Developing joint probability distributions of soil water retention characteristics

A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head [ h (θ)] and hydraulic conductivity [ K (θ)]. These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. The method employs a statistical multiple regression equation proposed in the literature for estimating [ h (θ)] or [ K (θ)] relationships using the soil saturated water content and the percentages of sand and clay. In the absence of known statistical distributions for either [ h (θ)] or [ K (θ)] relationships, the method facilitates modeling by providing variability estimates that can be used to examine the uncertainty associated with water flow or solute transport in unsaturated media.