Coastal Protection by Planted Mangrove Forest during Typhoon Mangkhut

Abstract

Mangroves provide many ecosystem services, including coastal protection against storm surges and waves. As an adaptive method for coastal defense, mangroves were widely restored and planted in tropical and subtropical regions, such as the coastal regions in Southeast Asia. Field surveys were conducted to quantify the nature-based coastal protection provided by a planted mangrove forest along the coasts of Shanwei, Guangdong Province, China, under typhoon influence. The resilience of mangrove trees was assessed under the impact of Typhoon Mangkhut (2018), which induced a maximum storm surge of 1.74 m with a maximum wave height of 1.16 m in the study area. The pre- and post-typhoon surveys and hydrodynamic measurements were conducted at a mudflat with planted mangroves. The wave height reduction reached 77% over 100 m wide mangrove forest. Our results suggest that a six-year-old planted mangrove forest with a ~100 m width might withstand a super typhoon impact and provide substantial protection for the fish ponds and embankments behind the mangrove forest. No uproots or deadly breakage of stems were observed in the mangrove forest, while severe defoliation was spotted for a small portion of trees in the study area, mainly along the wind path, the windward edge of the forest, and among the taller plants. Obvious sedimentation in the mangrove front and the tidal flat was observed during the typhoon Mangkhut (2018) and the entire typhoon season of 2018.