Impact of highly permeable sediment units with inclined bedding on solute transport in aquifers

Investigations in outcrops of non-homogeneous gravel deposits in north-eastern Switzerland by Jussel et al. [Jussel P, Stauffer F, Dracos T. Transport modeling in heterogeneous aquifers: 1. Statistical description and numerical generation of gravel deposits. Water Resour Res 1994;30:1803–17] revealed distinct sedimentary structures or facies elements appearing as more or less horizontal lenses and layers embedded in extended patches of background gravel material. One of the observed sediment units consists of highly permeable inclined sequences of gravel layers. This inclination manifests itself as a strong anisotropy of the hydraulic conductivity with inclined principal directions. In this paper, the role of highly conductive sediment units with inclined bedding is investigated by a series of three-dimensional numerical flow and advective transport experiments. A typical single lens with inclined principal axes of the hydraulic conductivity tensor is investigated, which is embedded in homogeneous background matrix material. Particle tracking shows pronounced lateral (horizontal and vertical) distortions of the flow path depending on the angles of the bedding of the lens. The results allow better understanding of the flow and transport phenomena that are finally responsible for macrodispersion effects in similar gravel aquifers.