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Infiltration Prediction based on Estimation of Green-Ampt Wetting Front Pressure Head from Measurements of Soil Water Redistribution¹

ABSTRACT

A simple, physically based algebraic equation was derived to calculate the wetting front matric pressure head, H_f, in the Green-Ampt equation of infiltration. The derivation of the equation involved combining the simple hydraulic conductivity function with the wetting front matric pressure head function proposed by R. G. Mein and C. L. Larson (1971). The parameters in the derived equation were determined from fitting a power function to the experimental data of soil water content and soil water pressure head vs. elapsed time obtained during the post-infiltration redistribution period. In the derived equation, H_f is expressed as a function of antecedent soil water content. At low initial water contents, the equation shows that H_f is essentially a constant. Evaluation of the calculated H_f values was accomplished by utilizing H_f in the Green-Ampt equation to predict infiltration at seven field sites for soils at initial water contents below field capacity. Predicted cumulative infiltration was compared with infiltration measured with a double-ring infiltrometer. The resulting Green-Ampt predictions were accurate for initially dry soils, with a correlation value of r = 0.94 and a relative error of 12.1%.

¹ Contribution from the Water Resources Research Center and Hawaii Institute of Tropical Agriculture and Human Resources, Univ. of Hawaii at Manoa.

² Research Assistant. Now Assistant Professor of Forest Hydrology, Dep. of Forestry, Southern Illinois Univ. at Carbondale, Carbondale, IL 62901; Professor of Soil Science, Dep. of Agronomy and Soil Science, Univ. of Hawaii at Manoa, Honolulu; and Associate professor of Soil Science, Univ. of Hawaii at Hilo. Now Soil Scientist (Physics), USDA-ARS, Southern Plains Watershed and Water Quality Laboratory, Durant, Okla.

Received for publication July 13, 1981. Accepted for publication November 17, 1981.