Testing an infiltration method for estimating soil hydraulic properties in the laboratory

Solving soil unsaturated flow problems requires knowledge of the water retention, theta(h), and unsaturated hydraulic conductivity, K(theta), relationships. The purpose of this study was to adapt to infiltration conditions the so-called Wind method previously described for evaporation conditions for determining theta(h) and K(theta) and from laboratory cores. Infiltration in a vertical column of soil was first simulated using the numerical solution of Richards' equation for two soils. The simulated data were then used to evaluate the ability of the method to provide estimations of the hydraulic properties, whether measurement errors on tensiometric data were taken into account or not. In the laboratory, a sandy and a loamy soil sample were used in infiltration experiments. The experimental equipment consisted of (i) a metal cylinder containing the soil sample placed on an automatic balance, (ii) a set of tensiometers inserted in the soil sample, and (iii) a drip infiltrometer placed horizontally above the soil surface of the sample. Pressure head profiles and the weight of the sample was recorded at constant time steps. The infiltration method is able to provide estimates of the retention curve as was shown by numerical and laboratory experiments. Estimating the unsaturated hydraulic conductivity was possible by applying Wind's method to infiltration conditions, but as with the evaporation method, the variance of the hydraulic conductivity estimates was high.