Effectiveness of restored mangrove wetlands in damping waves

Abstract

There has been a global attention on the feasibility and embodiment of integrating the mangrove wetlands into coastal defense. However, little evidence is related to the restored mangroves (with mangrove trees artificially planted), which is increasingly important under ongoing wetland restoration worldwide. Here, wave propagation across a restored Kandelia obovata mangrove wetland on the Hailing Island, Guangdong Province, China, was observed to examine the wave damping effectiveness of the restored mangroves and their potential in coastal defense. The results showed that waves were attenuated by 26 % as they passed through the studied mangrove wetland. The wave attenuation rate of the bare flat was inversely proportional to water depth, and that of the mangrove forest was linked to its submerged state, peaking when the canopy was partially submerged. The restored mangrove attenuated waves more effectively than the bare flat, and showed reliable wave damping ability even in comparisons with natural marsh and mangrove vegetations. This evidence supports the feasibility of utilizing the restored mangroves in nature-based coastal defense. Furthermore, an idealized model was established to examine how the width of the restored mangrove impacts the gross wave attenuation. It is found that wave height reduction increases under a larger restored mangrove width, while the increase is nonlinear. We then proposed an optimal mangrove width proportion of 15 % for the studied wetland, under which the mangrove wetland showed a reliable gross wave height reduction together with a relatively large efficiency. These findings provide important insights into mangrove-induced wave attenuation and its implications for nature-based coastal defense worldwide.