This study intends to see the temporal and spatial evolution of groundwater salinization at the northern and western zone of the CT aquifer in the Sine-Gambie region (Senegal). To do this, a hydrochemical study was conducted in 2015 and compared with previous studies (2000 and 2012). This study is essentially based on the two parameters, electrical conductivity and chloride content. The results obtained show that the evolution of salinity observed in these areas is explained by a contamination of the groundwater by the waters from the Saloum River and the sea. The comparison of groundwater electrical conductivity maps showed a salinity increase between 2000 and 2015; with a salinization phenomenon which increases toward inland in phase with chloride levels that doubled in some wells. The study also shows that several calcium bicarbonate facies have evolved to calcium chloride facies, and calcium chloride facies to chloride sodium facies.

The Chari-Baguirmi aquifer, located East of Lake Chad, is the main source of water in this region. The groundwater piezometry is marked by a large depression. The work presented here aims to understand the development of this depression. The approach is based on a sedimentological study coupled to a hydrogeochemical study of the groundwater. The sedimentological analysis revealed the grain size heterogeneity of the different layers. Clay mineralogy showed that the deposition of sediments takes place from the periphery to the center of the depression. This sedimentation mode suggests the existence of a morphological cuvette to which sediments are driven by the transport agent. We deduced the existence of a "structural" depression unlike the common assumption of an origin due to accentuated evaporation of the groundwater over the depression area. The combined study of chloride and oxygen-18 has shown that the area between Lake Chad and the piezometric depression is a special evaporation zone. This means that the process of evaporation of groundwater does not occur mainly in the center of the depression. The first results of this work provide new insights into the functioning of this important aquifer system and the establishment of the large Chari Baguirmi piezometric depression.