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Absorption of Water by Soil: Some Effects of a Saturated Zone¹

ABSTRACT

Absorption by soil of water supplied at constant pressure and at constant rate is described. Particular attention is paid to the process when the surface water potential is greater than that at which the soil saturates.

Analyses, which directly integrate Darcy's law for both saturated and unsaturated regions using the flux-potential relation (related to the flux-concentration relation of Philip through the appropriate moisture characteristic), predict behavior in accord with experimental data. Analyses which treat the unsaturated region as a problem of diffusion-of- are "correct" only if the soil water diffusivity, measured using the method of R. Bruce and A. Klute, is interpreted with care.

To avoid erroneous prediction it is imperative that the measurement of diffusivity be preceded by an independent measurement of the moisture characteristic. This latter relation is a necessary specification of the soil water system. It should always be presented in a test of flow theory, and it identifies the suction at which the soil saturates and hence the suction at which Bruce and Klute type experiments should be performed.

¹ Contribution from CSIRO, Australia.

² Chief, Experimental Officer, and Technical Assistant, respectively, CSIRO Div. of Environmental Mechanics, P. O. Box 821, Canberra City, A.C.T. 2601, Australia.

Received for publication November 21, 1979. Accepted for publication June 20, 1980.