Contribution of Electrical Resistivity Tomography to the Characterization of Aquifers in a Sub-Outcrop Context in the Basement Zone of the Oubri Region (Burkina Faso)

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Résumé

Population growth and climate change are putting drinking water resources at risk, making groundwater a key solution to these challenges. In Burkina Faso, more than 80% of the geology consists of crystalline bedrock, which necessitates the search for bedrock aquifers for water supply. The complexity of these aquifers has led to numerous unsuccessful water drillings. Electrical resistivity tomography (ERT) profiles were therefore conducted in the cities of Loumbila and Ziniaré using the resistivity-meter SYSCAL Pro system, in a Wenner-Schlumberger configuration, to better identify the characteristics of potential aquifer zones. ERT field measurements use a series of electrodes spaced 5 m apart to measure electrical resistivity along the profile. The inversion results are presented as cross-sections showing the distribution of the subsurface’s true resistivity as a function of depth along each profile. The (2D) inversions reveal four geoelectric zones: a first zone characterized by low resistivities (<150 Ω∙m), indicating a favorable zone containing water, followed by a second layer with values ranging from 150 to 400 Ω∙m, representing weathered zones, a third layer with values ranging from 400 to 2000 Ω∙m, representing zones of fissured and fractured bedrock, and a fourth layer with resistivities greater than 2000 Ω∙m, indicating sound bedrock. The study demonstrates that the use of the Wenner-Schlumberger array improves the characterization of aquifers in bedrock terrain.

Mots-clés

Burkina Faso, Bedrock, Aquifer, Tomography, Water Drilling