Using VLF-EM, vertical electrical sounding (VES) and pumping test in large-diameter wells to characterize shallow groundwater — A case study of the Karfiguela paddy field in Burkina Faso

Abstract

Shallow groundwater is a potential and profitable resource for developing countries. Appropriate and cost-effective methodologies are therefore needed to characterize these resources in order to understand their productivity and identify the best locations for their exploitation. These methods are simple, effective, robust and easy to implement in alluvial and agricultural contexts. The VLF-EM electromagnetic survey of 6 traverses provided a 2D image of subsoil conductivity. Combined with vertical electrical soundings and logging, it highlighted the lateral and vertical heterogeneity of the subsoil, as well as the thickness of the deposits that constitute the shallow aquifer. These geophysical investigations, coupled with piezometric monitoring and pumping tests in large-diameter well data have enabled the estimation of the groundwater productivity. The results show that the surface aquifer consists of alluvial, sandy, gravelly and clayey materials resting on the intrusive bedrock of the weathered fringe. The thickness of these weathered deposits varies from 27 m to 31 m. Pumping tests showed transmissivity of around 10−3 m2/s and storage coefficients of around 10−1. Operating rates range from 4.4 m3/h to 32.73 m3/h, with drawdowns of less than 1 m for 6 h of pumping. The shallow groundwater could therefore be an interesting resource for irrigation.