Reproduction of tsunami attenuation effects by coastal vegetation using three-dimensional numerical calculations

The tsunami attenuation effect by coastal vegetation, such as mangroves, called green infrastructure, is widely known through field surveys of disasters and has been studied experimentally and numerically. Previous studies have investigated wave attenuation effects using two-dimensional numerical calculations. However, three-dimensional numerical calculations are necessary to model various wave conditions, including surf zones. Moreover, mangrove prop root shapes are complex and require small grid sizes for detailed reproduction. In addition, the resistance calculation depends on the grid size in the previous method, and applying this method to field calculations incurs high computational costs. Therefore, CADMAS-SURF/3D was employed in this study to reproduce and model mangrove forests as porous structures, and the Dupuit-Forchheimer (DF) law, whose resistance calculation is independent of grid size, was used to establish a low-cost numerical modeling method for mangrove forests. The coefficients and , which depend on the constituent materials of the porous structure, were obtained by sensitivity analysis. When =1000 and =1.0, the wave height attenuation effect is replicated with relatively good accuracy, regardless of the grid size resolution, by a calculation process reproducing the physical experiment. The relationship between the mangrove shore width and the attenuation effect was verified by three-dimensional numerical field calculations to confirm the validity and generality of the model. Upon establishment, this modeling method can evaluate the effects by of coastal vegetation on disaster attenuation in detail on a large scale.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)