Seepage into Variably Saturated Porous Medium

Abstract

A numerical model is developed for simulating the interaction of a surface water body with a variably saturated porous medium. A boundary condition simulating the soil‐water pressure head at the boundary between the porous medium and the surface water body, expressed as a function of the soil‐water flux at the boundary, is also integrated into the model. The interaction of the surface and subsurface flow system leads to a more accurate simulation of soil‐water flow velocity, which is of importance in problems dealing with the seepage of pollutants into the subsurface environment. The Galerkinfinite element method is used to solve the variably saturated flow equation and the Darcy equation, employing isoparametric elements that simulate the physical geometry of the porous medium. Solutions to the model give the transient position of the stage of the surface water body and the distribution of the phreatic surface in the porous medium, providing robust estimates of the rate of seepage into the porous medium. The capability of the model is illustrated by considering the interaction of a semipervious surface pond with a variably saturated stream‐aquifer system.