Latest international research: Salt marshes can effectively cope with extreme wave damage and promote coastal protection

China News Service, Beijing, October 23 (Reporter Sun Zifa) A newly published ecological paper in the international academic journal "Nature" stated that the results of an experiment conducted in a giant wave tank showed that salt marshes can survive extreme wave events with only slight erosion. The results help determine where protecting and restoring salt marshes can most effectively contribute to coastal protection.

Site diagrams and schematics related to this research (pictures from the paper). Photo courtesy Springer Nature

The authors believe that although the ground beneath the salt marsh appears stable during extreme storms, plants in the soil are severely damaged, which reduces its ability to dissipate waves. Therefore, salt marshes may be best suited to provide flood protection for coastlines experiencing moderate storms.

According to the paper, flood control strategies focused on dissipating wave energy are becoming increasingly important in the face of rising sea levels and increased exposure to storms. Saltmarshes, with their high beds and roughness of vegetation, can be a natural solution for dissipating wave energy. However, the behavior of salt marshes during extreme wave events has not been fully studied.

In this study, Pim W. J. M. Willemsen, the first author and corresponding author of the paper and Wageningen University in the Netherlands, and his collaborators conducted a large-scale experiment to analyze the response of salt marshes to extreme waves. They transported and installed 306 square meters of salt marsh and vegetation into one of the largest wave tanks in the world, the Delta Tank Wave Generator.

Waves in a delta flume (photo by Guus Schoonewille, Netherlands Delta Institute). Photo courtesy Springer Nature

The study found that after 2-meter-high waves interacted with the salt marsh and vegetation for 21 hours, the surface of the salt marsh was only eroded 7 millimeters; after the first wave test, the amount of vegetation decreased by 33%, from 831 grams per square meter to 558 grams per square meter; after 21 hours, the above-ground biomass dropped to 20%-25% of the initial biomass, and the stem length decreased by 47%; compared with larger waves, vegetation has the strongest attenuation effect on small waves.

The authors used storm surge, coastal elevation and salt marsh distribution data to extrapolate the findings to a global scale. Their analysis shows that vegetation can weaken waves by more than 10%; on low-energy saltmarsh coasts (coasts with wave heights of no more than 1 meter), the weakening can be as high as 50%.

Photo of the salt marsh (photo by Guus Schoonewille at the Netherlands Delta Institute). Photo courtesy Springer Nature

The authors conclude that restoring and protecting salt marshes along coasts that experience low-energy storms could be a promising technology for mitigating the effects of extreme storms. Even on coasts experiencing high-energy storms, salt marshes may help attenuate waves, but will primarily need to be paired with engineered defenses such as seawalls.