From: Brendan Bane, MONGABAY.COM, More from this Affiliate
Published December 18, 2014 08:50 AM

Study finds reefs reduce wave energy by 97%

We have a lot of stake in the coast. Coastal waters are where we host fisheries, build homes and turn to for tourism and recreation. So how should coastal communities, which comprise nearly 40 percent of the world's population, safeguard against flooding, erosion and violent weather? Marine scientist Michael Beck suggests the solution is growing right beneath some waves and, in many cases, it has been waiting there for thousands of years.

Beck, who leads the coastal defense research group of Science for Nature and People and the Nature Conservancy's Global Marine Team, coauthored a study with lead author Filippo Ferrario of the University of Bologna, Italy, and several other scientists, in which they assessed coral reefs' ability to reduce ocean wave energy. They discovered that, on average, coral reefs can reduce wave energy by 97 percent. Their study holds broad implications for the 200 million people who live within 31 miles of coral reefs.

"We knew that reefs break waves and reduce their energy," said Beck, who was surprised by the findings. "We were not expecting to see a 97 percent reduction, though. But it really is that consistent and that strong across all the data." The team of scientists analyzed more than 255 studies on coral reefs and the buffering effect they have on waves that pass through them. When reefs break waves, they found, the process begins at the reef crest.

Coral reefs are composed of two parts: the crest and the flat. The crest is the tallest part of the reef, and it sees the most wave action. The study found that the majority (86 percent) of wave energy is reduced at the reef crest alone. The rest of the work is handled by the sprawling, broad flat, the part of the reef you sometimes see at low tide. After the crest, the first 150 meters (500 feet) of the flat mitigates half of the wave's remaining energy.

The reef's ability to dampen waves also depends on two physical qualities: height and roughness. Taller crests can handle taller waves, and coral species with rough texture can reduce wave energy more than ones with smooth texture. With the reef's important qualities identified and their wave-reducing abilities properly measured, coastal engineers can begin looking at reefs as honest defenses against natural hazards, and even compare them with artificial structures. 

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Reef and wave image via Shutterstock.

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