Characterization of superficial deposits using electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) geophysical methods: A case study

• Characterization of shallow aquifer heterogeneity in semi-arid and arid areas
• Integration of geological, hydrogeological and geophysical datasets
• Cost-effective use of ERT and HVSR to identify locations for groundwater uptake

In developing countries, superficial aquifers are potential water resources for irrigation in agriculture. Cost effective methodologies are required to characterize those deposits in order to identify better locations for groundwater abstraction. This study has investigated the potential use of combined electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) to characterize the heterogeneity and thickness of superficial deposits deployed along of a river. The ERT and HVSR methods are non-invasive geophysical techniques, simple, efficient, robust and easy-to-use in alluvial environment contexts. Using these geophysical methods in the Kou basin in Burkina Faso (West Africa), a good correspondence is obtained between ERT images and resonance frequencies determined on the HVSR profiles perpendicular to the Kou River. The superficial deposits and the bedrock depth have been characterized and mapped. The role of faulting and magmatic intrusions in the accumulation of fractured, deconsolidated and weathered bedrock materials and the filling of superficial deposits have been observed and highlighted. From a hydrogeological point of view, the thickness of (clay-free) superficial deposits presents a relatively important groundwater reservoir and potentially high productivity. The ERT and HVSR were proven to be efficient and complementary methods in superficial deposit environment characterization, and a viable option for exploration of superficial deposits in terms of groundwater reservoir in environments where the bedrock exhibits strong lateral variation due to faulting or volcanic activities.