Comparative Simulation of Hillslope Runoff Using Two Infiltration Equations

Infiltration is one of the major hydrologic processes affecting the generation of overland flow. Accordingly, different infiltration equations have been developed, applied for water loss calculations, and compared mostly at the watershed scale or the point scale. However, their inter-comparison has not been made in the context of runoff simulation at the hillslope scale that includes microtopographic features such as rills and interrills. Here, we simulate overland flow by using the Horton and Green-Ampt equations to compare their performance in calculating runoff over a hillslope that consist of rills and interrills, freshly cut along Highway 299 in Northern California, USA. We find the better performance of the Green-Ampt equation than the Horton equation when coupled with the overland flow model. This is thought to be due to the ability of the Green-Ampt equation to account for antecedent moisture conditions. In addition, overland flow is found to be more sensitive to infiltration parameters than to the friction factor of the hillslope surface. The proposed overland flow model coupled with the Green-Ampt infiltration equation looks promising for runoff simulation over a rilled hillslope.