Three questions to Wouter Bulthuis of Rijkswaterstaat

News item
sea lock, salizination

The new sea lock will be the largest sea lock in the world. This means that when the new lock will be used, more salt water will flow into the North Sea Canal. What is Rijkswaterstaat doing about the salt water? That is what we ask Wouter Bulthuis, Area Manager of the Selective Extraction of Saltwater at IJmuiden Project.


Why is it that more salt water will flow into the North Sea Canal?

'With a size of 70 metres wide, 500 metres long and 18 metres deep, the new sea lock will be the largest in the world. Each time one of the IJmuiden locks is used, a volume of sea water flows into the Canal. Using the new sea lock, however, involves a much larger volume than using the North Lock. Converting the extra volume into weight, it means that roughly 40 extra truckloads of road salt are brought into the Canal. That is a lot. There is also another factor playing a role in the background. That factor is sea level rise as a result of climate change. It means that more seawater - and more salt - is expected to be entering the North Sea Canal in the future. Also, due to the hydrostatic pressure of sea water, more seepage water will enter the low-lying polders. This is called salinization and especially in dry periods it can be detrimental to nature, agriculture, horticulture and the supply of drinking water in the vicinity of the North Sea Canal.’

What measures is Rijkswaterstaat taking to counter the effects of salinization?

‘The measures we are taking are aimed at preventing more salt from entering the Canal as a result of using the larger sea lock. This means that a so-called zoutvang (a salt water capturing system) will be built in the Binnenspuikanaal (the inner sluicing channel) at the beginning of the North Sea Canal. You can imagine this system as a kind of letterbox. The salt water near the bottom of the Canal will be transported back to sea through the slot in the letterbox. The zoutvang operates according to the phenomenon that in the Canal fresh water is layered over salt water due to the fact that salt  water is heavier than fresh water. That is why the bottom layers contain salt water and the top layers contain fresh water. By using the pumping station in the North Sea Canal, we will see to it that with this 'letterbox system' as much salt water as possible will be pumped or sluiced back to sea. The fresh water in the Canal will retained by the zoutvang.

Rijkswaterstaat has just ordered the design of the zoutvang and is busy preparing a contract for its construction. The contract will be put out to tender in 2019, and construction is expected to start by the end of 2020 or the beginning of 2021. The new sea lock will be completed a year earlier than the zoutvang. We will bridge this period with interim measures. These measures may include a more effective use of the lock - which will result in less salt water being transported into the Canal, or a longer use of the existing North Lock. A definitive package of measures will be announced later.'

What is the greatest challenge in designing the zoutvang?

'The greatest challenge is determining its effectiveness. We must look for the best possible location in the Binnenspuikanaal. We are now investigating the current in that area. The zoutvang must be located in a place with as little turbulence as possible to prevent the salt water from mixing with the fresh water. This is an important precondition. The integration of the zoutvang into the existing environment will also be quite a challenge. At the moment, the North Sea Canal Area is an environment with plenty of activities in a relatively small area. Due to the lack of space, it will be quite a puzzle to get everything in place. Because the activities for the zoutvang will take place in the Binnenspuikanaal and not in the North Sea Canal itself, shipping will not be affected. Lay-bys for inland barges in the Binnenspuikanaal, though, will have to be moved to another location within the lock complex and we think that will make the south side of the Canal a busier area. We have to strike a compromise between the available space and the diverse marine activities.'


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