  Using a Cauchy integral formulation of the boundary integral equations, we
simulate the erosion a porous medium comprised of up to 100 solid bodies
embedded in a Stokes flow. The grains of the medium are resolved individually
and erode under the action of surface shear stress. Through nonlinear feedback
with the surrounding flow fields, microscopic changes in grain morphology give
way to larger-scale features in the medium such as channelization. The
Cauchy-integral formulation and associated quadrature formulas enable us to
resolve dense configurations of nearly contacting bodies. We observe
substantial anisotropy to develop over the course of erosion; that is, the
configurations that result from erosion generally permit flow in the
longitudinal direction more easily than in the transverse direction by up to a
factor of six. These results suggest that the erosion of solid material from
groundwater flows may contribute to previously observed anisotropy of natural
porous media.
