Impacts of coastal vegetation on tsunami-induced overtopping scour behind embankments and local scour around buildings

This study experimentally investigates the role of coastal vegetation in adjusting tsunami-induced overtopping scour behind embankments and local scour around buildings. Laboratory experiments conducted in a recirculating flume quantified the effects of vegetation density, height, and rigidity on scour dynamics under varying overtopping flow intensities. Results reveal that vegetation significantly reduces scour dimensions by increasing upstream flow resistance, dissipating energy within the vegetation zone, elevating the trajectory of the overtopping jet, and physically trapping mobilized sediments. Rigid vegetation outperforms flexible counterparts in reducing overtopping scour rate (by 3.2 times) and volume (by 4 times) due to its ability to maintain constant flow resistance and geometric porosity under high flow velocities. Taller vegetation enhances upstream sediment retention, but its rigid configuration slightly increases the downstream local scour depth around the building due to intensified pressure gradients. While high-density, tall, and rigid vegetation configurations provided maximum overall scour reduction, the study highlights a trade-off: optimizing vegetation parameters for overtopping scour mitigation may slightly reduce effectiveness for local scour control directly around buildings. These findings provide crucial insights for designing ecologically integrated coastal protection strategies that leverage the hydraulic and sediment-trapping functions of vegetation to enhance resilience against tsunami-induced scour.