DIFFUSIVITY AND ONE-DIMENSIONAL ABSORPTION EXPERIMENTS

Profiles of normalized volumetric soil water content, THETA , during one-dimensional absorption are often found to provide a unique profile in terms of the Boltzmann similarity variable, lambda . Traditionally, lambda ( THETA ) data have been used to obtain the diffusivity-water content function D( THETA ) by the method of Bruce and Klute. This paper highlights the well-known inadequacy of this method, and outlines a procedure for deriving D( THETA ) by the fitting of a mathematical function to the primary experimental data set, namely lambda ( THETA ). An analytical expression for D( THETA ) scaled by sorptivity is provided.