Effects of Infiltration on Agricultural Runoff Contamination

Abstract

A procedure is presented for estimating the total pollutant mass loss from the interrill flow region of an agricultural field during a runoff event. It involves applications of an overland flow model and a mass transport model. A two-dimensional interrill flow model by Limback and other researchers provides lateral depth and velocity distributions that are used to determine the dispersion and entrainment coefficients required by the transport model. The transport model of Wallach and van Genuchten with variable rather than constant dispersion and entrainment coefficients served to model the transport process that carries solute from the soil interstices to the overland flow. Wallach's mass loss rate equation was integrated over space (laterally) and time to determine 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 analysis of the effect of infiltration rate on mass loss are presented. The procedure represents a significant improvement over the model of Parr and other researchers that did not account for the effects of infiltration and the model of Wallach and van Genuchten that did not account for mechanical dispersion.