ABSTRACT
South-western Burkina Faso and southern Mali share an aquifer system that forms part of the large West-African sedimentary basin of Taoudeni. With a surface area of around 40,000 km2 inside Burkina Faso and a depth that can reach over 2000 m, this sedimentary aquifer system provides most of the water for the human (drinking water) and economic (mainly agricultural) needs of the country. In the present semi-arid conditions characterised by a considerable decrease in the rainfall during the last 40 years and a demographic explosion resulting in a greatly increased need of water for both human consumption and economic development, the management of this important groundwater resource has become a priority not only for Burkina Faso but also for the international community. A hydrogeological, multi-disciplinary approach, combining, among others, stratigraphy, hydrodynamic field data, geochemistry and isotopic techniques with geological and hydrogeological modelling was used to improve the knowledge of the aquifer and the efficiency of its management. While the geochemical and isotopic techniques employed in the study area do not provide convincing arguments in favour of the existence of individual aquifers in the separate geological formations, the hypothesis of vertical hydraulic continuity throughout the Burkina Faso part of the sedimentary basin is still questioned as well the estimated effective recharge rate. The piezometry of the system indicates that the drainage basin locally discharges into the main Burkina Faso rivers. However, in view of the low relief of the topography as compared to the base level depth of the flow system, regional flow with major discharge into the Bani and Niger rivers in Mali cannot be excluded according to Toth’s (1963) model. On the basis of the results and interpretations of field data, a conceptual representation of the hydrogeological situation was put together and built into a geological (aquifer geometry) model. Further studies on both sides of the frontier with Mali should contribute to the validation of some assumptions that are still being considered as conceptual hypotheses as well as improvement of our knowledge of this important aquifer system.
