Eastern Scheldt Barrier
The Eastern Scheldt Barrier (Oosterscheldekering) is located in the Eastern Scheldt (Oosterschelde) and connects the islands of Schouwen-Duiveland and Noord-Beveland.
The storm surge barrier closes the Eastern Scheldt during impending high water, thereby protecting a vast area from the North Sea. This structure is the most well-known and complex of all the Delta Works. Never before had such a construction been made on such a massive scale. The Eastern Scheldt Barrier is even referred to as a modern Wonder of the World.
The Eastern Scheldt Barrier in statistics
- Built between 1967 and 1986
- 9 kilometers long, of which 3 kilometers are closable
- Withstands high water that occurs only once every 4000 years
- 65 pillars, 30 to 40 meters high, each weighing 18 million kilograms
- 62 sluices, 42 meters long, 6 to 12 meters high, weighing between 260 and 480 tons
- 5 billion kilograms of riprap and 450,000 cubic meters of concrete
- Closes in 1.5 hours at 3 meters above sea level
- Contains 32 wind turbines that generate 440,000 megawatt hours of electricity
Origin
The Eastern Scheldt storm surge barrier has the most complex history of all the Delta Works. According to the original Delta Plan, the Eastern Scheldt was to be fully enclosed with a dam. This would have eliminated tidal ebb and flow, turning the Eastern Scheldt into fresh water. This fresh water could then be used for drinking water and agriculture. Additionally, shipping on the busy route from the Port of Rotterdam to Antwerp would no longer be affected by tidal changes.
However, there was significant criticism of this plan. For example, certain harbors would no longer be accessible; the Ministry of Defense saw the Eastern Scheldt as a potential (emergency) harbor, and shellfish fishing would come to an end. The biggest concern, however, was the impact of the closure on the unique nature of the Eastern Scheldt area. The water would become stagnant from one day to the next, turning brackish, a mix of fresh and saltwater, and eventually, fully fresh. As a result, various plant species and animal species, such as shellfish, seals, and certain birds, would disappear from the area.
From 1962, the criticism grew louder, and it was clearly heard during the Eastern Scheldt Congress in 1967. The shellfish industry (mussels and oysters) in Yerseke was generally convinced to accept compensation or relocate to the Wadden Sea. However, the still-developing environmental movement did not give up easily. The action group "Oosterschelde Open" launched strong protests, followed by the "Vereniging Milieuhygiëne Zeeland," a precursor to the current Zeeland Environmental Federation. In 1973, these interest groups united under the committee "Samenwerking Oosterschelde" (SOS).
The protests reached the national government in The Hague, and in 1972, opposition parties PPR and D66 agreed to push for a new study into the consequences of closing the Eastern Scheldt. Two years later, the cabinet was convinced, and work on the Eastern Scheldt works was halted. A commission was formed to come up with a new plan. The goal was to preserve nature while maintaining as many of the benefits of the original plan as possible.
The commission advised partially closing the Eastern Scheldt with a semi-open barrier. Additionally, the concept of "compartmentalization works" was introduced: the Philipsdam, Oesterdam, Markiezaatskade, and Bathse Spuisluis. The water reservoirs behind these Delta Works were "compartmentalized," meaning they were separated from the salty Eastern Scheldt and its tides. This allowed for the creation of a supply of freshwater and a smooth shipping route.
In 1976, the government agreed, and work resumed, but now with an entirely different design. By constructing a semi-open barrier, the ebb and flow were preserved in a controlled manner. The closure rule still displayed at the Eastern Scheldt Barrier perfectly summarizes this approach: "Here, the tide, the moon, the wind, and we go together."
Construction
In the late 1960s, work on closing the Eastern Scheldt had already begun with the construction of two working harbors: one on Schouwen-Duiveland (Schelphoek) and one on Noord-Beveland (Jacobahaven). This was followed by the creation of work islands on sandbanks in the Eastern Scheldt estuary: Neeltje Jans, Roggeplaat, and Noordland. The plan was to fill in the channels between them—Roompot, Schaar, and Hammen—using a cableway that had already been used in the construction of the Haringvlietdam, Brouwersdam, and Grevelingendam.
