Lake Grevelingen is both a protected nature reserve and a popular recreational destination, as well as important for shellfish farming and fishing. The water quality and ecology of Lake Grevelingen are largely determined by its water management. Limited water exchange causes oxygen deficiencies on the lake bed. The benthic life suffers and possibly also fish and bird species, which are dependent on benthic animals for their food. To improve the oxygen balance and ecology of the lake, national and regional authorities want to introduce micro-tides. Wageningen University & Research is conducting research into the ecological functioning and sustainable use of Lake Grevelingen. This knowledge is important for proper management of the area.
Lake Grevelingen is the largest saline lake in Western Europe, located between the islands of Goeree-Overflakkee and Schouwen-Duiveland, on the border of the provinces of South Holland and Zeeland. With the construction of the Delta Works, the Grevelingen was closed off from the North Sea, Oosterschelde and the Volkerak. This changed the Grevelingen from an estuary into a closed saline lake in 1971. It had a major impact on nature. The flats and mud flats developed into overgrown islands and banks with valuable vegetation where unique species could establish themselves. Lake Grevelingen is particularly important for coastal breeding birds.
Because of their great natural value, the banks and islands of the lake have been designated as protected Natura 2000 areas. The estuarine nature under water made way for communities that are better adapted to reduced currents and that continued to change. The Brouwers' sluice provides a connection to the North Sea and the Flakkee sluice, which opened in 2017, provides a connection to the Oosterschelde. Through these connections with surrounding waters, Lake Grevelingen remains a saline lake and some exchange takes place.
What are the consequences of a culvert in the Brouwersdam?
Lake Grevelingen is a fascinating water system. After damming up the Grevelingen estuary, sluice management was adjusted several times. This has had an impact on the ecology of the lake. Habitats and species in and around the lake are still changing as a result of these adjustments. The occurrence of oxygen-deficient conditions on the lake bed is a result of limited water movement.
That is why the Getij Grevelingen programme is preparing plans for the introduction of micro-tides by constructing a culvert in the Brouwersdam. This will increase the water movement and thus improve the oxygen conditions. At the same time, there will be more exchange with the North Sea, which will cause the water system to adapt again. This will not only have consequences for the ecology, but also for the lake's users. In addition, the Natura 2000 areas on the islands and banks will also be influenced by micro-tides.