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The Maeslant Barrier

The Maeslant Barrier is a storm surge barrier that was taken into operation in 1997 and that is located where two waterways meet near Hook of Holland (Het Scheur and Nieuwe Waterweg). Building work on the Maeslant Barrier started in 1991 and it was inaugurated by Queen Beatrix on 10 May 1997. On this day, the barrier was closed for the very first time at 4.30pm. This storm surge barrier is part of the greater Europoort water defences, the final part of the Delta Works. The storm surge barrier consists of 2 arched steel sector doors, each consisting of a retaining wall and a half-timbered arm, which turn up the river from a parking dock at high tide. By ballasting the sector doors with river water, the retaining wall sinks on the threshold construction.


“The Maeslant barrier is part of the Europoort barrier, the last part of the Delta Works. Thanks to the storm surge barrier approximately one million people in South Holland are protected from the sea.”

Two enormous barrier gates

The barrier is made up of two enormous barrier gates. These barrier gates are basically two floating pontoons that can be positioned across the waterway while they are empty. Once they are in place, the gates are filled with water to create massive barriers. When the gates need to be opened again, the water is pumped out and they are moved outwards. When fully open, the gates are stowed in two dry docks on either side of the waterway. These docks are closed by dock gates. Once the barrier gates have been retracted back into their respective dry docks, the dock gates are closed and water is pumped out of the dry dock. Water is pumped out to keep the barrier gates dry, so as to prevent corrosion.

Autonomously closing of entire barrier

In the event of potential high water levels, a computer system called the Decision and Support System (BOS by its Dutch initials) decides automatically whether or not the barrier needs to be closed. The system will close the barrier when water levels in Rotterdam are threatening to exceed 3 metres above NAP or water levels further down river in Dordrecht are threatening to exceed 2.90 metres above NAP. What is special about this computer system is that it closes the barrier entirely autonomously, even when there is no personnel around.

Double redundant

Besides the Maeslant Barrier, this computer system also operates the Hartel Barrier. Seeing as the barriers are closed automatically, without human intervention, the computer system has to meet very strict requirements. It is a double redundant system to prevent outages as much as possible. If the computer were to be down completely, the decision to close the barrier will have to be made by operating staff. The barrier gates (circle segments of 22 metres high and 210 metres long, which float because they are hollow) will then turn towards each other. At the point where they (nearly) make contact in the centre of the waterway, water is let into the barrier gates to make them sink to the river bed and almost hermetically block the river (Nieuwe Waterweg). To prevent the gates from getting damaged, a small opening of approx. 80cm is left between the gates. This opening is so small that only a small amount of water will flow through.

The world’s largest ball points

The hinges of the two barrier gates were a major engineering challenge during the building project. Not only do they have to enable the barrier gates to open and close, they also have to allow the barrier gates to be raised and lowered. In the end, these hinges were made using the world’s largest ball joints; the balls have a diameter of 10 metres. These ball joints were built especially for this storm surge barrier.

Horizontal movement

The horizontal movement of the barrier gates is powered by redundant 6-cylinder oil pressure motors for each gate, whereby four motors is sufficient. This technology was chosen because of its great reliability, while it also delivers constant force, irrespective of the speed. The motors turn a rack rail along the top of the barrier gate outwards or inwards using cogwheels. The motors themselves are positioned vertically so that they can operate regardless of the water level.

Building of the Maeslant Barrier

As a consortium in “Bouwcombinatie Maeslantkering”, Hollandia has supplied, among other things, the 2 steel ball hinges with the jack construction, 26 upper cupboards for the retaining wall, various parts for the 2 lattice arms and the movement works for the doors. The lattice arms, each with a length of 240 meters, release the water pressure against the retaining wall to two ball joints placed on the bank. The ball joints each have a diameter of 10 meters and can transfer a load of 35,000 tons. The sector doors are set in motion by a hydraulic movement mechanism, the so-called “Locomobile”.

Revising gates in 2016 and 2019

Since Hollandia was involved in the building of the Maeslant Barrier in 1997, Rijkswaterstaat also commissioned Hollandia Services to revise the southern dock gate in 2016 and the northern dock gate in 2019. Thanks to this revision, the functioning of the dock gates is guaranteed for the coming 20 years.

Testing every year

To test its functionality, the Maeslant Barrier is closed once every year in what is referred to as a ‘functionality closure’. So far, this was always done on a Saturday in late September or early October (i.e. at the start of the storm season). Functionality closures are open to the general public. Anyone who wants to can watch the barrier being closed from the site around the barrier house (Keringhuis). This is the only time that the general public can see the storm surge barrier being closed.