USE OF TENSION INFILTROMETER DATA WITH UNSATURATED HYDRAULIC CONDUCTIVITY MODELS

A new method is presented to estimate the relationship between unsaturated hydraulic conductivity and soil-water pressure using tension infiltrometer data. In this method, both the early transient and the subsequent quasi-steady stages of the infiltration process underneath a tension infiltrometer disc are analyzed. Our investigation indicates that the infiltration rate at early times closely follows the aquare-root-of-time relationship (Philip, 1969). This behavior permits the evaluation of the sorptivity, which is an integrated measure of soil diffusivity. At later times, three-dimensional quasi-steady flow beneath the infiltrometer disc develops, and the Wooding equation for from a circular pond is used to evaluate the sorptive number and the saturated hydraulic conductivity. Simple algebraic expressions are introduced to relate the sorptivity and sorptive number to the parameters of the Brooks and Corey model of unsaturated hydraulic conductivity. The method described here extends the utility of tension infiltrometer data to a large class of hydraulic conductivity models and provides an in situ technique to determine suitable parameters values for these models.