DETERMINATION OF HYDRAULIC CONDUCTIVITY USING A TENSION INFILTROMETER

A new procedure is presented for in situ determination of saturated and near-saturated hydraulic conductivity [K(fs) and K(psi), respectively] from a sequence of steady infiltration measurements made at several tensions on a single infiltration surface. The method applies to tension infiltration from either a surface disk or from within a ring inserted a small distance into the soil. The analysis employs a modification of Wooding's solution for infiltration from a shallow pond, combined with numerically determined shape factors that account for the interaction effects between flow geometry and soil properties. The method is found, via numerical simulations, to have an overall accuracy within about +/- 7%, regardless of whether the predicted K(psi) function is flat with an indistinct air-entry value, steep with a distinct air-entry value, or very steep with no air-entry value. Some important practical features of the method are that it does not require measurement of the often-difficult square-root-of-time infiltration behavior, no special considerations are required regarding the thickness of the contact layer, it minimizes the effect of local spatial heterogeneity by using only one infiltration surface per set of K(psi) measurements, it avoids the use of potentially unstable simultaneous-equations solution procedures, and it can be applied to tension infiltration from both disk and ring infiltrometers.