KWRRI Research Reports


Capillary-diffusion coefficients were measured by use of inflow and outflow methods. With both methods the capillary-diffusion coefficients decreased very rapidly with decreasing water content. The lighter textured soils were found to have the higher diffusion coefficients over the entire moisture content range studied, 0 to 1 bar tension.

Self-diffusion coefficients were measured over a moisture content range from air dryness to saturation using 3H as a tracer of water. Each of the soils gave the same diffusion characteristics when the self-diffusion coefficients were expressed as a function of either water content or average number of water layers on the external surface of each mineral. As the water content decreased from saturation to near field capacity, the self-diffusion coefficients decreased very rapidly.

An attempt was made to separate the self-diffusion coefficients into a liquid and a vapor component by use of 36Cl as a tracer of liquid water. The results showed 36Cl not to be a good tracer of liquid water movement in soil. The results suggest that a functional relationship exists between capillary-diffusion and self-diffusion; however, before this relationship can be firmly established, the liquid and vapor components of water movement must be separated.

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The work on which this report is based was supported in part by funds provided by the Office of Water Resources Research, United States Department of the Interior, as authorized under the Water Resources Act of 1964.