation. The solubility rate equation proposed in this study is used to model the dissolution of a specified spatial distribution of solid pollutant into the liquid phase. The set of equations governing the complete system are integrated numerically using various finite difference algorithms. The model may be used to predict the ultimate fate of a surface applied solid pollutant by evaluating the proportions that are dissolved, infiltrate into the subsurface or are washed-off. The hydraulic portion of the model has been validated against published field data with satisfactory agreement. Verification of the complete model, however, is based on a comparison with limited laboratory test data. Proper validation would require extensive experimentation, preferably in the field which is, up to now, unavailable.