Contribution de la géophysique a l’étude des structures et leurs implications en Hydrogéologie (sud-Cameroun)

Abstract

The Kribi-Campo region is one of the most attractive areas in Cameroon due to its proximity to the sea. Despite its location, residents still have a lot of trouble getting enough water. The complex bedrock that dominates this area has an impact on the factors affecting groundwater recharge. The quality and availability of groundwater is essential for human consumption and social and economic activities in a locality. The geological, hydrological, topographical and hydrodynamic factors of a region influence the groundwater potential zones. The main objectives of this thesis are to identify potential zones groundwater for construction of productive boreholes and to assess the main sources of processes related to the origin of mineralization in the aquifers of the study area. Analytical Hierarchical Process (AHP), Frequency Ratio (FR), Shannon Entropy (SE) and Weight of Evidence (WofE), Geographic Information Systems (GIS) and Multivariate Statistical Analysis were used in this process. Fifteen (15) groundwater conditioning factors were selected using conventional data, remote sensing and vertical electrical sounding. Weights were assigned to the conditioning factors and their characteristics based on the AHP, FR, SE and WofE methods, and then integrated with ArcGIS software to generate the groundwater potential maps. The resulting maps were then categorized into four zones: very low, low, moderate and high. The areas under the Receiving Operating Characteristics (ROC) curve were calculated to assess the performance of the models. The results showed that the WofE model (success rate, 78.8%; prediction rate, 85.5%) has the highest prediction rate, followed by the SE model (success rate, 83.1%; prediction rate, 83.4%), the FR model (success rate, 77.4%; prediction rate, 74.9%) and the AHP model (success rate, 49.3%; prediction rate, 61.9%). According to the results, the PP model is the most reliable for delineating the groundwater potential zones in the study area The principal component analysis made it possible to determine the phenomena at the origin of the mineralization of the water and the links between these waters. Our results show two hydrogeochemical classes and their sources: interaction process between water and rock (main mechanism of ion production); a salinization process resulting from natural phenomena (seawater intrusion) or from anthropogenic activities due to wastewater discharges linked to agricultural activities. This thesis can serve as a roadmap for hydrogeological explorations and groundwater resource management in the study area.