2.6.2.6.2 Unsaturated flow

Single-phase unsaturated Darcy-Richards physics is used. A van Genuchten capillary suction function with index 0.4 and inverse-head 0.1 m^–1 is used along with a relative permeability function of the form:

where S is the water saturation. The capillary function and relative permeability function are kept fixed and are not part of the uncertainty analysis. The van Genuchten parameters are reasonable for rocks and soils (van Genuchten, 1980).