To protect the Groninger village of Zoutkamp from high water at least until 2050, a new pumping station is being built and the monumental Hunsingo lock from 1859 is undergoing a transformation from a former sea lock to a lock. Royal Oosterhof Holman is taking on the complete restoration of the monumental part, but the scope extends much further. For example, the 112-year-old young family company is manufacturing the new wooden lock gates and steel brake works in-house, and has even preserved the entire construction site with sister company Elize Energie.
Oosterhof Holman is working in Zoutkamp on behalf of Strukton. Both companies have a long history with each other. "We complement each other well," says Taeke Visser, company director at Oosterhof Holman Beton- en Waterbouw. "For example, we previously successfully executed the 'approach 17 bridges' for Noorderzijlvest Water Board, where we worked intensively with Strukton in a construction team. The Blauwe Loper, Europe's longest bicycle bridge, is another example of a recent successful collaboration. At Nieuwe Waterwerken Zoutkamp, although on paper we act as a subcontractor, here too we act more as partners. We initially provided capacity during the tender and offered solutions that contributed to the winning bid. From there, we also expressed our intention to proceed together in the execution as far as the restoration of the Hunsingo Lock is concerned."
In the new situation, the monumental Hunsingo lock will become part of the new lock. "Strukton takes care of the new construction, we take care of the restoration of the existing lock," continues Taeke. "That is also really Oosterhof Holman's specialty: restoration with respect for the monument. Nevertheless, there is also a considerable demolition task because the drive points of the new doors will be integrated into the lock wall." Jan Sluiter, project manager at Oosterhof Holman Beton- en Waterbouw, can also agree and adds: "Moreover, the lock has quite a bit of overdue maintenance. A lot of masonry is in bad shape. It will soon be up to us to indicate the point 'up to here and no further', in consultation with the restoration architect, of course. But that won't be clear until we have started construction, in February 2025. Also, the quality of the masonry under the natural stone cover plates cannot be properly assessed at this time." It will still be busy months in the lock, Taeke says with a smile. "Because it all has to be done in one season."
For the radical restoration task of the Hunsingo lock, Oosterhof Holman is working with a number of regular partners. Jan: "For the masonry we use the expertise of Siegersma and the natural stone restoration is carried out by Meesters In.
In this composition, we recently carried out a similar project in which the monumental Aduarderzijlen lock complex was completely renovated. We will soon be working here in Zoutkamp with mortars according to an old recipe. It is pure craftsmanship. The mortar draws slowly, which means you can't reach the speeds of today. Moreover, you are also dependent on the weather. Too cold or too wet is disastrous. So it listens very closely. We are not going to blast the lock completely clean either, the aim of the monumental restoration is to make the restored lock look as old as possible, so that the contrast between the existing and new part that Strukton is building is clearly visible."
Initially, Oosterhof Holman's experts also looked to save the old wooden lock doors, but they proved to be in too poor a condition. "The doors were taken out and extensively inspected at our location in Harlingen. Here they were definitively rejected," says Taeke. "We are currently building a three set of new wooden doors, measuring 9.60 meters high by 5 meters wide. The old steelwork on the lock doors does get a second life. For example, the capstans for manual operation are being restored at our steel shop and will be given a 'ceremonial function' on the new doors, since the new lock doors will be operated electromechanically. The intention is to retain as many old elements as possible, provided it is technically possible and safety is not compromised. The brake works are also in our scope, although this is not restoration work. We prepare them completely in our workshop, and assemble them before the new lock against the tubular piles that we install with our own ships."
The New Waterworks Zoutkamp project demonstrates the versatility of Oosterhof Holman. "We have an awful lot of disciplines within our company and make grateful use of each other's expertise," says Taeke. Even making the construction site more sustainable can be left to Oosterhof Holman's experts. They set up a sister company for it some twelve years ago. "We make sustainability from an intrinsic motivation, but in a realistic and workable way so that it has a chance of success," says Aletta Zwart, business unit manager at Elize Energie. "We do that for our parent company as well as for third parties. At Nieuwe Waterwerken Zoutkamp, we were commissioned by Strukton to install solar panels and provide the charging infrastructure." And speaking of sustainability and circular efforts, Oosterhof Holman tries to make work with work whenever possible. "In Zoutkamp, linkage opportunities are being exploited, where we were commissioned to build two wooden jetties. For the foundation we are using sixty mooring piles released from a project of ours in Alkmaar," explains Taeke. "We guarantee the same lifespan as from using new piles."
So there are busy times ahead for Oosterhof Holman in Zoutkamp. "We will start in February next year and eight months later everything has to be completed," he says. By the way, the family business is no stranger to this region. "With the municipality of Het Hogeland we have a multi-year maintenance contract for the maintenance of roads, civil objects and the water chain. Quite a job, as it is the second largest municipality in the Netherlands in terms of surface area."