Oesterdam
The Oesterdam is the longest dam of the Delta Works, but was originally not part of the Delta Plan.
The Oesterdam separates the salty Eastern Scheldt (the Tholense Gat) from the fresh Bergsche Diep and connects Tholen and Zuid-Beveland. The Oesterdam includes the Bergse Diepsluis and is located next to the two Kreekkraksluizen.
The Oesterdam in statistics
- Built between 1979 and 1986
- 10.5 kilometers long
- A sluice of 37 meters long and 6.5 meters wide
- Supported by the 4-kilometer-long Markiezaatskade
Origin
The Oesterdam was not originally included in the Delta Plan. This is because the plan was to completely close off the Eastern Scheldt. This would eliminate the ebb and flow, turning the Eastern Scheldt into fresh water, which could 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 tides. However, closing off the Eastern Scheldt would come at the cost of nature.
It was then decided to preserve the nature in the Eastern Scheldt, while simultaneously retaining as many of the benefits of the planned freshwater reservoir as possible. To achieve this, the 'compartmentalisation works' were constructed: the Oesterdam, the Philipsdam, the Markiezaatskade, and the Bathse Spuisluis. The water basins behind these Delta Works were 'compartmentalised', meaning they were separated from the Eastern Scheldt and its tides.
These Delta Works were not built to protect against the sea, but to regulate water management in the hinterland. The Oesterdam, along with the Philipsdam, reduced the surface area of the Eastern Scheldt, thereby increasing the tidal effect and preserving the natural area. To allow for large-scale shipping, two sluices were constructed next to the dam: the Kreekkraksluizen. A sluice for recreational boats and small fishing vessels heading to Bergen op Zoom was also built within the Oesterdam itself.
Construction
The construction of the Oesterdam began in 1979, with a work island being created not far from the island of Tholen. On this work island, the Bergse Diepsluis was built, and the dam towards Zuid-Beveland would then be constructed. However, this could only begin after the construction of the Markiezaatskade in 1983. This supporting dam, located to the east of the planned Oesterdam, already separated part of the water from the Eastern Scheldt, creating what is now the Markiezaatsmeer. This reduced the current strength in this section of the estuary and minimized some disruptive currents that lay across the shipping route. As a result, the construction of the Oesterdam became easier and cheaper.
The lower costs were mainly due to the use of sand to construct the Oesterdam, instead of large concrete caissons. A sand dredger pumped sand from the seabed further along and sprayed it continuously until the dam formed. This was quite a task because, as the remaining gap to be closed became smaller, the current became stronger. Therefore, precise measurements were made to determine how much sand was flowing away and how much needed to be sprayed back in. This knowledge would later be applied during the construction of the Philipsdam.
The short section towards Tholen was the last to be completed. By this point, the current was so strong that it was impossible to spray the sand against it. To make it possible, the Eastern Scheldt Storm Surge Barrier had to be temporarily closed, but it wasn't yet operational enough to allow this. In 1986, once the Eastern Scheldt Barrier was fully functional, the Oesterdam could be completed.
Space was made on the Speelmansplaten near the Bergse Diepsluis for vacation villas, events, and water sports. The N659, which runs over the Oesterdam, was opened in 1989.
Around 2010, the Oesterdam was no longer strong enough to withstand the waves it had to endure. However, instead of reinforcing the dam with the usual riprap, a large amount of sand was placed on the western side of the dam, not far from Zuid-Beveland. The sand breaks the power of the waves and simultaneously formed a new recreational beach.
Markiezaatskade
The Markiezaatskade is usually not included in the list of Delta Works, but it could very well be considered a separate Delta work. The dam lies between Zuid-Beveland and the Molenplaat near Bergen op Zoom and was constructed between 1981 and 1983 to simplify and reduce the cost of building the Oesterdam. The Markiezaatskade cut off the shallow water near Bergen op Zoom from the Eastern Scheldt, creating the Markiezaatsmeer. This reduced the current for the construction of the Oesterdam and redirected the flows that interfered with the shipping route between the Rhine and the Scheldt.
The Markiezaatskade consists of two parts: a northern section between the Molenplaat and Noordland, and a western section from the Molenplaat towards the Kreekkraksluizen. Construction began in late 1980 with the spraying of sand on the northern part. Before starting on the western section, a stretch of about 800 meters was constructed in the middle as a permeable dike, which would gradually silt up over time. This gap was designed to allow a gradual transition from saltwater to freshwater in the new Markiezaatsmeer.
Work on the western section began from the south, starting at the Kreekkraksluizen, but a dike breach in March 1982 caused a setback. Part of the dike was destroyed and had to be repaired before work could continue. On March 30, 1983, the Markiezaatskade was completed.
The Markiezaatsmeer now lies in the area once described as "the drowned land of the Markiezaat of Bergen op Zoom." Today, it is a nature reserve.
Bergse Diepsluis
The Bergse Diepsluis (also known as the Bergsediepsluis) is a lock located in the Oesterdam, connecting the Zoommeer with the Eastern Scheldt (or Tholense Gat). Bergen op Zoom wanted a large lock to make the city easily accessible to ships. However, this request was difficult to combine with effectively separating the saltwater from the Eastern Scheldt and the freshwater from the Zoommeer. Initially, a lift lock was considered, a large basin that could move up and down to bridge the height difference, but this proved to be very expensive. When the cost of the Eastern Scheldt Barrier turned out to be higher than expected, the plan for a large lift lock was abandoned. Instead, the Bergse Diepsluis became a small lock designed only for pleasure yachts and small (fishing) boats. Larger ships heading for Bergen op Zoom would have to sail around.
The lock was constructed at the site where the once-thriving city of Reimerswaal disappeared beneath the waves in the 17th and 18th centuries. As a result, an information point was opened near the Bergse Diepsluis in July 2022 to provide insights about the approximately 250 drowned villages in Zeeland.
Kreekraksluizen
The Kreekraksluizen are two identical locks located next to the Oesterdam and at the southern end of the Markiezaatskade. They were constructed before these two dams and were put into operation in 1975. The locks are 320 meters long and 24 meters wide. They are situated on the busy shipping route between the ports of Rotterdam and Antwerp, with 80,000 ships passing through annually.
The Kreekraksluizen serve as the connection between the brackish Schelde-Rijn Canal and the freshwater Zoommeer, which was created by the construction of the Oesterdam and the Markiezaatskade.
The locks originally used the same system as the Philipsdam to prevent the mixing of fresh and saltwater. When the lock opened and a ship passed through, the waters would mix. However, fresh water is lighter than salt water, so once the lock was closed, the saltwater was pumped out from the bottom, or the fresh water from the top, depending on the direction of the vessel. After this process, the lock could open again, and the ship would sail away in a uniform type of water.
Since 1997, the Kreekraksluizen have operated in a different way. They now function as a pump station that, at certain times, pumps fresh water into the Antwerp Canal area (the southern side of the Kreekraksluizen). This has artificially shifted the salt-freshwater boundary further south. This method uses less energy, is more cost-effective to maintain, and reduces the waiting time for ships in the lock.
