Around 10 million m³ of sand needed to be deposited around the dike – equivalent to the amount of sand used to maintain the entire seashore of the Netherlands from erosion in a year. Following the reinforcement, the dike should be able to withstand storms up to an intensity likely to happen only once in every 10,000 years.
Pioneering non-tidal freshwater project
The project is unique because, although such sand-based reinforcement has been used in coastal defenses against seawater, it has not been used before in non-tidal freshwater conditions.
Specialists from the EcoShape knowledge consortium initially conducted extensive research in a test area to see how the sand behaved. The results of the test were used for techniques to realize the full-scale application.
Henk Meuldijk, Reinforcement Project Manager at Rijkswaterstaat, says: “It is really good that measurements were taken at the pilot site for a number of years. We can see that the shape of the sand mass is relatively stable after two years. We have used this knowledge for the construction of the reinforcement as well as for our management and maintenance plan.”
Rijkswaterstaat forms part of the Dutch Ministry of Infrastructure and Water Management, handling the design, construction, management and maintenance of infrastructure facilities in the Netherlands.
A research and monitoring program now running for the full, scaled-up solution is designed to ensure experience gained so far regarding the reinforcement of the Houtribdijk can be applied in the future. This program is being led by Rijkswaterstaat in collaboration with Delft University of Technology.
“The knowledge that we are gaining here will be very useful in the Netherlands and beyond,” Meuldijk says.
Video: Take a closer look at how the dynamic behavior of the sand in the Houtribdijk reinforcement is being monitored.
On-site ADCP monitoring proves its value
Desktop modeling could only help to a limited extent on the project, given the many forces at work and the complexities of the feedback between them. If the sand started shifting on test sections of the beach or holes started appearing in it, then the researchers needed to know exactly what forces were at play.
Detailed monitoring of the interaction between the water and sand was essential to ensure the defenses were fit for purpose, which is where Nortek’s expertise in current profiling and wave measurement came in.
“With traditional coastal protection works, you only deal with physical problems, such as currents, waves and rock forces. But with these nature-based solutions, you need a much greater degree of monitoring, because the outcomes are much harder to predict and you need to take into account ecological elements like flora and fauna,” says Sicco Kamminga, Managing Director at Nortek’s subsidiary in the Netherlands.