Grevelingendam
The Grevelingendam is located between Goeree-Overflakkee and Schouwen-Duiveland and, along with the Brouwersdam, encloses the Grevelingenmeer.
The Grevelingendam was, and still is, necessary to reduce the flow at the Haringvlietdam, Brouwersdam, and the Eastern Scheldt storm surge barrier.
The Grevelingendam in statistics
- Built between 1958 and 1965
- 6 kilometers long
- A lock and a two-way sluice
- Along the largest saltwater lake in Western Europe (11,000 hectares)
Origin
The Grevelingendam is the fourth Delta project, primarily designed to simplify the construction of the future Haringvliet Dam, Brouwers Dam, and Oosterschelde Barrier. The water flow was too strong to close off the sea arms, so a dam was built in the Grevelingen, where water flow was slower. This reduced the flow at other locations. The Grevelingendam continues to protect water defences closer to the North Sea from excessive strain.
The Grevelingendam was the first connection between Goeree-Overflakkee and Schouwen-Duiveland via a motorway. It also created space for recreation and nature. The construction led to the draining of 3,000 hectares of land, which has since become a nature reserve.
Construction
Construction began in 1958 with the installation of the lock at Bruinisse. In 1960, the main dam construction started. The calm flow of the Grevelingen made the Grevelingendam an ideal project to experiment with various techniques. Three methods were used in the design: sand deposition, sinking caissons, and pouring concrete blocks.
First, sand was pumped onto the sandbank, the Plaat van Oude Tonge, which already became dry at low tide. This sand dam covered a significant portion of the crossing and was immediately used as a work island.
Next, caissons, enormous hollow concrete structures, were used to fill the southern gap. Caissons had already been used for the Zandkreekdam, so this was an opportunity to refine the technique. In later projects (such as the Veerse Gatdam), more advanced "through-flow caissons" were employed. These allowed water to pass through while sinking, preventing them from being carried away by the current before settling into place.
The northern part of the dam remained, where the seabed was not suitable for caissons. Therefore, the idea was to fill the gap with concrete blocks, stones, and asphalt waste. A cableway was built between the working island and Goeree-Overflakkee, transporting large gondolas filled with rubble, which was dropped into the water. This technique proved successful and was later used for the construction of the Brouwersdam and Haringvlietdam, with the same cableway even being reused.
Minister Van Aartsen proudly opened the Grevelingendam on April 1, 1965.
Grevelingenmeer
After the completion of the Brouwersdam in 1971, the Grevelingenmeer was created between the two dams. The water became stagnant overnight, turning brackish—a mix of fresh and saltwater. This caused several plant and animal species to disappear. Small shellfish died within days, and plants dependent on saltwater also perished. Within weeks, decaying plants and animals were floating in the water.
To restore nature, Rijkswaterstaat opened the Brouwerssluis in 1978 in the Brouwersdam. This allowed seawater to flow in and out of the Grevelingenmeer. As a result, the lake became the largest saltwater lake in Western Europe, covering 11,000 hectares.
Plants and animals are slowly returning to the area. Plaice can swim freely from the Grevelingen to the North Sea again, and oysters, thought to be extinct, have returned. However, the deeper layers of the Grevelingenmeer lack enough oxygen for underwater life. Therefore, plans are in place to introduce controlled tidal movements through openings in the dam to help refresh the water.
In other parts of the Grevelingenmeer, nature has changed due to land that has been exposed by limited tides. Oystercatchers have disappeared, replaced by avocets, ringed plovers, pied avocets, and little terns. The Hompelvoet, an island in the Grevelingen, has now become one of the largest breeding sites for common terns in the delta area, with 3,000 breeding pairs.
Flakkeese sluis
In 1983, the Flakkeese Spuisluis was constructed on the northern side of the sand dam to bring saltwater to the Oosterschelde once it was to be separated from the North Sea. However, since the Eastern Scheldt remained an open barrier, the sluice became unnecessary.
Twenty years later, a new function was found for the sluice. In January 2016, the Flakkeese Spuisluis was renovated with a two-way sluicing connection between the Eastern Scheldt and the Grevelingenmeer. This allows the Grevelingenmeer to be refreshed with saltwater from the Eastern Scheldt, improving the oxygen levels in the water of the eastern part of the Grevelingenmeer.
