Abstract: A three dimensional numerical approach based on IHFOAM to study the interaction of tsunami waves with mangrove forest is presented. As a first approximation, the problem is modelled by means of solitary waves impinging on emergent rigid cylinders. Two different conceptual approaches are implemented into IHFOAM. Solving the URANS equations provides a direct simulation of the flow field considering the actual geometry of the array of cylinders. A modified version of the volume-average URANS equations by introducing a drag force to model the momentum damping created by the cylinders is used in the second approach. Both the direct and macroscopic simulations are validated against laboratory experiments for wave damping with very high agreement. A large set of numerical experiments to analyse flow parameters and uniform and random cylinder array distributions are analysed and use to compare pros and cons of the different approaches. Large differences are found in the forces exerted on the vegetation for uniform and random distributions. Generalizations obtained from uniform arrangements could lead to underestimation of wave-exerted forces, especially for low dense configurations. Wave forces calculated with the macroscopic approach by means of the drag coefficient yields clear underestimations.

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