Résumé
In the semiarid Lake Chad Basin (LCB), the transboundary quaternary sedimentary aquifer is the main source of drinking water. Climate variability and the increase in population around the Lake raise concern on the issues of water supply and water management. The knowledge about the availability of groundwater resources in LCB is limited due to the scarcity of information about hydrodynamic parameters of the aquifers. To fill this gap, geophysical surveys based on Magnetic Resonance Sounding (MRS) method were performed in the Yaere aquifer (Northern Cameroon) and in the Kadzell aquifer (Southeastern Niger). The MRS method is a non-invasive technic which has the advantages to be directly sensitive to groundwater, and to allow estimating hydrodynamic parameters. Six representative sites were investigated by MRS (three per aquifer) and are presented in this paper. MRS results are compared to measured piezometric level and to geological description when available. Despite naturally challenging field conditions (high natural electromagnetic noise, and low geomagnetic field), MRS data of good quality were obtained. The piezometric levels estimated with MRS are close to the water level measured in neighboring wells or boreholes. The results also show contrasts in MRS water content and transmissivity in good agreement with expected behavior of aquifers: high values of water content (16%-32%) and transmissivity (2 10-4 m2/s– 4 10-2 m2/s)were recorded near the Lake and the rivers (e.g. near the Komadugu Yobe and the El beid River), and lower values were obtained at distance or in flat clayey areas. These encouraging results promote the use of MRS at the basin scale, to better estimate the available volume of fresh groundwater resources.