Benin transboundary aquifers are inventoried in the framework of the UNESCO-ISARM project entitled “Inventory of transboundary aquifers in West Africa”. Data and information collected through this project will enable to establish the database of UNESCO-IGRAC Centre of the transboundary aquifers in West Africa. They will also help to develop a GIS inventory of transboundary aquifers of the West Africa as a contribution to ISARM Africa. This inventory will lead up to elaboration of specific cooperative projects. Identification of transboundary hydrogeological layers was based on hydrogeological cross-sections used to verify the continuity of different aquifers across international borders. In addition, characteristics of each transboundary aquifer were investigated.
The results of this study show that Benin has transboundary continued aquifers in two sedimentary basins: the coastal sedimentary basin in the Southern and the sedimentary basin of Kandi in the North-East. In the first basin, there are four aquifers shared with the Togo in the West and Nigeria in the East. From the bottom to top, we are: the Turonian-Coniacian (Upper Cretaceous) aquifer (sands and sandstones), the Paleocene aquifer (limestones and sands), the Continental terminal aquifer (sands) and the Quaternary (the coastal and alluvial sands). In the second basin, there are two aquifers shared with Niger in the North and Nigeria in the East: The Paleozoic (Cambrian-Ordovician) aquifer (conglomerates and sandstones) at the base and the Silurian and Quaternary aquifer (sandstone and alluvial sands of Niger River) at the top. These inventoried aquifers are of varied hydrodynamic type (free, captive or semi-captive) and of varied quality (including facies and total mineralization).