ELECTRICAL RESISTIVITY PROFILING OF BURIED VALLEY AQUIFERS IN THE EDMONTON REGION

Buried valley aquifers underlying the Edmonton region are a potential source of potable groundwater in the area. Although these valleys have been mapped previously, the sedimentology of the valley fills is less known and is vital for assessing the buried valley flow systems. Greater understanding of the extent, depth, and geometry of these sediment packages that make up the valley fills is critical when considering these as an alternative water resource for the area.

This study utilizes previous work assessing the valley network geometry via water well reports to select electrical resistivity tomography (ERT) sites for further valley characterization in areas of considerable sediment thickness and valley convergence. Resistivity values ranged from saturated sediment at 15-30 Ωm to unsaturated sediment at 70-300 Ωm. ERT surveys done over the proposed mapped extent as well as the main thalwegs provided an understanding of geometry and further definition of the actual extent of the buried valleys with thalweg depths up to 80 m. Comparisons of geophysics results and surface outcrops in addition to well log data has confirmed that buried valleys can be composed of finer sand to coarse gravel, where coarser sediment with higher resistivities are indicated in the larger channels such as the Beverly valley.

This improved understanding of buried valley sedimentology and extent permits future groundwater modelling for the area to better assess the Beverly valley network flow systems. The ERT data combined with well logs and outcrop identification has provided better characterization of buried valleys in the Edmonton area; these results can be used to make informed decisions regarding the water security of central Alberta.