Co-Authors:
Russo, D.
Jury, W.A.
Butters, G.L.
Abstract:
In this study, the two‐component mobile‐immobile water model is modified to describe solute transport under transient water flow induced by periodic cycles of irrigation, evaporation, and redistribution. To characterize transient flow, the soil water content is divided into a time‐invariant immobile water content Θi, and a time‐dependent mobile water content Θm which obeys the Richards equation. Solute transport is described by the two‐component mobile‐immobile water model, modified to take into account the time dependence of Θm. Results of the calculations show important differences between the behavior of the flux and residence concentrations under steady state water flow, particularly when the mass transfer coefficient α is relatively small. In this case, both resident and flux concentrations show a dispersion scale effect in their rate of spreading about the center of mass position in the soil. There were significant differences in solute transport predicted by the transient two‐component model compared to the steady state model. The apparent velocity derived from the time variations of the position of the center of mass of the resident concentration decreased with time in the transient model, but was relatively constant in the steady state one. Apparent dispersion about the center of mass increased with time in both models, but was much higher in the transient model, caused principally by a buildup of solute at the surface during evaporation cycles. Copyright 1989 by the American Geophysical Union.
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