EFFECTS OF INFILTRATION ON AGRICULTURAL RUNOFF CONTAMINATION

A procedure is presented for estimating the total pollutant mass loss from the interrill flow region of an agricultural field during a runof f event. It involves applications of an overland Row model and a mass transport model. A two-dimensional interrill Row model by Limback and other researchers provides lateral depth and velocity distributions th at are used to determine the dispersion and entrainment coefficients r equired by the transport model. The transport model of Wallach and van Genuchten with variable rather than constant dispersion and entrainme nt coefficients served to model the transport process that carries sol ute from the soil interstices to the overland Row Wallach's mass loss rate equation was integrated over space (laterally) and time to determ ine total mass loss. The effects of rainfall rate, infiltration rate, surface roughness, surface slopes, and soil properties are included in the analysis. An example application and an explicit sensitivity anal ysis of the effect of infiltration rate on mass loss are presented. Th e procedure represents a significant improvement over the model of Par r and other researchers that did not account for the effects of infilt ration and the model of Wallach and van Genuchten that did not account for mechanical dispersion.