Optimizing tree crown density of finite coastal vegetation patches for enhanced tsunami mitigation

Tsunamis cause a significant risk to coastal populations, necessitating effective mitigation strategies to minimize their impact. Coastal vegetation, particularly trees, has been recognized for its potential in reducing tsunami forces; however, the influence of tree crown density on internal flow dynamics remains inadequately explored. The crown structure plays a crucial role in dissipating wave energy and altering flow characteristics. This study employs experimental and numerical simulations using ANSYS Fluent to examine the influence of crown density of vegetations on tsunami reduction. Initially, model validation was performed against experimental data before analyzing four vegetation configurations with varying crown densities: (Case-1) fully dense crowns, (Case-2) alternating sparse, dense, and sparse crowns, (Case-3) fully sparse crowns, and (Case-4) a combination of sparse and intermediate crowns. The effectiveness of these configurations in reducing velocities and limiting inland tsunami damages was assessed through flow parameter analysis. Results, presented in form of contour plots and graphs, indicate notable variations in velocity distribution among the different vegetation cases. In the gap region, average velocity reductions of 18% and 24% were observed in Case-4 and Case-3, respectively, compared to Case-1, demonstrating the effectiveness of sparse and intermediate crown combinations in reducing flow velocity. Turbulence kinetic energy (TKE) was highest within the vegetation patch due to flow resistance and turbulence around tree structures, while pressure distribution showed peak values at the front of the vegetation patch, decreasing as the flow entered the gap region. The findings indicate that vegetation patches characterized by a combination of sparse and intermediate crowns (Case-3 and Case-4) provide more effective tsunami protection than patches with totally dense crowns (Case-1). This study highlights the significance of selecting an appropriate crown density in coastal forests to enhance natural coastal protection. Findings suggest that forests with sparse or moderately dense/intermediate crowns offer more effective protection than those with densely packed crowns.