Reduction of Wind and Swell Waves by Mangroves

Background

Coastal ecosystems can mitigate the damage from extreme weather events like tropical storms and hurricanes. With human populations increasing in coastal areas, policymakers and stakeholders are interested in coastal ecosystems, like mangrove forests, as a nature-based form of coastal defense and resilience. This report aims to examine the potential for mangroves to reduce wind and swell waves in order to inform decision makers about the potential for mangroves to decrease the risks faced by coastal communities.

Goals and Methods

The authors reviewed available information and literature on mangrove forests’ ability to reduce wind and swell. They compiled this information into a report intended for decision makers, planners, and coastal engineers that focuses on wave attenuation in mangroves and models for predicting wave attenuation. The authors also highlight three different numerical and statistical models for wave attenuation in mangroves: the Wave Propagation in Mangrove Forest (WAPROMAN) model, the Simulating Waves Nearshore (SWAN) model, and a regression model with forest structure characteristics as inputs. 

Conclusions and Takeaways

Multiple studies determined that mangrove forests can attenuate wind and swell, with attenuation rates in a 500 m wide forest reducing wave height by 50-99%. However, most of the research on wave attenuation in mangroves focuses on relatively small waves (less than 70 cm), and research on larger waves from extreme weather events is lacking. The driving factors affecting wave attenuation in mangroves are the density of obstacles that the waves encounter, like aerial prop roots, pneumatophores, trunks, branches, and leaves, and the height of these obstacles relative to water depth. By using the highlighted models, practitioners and decision makers can restore and manage mangrove forests in ways that optimize the mangroves’ ability to provide coastal protection.