An essential resource for the environment and all living beings, water travels along paths that are often little-known and can speed up or slow down its progress. In a Luxembourg environment where floods can be sudden as well as hot summers, following a drop of rainwater from its impact on the ground to its arrival in a watercourse is essential to guarantee good management and quality of water resources, and also to establish forecasts.
On the strength of their experience in hydrology and hydro geology, the research efforts carried out over several decades by Laurent Pfister and his team have been rewarded at the FNR Awards 2020 with the "Outstanding Scientific Publication" prize. This distinction is national recognition of their work published in 2017. With more than 10 years of monitoring water circulation in Grand Duchy catchment areas and numerous international collaborations, the researchers were able to demonstrate for the first time the predominant role of rock type on the age of water and its storage capacity. The more permeable or impermeable a rock is, the more it will respectively delay or accelerate the reappearance of water. This can be days, months, years or even decades.
"Luxembourg is a unique site, an open-air laboratory where numerous watersheds with different geologies rub shoulders in a relatively homogeneous climate. This makes it possible to make precise comparisons,” explains Laurent.
Thanks to this precise knowledge of Luxembourg’s soil, researchers are able to make very useful predictions in the event of floods, for example. In the south of the country – upstream of Luxembourg City and on the left bank of the Alzette – the catchment areas are mainly made up of low-permeability rocks called marls. These marls react very quickly in the event of heavy rainfall (e.g. in winter) and contribute to the bulk of Luxembourg’s floods.
In contrast, other watersheds are made up of permeable rocks such as sandstone. Like sponges, they can store a large amount of water and release it gradually. By the time the water leaves the underground water table to reach its outlet, the water can therefore be very old. "In theory, rock can filter water, but some substances such as pesticides and nutrients will remain underground. The older it gets, the more vulnerable this aquifer will be in some way," says Laurent.
This is particularly important for water resource managers working closely with LIST. In the event of pollution in such a system, the water will indeed be impacted for several decades.
Christophe Hissler, Julian Klaus, Núria Martínez-Carreras, Gwenael Carrer, as well as Mike Stewart (GNS, Nlle-Zélande) & Jeffrey McDonnell (Uni. Of Saskatchewan, Canada)
Picture: © SIP / Uli Fielitz, tous droits réservés