|Van Genuchten, Martinus|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 1, 1999
Publication Date: N/A
Interpretive Summary: Not Required
Technical Abstract: A number of simple theoretical models are widely used to predict the unsaturated hydraulic conductivity of a soil. These models are based on the Hagen-Poiseuille equation, the Young-Laplace equation and several simplifying assumptions regarding the properties of the pore space. We propose a general model which is based on these assumptions but offers greater flexibility than the existing models. The models of Burdine, Muale and others correspond to particular cases of this general model. A 'soil hydraulic index' is defined to compare the different models. We then evaluate the validity of some common assumptions by applying different models to data sets taken from the UNSODA data base. To obtain a good fit, at least two parameters of the general model need to be optimized for each data set. In many cases, a reasonable fit requires parameter values that are not physically meaningful. We therefore believe that neither the general model nor the simpler models of Burdine and Mualem should be interpreted as physically-based models.