Hydraulic conductivity of variably saturated porous media: Film and cornerflow in angular pore space

Many models for hydraulic conductivity of partially saturated porous media rely on oversimplified representation of the pore space as a bundle of cyli ndrical capillaries and disregard flow in liquid films. Recent progress in modeling liquid behavior in angular pores of partially saturated porous med ia offers an alternative framework. We assume that equilibrium liquid-vapor interfaces provide well-defined and stable boundaries for slow laminar fil m and corner flow regimes in pore space comprised of angular pores connecte d to slit-shaped spaces. Knowledge of liquid configuration in the assumed g eometry facilitates calculation of average liquid velocities in films and c orners and enables derivation of pore-scale hydraulic conductivity as a fun ction of matric potential. The pore-scale model is statistically upscaled t o represent hydraulic conductivity for a sample of porous medium. Model par ameters for the analytical sample-scale expressions are estimated from meas ured liquid retention data and other measurable medium properties. Model ca lculations illustrate the important role of film flow, whose contribution d ominates capillary flow tin full pores and corners) at relatively high matr ic potentials (approximately -100 to -300 J kg(-1), or -1 to 3 bars). The c rossover region between film and capillary flow is marked by a significant change in the slope of the hydraulic conductivity function as often observe d in measurements. Model predictions are compared with the widely applied v an Genuchten-Mualem model and yield reasonable agreement with measured rete ntion and hydraulic conductivity data over a wide range of soil textural cl asses.