After the decision was made to turn the Eastern Scheldt Barrier into a permeable barrier, the design had to be fundamentally changed. Instead of filling the channels with stone, a row of 65 massive pillars was planned, which would stand on the meters-deep seabed. Between these pillars, 62 sluices were to be installed to close off the Eastern Scheldt during high water.
Construction began in 1976. Eleven contractors joined forces under the name 'De Oosterschelde Stormvloedkering Bouwcombinatie' and transformed the Neeltje Jans work island into a giant construction site.
The first challenge was to reinforce the seabed. Due to the immense ebb and flow currents, the pillars had to be placed with millimeter precision. The sluices between them absolutely could not be tilted, as this would create a gap with a current that was far too strong. Work began to pump sand onto the seabed, which was sturdier than the silt that lay there. A special ship, the Mytilus, was built to drive four massive steel vibro-piles into the ground. These vibrated the sand grains together up to a depth of 15 meters, creating a solid foundation with as little air as possible between the grains.
On top of the sand layer, plastic mats filled with gravel were laid. This was done by another specially designed ship, the Cardium. This created a carpet in the sea: a smooth surface that prevented the sand grains from washing away beneath the pillars. The mats were hundreds of meters long, ensuring there were as few gaps as possible where water could erode the ground between two mat bases. In 2011, it was found that deeper 'scour pits' had formed at these spots than expected. As a result, additional stone was deposited to prevent further sand shifts.
After the seabed reinforcement, it was time for the pillars. These were, like the caissons used elsewhere, hollow concrete structures that had to be filled with sand after placement. They were built, like most other parts of the barrier, on the work island. Constructing a single pillar took almost 1.5 years because the concrete needed to fully cure. Every two weeks, a new pillar was started, and work continued around the clock.
"The storm surge barrier is closed. The Delta Works are completed."
The specially designed lifting vessel Ostrea transported the pillars one by one to their destination. Using the mooring pontoon Macoma, the pillars were placed with centimeter precision on the mat. To anchor the pillars securely in place, a foundation was created using a mixture of sand, cement, and water. The pillars themselves were partially filled with sand, and their bases were weighted down with natural stone. In total, 5 billion kilograms of this stone were used.
Once the pillars were securely in place on the seabed, the final phase began. The steel sluices were hung between the pillars using the large crane Taklift 4. Concrete tubes were attached to the pillars, housing the equipment to operate the sluices. The roadway was then constructed on top of the concrete structure.
In total, the barrier took 10 years of work and cost €2.5 billion. On October 4, 1986, Queen Beatrix officially opened the barrier with the historic words: “The storm surge barrier is closed. The Delta Works are complete.”
On the work island of Neeltje Jans, an amusement park was established, attracting thousands of visitors annually. In one of the former construction docks, a (reserve) pillar is still on display and has been turned into a climbing wall. In another dock, where the mats were made, hanging mussels are now cultivated. The barrier is equipped with 32 wind turbines, and five turbines are installed within the barrier to generate power from the tides.
Functioning
In the Topshuis on Neeltje Jans, there is the "red button," which automatically lowers the sluices in the barrier. The barrier closes when the water level reaches about 3 meters above NAP, and it takes approximately 1.5 hours for all the sluices to be lowered. On average, the barrier closes once a year, but due to rising sea levels, this will happen more frequently in the future.
The barrier does not close completely. Between the pillars closest to the Topshuis, there is no sluice, only rubble stone. Water can flow through this gap. Waves can also break over the barrier. This is not a problem, as the Eastern Scheldt has enough space to store the excess water.
Eastern Scheldt
After a long debate, the Eastern Scheldt was not fully closed, but partially closed with the half-open Eastern Scheldt Barrier on one side and the Zandkreekdam, Oesterdam, Grevelingendam, and Philipsdam on the other. These ‘compartmentalization works’ reduce the size of the Eastern Scheldt, ensuring that there is still enough ebb and flow for the nature in the area. However, the strength of the tides is much less than when the Eastern Scheldt was completely open.
The limited tides also lead to the phenomenon known as 'sand hunger.' This means that the sandbanks in the Eastern Scheldt gradually wash away. They are no longer replenished with sand from the sea, as the weaker current is not strong enough to stir up the sand and bring it onto the banks. The sandbanks are important for birds to find food and for seals to rest. Therefore, in 2019 and 2020, large amounts of artificial sand were placed on the Roggeplaat to counteract this.
