Protonic Magnetic Resonance Properties of the Hard Rocks Fracture Zones in the Department of Donga

Abstract

The Donga Department is located in the northwest of Benin in an area made up of crystalline and crystallophyllic basement rocks where most of the groundwater resources are found in the area of weathered and conductive fractures. The carrying out of drilling campaigns in this department are often crowned with a significant number of negative boreholes (<0.7m3 /h) due to the poor choice of sites for drilling. This leads to situations of difficulties in supplying drinking water, or even more frequent shortages during the dry season. The objective of this study is to use geophysical methods characterize the fractured basement areas, with a view to improving the implantations and the sustainable management of the aquifers they contain. The application of the Protonic Magnetic Resonance (PMR) method made it possible to determine the hydrogeological properties of the fracture zones. As a result, the determination of the hydrodynamic properties shows that the WPMR, T2* and Sy values in 5 different localities of the study area are between 4 and 13% respectively, between 150 and 212.5 ms and between 2.3 and 8.2%. The minimum height of the water slide is 820 mm and the maximum height is estimated at 3672 mm for a water reserve of up to 2313 mm in the Donga gneisses. It emerges from this study that in the department of Donga the PMR water content is also a function of the particle size. T2* of the fractured zone.