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Coral reefs are abundant in tropical and subtropical coastal regions. Besides their important role to ecosystems, coral reefs also act as natural buffers that help protect coastal regions from impacts of extreme surge and waves, such as those generated during hurricanes and tsunamis. Recent studies revealed that the bottom of coral reef has very similar properties as porous media. This paper investigates the hydrodynamic characteristics of the transformation and runup processes of tsunami-like wave impinging on a permeable fringing reef by applying a nonhydrostatic numerical wave model (NHWAVE). Effects of prominent factors, such as wave height, water depth, and thickness, median diameter and porosity of the permeable layer of fringing reef, on the hydrodynamic characteristics of tsunami-like wave over permeable fringing reef are discussed in detail. Results show that when the friction effects of the bottom of fringing reef are modelled using the classical quadratic friction law, the protective function of fringing reefs can be grossly underestimated. Research findings drawn from this study can further broaden our understanding on the hydrodynamic characteristics of fringing reefs under the impact of extreme surges and waves. • Transformation and runup processes of solitary wave over the permeable fringing reef are numerically investigated by applying a nonhydrostatic wave model. • Effects of prominent factors, such as wave height, water depth, thickness, median diameter and porosity of the permeable layer of coral reef are discussed in details. • Results indicates that if the friction effects are modelled by applying the classical quadratic friction law, the protection function of coral reef to the coastal regions can be grossly underestimated. [ABSTRACT FROM AUTHOR]

Attributed to the processes of wave focusing, extreme waves often occur unexpectedly with huge wave height in both deep and shallow water regions, which can cause serious damages to the coastal infrastructures, and threaten the intactness of coastal communities. Field observations after extreme weather events have revealed that as a type of natural barrier, coastal vegetations can effectively attenuate the intensity of extreme surges and waves and thus play a good role in naturally protecting the coast. Usually, focused wave is used as a typical extreme wave model to study the great impact of extreme waves on the coast. To numerically evaluate the wave attenuation of extreme waves by the emergent rigid vegetation patch, a high-resolution numerical wave tank has been established by applying the nonhydrostatic numerical wave model (NHWAVE), where both 2nd-order crest and trough focused waves can be generated by considering wave-wave interactions. The efficiencies of the rigid emergent vegetation patch in mitigating the maximum wave amplitude and total wave energy of both crest and trough focused waves as function significant wave height, peak wave period, water depth, vegetation density and width have been well analyzed and discussed. The results indicate that the emergent rigid vegetation patch can effectively reduce the maximum wave amplitude of focused wave by averagely 31% and the total wave energy by averagely 45%, thus, showing that coastal vegetation can effectively protect the coast from extreme waves. It is hoped that the research findings drawn from this study can further broaden our understanding on the wave attenuation of extreme waves by coastal vegetations. • Interactions between extreme waves and emergent rigid vegetation patch are investigated as function of parameters such as significant wave height, peak wave period, water depth, vegetation density and width. • ▪Results indicate that the emergent rigid vegetation patch can effectively reduce the maximum wave amplitude of focused wave by averagely 31% and the total wave energy by averagely 45%, thus, can effectively protect the coast from extreme waves. • The wave energy loss caused the bottom friction is much smaller compared to the energy dissipated by the vegetation patch, hence can be ignored. [ABSTRACT FROM AUTHOR]