Contribution for better understanding the quaternary aquifer of Lake Chad basin in Cameroon.

International audienceIn the Far north of Cameroon, the main source of drinking water is the Quaternary sedimentary aquifer. In this semi-arid region, with high population growth, the groundwater resource is affected by climate and land-use changes but also by the impact of Lake Chad level variation. For better quantifying the role of each of these processes, it is necessary to improve our knowledge about aquifer characteristics. Thus, 13 MR soundings were performed in 2012 and 2103 for characterizing hydrodynamic properties of aquifer in the vicinity of the Limani-Yagoua sand-ridge which is considered by many authors as the limit of the Mega-LakeChad during the last humid period of Holocene (~-6000 years BP). Despite of difficult conditions of measurement (high natural electromagnetic noise in the afternoon and low Lamor frequency), data of acceptable quality were obtained with a fairly efficientvelocity of execution (1 sounding per day). MRS results are in good agreement with available geological logs and with the water levels measured in neighboring wells. They also show high heterogeneity of aquifer characteristics: the water content ranges from less than 2% to 25.5 %, the thickness from 4 to 25 meters and the transmissivity (calibrated with available data in literature) varies from 6×10-5 to 1 ×10-4 m2/s. No water was found within the first 30 m of the Limani-Yagoua sand ridge, confirming the absence of water storage in this formation laid on the regional quaternary aquifer. During this study, the main limitation for MRS was the depth of investigation (~ 30 meters) with the equipment we employed (Numis Lite). Thus a new field survey is scheduled in March 2015 with more powerful equipment (Numis Plus)