Confirmation of rate-dependent behavior in water retention during drainage in nonswelling porous materials

Water Resources Research
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Abstract

In the water retention process in porous material, changes in water content are assumed to be independent of the rate at which the matric potential varies. Periodically, researchers have presented results that do not support this assumption, indicating that water retention may be rate-dependent under certain conditions. In the present study, long-term experiments were performed on five porous materials in which core samples were drained at different rates down to matric potentials of −50 kPa. Comparisons of these results with previous results confirm that slight rate-dependent behavior occurs during drainage of porous materials in this matric potential range. Specifically, new and previous results indicate that on average 4–5% more water was retained for a slow, multistep drainage versus a fast, one-step drainage treatment. For the present study, average results for individual materials were variable, ranging from a 1 to a 10% difference in water content due to treatment. Several possible mechanisms for the observed rate-dependent behavior are discussed. The only plausible mechanism is related to variations in pore water salt concentrations that induce differences in the pore water surface tension for fast versus slow drainage. Regardless of the mechanism, results suggest that rate-dependent behavior during water retention may contribute to an enhanced temperature dependence of water retention, due to higher rates of water redistribution at higher temperatures.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Confirmation of rate-dependent behavior in water retention during drainage in nonswelling porous materials
Series title Water Resources Research
DOI 10.1029/93WR00005
Volume 29
Issue 4
Year Published 1993
Language English
Publisher American Geophysical Union
Contributing office(s) Toxic Substances Hydrology Program
Description 4 p.
First page 1331
Last page 1334