BEVEREN, Belgium—The world’s levees are losing the battle against rising seas and overflowing rivers, so experts here want to learn how to fight smarter.

Locals in the coastal regions of northwest Europe, long known as the Low Countries, for centuries have expanded their space for farming and living with earthen barriers that hold back the saltwater and stop freshwater floods. Those triumphs of engineering now face unprecedented assault from oceans and rivers.

Few...

BEVEREN, Belgium—The world’s levees are losing the battle against rising seas and overflowing rivers, so experts here want to learn how to fight smarter.

Locals in the coastal regions of northwest Europe, long known as the Low Countries, for centuries have expanded their space for farming and living with earthen barriers that hold back the saltwater and stop freshwater floods. Those triumphs of engineering now face unprecedented assault from oceans and rivers.

Few parts of the world are more directly exposed to the impact of climate change on water levels than the Low Countries, an issue addressed by world leaders at the recent United Nations climate summit in Glasgow. 

More than half of the 17 million people in the Netherlands live on land that sits below sea level. Millions more people across the country, Belgium and nearby parts of France and Germany reside in areas easily inundated, as fatal floods this summer showed. 

A flooded area near the De Dem water buffer in Hoensbroek, the Netherlands, in July.

Photo: marcel van horn/Shutterstock

Faced with a hydraulic onslaught that is overwhelming traditional defenses, specialists are seeking new ways to manage water that are more in tune with nature than simply building higher walls. They are studying how foliage affects dikes’ strength, how resilient the barriers are against overflowing water and how much danger burrowing animals such as moles and rabbits pose.

“We need to understand for the future which things really do matter for us in levee design and maintenance,” said Patrik Peeters, a levee expert at Flanders Hydraulics Research, a government institution in Belgium’s Dutch-speaking region.

Since floodwaters ignore national boundaries, the researchers are also learning to work across borders. Their subject of study is the Scheldt River, which flows from France through Belgium and empties into the North Sea on the Dutch coastline. (The words “dike” and “levee” come from the Dutch and French words for the same flood barriers.)

The researchers are working at what they call a living lab: a stretch of reclaimed land—a polder in Dutch—that has been shielded from the Scheldt estuary’s waters for generations by dikes paralleling the river. Authorities earlier this century decided to give the Scheldt back some space to overflow, improving sustainability and lowering the river as it passes through Antwerp, about 15 miles upstream, and beyond.

Levee guards who monitor barriers in Belgium and the Netherlands learn new techniques including using a special mobile-phone app.

Photo: Francien Horrevorts

Hydrologists over recent years have realized that constraining rivers only intensifies flooding in the most vulnerable spots, as has happened this year in areas from Louisiana to China. Instead, rivers need room to expand. The Flemish Waterway authority since 2005 has been adapting how it manages the Scheldt. Experts along the river are identifying areas most in danger.

“You gain a lot by knowing in advance where your potential weak points are,” said Ludolph Wentholt, a water-defense program manager at the Netherlands’ Foundation for Applied Water Research.

Adding an extra dimension to the study, the Dutch and Belgian experts are comparing their approaches to dike construction and maintenance, which differ slightly along the barrier when it crosses their border.

Money is a sticking point in climate-change negotiations around the world. As economists warn that limiting global warming to 1.5 degrees Celsius will cost many more trillions than anticipated, WSJ looks at how the funds could be spent, and who would pay. Illustration: Preston Jessee/WSJ The Wall Street Journal Interactive Edition

“We decided to have a kind of competition between the Belgians and the Dutch to see whose levee is best,” joked Mr. Peeters.

The Belgians mow grass on their side twice annually, for example, while the Dutch mow at least three times and use fertilizer. The different approaches yield differing root systems that researchers are assessing for their impact strengthening the levee.

The competition—and cooperation—are possible because Messrs. Wentholt and Peeters have known each other for almost a decade and speak with one voice on their objectives.

“If we can say as levee managers that this vegetation makes it stronger,” said Mr. Peeters.

“Then we can have another type of climate adaptation to make the system more robust,” said Mr. Wentholt.

Research on the Dutch-Belgian polders will even inform the new U.S. National Levee Safety Program being developed by the Army Corps of Engineers and the Federal Emergency Management Agency, said Phoebe Percell, chief of dam and levee safety at the Corps of Engineers, which for almost a decade has had a partnership to share levee-safety information with Dutch and British counterparts.

Patrik Peeters, right, a levee expert at Flanders Hydraulics Research in Belgium, and Ludolph Wentholt, a water-defense program manager at the Netherlands Foundation for Applied Water Research.

Photo: Daniel Michaels/The Wall Street Journal

“It definitely makes us better in levee safety—which is something we’ve focused on since Hurricane Katrina and what happened in New Orleans—to expose ourselves to other ideas,” said Ms. Percell, who recently visited the living lab.

At the polders, Flemish and Dutch crews for almost a decade have been building 3 miles of new dikes that snake inland nearly a mile and a half. Next year, they plan to start breaching the current levees. More than 1,000 acres between the old and new barriers will return to nature. Wildlife is already returning.

With the new levees almost complete, hydrological experts and water managers from the three Scheldt countries and England are conducting batteries of tests and experiments on the old dikes. They have built sluices to deliberately overflow and erode the sand-and-clay structures and then tested repair methods. They have pumped colored smoke into animal burrows to see how far they extend, and enlisted students to experiment with repairing damaged surface vegetation.

Among their findings: The levees withstand water much better than expected, even when it flows over the top. But if damage lets water through a levee’s outermost layer of clay—just beneath covering foliage—to a levee’s sandy interior, the barrier can collapse surprisingly quickly.

Small upkeep differences can ripple through the increasingly complex local ecosystem, they are finding. As the former farmland has returned to nature, animal activity has increased. Tunneling at the base of a levee by rabbits, foxes or similar-size animals can allow significant inflows during floods, weakening the sand core. Extensive tunneling could cut a levee’s ability to hold back water to as little as 15 minutes from up to 30 hours if it is intact, the teams have found.

More-frequent mowing can upset burrowing animals, prompting them to dig elsewhere, the researchers have discovered. Grazing cows similarly tend to reduce mice activity in a field.

“You don’t want to live with neighbors upstairs who are partying every night,” said Mr. Wentholt, framing the analysis in human terms.

SHARE YOUR THOUGHTS

How should world leaders be addressing the issue of rising seas and rivers in order to prevent flooding? Join the conversation below.

Marian Booltink, a crisis coordinator at a Dutch water board near Utrecht, uses the verdant outdoor laboratory to train levee inspectors from around the Netherlands, who will walk their local embankments seeking cracks, burrows or other problems. Along the disused dike, they can probe and excavate in ways considered dangerous on a working one.

“Here we can demolish the levee, and it’s great,” said Ms. Booltink.

With the freedom to damage levees comes a chance to test repairs, using materials including traditional sandbags, giant mesh bags of rocks and synthetic tarps. This year, project leaders conducted a competition between teams of engineering students from Belgian and Dutch technical universities, challenged with repairing a damaged levee most efficiently.

The Belgians won by using a large roll of woven coconut fibers, which beat the Dutch team’s plastic film. The coconut fibers proved cheaper, more durable and are biodegradable. Months after the test, plants had popped through and overtaken the slope.

Rising water at a temporary flood defense in Arcen, the Netherlands, in July.

Photo: remko de waal/Shutterstock

Write to Daniel Michaels at daniel.michaels@wsj.com