Min, Xinying2023-08-012023-08-012023-08-01https://hdl.handle.net/1813/113352Understanding gravity-driven preferential flow in uniform porous materials is important as they can facilitate the movement of pollutants, pathogens, and pesticides to groundwater. Previous studies suggested the dynamic contact angle could be used to model unstable gravity-driven flow in coarse sand. This study aimed to examine this theory in a broader context involving a range of porous media with different static contact angles. The results show that pore water movement was discontinuous. After a period in which the pressure in the water increased, the water moved through the smallest pore with high velocity. After the initial breakthrough, the flow stopped within 0.01 seconds. The relationship between the dynamic contact angle followed the Hoffman-Jiang equation for media that exhibited unstable gravity drive flows. The acid-washed sand that only under very dry conditions had an unstable wetting front did not show a relationship between velocity and contact angle.CC0 1.0 UniversalInfiltrationUnsaturated flowPorous mediaPreferential flowvideo/moving image