It is estimated that 700.000 people live in Cotonou, the biggest city in Benin, and another 700.000 in Cotonou’s suburban area. In total, one Beninese out of 6 lives in the Greater-Cotonou region. Groundwater is the major source of drinking water. The public water supply network is fed by two wellfields. It is estimated that half the people of Cotonou is connected to the public network. In the suburban area, this ratio varies. The residents of the Greater-Cotonou who are not connected to the public network rely on private local distributors or have their own well. While the wellfields tap the Mio-Pliocene aquifer, most of private distributors and private well-owners tap the shallower Quaternary aquifer (mostly via hand-dug wells).
The demographic growth is high in the suburban area and the water demand is increasing. At the same time, there is a risk that human activities contaminate groundwater. Solutions are sought to address this double pressure.
Supported by VIA Water, the NOEVA project aims at assessing the groundwater resources on which the Greater-Cotonou area relies, in order to improve the management of water supply to the residents. Concretely, the project aims at determining the geometry of the aquifers and their properties, as well as the recharge rate.
An innovative approach
The project consists in a hydrogeochemical study, a survey of piezometers, pumping tests, as well as an innovative coupling of two geophysical methods: PMR (Proton Magnetic Resonance) and TDEM (Time-Domain Electromagnetic Method).
The project is carried out by 3 young Beninese researchers affiliated to INE (the National Institute of Water in Benin) and IRD (the French Research Institute for Development): Valerie Kotchoni, Christian Alle et Fabrice Lawson.
The role of IGRAC
IGRAC supports the project team in communication and dissemination, so that the scientific results translate in messages for the key stakeholders, and eventually in concrete actions.
The results of the NOEVA project provide insight on the dimensions of the aquifers, the water table depth, the volumes of groundwater, the recharge rate, etc. These data will serve to develop groundwater numerical models, in order to determine the position for new wellfields and delineate protection zones around the wellfields, among others.