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

Abstract

AbstractA simple, physically based algebraic equation was derived to calculate the wetting front matric pressure head, Hf, 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, Hf is expressed as a function of antecedent soil water content. At low initial water contents, the equation shows that Hf is essentially a constant. Evaluation of the calculated Hf values was accomplished by utilizing Hf 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%.