Three‐dimensional analysis of infiltration from the disc infiltrometer: 1. A capillary‐based theory

The hydraulic properties of an unsaturated homogenous and isotropic soil can be obtained from the unconfined flux out of a disc infiltrometer into the soil over the depth of wetting. The disc infiltrometer is becoming increasingly popular, but methods of analysis have generally relied on the restrictive assumptions of one‐dimensional flow at early times or quasi‐steady state flow at large times. We provide an approximate analytical expression for three‐dimensional unsteady, unconfined flow out of a disc infiltrometer, and this includes the geometric effect of the circular source but ignores gravity. This physically based solution is tested against data obtained from laboratory experiments on repacked material. The results illustrate that the difference between three‐dimensional and one‐dimensional flow is linear with time.