Laboratory Experimental Investigation of Infiltration by the Run-on Process

This paper describes laboratory experiments that provide evidence of infiltration of excess runoff water from upstream areas that moves downslope over unsaturated areas (run-on process). The experiments were carried out using a tilting tank that was packed with two different natural soils to a depth of 70 cm and subjected to artificial rainfalls from a rainfall simulator. Different rainfall patterns were generated over the surface at different slope settings. Measurements of overland flow, deep flow, and soil water content, together with photographs of soil surface, were used to quantify the main features of the run-on process. The results indicate that the interaction between Hortonian overland flow and local infiltration over the permeable areas can be appropriately described by representing the flow depth per unit time as an “additional” rainfall rate. Thus, these experimental results support the representation of the run-on process that was adopted in previous numerical studies that evaluated the effects of the run-on process.