Temperature dependence of unsaturated hydraulic conductivity of two soils

Packed columns of Oakley sand (mixed, mesic Typic Paleudalfs) and Hanford sandy loam (mixed, nonacid, thermic Typic Xerorthents) were used to develop isothermal steady-state fluxes. Soil matric potentials were measured and unsaturated hydraulic conductivities were calculated over a range of matric potentials at 2°, 25°, and 45° ± 0.5°C. In addition, water retention characteristics (to −100 kPa) were measured at these same temperatures for both soils. In this paper, the calculated results are compared to an equation that relates unsaturated conductivity to the intrinsic permeability, the relative permeability, and the viscosity of water. The equation considers viscosity to be the only parameter that changes with temperature. The results show a much greater temperature dependence in the unsaturated conductivity than would be predicted by this equation. The results indicate that the relative permeability may be a function of temperature. The temperature dependence of the soil water matric potential, surface tension, and diffuse double-layer thickness are discussed in terms of their possible interaction with the unsaturated conductivity values obtained. A case is presented for further study to isolate these temperature-sensitive parameters as well as additional parameters related to fluid flow path changes with temperature.