Infiltration Models for the Disk Infiltrometer

Abstract

The disk infiltrometer is becoming a widely used device for determining soil hydraulic properties in the field. To describe the infiltration process from the disk infiltrometer, a two‐term equation was developed. The first and second terms characterize water flow out of the disk due to capillary forces and gravity, respectively. The parameter of the first term in the equation was a product of a nondimensional coefficient and soil sorptivity. The parameter of the second term was a product of another nondimensional coefficient and soil hydraulic conductivity. Time‐dependent relationships were obtained from numerical models to determine the coefficients based on physical parameters of the infiltrometer, such as the radius and tension used, and soil retention parameters. The cumulative infiltration and steady‐state infiltration rate calculated using the two‐term equation were in excellent agreement with numerically simulated results for various soils, and radii and tensions of disk infiltrometers. Absolute relative errors of predicted infiltration were <5% for soils ranging from clay to sand. The infiltration solution is an accurate, yet simple approach to estimate fluxes from an axisymmetric source. It can also be applied to estimate soil sorptivity and hydraulic conductivity using inverse methods.