Solutions for combined saturated and unsaturated flow

This chapter considers the processes of water flow in variably saturated soils. It begins with the presentation of the currently accepted forms of governing differential equations used to represent variably saturated flow in porous media. The numerical methods for solving the equations of continuum mechanics in the many areas of engineering also have been adopted to the solution of the equations for flow in variably saturated porous media. These methods include classical finite difference methods, integrated finite difference methods, finite element methods, and boundary element methods. Of these methods, the classical finite difference method and the finite element methods have received most of the attention for applications in modeling flows through agricultural soils as well as in other applications related to modeling flows in subsurface hydrology. The chapter considers representative applications of the various numerical methods to the solution of the variably saturated flow equations.