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The Significance of Hysteresis in Modeling Solute Transport in Unsaturated Porous Media

Dep. of Geology, Western Washington Univ., Bellingham, WA 98225

Alex S. Mayer^*

Dep. of Geological Engineering and Sciences, Michigan Technological Univ., 1400 Townsend Dr., Houghton, MI 49931

*Corresponding author (asmayer{at}mtu.edu).

ABSTRACT

Previous investigations disagree as to the appropriateness of neglecting hysteresis with regard to predicting solute transport under transient conditions, primarily because of the unique porous media and conditions used in these studies. In the present study, the significance of hysteresis in predicting solute transport in the near-surface region is investigated using one-dimensional, homogeneous numerical experiments with a fully hysteretic flow and transport model. The experiments involve introduction of a solute pulse, followed by intermittent cycles of infiltration, redistribution, and evaporation. Comparisons are made between transient hysteretic simulations and simulations ignoring hysteresis. Hysteretic and nonhysteretic simulations conducted with porous media that have large differences between wetting and draining characteristic curves exhibited the greatest variation in solute migration behavior. Larger differences between maximum and minimum water contents also produced greater impacts when hysteresis was considered. However, the results indicate that the magnitude of the deviations between hysteretic and nonhysteretic simulations is not a simple function of each independent parameter, but rather depends on the combined values of many or all of the hydraulic parameters. As the solute travels further into the vadose zone, the effects of hysteresis are reduced. In general, hysteresis had a minor effect on solute transport in the systems considered in this work.

Received for publication June 25, 1997.