Maeslantkering
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The Maeslantkering is a storm surge barrier in the Nieuwe Waterweg waterway located between the towns of Hoek van Holland and Maassluis, Netherlands, , which automatically closes when needed. It is part of the Delta Works and it is the largest moving structure on earth.
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[edit] The Maeslant Barrier
[edit] The initial plan
The construction of the Maeslantkering was a part of the "Europoortkering"-project which, in turn, was the final stage of the Delta Works. The main objective of this Europoortkering-project was improving the safety against flooding of the Rotterdam harbour, of which the Europoort is an important part, and the surrounding towns and agricultural areas. This had to be carried out by the reinforcement of existing dikes as far as 50 kilometers inland. During the 1980s it became clear that this project would take at least 30 years and would cost a huge amount of money. It would also mean that historic town centres, sometimes built more than four centuries ago, had to be broken down and rebuilt behind renewed, larger dikes.
Therefore the initial plan was put aside and the Ministry of Waterways and Public Works organised a competition in which construction companies could make plans for the construction of a reliable yet relatively cheap storm surge barrier.
[edit] The storm surge barrier
This storm surge barrier had to be located in the Nieuwe Waterweg waterway. This played an important role in the planning stage of the construction, as this waterway is the main route to the port of Rotterdam, at that time the world's largest port. Therefore a barrier like the Dutch Oosterscheldekering and the Thames Barrier could not be constructed, as such a barrier would block the shipping route.
The winning plan called for two large floating gates on both levees of the waterway. A major advantage of this plan was that construction of the storm surge barrier could take place under dry conditions, in dry docks. Other advantages were that no vital parts of the barrier had to be placed under water, and maintenance of the barrier would be easy because of the dry docks. And, of course, there would be almost no inconvenience for passing ships.
[edit] Construction of the barrier
The construction of the barrier started in 1991. First the dry docks were constructed on both shores and a sill was constructed at the bottom of the Nieuwe Waterweg. Then the two 22 meter high and 210 meter long steel gates were built. After this, 237 meter long steel trusses were welded to the gates. Standing upright, these arms would be as high as the Paris Eiffel Tower, but each one weighs two times more than the Eiffel Tower. The main purpose of the arms is transmitting the immense forces, exerted on the gates while closed, to one single joint at the rear of each gate. During the closing or opening process, this ball shaped joint gives the gate the opportunity to move freely under the influences of water, wind and waves. It acts like as a ball and socket joint, such as in the human shoulder or hip. Joints were made in Czech republic at Škoda Works. The ball shaped joint is the largest in the world: diameter 10 meter, weight 680 tons. The construction of the barrier cost 450 million Euro. The total Europoortkering-project had cost 660 million Euro.
A working 1:250 scale version of the barrier was constructed in the Madurodam miniature village. Its construction took six months. It took six years to construct the real barrier. Another miniature version can be seen in visitors centre het Keringhuis next to the Maeslantkering. This information centre is opened everyday, and entrance is free.
[edit] Maeslantkering in operation
On May 10, 1997, after six years of construction, Queen Beatrix opened the Maeslantkering. The barrier is connected to a self-operating computer system which is linked to weather and sea level data. Under normal weather conditions the two doors themselves are well protected in their dry docks and a 360 meter wide gap in the waterway gives ships enough space to pass without any inconvenience. But when a storm surge of 3.00 meter above normal sea level is anticipated in Rotterdam, the barrier will be closed automatically. Four hours before the actual closing procedure will begin, in and out going ships are warned. Two hours before closing the traffic at the Nieuwe Waterweg will come to a standstill. Thirty minutes before closing the dry docks that contain the gates are flooded. After this the gates start to float and two so-called "locomobiles" move the gates towards each other. When the gap between the gates is about 1.5 meter wide, water is let inside the hollows of the gates, so that they submerge to the bottom of the waterway. The bottom has been elaborately dug and then laid with layers of broken stone, so that the gates are able to form a relatively watertight fit when submerged. In case the gates will have to be shut for a prolonged period, so that the waters of the Rhine starts rising behind them, the gate hollows are partly emptied and floated, so that excess river water runs out to sea, before they are submerged again. The decision-making algorithm that sequences storm surge-triggered events in the Maeslantkering is run entirely by computer.
The Maeslantkering is expected to be closed once every ten years due to a storm surge. With the rise in sea levels the storm surge barrier will need to close more frequently in 50 years time, namely once every five years. In its first ten years of operation the barrier was never closed due to a storm. There was one incident when a storm surge of 3 meters was predicted and the protective sequence was commenced. However, during the course of the storm, predictions were revised to a 2.99 m surge and the computer cancelled closure. Eventually the surge passed harmlessly and the waterway remained open. During the evening of November 8, 2007 the barrier was closed due to a storm surge for the first time. The barrier is closed for testing once a year, usually in September or October, just before the beginning of the storm season in November.
The Calandkanaal (Caland canal), located just south of the Nieuwe Waterweg and visible in some images on this page, is protected by the much smaller Hartelkering storm surge barrier. This barrier is constructed some 5 kilometers further inland.
The software that drives it is written in C++ and consists of 200,000 lines of code for the operational system and 250,000 lines of code for the simulation systems[1]
The barrier is designed to withstand a storm that has an occurrence of only 1/10,000 per year (based on the climate at the time, but this may have to be adjusted for the climate change).
[edit] 8 November 2007 storm
In order to test the barrier in actual stormy conditions, the water level threshold at which the barrier will start the closing procedure had been lowered from 3.0m over NAP to 2.6m, for the duration of the 2007 storm season. On 8 November 2007 a storm from the north-west hit the Dutch coast. A storm surge, high enough to start the barrier's closing procedure, occurred. The barrier was closed due to a storm surge for the first time since its construction[1]. As the Oosterscheldekering and Hartelkering storm surge barriers were also closed, the entire Dutch coast was protected against flooding for the first time since 1976. At 22.00h local time (CET), Dutch TV brought the news that maritime traffic on the Nieuwe Waterweg was shut off. The closing procedure of the Maeslantkering started at 23.10h. The barrier was completely closed at 01.00h and was reopened on 9 November around 18.00h.
[edit] References
- ^ Jan Tretmans. (2000-10-22). Software Engineering with Formal Methods: The Development of a Storm Surge Barrier Control System. Telematica Instituut. Retrieved 2008-04-14.
- The barrier was featured on the US television program Extreme Engineering.
- The barrier was also featured on the History Channel television program Modern Marvels during Levees Education. (2006)
[edit] External links
- www.keringhuis.nl - Comprehensive home page of the Maeslant Barrier, with a lot of interesting flash movies
- DeltaWorks.Org - DeltaWorks Online reports on Maeslantbarrier. Includes video, virtual tour and flash animations
- Storm Surge Warning Service - home page of the Dutch storm surge warning service
- Google Maps - Aerial photograph on Google Maps
