Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2003
Publication Date: 4/5/2004
Citation: Dicarlo, D.A. 2004. Experimental measurements of saturation overshoot on infiltration. Water Resources Research. 40. W04215, doi:10.1029/2003WR002670. Interpretive Summary: When water infiltrates a soil, the infiltration is often not homogenous. Frequently, the water moves downward in small preferential paths bypassing most of the soil, leading to less water retention for crops and more possibility of contaminants reaching ground and surface waters. In this paper it is shown that a signature of preferential flow can be found in fast column experiments. Thus it can be quickly determined under which moisture regimes and soil types that preferential flow is likely to occur.
Technical Abstract: Gravity driven fingers in uniform porous medium are known to have a distinctive non-monotonic saturation profile, with saturated (or nearly so) tips and much less saturation in the tails. In this work, constant flux infiltrations into confined porous media (laterally smaller than the finger diameter, thus essentially 1-dimensional) are found to produce saturation overshoot identical to that found in gravity driven fingers. Light transmission is used to measure the saturation profiles as a function of infiltrating flux, porous media grain size, grain sphericity, and initial water saturation. Saturation overshoot is found to cease below a certain mininum infiltrating flux. This minimum flux depends greatly on the grain sphericity and initial water content of the media and slightly on the grain size. The observed saturation overshoot is inconsistent with a continuum description of porous media, but qualitatively matches well observations and predictions from discrete pore-filling mechanisms. This suggests that pore-scale physics controls saturation overshoot and in turn gravity driven fingering.