An example of hydrogeological modelling and transboundary management between France and Belgium: the Carboniferous Limestones Aquifer
Résumé
The Carboniferous limestones aquifer is 150 km long and 30 km wide, and crosses the administrative France-Belgium boundary. Recharge areas are located on the eastern part of the aquifer, in Belgium, where limestones lay under a few meters of sedimentary terrain. Slightly dipping toward the south-west, the aquifer geometry and groundwater flow directions were not accurately known. Moreover, since the very late 19th century, it has been pumped to provide drinkable water and supply heavy factories in France and Belgium. Due to over-pumping during the second part of the 20th century, its water level dramatically decreased, to 90 m deep. From the 90’s until now, corresponding to the end of industrial period, groundwater consumption has decreased and water table is now stabilized and slowly coming back to a more “natural” level in some areas. In 2009, a new transboundary cooperation program named “ScaldWIN” was launched in order to improve sustainable management of this resource.
Despite technical problems due to the lack of data before 1950, an updated transboundary geological log, a comprehensive “chronicle” of groundwater pumping rates, new boreholes and results from geochemical sampling campaigns have allowed to precise the aquifer recharge processes and groundwater flows since 1900. With the help of French drinking water suppliers and Belgian quarries representatives, groundwater consumption scenarios have been drawn up for the 2010-2050 period at a large scale. Thanks to a new 3D numerical model, these scenarios have been used to generate piezometric maps and groundwater level charts. These tangible results helped to better understand where, when and how pumping rates restrictions or increases will influence groundwater levels and aquifer productivity. Furthermore, 3D model outputs have been compared to “balance test” criteria described in the Water Framework directive. For public and private stakeholders, “ScaldWIN” project results are now seen as useful tools to decide which kind of transboundary management will be set up in the near future.