The Delta Works, The Oosterscheldekering
The Oosterscheldekering (Eastern Scheldt storm surge barrier) is the largest of the Delta Works dams and sturge barriers. It connects the islands of Schouwen-Duiveland and Noord-Beveland over a distance of almost 9km. This dam was built between 1976 and 1986 to limit marine flooding following the North Sea Flood of 1953. It is the most famous work of the Delta Works because of its monumental size but also its innovative hydraulic technology and its complex and unique construction.
A unique work of hydraulic engineering
Conceived to close the Oosterschelde (or Eastern Scheldt), the project finally consists of a 3km long system of opening doors. This guarantees the salinity of the water and therefore does not disturb the ecosystem. However, it also complicated the work, multiplying the costs and requiring a new structure. In fact, work on the shelter had alreadystarted in the late 1960s and by 1973, 5km had already been dammed up. The project was therefore reconsidered and transformed between 1976 and 1986 to be permeable. Thus the Oosterscheldekering is open and only closes in case of force majeure. More precisely, it closes when the sea level reaches 3m above the NAP (Normaal Amsterdams Peil or Amsterdam Ordnance Datum, a vertical datum nowadays used in Western Europe to measure the water level according to the Amsterdam reference level). Sixty-two openings, each forty metres wide, were installed to allow as much salt water through as possible. Its doors have only been closed about thirty times since it was commissioned.
A complex and innovative construction
The construction of a structure of this size required a unique technology and organization. The Oosterscheldekering was by far the most expensive of the Delta Works because of the desire to have a large open dam. The Oosterscheldekering was by far the most expensive of the Delta Works because of the desire to have a wide open barrier. The Oosterscheldekering is also used as a road for cars, as the N57 connects the islands with the country.
A Pillar D Steel Slide
B Sill Beam E Cylinder
C Top Beam F Upper Bow
The construction of the structure was done in a shallow part of the Oosterschelde, which was transformed into a work island. This island is called Neeltje Jans and was saved to facilitate the construction of the Oosterscheldekering. Today it is an area of 2.85km² dedicated to maintenance and converted into an educational centre, located between the two parts of the barrier. The 65 pillars were built on this island, as well as the foundation mats, beams and most parts of the barrier. Each pillar is colossal in size, measuring between 30 and 40m high and weighing 18,000 tons. They are made of concrete, hollow inside, filled with stones and sand once installed. Nearly 7000 cubic metres of concrete was needed for each pillar. After the construction of the pillars, the working area was flooded and specially designed and customed boats came to transport and install them. The pillars are placed on a mat to stabilise the seabed. After the transport, 62 steel slide carriers were installed between the pillars. They are 42m long and are activated by hydraulic jacks capable of lifting and supporting their weight (between 260 and 480 tons) and height (between 6 and 12m). Two additional pillars had also been built in case of damage, but they were not necessary and one of them is now used as a climbing wall in the bay of the island.
The most important of the four boats transporting and installing the pillars is the Ostrea, a red tugboat 85m long, with a reach of 50m in height that can carry 10,000 tons and thus leave the main part of the pillars out of the water during transport.