Numerical Investigation of the Attenuation of Tsunami-like Waves by a Vegetated, Sloped Beach

Tsunamis, such as the 2004 Indian and 2011 Japan tsunamis, routinely cause severe damage along coasts. Coastal vegetation serves as an excellent, naturally occurring protection from tsunamis. However, prior studies focusing on the wave attenuation by vegetation assumed that solitary waves would adequately represent the major aspects of tsunamis. However, there are substantial differences between solitary tsunami waves with regards to their wave profiles and how it evolves with time. This study aims to improve our understanding of the wave-vegetation interactions by employing a more realistic wave profile (tsunami-like instead of solitary). This work uses measurements obtained during the 2011 Japan tsunami to parameterize the observed tsunami-like wave profile, which is then used to investigate the wave-vegetation interaction on a sloped beach, using a nonhydrostatic wave (NHWAVE) model. The work investigates the efficiency of vegetated sloped beach in mitigating the maximum run-up height and total wave energy as function of wave height, water depth, vegetation width, vegetation density and wave model (solitary vs. tsunami-like). Results show that a vegetated sloped beach is effective in reducing the wave energy of both kinds of waves. However, when a solitary wave is used, the vegetation patch is shown to be relatively better at attenuating wave energy and in reducing maximum run-up heights. The findings indicate that the solitary wave model overestimates protections afforded by coastal vegetation, and that it underestimates maximum run-up heights. The findings drawn from this study further broaden our understanding on the wave attenuation of tsunami surges and waves by a vegetated sloped beach.