Describing Soil Hydraulic Properties From Oven-Dry to Full-Saturation Conditions.

Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that matric potential is attributed to capillary forces only and ignores the adsorptive surface forces. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which water content is less than the residual water content. We extend the existing effective-saturation-based retention and relative permeability models to the oven-dry condition in the form of water content formulation. The extended retention models are compatible with the commonly-used relative permeability models. The extended models are identical to their un-extended counterparts when a soil is at high and medium water contents and start to deviate when a soil is at low water content. There is no need for a refitting of parameters or an introduction of additional parameters. The extended models were verified using data from literature and were applied to typical soils.