Predicting hydraulic conductivity changes from aggregate mean weight diameter

Abstract

[1] Rapid wetting of structurally unstable soils results in aggregate disintegration, soil densification, reduced porosity, and changes in the pore-size distribution and intake hydraulic properties. Knowledge of changes in these properties is critical for use in hydrological, solute transport, or erosion models. Multiple determinations of these parameters as they evolve over time are needed for short time step models. Routine measurement of all these properties is time-consuming, and it would therefore be practical if some of them could be used to predict others. A model is proposed to predict hydraulic conductivity changes based on aggregate size distribution, stability, and wetting rate information in order to determine the stability of the pore network during wetting. Two independent experiments were conducted in the laboratory on two different soil types to evaluate the proposed model. The decrease in mean weight diameter of aggregates exposed to different rates of wetting was used to predict the mean weight diameter after wetting, which was then used in a model to predict changes in hydraulic conductivity. The results show that the changes in predicted and measured hydraulic conductivities between the potentials of -0.5 and -4 kPa were significantly correlated for both soils, despite an overestimation of the measured changes. The close correlation suggests that this bias could be empirically estimated from measurements of aggregate size and that information on aggregate size and stability would be useful for predicting changes in hydraulic conductivity.