ABSTRACT
The relationship between suction, s, and volumetric water content, θ , or degree of saturation, i.e. the soil water retention curve SWRC, can be experimentally measured in the laboratory by means of pressure plate or volumetric pressure plate extractor. Several mathematical expressions, both empirical and theoretical in nature, have also been proposed in the literature to describe the SWRC (see Scott et al., 2001). Moreover, the soil water characteristic curve can also be computed from the particle size distribution (PSD); this approach is based mainly on the similarity between shapes of the cumulative grain size distribution and the s(θ) curves. The methods originally proposed in the field of soil physics by Arya & Paris (1981) and Arya et al. (1999) seem to be very effective in predicting the SWRC, as well as being very advantageous for their simplicity. However, since most predictions models are based on PSD information, the accuracy of a PSD curve may affect the estimate of s(θ). At present, there are a few attempts to quantitatively investigate the effect of the choice of a PSD model on the prediction of the soil water retention curve as well as the conductivity function k(s). A review of such models is critically examined in Hwang et al. (2002) and Hwang & Powers (2003).
