Mangroves can attenuate tsunamis, storm surges, and waves and significantly reduce coastal hazards. Their protective functions as natural barriers have drawn attention as a prime example of green infrastructure/Ecosystem-based Disaster Risk Reduction (Eco-DRR)/Nature-based Solution (NbS) for coastal resilience. While hydrodynamic models are commonly used to estimate wave attenuation by mangrove forests, critical thresholds for mangrove tree failure under wave impacts and the associated wave conditions remain underexplored and are often excluded from such assessment. This study investigates the maximum bending moment of the mangrove tree, mainly Rhizophora stylosa, based on a field survey conducted on Iriomote Island, Okinawa, Japan. A practical estimation formula is developed by integrating field data with linear small amplitude wave theory. The results, including empirical relationships for critical wave conditions leading to the bending failure of mangroves, offer valuable insights for designing and optimizing mangrove-based coastal protection strategies.
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