Experiments were conducted on large field cores to determine the relationship between drainage volume and water table depth for five soils. The measured drainage volumes were less than predicted from the soil water characteristics for three soils, but were in good agreement for the other two. Drainable porosities were calculated from both theoretical and experimental drainage volume-water table depth relationships by assuming that the unsaturated zone is essentially 'drained to equilibrium, with the water table. The experimental drainable porosities thus obtained were less than predicted.

Drainable porosities for drainage in two-dimensions were calculated from experimental results for one-dimension by assuming an elliptical water table profile. These results gave nearly constant drainable porosities for the layered soils and a variable drain-able porosity for Wagram, a homogeneous, sandy soil.

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Published in Transactions of the ASAE, v. 21, issue 3, p. 522-528.

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