Rijkswaterstaat currently reinforces the Houtrib Dike in Lake IJssel, located in the center of the Netherlands.
Before the start of the reinforcement, a test section was first laid along the dike. The reason to do this was simple: the company knew quite little about sand reinforcements in a freshwater lake. Thanks to the pilot that has recently been completed, this has now changed.
The Houtrib Dike will have wide, sandy banks on the western half. These so-called foreshores reduce the wave action against the dike, making it much less heavily attacked by waves. Because sandy banks have not been used before in a freshwater lake for flood risk management, Rijkswaterstaat has commissioned a pilot for which a test section has been constructed along the dike.
This test section has been monitored for four years during which, among other things, the water levels and wave attacks have been continuously measured. Cameras took a picture every hour and the body of sand was measured several times a year. The trial area has now merged into the wide, sandy banks. The pilot has been formally completed this week with the publication of a research report.
Henk Steetzel, the project leader on behalf of EcoShape commented: “We already know very well how sandy reinforcements in the coastal area respond to the waves. And what this means for the desired profile of, for example, sand reinforcements along the coast.”
“But in a lake without a tide, such as the IJsselmeer or Markermeer, it works very differently. The water level is constant and wave movements are less predictable, partly because of the influence of the wind,” added Henk Steetzel.
Steetzel added that thanks to the test section along the dike “we found out that you have to reinforce the dike especially just below the waterline. The action happens between the water line and a meter below it.”
Rijkswaterstaat has incorporated this result in the design of the Houtribdijk reinforcement.
The knowledge gained in the Pilot Houtrib Dike has also been used in other nature and dyke improvement projects, such as the Marker Wadden and the reinforcement of the Markermeer dikes. In addition to the IJsselmeer region, Steetzel expects more applications for sandy banks in the future.