Test setup

A wave overtopping simulator was already in place on the levee in the Living Lab Hedwigepolder to test the erosion resistance of the levee. This machine was used to create the waves on the levee. “The purpose of the experiment was to test how well people can withstand wave overtopping on the slope of a levee. Test persons were asked to stand at various positions on the slope with a neutral stance to see at what overtopping discharge they would lose their footing,” explains Robert. The maximum discharge varied. Stephan: “We started with small wave volumes and increased it until the test person was not able to remain stable anymore and fell over. In some test runs, large wave volumes of 1500 liters per meter (L/m) were reached.”

See this small clip of the wave overtopping test on people, made by Robert:

Safety measures

Safety was an important issue for the team. Stephan: “Because we were testing on people, we needed to be extra careful and think everything through. We identified all the risks beforehand and wrote everything up in an extensive safety plan. The test subjects were safely secured, to prevent injuries when they lost their stability.” Robert adds: “The participants were wearing a safety harness and hard hat. A safety line was attached to the test person through a pulley above them, and  a second person was holding the other end of the rope to catch the participant when knocked down by the wave. As we did not have any previous experience in these kinds of tests, we were greatly helped by the experience and advice of Jentsje van der Meer and Infram Hydren regarding the setup and wave discharge conditions.”

"This was an exciting experience, like a ride on a roller coaster. Great experiment to take part in as a test person."

Ludolph Wentholt

Position, wave volumes and weight matter

What are the conclusions from the test? Stephan: “The tests showed that for smaller overtopping volumes of up to around 500 L/m, the participants were able to maintain their stability. Overtopping volumes larger than that often resulted in instability or falling over. If the participant was facing away from the wave, stability decreased. Possible explanations are that the person does not see the wave coming and has a different position of the feet. Another thing we saw: it appeared that the weight of the test subject was an important factor in the stability. Heavier participants were able to withstand larger wave volumes than lighter people.”

Enjoyable and terrifying

Robert and Stephan look back on a good day in the field: “Wave overtopping and overflow tests have been carried out often. But it is not every day that you get to be part of the experiment and experience the force of the water. Many of the participants said they enjoyed the experience, also because they were safely secured. At the same time, seeing a big wave coming right at you was quite terrifying.”