Oosterscheldekering
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The Oosterscheldekering (Eastern Scheldt storm surge barrier), between the islands Schouwen-Duiveland and Noord-Beveland, is the largest of 13 ambitious Delta works series of dams, designed to protect a large part of the Netherlands from flooding. The construction of the Delta Works was a response to the North Sea Flood of 1953.
The surge barrier
The nine kilometer-long Oosterscheldekering (kering meaning barrier) was initially designed, and partly built, as a closed dam, but after public protest huge sluice-gate-type doors were installed in the remaining four kilometers. These doors are normally open, but can be closed under adverse weather conditions. In this way the saltwater marine life behind the dam is preserved and fishing can continue, while the land behind the dam is safe from the water.
On 4 October 1986 Queen Beatrix officially opened the dam for use.
At the artificial island Neeltje-Jans, at one end of the barrier, a plaque is installed with the words: "Hier gaan over het tij, de wind, de maan en wij" ("here the tide is ruled, by the wind, the moon and we(man)").
Construction
The Oosterscheldekering was the biggest, most difficult to build and the most expensive part of the Delta works. Work on the dam itself started in April 1976 and was completed in June 1986, though the road over the dam was completed only in November 1987. To facilitate the building, an artificial island Neeltje-Jans was first created in the middle of the estuary.The dam is constructed out of 65 concrete pillars with 62 steel doors of 42 metres wide. The parts were constructed in a dry dock. The area was flooded and a small fleet of special construction ships would lift the pillars and place them on their final place. Each pillar is between 35 and 38,75 metres high and weighs 18000 tonnes.
The Oosterscheldekering is sometimes referred to as the eighth Wonder of the World, and has been declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers.
The dam was designed to last 200 years.
Construction fleet
Four ships were custom designed and built for this project:- Mytilus, a ship equipped with various groundworking tools, such as needles to make the seabed more dense and stable.
- Cardium, a ship to transport and lay a special foil carpet on the seabed for the pillars to rest on.
- Ostrea, a ship capable of lifting a concrete pillar from the dry dock and placing the pillar within a tiny margin on a special foil on the seabed. The ship is 85 meters long and has a portal of 50 meters high. The ship can lift 10000 tonnes, the pillars are under water for a large part and require less lifting power than the 18000 tonnes. This ship is considered the flagship of the construction fleet mainly because of its impressive size and power.
- Macoma, a ship that works closely with the Ostrea, cleaning the foil and helping in navigating the pillar to the final place.
Operation
The dam is operated by humans but if human controls fail an electronic security system acts as a backup. A Dutch law regulates the conditions under which the dam is allowed to close. The water levels must be at least 3 meters above regular sea level before the doors can be completely shut. For testing, all doors are shut once in a while (each door once per month). Also emergency procedures are tested on prescheduled dates. Once the test is passed, the shutters are immediately opened again to create a minimum impact on tidal movements and the marine ecosystem. It takes approximately one hour to close one of the doors.The dam has been closed 23 times since 1986, due to water levels exceeding or being predicted to exceed the 3.00 meters.
The cost of operation is €17 Million per year.
External links
- [Satellite view from Google Maps]
- [DeltaWorks.org] - DeltaWorks.Org about Oosterscheldekering. Includes text, photos, video and virtual tour.
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