DETERMINATIONS OF UNSATURATED HYDRAULIC CONDUCTIVITY FOR CANDLER SAND

Abstract

Using an instantaneous profile (IP) method we generated in situ distributions of volumetric water content, θ(z, t), and water suction head, h(z, t), in two field profiles of Candler sand during a cycle of soil-water redistribution. With these data, we then calculated hydraulic conductivity, K, values over the narrow suction head range 0 < h < 80 cm of water. Field-determined values for saturated hydraulic conductivity, Ko, exceeded 100 cm h−1 for this very coarse-textured soil. Values of K determined by the IP method were used to evaluate two methods commonly used to predict unsaturated hydraulic conductivity. The two methods utilized field-determined soil-water characteristic curves, θ(h), experimentally determined values of saturated hydraulic conductivity Ko, and Poiseuille's equation for flow in cylindrical soil pores to calculate unsaturated hydraulic conductivity. For values of θ > 0.10 cm3 cm−3 and h < 40 cm of water, K values predicted by each of the methods agreed well with values determined in situ by the IP method. However, for lower water contents (i.e., θ < 0.10 cm3 cm−3), values of K determined by both predictive methods overestimated those obtained by the IP method.