Large changes in the Lake Chad surface area occurred during the Holocene and had an impact on aquifer recharge, yet little is known on past and present pattern of the aquifer hydrodynamics. Two complementary MRS field surveys (23 soundings) were conducted in 2008 and 2010 for accessing of the free water content and hydraulic properties of aquifers in the semiarid northwestern part of Lake Chad Basin. High MRS water contents (10-35 %) and permeability values (10-3 to 10-2 m/s) were shown below present-day Lake Chad. At distance, below the former clayey deposits of the Megalake Chad, lower MRS water content (8-13 %) and permeability (10-4 to 10-3 m/s) values were estimated for the unconfined aquifer. These low porosity and permeability values suggest limited aquifer fluxes, in accordance with the occurrence of isotopically determined palaeo-groundwaters below the clayey plain. Intermediate and homogenous hydraulic properties (MRS water content and permeability values ranging from 16 to 25% and 1.10-3 to 3.10-3 m/s, respectively) were found in the valley of the Komadougou River which currently represents the main source of recharge for the aquifer. This study proved the decisive contribution of MRS for quantifying past and present surface-water/groundwater exchanges interactions in flat sedimentary basins.


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