Modeling overland flow contamination by chemicals mixed in shallow soil horizons under variable source area hydrology

Agricultural chemicals (fertilizers, nutrients, pesticides, etc.) are frequently mixed into the shallow soil layers so that they may be leached down during water applications (rainfall/irrigation). These events often generate overland flows which cause the release and migration of these chemicals into surface waters. in many such applications, overland flow does not immediately develop as a sheet over the whole plane, but gradually increases in extent in accordance with the variable source area (VSA) concept. This paper deals with the modeling of surface contamination under such circumstances. Results were obtained for a single hypothetical agricultural plot. Some comparisons were made regarding the relative amounts of solute lost to overland flow and to those leached into the soil as a function of time.