DELFT, THE NETHERLANDS—Dutch scientists are making waves—big ones. A new experimental facility at Deltares, a research institute here, has begun producing the largest humanmade waves in the world. Like kids building sandcastles below the tideline on the beach, scientists will let the walls of water crash on dikes of different designs and other structures—sometimes until they're destroyed.
The Delta Flume, to be inaugurated on 5 October, is a 300-meter-long water-filled trough that is 9.5 meters high and 5 meters wide. At one end sits a gigantic metal plate called a wave board; four pistons move it back and forth to whip up the kind of waves that the sea can unleash. The waves travel along the flume and crash onto whatever researchers have built at the other end—which could include a novel type of dike, an artificial sand dune or gravel beach, or a pylon used to hold up an offshore wind turbine.
Watch Deltares's “trailer” for the Delta Flume:
The flume is largely inspired by Holland’s historic battle against the sea. Half of the nation is below sea level and a 1953 flood killed more than 1800 people, which is why this small country is obsessed with keeping its 3000 kilometers of primary flood defenses up to date. But Deltares hopes that foreign researchers, governments, and private contractors will also find their way to the Delta Flume, says Marcel van Gent, who heads a team of 35 scientists and consultants at the institute.
"It's a very nice facility," says Javier López Lara, a coastal engineer at the Environmental Hydraulics Institute “IH Cantabria” in Santander, Spain. He predicts that the wavemaker will be "of great importance in our field for many reasons." Coastal defenses are becoming more important as sea levels rise, he notes, and climate models suggest some parts of the planet will become stormier. The flume will also provide new insights into natural processes such as sediment transport along shorelines and the mechanical properties of coastal soils, López Lara says.
Other countries have large wave facilities as well, although the exact design differs from one to the next. Japan's Port and Airport Research Institute has a flume to mimic tsunamis, built to generate one wall of water instead of a steady onslaught of waves. Other facilities recently completed or currently under construction are designed more for marine and offshore engineering, López Lara says.
This video shows how the new flume works:
The new Dutch flume replaces an older, smaller version that will be retired after 35 years of service. The Delta Flume boasts bigger waves; the maximum significant wave height—a measure of a storm's intensity—is 2.2 meters, but individual waves may top out at 4.5 meters. There are other innovations as well, such as radar and laser systems to measure wave heights at any location. Researchers can also change the amount of water in the flume during an experiment to simulate tidal variation.
The facility needs to be so big because in hydraulic engineering, small-scale models often aren't good enough. A few structures, such as breakwaters built of rock, can be studied using miniature versions, but materials such as sand, clay, and grass behave differently in small-scale models than in the real world, van Gent says. So does water, in some cases: Around a small model of a rock-and-concrete dike, for instance, water may display a so-called laminar flow pattern, whereas in the real world it displays more chaotic turbulent flows. The flume will allow researchers to build realistic, 1:1 scale models of 85% of Dutch coastal defenses.
The first study in the new flume was actually done in July. Watch here how the first waves rolled in:
Plenty of other studies are on the drawing board, van Gent says. Engineers have begun developing so-called nature-based coastal protection, such as willow forests, to absorb the power of waves. Such “living shorelines” have been shown to do well under many circumstances, but an experiment in the Delta Flume might be the only way to show how they behave during very rare and very powerful storms. Another area that has not been studied much is how dikes behave after their coverings have eroded away. The dike’s core—often made of sand and clay—may still withstand the water for some time. That means "you might have a damaged dike, but not a flood," van Gent says. "That's important to know."