Hybrid test dune to measure erosion during storms

Last week, a hundred-metre-long test dune rose on the coast near Monster. A hybrid dune, consisting of a combination of sand and hard elements. Researchers from TU Delft are monitoring how different configurations erode during stormy weather conditions. This will allow hybrid dyke-dune structures to be designed more efficiently and safely in the future. 

“We don't know exactly how long the set up will stand. We expect the dune, which is close to the coastline, to completely fade in the next two to three months”, predicts Daan Poppema, postdoc Hydraulic Engineering. With hydraulic engineering companies Van den Herik and Boskalis, thousands of cubic metres of sand were moved for the construction of the test dune. This week, the last measuring instruments will be installed, and then it will be waiting for nature's elements.  

The best of both worlds 

The Dutch coastline is traditionally protected by sandy dunes and hard dykes. The coast is being protected with hybrid dunes more often now, such as the dyke-in-dune constructions in Noordwijk, Katwijk and Groede. The idea is to combine the best of both worlds: dunes match the natural character of the Dutch coast and help valuable nature. In addition, dunes can grow with sea level rise. Dykes, on the other hand, offer better erosion resistance than dunes.

Due to interactions between sandy and hard elements, erosion occurs differently in hybrid dunes compared to sand dunes. The Hybrid Dune field experiment is a unique opportunity to better understand this process. The test dune consists of four different cross sections: A sandy dune; a dyke (sand covered with hard dyke slope); a dyke-in-dune (dyke slope covered with sand); and a barrier-in-dune (a core of containers in the dune).  

Measuring during storms

Thanks to colleagues and Civil Engineering students, the test dune and shoreline are equipped with a wide range of measuring instruments, says Poppema: “With the sensors we will measure the water flow, height of the waves and erosion of sand.” When storms are approaching, researchers and students spring into action. Then drones and LiDAR (laser) take additional measurements to map dune erosion. 

Climate adaptation

The dune is close to the high-water mark. This way, it will be possible to observe effects of extreme weather conditions as early as next year. ‘We don't want to wait ten years for that one extreme storm, so at this carefully chosen location we are deliberately placing the dune in a vulnerable position”, he says. Sea level rise and extreme weather events increase the urgency to work on new technical and natural solutions for climate-adaptive coasts and rivers.