Optimizing coastal forest arrangements for tsunami flow dynamics using a three-dimensional approach

Flooding due to extreme events like tsunamis poses a significant threat to coastal areas, often resulting in severe inland inundation. However, coastal vegetation can provide natural defense, helping to minimize the extent of flooding and dissipate tsunami waves. Considering that vegetation can exist in various forms, each potentially influencing wave dynamics differently. In this study, five coastal vegetation configurations were evaluated: tall vegetation (TV), short vegetation (SV), mixed vegetation (MV), short-then-tall vegetation (STV), and tall-then-short vegetation (TSV). A three-dimensional computational fluid dynamics approach while using the volume-of-fluid technique with FLUENT software was utilized to confirm the accuracy of the numerical model through physical experiments in a rectangular open flume. The results showed that the numerical model successfully captured the flow patterns. The TSV configuration outperformed in dissipating energy, reducing downstream flood depths, and lowering fluid forces by up to 15%. This arrangement showed significant potential in protecting downstream regions and minimizing hydraulic impacts. However, SV and STV offered less resistance and showed limited energy dissipation, making them less effective. Although the TV configuration helped reduce the initial flow impact, it also increased near-bed velocities, which could lead to erosion. The MV configuration offered a balanced solution, considering the benefits of both SV and TV. This study shows the importance of strategically positioning coastal vegetation to strengthen resilience against tsunami-induced flooding. These findings highlight how optimizing coastal forest arrangements can significantly improve coastal protection and reduce flood damage.