The Oosterschelde storm surge barrier

The Oosterschelde storm surge barrier (1976-1986)

The construction of the 9 kilometer long storm surge barrier the “Oosterscheldekering” is a complex and unique project. A structure of such enormous dimensions has never been built.  The barrier consists of 65 pillars of 30 to 40 meters high and 62 sliders of 42 meters wide and 6 to 12 meters high. That makes the defense barrier (cost 2.5 billion euro) one of the most impressive hydraulic constructions in The Netherlands.

A lot of discussion precedes the construction of the barrier. At first, the plan is to close off the Oosterschelde with a solid dam. However, fishermen and nature conservationists revolt against this plan. The Oosterschelde is a unique nature reserve with more than 70 species of fish, 140 species of aquatic plants and algae and 350 species of benthic animals, which live on the sea bed. Building a solid dam would result in this nature reserve suffering irreparable damage.

Oosterschelde Open

Completely closing off the sea arm means the end of the salt water environment in the Oosterschelde and therefore also the cultivation of mussels and oysters. The protest – with the Oosterschelde Open as  battle cry – does not fall on deaf ears. In 1975, the then Cabinet came up with the proposal to build an open barrier that could be closed by means of gates – if necessary.

A permeable barrier is much more expensive than a solid dam and thus the Cabinet’s proposal  leads to fierce debates. In 1979 parliament approved the plan for the construction of the Oosterscheldekering.

Oosterscheldekering Watersnoodmuseum
Oosterscheldekering

Channels

The barrier will be passing through three channels in the Oosterschelde: Hammen, Schaar van Roggeplaat and Roompot. Earlier – when it was still assumed that a solid dam was going to be built- artificial (work) islands had already been constructed, including the Roggeplaat (1969), Neeltje Jans (1969) and Noordland (1971). The construction sites Neeltje Jans and Noordland, together with the sandbank Geul that was raised for that purpose, form the solid part of the storm surge barrier. The Neeltje Jans work island is pivotal in the construction project. The majority of the necessary pillars, shafts and foundation mats are prefabricated there. The pillars are the most important elements of the barrier. They are made in a construction pit whose dimensions are ​one square kilometer and which extends to more than 15 meters below sea level. The construction of one pillar requires 7,000 cubic meters of concrete and takes almost a year and a half to complete.

Every two weeks, the construction of a new pillar is started. To be on the safe side, two additional (spare) pillars are also built. Work on the pillars continues day and night because otherwise the concrete cannot harden in the right way. When all pillars are completed, the construction pit is flooded, after which lift vessel the Ostrea lifts the pillars one by one and takes them to floating pontoon Macoma. The Macoma marks the place where the pillar has to be submerged

Immovable

The pillars must be absolutely immovable. Before they are put into place, the soil on the bottom of the Oosterschelde is thoroughly examined for its load-bearing capacities. Its density, composition and geological layers are being assessed. Because the bottom turns out to be too weak, it is strengthened.In order to compact the soil, the ship Mytilus, built especially for that purpose, inserts four gigantic steel rods into the sea bed and makes them vibrate.  After the vibration, the grains of sand are compacted up to a depth of 15 meters. In order to provide the soil with an even greater carrying capacity, custom-made mats filled with sand and gravel are laid down by the Cardium wherever a pillar is to be placed. The Cardium is one of the many custom-made ships that is deployed during the construction of the barrier.Around the area where the pillars are due to be installed,  the Cardium lays down mats which are then covered with concrete blocks. Sludge is dredged and replaced by sand. Inspection vessel Wijker Rib, aided by underwater vehicle Portunus, examines whether everything is going to plan on the bottom of the Oosterschelde.After sinking the hollow pillars, they are filled with sand. Finally, the pillars are ‘wrapped’ in a mantle of stone, originating from Germany, Finland, Sweden and Belgium. The placement of the pillars is precision work. It is only possible when the current is at its weakest: during slack tide.

Oosterscheldekering Watersnoodmuseum
Oosterscheldekering

Sliders

Once the pillars are anchored onto the bottom of the Oosterschelde, building the barrier continues. Attachments are placed on top of the pillars, onto which the sliders are then mounted. Hollow tubes are also placed on top of the pillars. These provide space for all equipment needed to move the sliders. The sliders are driven by hydraulic cylinders. The controls for these are located in the Ir. J. W. Topshuis on the Neeltje Jans.The storm surge barrier is officially opened on 4 October 1986 by then Queen Beatrix. The road over the storm surge barrier is opened a year later by then Princess Juliana.  Commissioning  the flood barrier reduces the probability of flooding in the Delta area to once every 4000 years. The flood barrier will be closed at an expected high water levels of above 3 meter NAP.

The ships

Nothing found.