Water Board Rivierenland continuously balances between the technical requirements and the desired appearance in dike reinforcement of the city of Tiel

Since the end of 2022, the Rivierenland Water Board has been working hard to reinforce the dike near the city of Tiel. Before even a shovel could be driven into the ground, a whole process of thinking, puzzling and designing preceded. Consideration was given to every piece of dike: what is needed technically and what does the environment require? The result was a fully developed design. Nevertheless, during the work it was still regularly a balancing act between the technical requirements and the desired appearance.

"Together with engineering firms Tauw and Iv-Groep, we spent a total of just under four years on the design," says Koen van Gerven, technical manager at Waterschap Rivierenland. "The advantage of a well-thought-out and well-developed design is that it provided clarity in the tendering phase about the risks, among other things." Speaking of the procurement phase, it was at the time of the corona crisis and the start of the war in Ukraine. Resulting in a sky-high steel price. "In view of the many steel sheet piles needed, we deliberately chose, in consultation with the High Water Protection Program (HWBP), to set the steel price in the tender and settle it afterwards with the current price. This created a level playing field for all tenderers and the financial risk did not lie with the market parties. By also assuming responsibility for the sheet pile design as a water board, contractor FPH Ploegmakers was able to purchase steel at an early stage and we were able to start work on schedule."

Active role of water board

According to project manager Hans van Kooten, the dynamic playing field between what is technically possible and what the environment (municipality, local residents and other stakeholders) needs requires an active role from the water board. "We have to actively think along and be critical, because there are a lot of interfaces. An example of a safe dike fitting into the environment is the design of the fortress wall. We could have chosen a steel wall here. Then the dike would also have been safe, but given the monumental status of the fortress wall, that was not really an option. Here we worked together with the municipality, the monument committee, FPH Ploegmakers and the Flood Protection Program to find a suitable solution for the area that also technically meets the safety requirements. The result is a new wall with authentic stones that gives Tiel a very beautiful appearance. Another example where we very specifically took the surroundings into account is part of the route near Grand Café Bellevue. Here we made the dike less high than planned. A higher dike also means widening it. However, we were limited here by the river on the one hand and the adjacent backyards of local residents on the other. In order to prevent everyone from having to give up a piece of garden, which is very drastic, we opted to look ahead 25 years rather than 50 years with regard to the life span of the dike. Very early on in the process we entered into a cooperation agreement with the municipality of Tiel. We started talking to each other about the wishes and activities of the municipality in order to include these in the project activities immediately. We as a water board will take care of the implementation, the municipality will contribute financially. We have a very intensive collaboration throughout the project so far, with consultations every two weeks."

Milestone

AND of the milestones so far in the project is the coarse sand barrier (GZB), an innovation of the Rivierenland Water Board. Koen: "With this coarse sand technique, we use the natural raw materials coarse sand and clay. As a result, the coarse sand barrier lasts a very long time. As a water board, we are leading the way in the Netherlands with this. We even organized a special day where other water boards, provinces, municipalities and other interested parties could gain knowledge on how to construct such a barrier."

Goodwill thanks to short lines of communication

Koen and Hans are very satisfied with the cooperation with FPH Ploegmakers. Hans: "The moment they came 'on board' with the project was quite exciting for us. After years of preparation, our role changed. The contractor was put in charge and the work started. But looking back on that period, it all went very well. The great thing about a relatively small team like FPH Ploegmakers is that the lines of communication are very short. You only have to make one phone call and it's taken care of. Not only to us, but also to the local residents. That has certainly earned us a lot of goodwill. Moreover, they are very solution- and result-oriented, something that certainly came in handy in the project."