Abstract
Fingerlike partial flow, or fingering flow can occur during vertical downward infiltration with sharp wetting front under the conditions of wetting front instability. To clarify the physical features of fingering flow, in particular, the change of the water pressure at the interlayer plane with increasing finger length and the degree of saturation within fingers, experiments of infiltration into fine over coarse textured layered glass beads were conducted. It was confirmed that distinct fingers occurred and grew in the sublayer when it was initially dry and the criterion for wetting front instability was satisfied. On the other hand, it was observed that when the sublayer was initially wet, the wetted region in the sublayer formed a wavy pattern rather than a fingerlike one. The water pressure at the interlayer plane decreased with the increase of finger length after it reached a maximum value at the onset of water entry into the sublayer when typical fingering occurred under initially dry sublayer conditions. The change of the flux through the top layer was corresponded to the change of the water pressure at the interlayer plane which consisted of one of boundary conditions for percolation in the top layer. Furthermore, it was estimated that it was not saturated within fingers but was under unsaturated condition with entrapped air.
