A BOREHOLE FIELD METHOD TO DETERMINE UNSATURATED HYDRAULIC CONDUCTIVITY

Unsaturated hydraulic conductivity is often the single most important soil property in vadose zone flow and transport. However, at depths below the root zone there is no field method available to determine it. The proposed method is directed toward developing a practical field tool to determine unsaturated hydraulic conductivity in discrete intervals over any depth. The basic idea is to inject water at a point and monitor the steady state pressure distribution surrounding the source. We have developed an analytical solution to use either the observed steady state pressure heads at several points due to a single injection, or steady pressure heads at a single point due to multiple injections, to determine the unsaturated hydraulic conductivity. The approach is based on a linearization of the unsaturated flow equation which uses the piecewise exponential model of unsaturated hydraulic conductivity. Examples of hydraulic conductivity calculations for three different soils give excellent results.