Combination of Structural Data and GIS Tools in the Delineation of Groundwater Potential Zone in Crystalline Terrain: The Case of Southeastern Senegal

In some West African regions, the craton is made by birimian formations that constitute the basement in these areas. In Senegal, the Kedougou Kenieba inlier is characterized by the presence of fractured aquifers, thus constituting a problem of availability and mobilization of groundwater resources in this zone. Evaluation of groundwater potentiality zone is studied by using Remote Sensing and GIS technics integrating eight thematic parameters (Rainfall, geology, lineaments, regolith thickness, and weathered thickness proximity of rivers). The weighted overlay technic is used and appropriate weight were evaluated by statistical approach with a linear regression model in order to determine and built influence percentage of groundwater storage related to each parameter. Results showed a map of five groundwater potential classes ranging from very good to very low potentiality. High groundwater potential areas are located in the southern part of the Sabodala mining area and contrast with the northern part where groundwater potential is low due to lower rainfall and rock types dominated by granite formations in most parts of the area. Very good potentials occupy about 5% of this study area. These areas are mainly located in the southern part of the Gambia River watershed between the isohyets 1250 to 1150mm and on the MTZ. Areas with good potential are mainly found on volcano-sedimentary formations, but they are more concentrated on the southern part of the Gambia watershed where interesting flows can be observed (8 to 20 m3/H). This result is in compliance with the flow rate data observed in this southern part. On the other hand, the moderate potentialities constitute the class which is found on all lithology types and represent 35.1% of the total surface of the study area (1280.6 Km2). However, the very low potentialities are only found in the northern part and occupy an area of 873.10 square kilometers corresponding to 10.5% of the total area of the area. These results confirm that in the northern part and the granitic terrains have weak potentialities and the risks to get a negative boreholes remain high at these zones. Results show that there is a good correlation between the good potential areas identified by the GIS and the areas with appreciable borehole yields and the tectonic basins.