Defending shorelines

Marsh plants can play a major role in mitigating the damage to the world’s shorelines as sea levels rise and storm surges increase. Now an MIT study provides more specifics about how these protective benefits work under real-world conditions shaped by waves and currents.

The study, which combined mathematical modeling with laboratory experiments using simulated plants in a large wave tank, reveals how the effects are shaped by the different types of plants that grow near coastlines and the complex interactions of currents and waves.

“When you go to a marsh, you often will see that the plants are arranged in zones,” says Heidi Nepf, a professor of civil and environmental engineering. As the zones progress, the plants become stiffer and leafier, which makes them more effective at absorbing wave energy. And once established, the marsh plants provide a positive feedback cycle that helps to stabilize and even build up these delicate coastal lands.

The modeling done in this research could help planners know just how much marshland, with what types of plants, would be needed to provide the desired level of protection. It also provides a way to quantify the value provided by marshes, Nepf says. “It could allow you to more accurately say, ‘Forty meters of marsh will reduce waves this much and therefore will reduce overtopping of your levee by this much.’ 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.”