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Waterontspanner dijk Schoonhovenseveer-Langerak Heijmans maart 2021 (1)
What about … dyke Schoonhovenseveer-Langerak

Gradually stronger

31 March 2021

Consistently reinforcing a dyke: a challenge Heijmans colleagues Ricardo van der Kroon and Ralf Smits face every day. Together with Water Board Rivierenland they are improving the six-year-old Waterontspanner (water relaxation well) innovation along the river Lek.

Under the bright winter sun, with the occasional threat of rain clouds, a heavy wind is blowing over the Lek near the town of Groot Ammers. A wide dyke completes this characteristic image of the South Holland river landscape. In the lee of the flood defence, Heijmans colleagues Ricardo van der Kroon and Ralf Smits look around, satisfied, at the resting place for hikers along the Nieuwe Hollandse Waterlinie.

Which is looking good: budding cherry trees, nicely kept green areas, decent picknick furniture and a properly working water pump. The pump shows, accompanied by an information sign, how the river dyke between Schoonhovenseveer and Langerak has been reinforced. Instead of drinking water, the pump supplies groundwater, from the Lek.

The Waterontspanner is linked to the groundwater underneath the dyke and thus functions as a sort of pressure relief valve. It drains off excessive water below and behind the dyke through pipes to the ditches. This prevents soil behind the dyke from floating and the dyke from collapsing.

The wind at your back

Innovative reinforcement solutions such as the Waterontspanner have had the wind at their backs for some time now. The Netherlands is facing an enormous challenge, all flood defences must meet new water safety demands in 2050. Traditional reinforcement techniques such as sheet piling and expansions are often too costly and too slow. “We won’t be able to succeed with only these techniques”, says Ricardo. Water Board Rivierenland has put the knowledge of construction companies to use for this dyke section. The fortification plan including the Waterontspanner by Heijmans, De Vries & van de Wiel and Movares was realised between 2014 and 2016.

Showing courage

“An innovation like this is exciting for a water board”, says Ricardo, who has been involved from the start of this project. “An innovative technique such as the Waterontspanner has not proven itself yet like traditional techniques have done. Another matter is the maintenance involved in the Waterontspanner, we did not have any previous experiences. Upon delivery, a water board has to know for sure that their dyke is and stays safe. Our measurements and maintenance vision assured them of that. It is great that they really showed courage!”

Waterontspanner dijk Schoonhovenseveer-Langerak Heijmans maart 2021 (7)


It turned out that a beautiful relationship flourished below the Veersedijk, because Water Board Rivierenland decided to prolong the relationship with Heijmans for another five years through a maintenance and management contract. The ball that started rolling in 2014, could now be scored. Ralf: “What is nice about this contract is that it allowed us to submit a joint bid. As this is a new system, there are no reference projects and a water board cannot assess our approach per market conformity. So, in addition to shared knowledge and experience, the client and contractor really need to trust each other.”

That trust is mainly built outside, according to Ralf. “You take the water board project manager along with you on maintenance rounds to show what work is involved.” The room that asset management projects offer to improve work together with the client, gives him a great deal of satisfaction. “It might seem less spectacular, because it does not often involve grand equipment, but management and maintenance contracts enable you to gradually improve. The pressure from delivery dates and fines often make it difficult to innovate when it comes to new-build projects.”

Common interest

Ricardo knows the handful of residents at the Veersedijk well by now. “As the outflow wells to the ditches are located behind their gardens, residents often come up to me asking questions. Satisfied residents are very important to Rivierenland, but also because they support our innovation. In area management we share a common interest.”

An outflow well shows that suggestions made by residents led to the first continued development of the Waterontspanner. Ralf: “Because the little water drainage pipe was hanging above the pit, residents heard a constant dripping sound in their gardens. We simply solved that with a longer pipe.” Ricardo adds: “During the maintenance phase, it is a challenge to continuously learn from your experiences. Based on these experiences you are able to develop further.”

Dyke data

We are waving at the resident who is keeping an eye on the Heijmans crew through his window, and walk on to a little meter cupboard half way up the slope. The sensors which are connected to the tubes in the dyke emerge here, Ricardo points out. These pass on the current water pressure via an internet connection. Heijmans then turns this into reader-friendly dashboards. This data provides proof: does the Waterontspanner deliver what it says it will do? “This is the solid base of your maintenance contract”, says Ralf.

A dyke which is managed by a construction company is unique, according to Ricardo. “Usually, water boards maintain their flood defences themselves. What makes it more unique, is the fact that Heijmans is now training the water board for future maintenance.” They are doing this with a self-developed training programme, which consists of multiple courses, varying from how one reads data to actually carrying out certain maintenance activities. Ricardo: “We are educating the water board on how they can maintain the Waterontspanner in an increasingly efficient manner. That is what you do as knowledge partner.”

What makes it more unique, is the fact that Heijmans is now training the water board for future maintenance
Waterontspanner Schoonhovenseveer Langerak Heijmans assetmanagement infra rivier


Looking out over the dark water of the river Lek, Ricardo and Ralf continue to brainstorm for a while on the prejudices concerning asset management. “Simple work, swiping a cleaning cloth over your acreage? A big misconception”, says Ralf. Ricardo adds: “Carrying out the same activities time after time is not boring, because you want to do it smarter, faster and better each time. For example, can you combine certain tasks? You are always thinking about things, you are constantly optimizing. It is a challenge to make visible improvements, to collect proof of less tangible results.”

Ricardo standing at the cabinet where the Waterontspanner sensors emerge: “Data from the dyke can contradict or confirm your assumptions. This way you can further improve the Waterontspanner.” The wells contain cards with numbers on them.

That data helps you to do so, Ralf nods. Ricardo concludes: “Thinking about how maintenance can be done better, cheaper and smarter is a joint effort. This collaboration stimulates the water board to maintain in a smarter manner and stimulates Heijmans to further develop the Waterontspanner technique. You continue to innovate through asset management.”