What Defines the Effective Hydraulic Conductivity of a Heterogeneous Medium?

Mauricio Vera and Ty P.A. Ferré

Department of Hydrology and Atmospheric Sciences

The University of Arizona, Tucson, AZ

Most geologic processes produce heterogeneous porous materials; therefore, these media have different characteristics, which make them complex systems to analyze. This research, is focused on the bulk behavior of these heterogeneous media, which mostly depends on the particle size distribution and the spatial distribution of the particle size fractions. Thus, we study a medium comprised of two particle sizes as simplest of heterogeneous systems, in order to examine the effect of the percent composition of small and large particles on the bulk hydraulic properties, which are characterized by the effective hydraulic conductivity (Keff). The methods are based on upscaling of an alpha or connectivity parameter to weight the Keff. For this, we examine the full range of geometries that lies between the two end members of a binary medium, when the conductivity (K) is distributed parallel and perpendicular to the flow direction. The results are computed by using groundwater numerical model (MODFLOW) and they validate the hypothesis that one important method analyzed (energy dissipation) explains the Keff by computing the volume weighting of K. This energy dissipation, the alpha parameter, and the changes in the fraction and the distribution of the K inclusions, could make significant changes in Keff results.