COMPARISON OF 6 METHODS TO DETERMINE UNSATURATED SOIL HYDRAULIC CONDUCTIVITY

Knowledge of soil hydraulic properties is required for soil-water how models. Although many studies of individual methods exist, comparisons of methods are uncommon. Therefore, we compared application ranges an d results for six laboratory methods for determining hydraulic conduct ivity or diffusivity on eolian sand, eolian silt loam, marine sandy lo am, and fluviatile silt loam. The methods, hot air, sorptivity, crust, drip infiltrometer, Wind's evaporation, and one-step outflow, fall in to three groups: (i) those that only yield a conductivity curve; (ii) those that yield a simultaneous estimate of conductivity, diffusivity, water content, and pressure head; and (iii) those that yield a diffus ivity curve. Diffusivities were converted to conductivities with a wat er retention curve. One main difference between the methods was the pr essure head-water content range. Despite the large differences between the methods, the results for the first two groups tended to be simila r. The results of the third group did not match well with those of the first two. It proved difficult to compare these methods correctly due to hysteresis.