Alluvial aquifers at geological boundaries: geophysical investigations and groundwater resources

Alluvial channel sands in active ephemeral streams are potentially highly productive aquifers that are normally fully recharged annually. The groundwater resource is constrained by the limited three-dimensional extent of these aquifers. Concepts are developed that propose an increase in alluvial aquifer dimensions at geological boundaries. Multi-electrode resistivity and ground penetrating radar are used to investigate the dimensions of an alluvial channel at a geological boundary with the more resistant lithology upstream. These investigations reveal that alluvial channel fill dimensions are increased in the overlying less-resistant lithology downstream of the boundary. Groundwater flow modelling has been used to determine aquifer potential and identify key fluxes, indicating that significant irrigation potential exists from these aquifers.