Pollutant washoff by overland flow

A physically based mathematical model is presented for the process of pollutant washoff by overland flow on impervious surfaces. The model is based on the kinematic overland flow and convective pollutant transport equations. The pollutant detachment rate at any point along a surface is assumed to be proportional to the overland flow bottom shear stress and the amount of the pollutant on the surface. The constant of proportionality depends only on the pollutant characteristics, and therefore it can be treated as a calibration parameter insensitive to changes in the hydrologic conditions of the basin. The governing equations are written in dimensionless form, and are solved using an implicit finite difference scheme. The mathematical model is verified with a set of published experimental data. Based on the concept of hydraulic similarity, the results of the model are generalized and presented in chart form.