Prediction of the soil boundary wetting curve

A previously developed model of hysteresis is formulated on a nondimensional scale using the effective saturation rather than the capillary head as the independent variable. The theoretical equations of the various hysteretic curves suggest that a universal hysteresis of unsaturated porous media prevails on the dimensionless scale. This study also proves that the common use of a primary loop instead of the main loop of hysteresis for calibrating the model is actually compatible with theory. Data of 10 soil-water hysteresis studies were used to examine the applicability of the theory. Based on the findings, this study suggests a method for predicting the soil boundary wetting curve from the measured primary loop. The computed and the measured parts of the boundary loop can be used concomitantly to calibrate Model II of Mualem (1974) in the complete domain of hysteresis. The proposed method was illustrated using the data of a sand sample.