Présentations Colloques

Oral Presentation
Session 2.01: Groundwater in semiarid regions – a long-term view on changes in aquifer balances. Hydrogeology in developing countries.
Groundwater Resources in the Aquifer Systems of the Iullemeden and Taoudéni Tanezrouft Basins, Sahelo-Saharian Region
In the Sub-Sahara and Sahel Region, the aquifer systems of the Iullemeden and Taoudeni Tanezrouft Basins cover 2.5 million kmC, and are spread over seven countries (Algeria, Benin, Burkina Faso, Mali, Mauritania, Niger and Nigeria), with isohyets ranging from 50 to 1 300 mm yr.**The assessment of the potential groundwater resources of these aquifers and their relationship with the Niger River, together with climatic change impacts, were undertaken in 2012 & 2013. Such a study led to a significant improvement on the knowledge of the aquifer systems behaviour, through the development of innovative scientific technics for highlighting data recorded since decades in the numerous national databases.**Results underlined the huge amount of available groundwater resources, of good quality, slightly sensitive to climatic changes and to pollutions, and under-exploited (0.5% to 3% of the renewable resource)-**- A huge groundwater reservoir spreads over 2.5 M kmC, in sandstone formations, up to 1000 m thickness (300 m average), with a quite good productivity almost everywhere and with some large areas of very high potential.**- Rainfall infiltration is the main source of aquifer recharge though recharge from the Niger River is not negligible but limited to the vicinities of the river. The recharge has been computed based on land and morphological parameters obtained from satellite imagery processing and on the spatio-temporal distribution of rainfall, at the mesh level of the groundwater flow model and for each time step.**- Exfiltration from the aquifer systems is by far the main output of the aquifer balance under the prevailing Sahelian climatic conditions. Five main widespread exfiltration areas were demonstrated in the studied area, with the particular case of the Gao Graben, which links - and proves - the continuity between the Iullemenden and Taoudeni aquifer systems. **This huge potential groundwater resource represents a great opportunity for the Region development. However, its management requires to be properly organized because this is a transboundary resource shared by seven countries in a very politically sensitive Region.**