Hydrogeological Information System Elaboration of Coastal Aquifer AQ-2 of Pointe-Noire, in the South-west of Congo-Brazzaville

Abstract

The region of Pointe-Noire (south-west of Congo-Brazzaville) located on a coastal sedimentary basin of about 6 000 km2 is primarily formed by unconsolidated rocks with very little interstice porosity. It is made by a complex multi-aquifers system interconnected. Previous studies have highlighted the lack of data and the need to acquire a better knowledge of the groundwater resource in Pointe Noire. This study intends to represent and schematize the functions of the reservoir and the hydrodynamic behaviour of aquifer AQ-2. A Hydrogeological Information System (HIS) of aquifer AQ-2 is drawn up from historical reconstitution of the piezometric heads data carried out of various series of measurements from boreholes and piezometers .Two hydrological zones related to the topography and/or relief of study zone were identified: a zone of the littoral plain, characterized by protuberances and a strong depth of piezometric surface with hydraulic gradient of 0.03, revealing a flow of significant rate and an average permeability which represents a drainage weaker than the recharge; and a zone of the plateaux, characterized by a type of hydrogeologic structure called hydraulic threshold representing a fall of piezometric surface and hydraulic gradient (0.005 and 0.006), which can be explained by variations of flow rate or permeability. This morphology is imposed by two phenomena, the contribution of water of the plateau of Hinda on one hand and on the other hand, the general drainage direction revealed by the presence of the semipermeable facies.