Rijkswaterstaat has awarded the construction of the 'Selective Extraction' measure at IJmuiden to Van Hattum en Blankevoort, part of VolkerWessels Infrastructuur. They are building a construction in the Binnenspuikanaal to counteract the increase in salination of the North Sea Canal caused by the use of the IJmuiden sea lock. Much more seawater will soon be flowing into the North Sea Canal through the sea lock. Using selective extraction, some of the salt water will be discharged back into the sea. Work is expected to start at the end of 2021.
The agreement with Van Hattum en Blankevoort concerns a Design & Construct contract (D&C). The contractor is responsible for the design and realisation of the construction. The offer that the company submitted was judged to be the best. They scored well on, among other things, the risk of sand drift. Additional measures will be taken, such as low-vibration installation of sheet piling. Van Hattum en Blankevoort also has the best plans for limiting the nuisance for the surrounding area as much as possible.
10,000 tonnes of salt
When ships pass through the IJmuiden sea lock, approximately twice as much salt will flow into the North Sea Canal as through the current Noordersluis because of its size. This amounts to about 10,000 tons of salt per lock. Rijkswaterstaat is therefore taking measures to remove the extra salt and to prevent the adverse effects of an excessively high salt concentration in the North Sea Canal on nature, agriculture, horticulture and the drinking water supply in the surrounding area.
The solution was found in the selective discharge of salt water via the Spui and Gemaalcomplex IJmuiden. A concrete wall will be built in the Binnenenspuikanaal in front of the sluice and the pumping station. There will be an opening at the bottom of the wall at a depth of between 16 and 23 metres. The bottom of the wall will be deepened considerably so that the heavier salt water will collect in it. When the water is discharged, the salt water flows from the lowest water layer through the opening. The wall stops the fresher water in the upper water layer of the North Sea Canal.
Research by Rijkswaterstaat and external parties has shown that selective extraction is the only solution to prevent further salinisation in the area on this scale. The method is not new. It is used on a much smaller scale at the De Helsdeur pumping station in Den Helder. The method works well here. Given the scale, the selective extraction of salt water in the North Sea Canal is a unique construction.
During the tendering procedure, it emerged from discussions with various market parties that additional budget is required for the construction. It turned out, for example, that the soil retaining structures, necessary for deepening the soil, had to be built heavier and deeper than anticipated. Also, more time is needed for the execution.
Noordersluis longer in use
Work is scheduled to start at the end of 2021 and the construction is scheduled to be completed at the end of 2024. Because the IJmuiden sea lock is expected to be taken into use at the end of January 2022, the Noordersluis will remain available longer in order to prevent further salinisation of the North Sea Canal. Together with regional partners in water management and the shipping industry, Rijkswaterstaat is also investigating possible measures to control salination in the meantime.
Photo above: Gerrit Serne
Photo below: Topview Aerial Photography