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Pressure Distribution in Soil Columns Draining into the Atmosphere¹

ABSTRACT

Columns of soil 122 cms long were first wetted with water and then allowed to drain into the atmosphere. During the drainage period, measurements were made of the pressure distribution in the soil columns and of the rate at which water drained out of the columns into the atmosphere. At the conclusion of the experiment, the soil columns were sectioned and the moisture distribution measured.

The experimental results emphasize the importance in drainage of the tension required to produce entry of air into the soil surface. The difficulty experienced in the drainage of tight clay soils may be due more to the high tension required to produce entry of air into the soil than to the low hydraulic conductivity of the soil.

Indirect evidence indicates that in the field, movement of water in the capillary fringe above the water table may be of considerable importance. This is especially true for the case of the falling water table. The use of Laplace's equation in the study of flow in the capillary fringe is discussed briefly.

¹ Contribution from the Dept. of Irrigation and the Dept. of Soils, Univ. of California, Davis and Berkeley, Calif. Presented before Division I, Soil Science Society of America, Cincinnati, Ohio, Nov. 19, 1952.

² Assistant Professor of Irrigation at Davis and Associate Professor of Soils, Cornell University, formerly Assistant Soil Physicist, University of California, respectively.

Received for publication June 16, 1953.