A Review of Porous Media Flow Theory and Application

Modern software packages allow the easy development of ground water flow models by a wide range of users.  Implicit in these models, but not readily apparent to users, are a series of fundamental assumptions.  Models like MODFLOW that built on assumptions of laminar flow in isotropic, homogeneous media changed our view of gravity driven ground water flow, for example Toth in the early 1960’s.  As computing power has grown over the last 50 years the complexity that can be represented in models has similarly grown.  The ability to represent complex geologic environments has not, however, always led to accurate simulations of ground water flow.  In particular, total fluxes and contaminant transport velocities have proven difficult to realistically simulate. 

New modeling techniques are being developed that can address more complex flow systems.   For example, Lattice-Boltzmann simulations are adept at reproducing complex and changing boundary geometries, turbulent and laminar flows, multiphase-multi-component flow of miscible and immiscible fluids, and buoyancy-induced convection due to solute and thermal gradients. This makes these methods particularly attractive for a wide range of geofluid-mechanical applications.  While these models remove many limiting assumptions they require significant increases in computing and modeling effort.

While improved computer interfaces allow easy model development they can also hide some of the fundamental assumptions behind the models.  By understanding and applying the assumptions built into their models ground water hydrologists can use these tools to full advantage.