The seven weirs used to regulate the water level in the Meuse between Borgharen and Lith are all in need of major maintenance or replacement. A major operation for Rijkswaterstaat (RWS), especially since most of them are national monuments and each location involves a great deal of environmental management. After inspections, the weir at Grave proved to be in such poor condition that this sub-project was brought forward five years. Together with contractor combination Mourik Swarco (CMD), consisting of Mourik Infra B.V. and SWARCO Nederland B.V., an accelerated renovation process was initiated. This year, for example, the yokes and sliders have already been replaced. Next year the replacement of the drives, operating and control installation and crane truck is planned.
Since RWS constructed seven weirs in the rain-fed Meuse River between 1915 and 1942, this waterway in the Netherlands is generally navigable year-round. In its journey to the North Sea, the Meuse bridges some 45 meters in height, which is met incrementally in seven weir-lock combinations. The weirs are lowered (removed) at high water. Beyond that, an agreed water level in the various weir stations is maintained as much as possible. This keeps the Meuse navigable. In order to continue to guarantee the functioning of these important hydraulic works, the weirs (Grave, Sambeek, Belfeld, Roermond, Linne, Lith and Borgharen) will be renovated and replaced in the (very) long term.
In the original program, the weir at Grave (1926) was not due until 2028. "However, we were overtaken by reality when further inspections revealed hairline cracks in the yokes supporting the sliders," says Paul Uijlenbroek, RWS environment manager for the Performance Contract that includes all seven weirs. "That's why this sub-project was brought forward for accelerated replacement of the yokes and sliders. Grave is complex and special because it is simultaneously a weir, lock and road bridge and all parts interact. The bridge connects the Nijmegen region and the municipality of Land van Cuijk and is widely used by schoolchildren and farmers. Closing it means 40-minute detours, so that was not an option. In terms of working environment, it is also challenging. Strong current due to high water discharge via the Meuse through the weir is difficult work anyway and has a high risk profile. And the working island for the chain and storage is flooded in case of a Meuse discharge of more than 2,000 m3/s. For all situations, a script was ready for demobilization or even the complete evacuation of the construction site."
According to the National Cultural Heritage Agency (RCE), the Grave lock and weir complex is a national monument "of general interest. This presented an extra challenge for the Mourik Swarco (CMD) consortium of contractors, according to Ivo Thuijls, Project Manager on behalf of Mourik Infra B.V., who briefly explains the weir mechanism: "In short, the Grave weir consists of yokes and gates. The yokes are uprights, which in this weir are connected to the bridge by a pivot point and support the bottom of the Maas. The gates are attached to the yokes. This position of the gates is continuously adjusted as the Meuse discharge increases or decreases. This realizes a fixed water level which is necessary for shipping. At high water, in the case of the Grave barrage at 1,700 m3/s, the entire barrage must be lowered. The gates are then already fully opened and are located at the top of the yokes. The yokes are then pulled horizontally against the underside of the bridge by means of the crane truck. This creates a large opening that shipping can then use. In fact, at these water discharges, the lock is blocked and no longer usable for shipping." Weir Grave works with two weir openings containing 11 and 9 yokes, respectively. On each yoke there are always 3 slides with which Rijkswaterstaat regulates the water discharge. One slide is good for allowing 20 m3/s more or less water through.
Shipping normally uses locks to overcome the difference in elevation. "At high tide, these cannot be used," Thuijls said. "To allow shipping through then, the weir is lowered. It is a beautiful 100-year-old technique, but with today's calculation and safety rules, large-scale renovation is not an easy job. Especially since the image-defining character must be maintained given its monumental character. The new structures and installations must optically resemble the old structure."
To properly handle this complex assignment, intensive collaboration between various organizational units of RWS, CMD and several of CMD's subcontractors, including several engineering firms, began from the design phase. "RWS asked CMD to take a steering role in the entire process," Uijlenbroek continues. "There is a lot of knowledge and expertise in the implementation world. Mourik and Swarco are reliable partners whom you can also entrust with a major role in the engineering process. Especially in such a complex project with urgency in a critical environment."
Optimizations were sought on all fronts in the preliminary project, during execution and in the operation of the weir. Thuijls: "You are in fact designing and building a smarter, stronger and safer weir with new yokes, sliders, yoke drives, slide drives, crane truck, operation and control system, which is Arboveilig and meets CE standards, but which also looks almost exactly like the monumental old weir. Thus the structure has been made stiffer, the operation of the weir has been partially automated and made Arboveilig for operation and maintenance personnel, and spaces have been devised to house these new techniques. Each yoke will have its own automated drive at the rear, reducing the amount of work the crane truck has to do. This means visually a modest encroachment, but functionally a huge gain. Namely, it allows three people to completely and safely lower or set the weir faster, with fewer risks. In the old situation, this required seven people. This is of great importance since ironing and setting is always done in bad weather conditions. We therefore involved the operators intensively in the requirements retrieval and design. The great thing is that despite all the modifications, the difference in appearance from the old weir is hardly noticeable."
The replacement of the yokes succeeded within the contractual milestone of the end of 2024. "We were quite skeptical about this milestone at the beginning of the work, given the complexity and scope of the work combined with all the environmental influences such as the risk of high Meuse discharge," Thuijls confesses. "The big win here has been the strength of the entire project team. We worked in two 'trains.' The lead time for replacing a yoke is two weeks, but we developed a 'train' so that two yokes could be tackled at the same time and one yoke was delivered each week." Both Uijlenbroek and Thuijls are very proud of this achievement: "It's very nice when the optimizations the team comes up with come true. In fact, the train approach worked so well that we were able to make up for a slight delay by even placing two yokes in one week. After placing a yoke with sliders, we went through the site acceptance test with RWS to verify that everything was standing and moving as intended. This allowed the yoke with sliders to be put into service early."
Currently, production and further preparations are taking place of the drives and operating and control system which, when all the yokes and sliders are in place, will be assembled and installed. Next comes the new crane truck. "Replacing the drives is going to be exciting," Thuijls predicts. "That will be done piece by piece, and then temporarily the old installations in the weir will still be combined with the new ones, with the new ones having to be adjusted and the weir still having to be able to continue to operate. This hybrid approach of old combined with new is quite a challenge. Next year, at least, the weir at Grave will again have a technical lifespan of 50 years. For us it is an instructive process in which we, together with Rijkswaterstaat and our partners, have developed a nice methodology that we undoubtedly want to use in other projects. Ultimately, you do it to unburden the customer and to realize beautiful projects. That starts with trusting each other and by really working together."