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Marshes protect shorelines against inclement weather

A new study published in the journal Physical Review – Fluids has found that marshes, which are ubiquitous along the world’s shorelines, could play a significant role in mitigating the damage caused by storms and sea level rise

By combining laboratory experiments that use simulated marsh plants in a large, 24-meter-long wave tank with mathematical modeling, a research team led by the Massachusetts Institute of Technology (MIT) discovered that marsh plants provide a positive feedback cycle that helps not only to stabilize but also build up delicate coastal lands, making them more resilient to extreme events caused by climate change.

“When you go to a marsh, you often will see that the plants are arranged in zones,” explained study senior author Heidi Nepf, a professor of Fluid Mechanics at MIT. “Along the edge, you tend to have plants that are more flexible, because they are using their flexibility to reduce the wave forces they feel. In the next zone, the plants are a little more rigid and have a bit more leaves.” As the zones progress, the plants will gradually become leafier, stiffer, and more effective at absorbing wave energy.

Although the protective capacities of marsh plants against inclement weather have already been well-understood, this study is the first to incorporate details of plant morphology, such as the number and spacing of flexible leaves and stiffer stems, as well as the complex interactions of currents and waves coming from various directions, to find out how much marshland with what types of plants would be needed to provide optimal levels of protection. Furthermore, it can also provide a quantitative way to estimate the value provided by marshes.

 “It could allow you to more accurately say, ‘40 meters of marsh will reduce waves this much and therefore will reduce overtopping of your levee by this much,’” said Nepf. “Someone could use that to say, ‘I’m going to save this much money over the next 10 years if I reduce flooding by maintaining this marsh.’ It might help generate some political motivation for restoration efforts.”

Professor Nepf is already trying to include some of these findings in coastal planning processes, by working on a practitioner panel at the Water Institute of the Gulf, which serves the storm-ridden Louisiana coastline. “We’d like to get this work into the coastal simulations that are used for large-scale restoration and coastal planning,” she concluded.

By Andrei Ionescu, Staff Writer

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