A VANISHING DIFFUSION PROCESS IN UNSATURATED SOILS

A model for simulating water flow and air flow in unsaturated soils is presented herein. Drainage from a one-dimensional soil column is spec ifically investigated. A mathematical analysis of the equations reveal s that, due to a vanishing diffusion process, the gradient of the wate r degree of saturation is infinite at the water table. Moreover, this discontinuity propagates at a velocity that satisfies a local non-line ar equation involving only the properties of the material. A numerical simulation of this problem serves to confirm the results obtained. (C ) 1998 Elsevier Science Ltd: All rights reserved.