Green, Grey, or Both? Mangroves, Revetments, and Hybrid Systems to Mitigate Wave Overtopping

Abstract We performed a 1:2 scale experiment investigating the performance of green (mangrove), grey (revetment), and hybrid green-grey (mangrove + revetment) systems in mitigating wave overtopping. Six configurations were tested under irregular, regular, and transient (tsunami-like) wave conditions. This paper focuses on the performance of the systems under transient wave conditions, with amplitudes between 0.113 m and 0.228 m and rise times between 4.18 s and 15.40 s. Results indicated that while the conventional (revetment only) configuration reduced total overtopping volumes compared to the baseline (wall-only configuration) by 6% to 30%, the mangrove-only configurations reduced overtopping significantly (by 25% to 54%). Hybrid mangrove + revetment configurations produced the greatest reduction in overtopping, with overtopping reductions of 44% to 83% compared to the baseline configuration. These results show the potential for nature-based and hybrid solutions to provide similar engineering benefits as conventional systems to mitigate future coastal flood hazards.