CLOSED-FORM EXPRESSIONS FOR WATER-RETENTION AND CONDUCTIVITY DATA

Closed-form expressions for quantifying the unsaturated soil hydraulic properties are widely used in computer programs to model subsurface f low and transport in porous media and to investigate indirect methods for estimating these properties. For example, water retention data, wh ich relate soil-water pressure head (h) and effective water saturation (S-c), are frequently used to predict the unsaturated hydraulic condu ctivity (K), However, the suitability of different functions to descri be unsaturated hydraulic data has rarely been investigated comprehensi vely. We attempted to fit 14 retention and 11 conductivity functions t o 903 sets of water retention and hydraulic conductivity data measured on soil and rock samples or horizons reported in the unsaturated hydr aulic database UNSODA, Some of the best mean values for r(2) and MSE f or fitting S-c(h) data were obtained with the retention functions repo rted by van Genuchten (1980), Globus (1987), and Hutson and Cass (1987 ), A function reported by Gardner (1958) could describe K(h) data quit e well whereas functions reported by Brooks and Corey (1964) and van G enuchten (1980), which are respectively based on the conductivity mode ls by Burdine and Mualem, yielded a relatively good description of K(S -c) data.