Hydrogeochemical characterization of water in the Kadey watershed (Central Africa): An approach to the dynamics of groundwater/surface water exchanges

• The existence of a hydraulic connection between the water table and the rivers that drain it. • During high water, groundwater is fed by watercourses; during low water, the flow reverses. • The groundwater levels curves show that the rivers are then fed by draining groundwater. • River and groundwater both derive from rain, confirming hydrodynamic interpretation results. The Kadey watershed, a hydrogeochemical system in a quasi-isotropic fissured basement environment, presents distinct groundwater/surface water exchange functions. The analysis and interpretations of hydropluviometric, hydrodynamic, and hydrochemical data are used to understand these exchanges and their impact on the hydrodynamic behavior of the system. The results reveal that the watercourse and groundwater act as communicating vessels, with the direction of flow depending on the season. It also found that the river water and the groundwater predominantly originate from rain, as indicated by a principal components analysis (PCA). The first results show that the waters of the Kadey watershed are acidic (5.85 < pH < 6.17) and very weakly to weakly mineralized (18 < CE < 140 µS/cm) with two dominant facies: calcium-magnesium bicarbonate (HCO3-Ca-Mg) and the sodium-potassium bicarbonate facies (HCO3-Na-K). Several environmental factors control the quality of the waters of this basin: lithology, anthropogenic activities and climate. It is also at the origin of the noted presence of ETMs (Fe > Mn > Pb > Cr > Cu > Zn > Cd > As > CN) in the groundwaters of the locality. These insights contribute to the understanding of water exchange mechanism and have implications for the management of water resources in the Kadey watershed.