Entrepreneur consortium Van Hattum en Blankevoort (VHB) designs and builds this construction on behalf of Rijkswaterstaat: selective extraction. Jan Rienstra, environmental manager at Rijkswaterstaat and Rob Gordijn, environmental manager at VHB, talk about the importance and operation of the selective extraction measure and how this special construction is built.
Prevention of salting of the North Sea Canal
A larger sea lock also means that more salt water flows into the North Sea Canal. Jan says: ‘Every time a ship is closed through Zeesluis IJmuiden, 10,000 tons of salt water flows in. At Noordersluis it is’ only ‘6,000 tons.’
‘It is important that the salt water is drained off to prevent further salting of the North Sea Canal.’ Too much salt water is not good for the environment in the North Sea Canal due to the negative effects on nature, agriculture and horticulture and our drinking water supply.
Jan: The North Sea Canal is connected to the Amsterdam-Rhine Canal. Some of the water from the Amsterdam-Rhine Canal is used to make drinking water. Water also goes to the inner dike polders if there is a shortage of water. People want to use fresh water for agricultural functions. ‘
‘Especially plants and crops do not tolerate salt water well, so fresh water is needed to continue to replenish the water in the polders.’ In recent years, a method has been considered to send the extra amount of salt that comes in again. Selective extraction makes this possible.
What is selective withdrawal?
Selective extraction is a construction that selectively discharges the salt water via IJmuiden’s discharge and pumping station complex. Jan: ‘By selective extraction, we take advantage of the fact that salt water is heavier than fresh water.’
Rob explains how the selective abstraction construction works: “The heavier, salty water collects at the bottom behind the locks. That is why we are building a concrete wall in Binnenspuikanaal (see picture) with an opening in the bottom. This opening acts as a large mailbox. The heavier, salty water descends and passes through the opening under the concrete wall. The salt water is returned to the sea via the discharge and pumping system. The fresh water in the upper water layer is held back by the wall and remains in the North Sea Canal. ‘
The planning for the construction phase of the construction
At the beginning of July 2022, VHB will start with the first visible activities for the Selective Extraction measure.
Rob tells what the plan is: »This summer we will first create new moorings on the south side of the lock complex, along the Kanaaldijken in IJmuiden. We do this because Binnenspuikanaal is closed using selective extraction. The inland vessels and vessels from the Rijkswaterstaat, which normally moor in the Binnenspuikanaal, can then moor there along the Kanaaldijk. Then we can start the work of selective extraction in Binnenspuikanaal. ‘
In the autumn of 2022, VHB will start with the support construction along the walls on both sides of the upcoming dam, which Rob describes: ‘A retaining structure is actually a combination of hard tubular steel piles and punches along the width. We do this so that the bank remains standing if we have to dig deep to the concrete wall. When the retaining structure is ready, we can deepen the canal and place the concrete wall. ‘
While working on the retaining structure, the concrete wall is pre-built on the width. Rob explains why they first pre-construct the concrete wall on the width: ‘Because the flow to the discharge and pumping station complex is very important for water drainage in the Netherlands, we can not just build the concrete wall in Binnenspuikanaal. ‘
‘Due to the size of the structure; a total of 90 m wide (2 piers 28 m high, 20 m thick and 5 m wide with walls in between), we would then have to close Binnenspuikanaal completely «.
‘Therefore, we build the parts of the concrete wall on the width and then put it in place in one fell swoop. A movable steel door will also be placed in between so that maintenance vessels can occasionally enter the Binnenspuikanaal. We expect to be ready by 2024 and the removal of salt water via Selective Extraction will start. ‘
Cooperation with other parties
VHB is a combination of civil contractors who, among other things, specialize in large waterworks. VHB is the main contractor for the project. VHB also involves other parties.
Rob tells who they work with: “We have engaged partners with extensive experience with certain special components. For example, 2 other Volker Wessel companies; Volker Staal and Foundations and Vialis. mWe also visit the company Van den Herik as a hydraulic engineer and Spie for the technical installations. The partners help us with, among other things, the dredging work, the movable door for maintenance vessels and the foundation for the concrete wall. ‘