Caractérisation hydrogéologique des aquifères de socle altéré et fissuré du bassin versant de l’Olézoa à Yaoundé, Cameroun

Abstract

The ground water of the altered and fissured basement of the Olezoa watershed in Centre-South Cameroon provides water to its surrounding population. However, the hydrogeological characteristics of these basement aquifers have not yet been well studied. The present study is an attempt to better comprehend the structure and functioning of these basement aquifers. It mainly focuses on the description of soil profiles, structural investigations, as well as hydrometric and piezometric follow-ups. Preliminary results indicate that the soil profile is of a polyphase type similar to others observed in other parts of the world, particularly those developed on granito-gneissic formations, exposed to weathering and erosion. This is an ancient weathering system (10-20 m thick) derived from the degradation of lateritic systems and a more recent weathering (2-3 m thick) developed on the fresh rock. In addition, the profile contains alteration microreliefs, the spatial distribution of which can locally influence flow dynamics. These dynamics are similar to those that commonly occur in basement rocks under wet tropical climates. The hydrometric and piezometric characteristics indicate that the aquifers are quite heterogeneous in some areas. The old structural tectonics control the orientation of the drainage pattern. As such, the nature of the landscape designated by the drainage pattern is at the origin of the groundwater flow from the upstream towards the downstream. The distribution of water flows from the upstream to the downstream shows the possible influence of physical and hydraulic properties of the aquifer up-gradient from the well. This study is a contribution to the understanding of structures and the hydrodynamic functioning of basement aquifers. It shows a structural relationship with other aquifers in other parts of world and the regional specificities which influence the hydrodynamics in the weathered and fissured basement.