Equation for unimodal and bimodal soil-water characteristic curves

Soil-water characteristic curve (SWCC) data are usually curve fitted with an equation whose parameters were obtained by using optimization procedures. Due to the interdependency of the parameters in the SWCC equation, the parameters are non-unique and thus it is difficult to relate the parameters to other soil properties. This becomes more prominent for bimodal SWCC equations which have more curve-fitting parameters. In order to overcome this limitation, a new equation for both unimodal and bimodal SWCCs is proposed. The new equation uses parameters that can be obtained graphically and no curve-fitting procedures are necessary. Hence, its parameters are unique. The proposed equation was shown to be accurate in representing both unimodal and bimodal SWCCs with several examples.