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Sand-Model Experiments on the Distribution of Water-Pressure under an Unlined Canal¹

ABSTRACT

A study has been made of the seepage of water by capillary flow (movement at pressures less than that of the atmosphere). The analysis differs markedly from previous theories of seepage which ignore capillary movement.

An idealized flow system, which consisted of parallel furrows in soil overlying a gravel substratum, was postulated in the theory and simulated experimentally in a sand model. Pressures were measured tensiometrically. The water pressure found at various points in the sand model in the steady state agreed approximately with values calculated from theory.

The theory is applicable only to certain simple cases. However, the results show clearly that under certain conditions capillary flow accounts for the entire seepage flux. In such cases, the reduced pressure of the water prevents its entry into test holes placed in the seepage zone.

¹ Contribution from the University of California, College of Agriculture. Presented before Division I, Soil Science Society of America, Dallas, Tex., Nov. 18, 1953.

² Associate Professor of Soil Physics, Department of Soils (Berkeley) and Assistant Professor of Irrigation, Department of Irrigation (Davis), respectively. The authors wish to acknowledge the able assistance of Ali Al Hamdani and Charles D. Ripple in the performance of these experiments.

Received for publication December 7, 1953.