Method to Estimate Water Diffusivity and Hydraulic Conductivity of Moderately Dry Soil
1995
Globus, A. M. | Gee, G. W.
Water diffusivity and unsaturated hydraulic conductivity of moderately dry soils are seldom measured directly, yet are often needed by numerical models to simulate flow processes. We propose a relatively simple method to obtain water diffusivity or hydraulic conductivity in moderately dry soils. Steady-state profiles of water content and temperature in a closed, non-isothermal soil column are used to determine Sw = DT/D(θ) = − dθ/dT where Sw is the thermogradient coefficient, DT is the thermal water diffusivity, D(θ) is the isothermal water diffusivity, and dθ/dT is the rate of change of water content with temperature. The relative constancy of DT allows D(θ) to be estimated as D(θ) = -DT(dT/dθ) where dT/dθ is measured at various locations along the soil column. Using water retention data, the steady water content profile can be transformed into a suction head profile and the above procedures for estimating D(θ) can then be applied to estimate hydraulic conductivity, K(θ). Soil columns ranging in length from 5 to 10 cm, exposed to thermal gradients of 1°C/cm for periods as short as 7 d, at initial suction values ranging from 0.1 to 1.5 MPa, can be used to estimate water diffusivity and hydraulic conductivity with uncertainties of a factor of five or less in the suction range from 0.03 to 3 MPa.
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