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Non-Darcy Behavior and the Flow of Water in Unsaturated Soils^1,3,

ABSTRACT

Corresponding values of flow velocity and moisture gradient were calculated for water flow in unsaturated soil, using a graphical analysis of moisture profiles obtained during horizontal absorption of water into air-dry Salkum silty caly loam. Plots of flow velocity vs. moisture gradient were straight lines through the origin at the higher moisture contents, but Darcy proportionality did not hold at the lower moisture contents.

The observed deviations were of the same type as found in earlier studies for plots of flow velocity vs. hydraulic gradient for water-saturated materials containing clay, and could be fitted by a modified flow equation developed previously for the water-saturated materials. Physically, the non-Darcy behavior is tentatively attributed to non-Newtonian liquid effects caused by clay-water interaction.

Consideration of diffusion-type analysis from the stand-point of non-Darcy behavior shows that the diffusivity D becomes a function of moisture gradient w as well as moisture content . This provides a way of accounting for the nonuniqueness of D() recently reported in the literature.

¹ Journal Paper No. 2014, Purdue University Agr. Exp. Sta., Lafayette, Ind. Contribution from the Department of Agronomy. Presented before Div. I, Soil Science Society of America, Aug. 20, 1962, at Ithaca, N. Y.

³ The author acknowledges with thanks the cooperation of Dr. Stephen L. Rawlins, The Connecticut Agr. Exp. Sta., New Haven, Conn., and Dr. Walter H. Gardner, Washington State University, Pullman, Wash., who kindly supplied their original data for use in the present paper.

³ Professor of Soils.

Received for publication November 8, 1962. Accepted for publication February 15, 1963.