Wetting Front Instability in Homogeneous Sandy Soils under Continuous Infiltration

The boundary conditions required to produce unstable wetting have not been thoroughly investigated. Our experiments demonstrate that wetting front instability occurs in two‐ and three‐dimensional homogeneous columns of sandy soils under continuous nonponding infiltration, simulating rain‐fed conditions. Instabilities were visualized in two‐dimensional experiments by observing the light transmitted through partially saturated silica sand, and by dye staining in a three‐dimensional experiment. The dimensions of the instabilities observed corresponded well to the previous results found in studies of layered soils, indicating that the theories developed previously apply to rain‐fed infiltration without layering. Our study extends the range of situations where fingered flow is predicted to occur, which indicates that models used to calculate contaminant transport and loading in uniform coarse soils should include the effects of fingered flow.