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Title: Modeling observed saturation overshoot with continuum additions to standard unsaturated theory

item Dicarlo, David

Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2004
Publication Date: 2/15/2005
Citation: Dicarlo, D.A. 2005. Modeling observed saturation overshoot with continuum additions to standard unsaturated theory. Advances in Water Resources. 28:1021-1027.

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. It was previously shown that this behavior can be replicated in small column experiments, yielding behavior that is inconsistent with standard flow models. In this paper it is shown that an addition to the standard model is tested, and found to work in some cases, but not likely to include the correct physics of the process.

Technical Abstract: In uniform soils that are susceptible to unstable preferential flow, the water saturation exhibits a nonmonotonic profile upon continuous infiltration. This overshoot cannot be described by the conventional Richards equation. Here, solutions to the infiltrations using a popular nonequilibrium extension to the Richards equation are obtained using the traveling wave nature of the saturation profile. Quantitative comparisons are made to recent measurements of saturation overshoot. The nonequilibrium solutions can be made to fit the flux range of the overshoot, but the fit to the tip saturations is fair to poor at best. Also, small changes in porous media size and roughness require large changes in the magnitude of the nonequilibrium term to match the flux range. The results suggest that the nonequilibrium capillary pressure does not include the correct physics that controls the overshoot.