CONTRIBUTION OF REMOTE SENSING AND GEOPHYSICS TO HYDROGEOLOGICAL RECONNAISSANCE IN THE BASEMENT AREAS OF THE GUERA REGION: CASE OF THE CITY OF MONGO (CHAD)

The aquifers of the base cracked are excellent reservoirs of water in the Guera region in general and in Mongo town in particular. In fact, the basement fractures and fissures of the base are the areas of preferential flow to groundwater reserves in this area. The study of lineaments has been conducted using Landsat 8 images to highlight these fractures. All the techniques used in remote sensing resulted in the enhancement of the structural and linear elements contained in the raw images, thus allowing a better cartography of the geological accidents. The map obtained after the treatments shows a high density of lineaments of very variable sizes. This map can be used as a basic document for the implantation of boreholes in this basement area. The map of the lineaments obtained has been validated by electrical surveys allowing some of these lineaments to be intersected in order to determine those which generate good flows or those which reflect the influence of mega fractures. A statistical analysis of the parameters that can influence the productivity of the boreholes (total depth, alteration thickness, specific flow) was performed. This analysis reveals that total depth has no effect on drilling productivity. A large thickness of alteration increases the chances of having a significant flow. And beyond 60 meters deep in the cracked rock, the chances of getting a consistent flow decrease. This work has improved knowledge of the fractured aquifer in the study area. They will guide future hydraulic campaigns for the identification of potential sites for the implementation of structures in the basement area.