THE SOIL-WATER DIFFUSIVITY NEAR SATURATION

Many laboratory porous materials are considered to have a zone of tension-saturation in their water retentivity curve near saturation. This implies that the soil water diffusivity, D, is infinite in such a region. Here three new methods of measuring the diffusivity near saturation are presented. Experiments were carried out on a fine sand and all methods found D to be finite, yet large. This implies that the water retentivity curve near saturation has a finite but large slope of order 10**2 m. This was compatible with the measured retentivity data. The theory of one-dimensional absorption implies that the slope of the Boltzmann variable with respect to volumetric water content near saturation equals twice D divided by the sorptivity. The slope calculated this way was compatible with that found in absorption experiments.