Models for disc infiltrometers

Disc infiltrometers are popular devices for determining in situ hydraulic properties of unsaturated soils. This paper compares alternative solutions of Richards' equation for both steady state and time‐dependent cases. The steady state solutions were in general agreement using alternative hydraulic conductivity functions of the same capillary length scale. Small‐time solutions for the nonlinear cases were consistent with linear diffusion from a disc source using an average diffusivity value which is simply related to the capillary length. This offers a refinement over the one‐dimensional solution for short times in that the geometric effect of the circular source is included. Simulations for two examples indicate that the approach to the steady state solution may take considerably longer than what is commonly reported in the literature for field applications.