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Predicting Moisture Distributions in Rewetted Soils¹

ABSTRACT

Computed and measured soil moisture distributions were compared during second and third cycles of infiltration and redistribution. In order to obtain acceptable agreement, the hydraulic conductivity had to be reduced to about one-half of the value used in the first cycle for freshly packed soil. Two methods were adopted in obtaining adequate conductivity data. One method was to correct the conductivity by trial and error. The other was to measure the conductivity of the soil after it had been carried through an initial wetting and drying cycle.

Hysteretic effects on rewetting were minimized by adding sufficient water to the partially dried soil to bring it back to its initial wetted condition. The independent domain theory was found satisfactory for providing wetting tension data during the brief infiltration period.

Modified tension scanning curves for drying were used in second-cycle computations for clay soil but the original curves for freshly packed columns were used for sand. Changes in scanning curves due to consolidation during the first drying cycle were not studied in detail. Successive rewetting was predicted satisfactorily only after the boundary condition for infiltration was changed from ponded water at the surface to an applied flux which was below the maximum infiltration rate.

¹ Contribution no. 323. Soil Research Institute, Canada Department of Agriculture, Ottawa, Ont.

² Soil Physicist.

Received for publication November 19, 1969. Accepted for publication February 11, 1970.