Hybrid Approach for Tsunami Protection: Effect of Embankment-type Seawall and Vegetation on Tsunami Reduction

A hybrid system for tsunami mitigation made up of a seawall and a vegetation belt (Pohutukawa trees) was numerically modeled and analysed to see how it performed under a simplified tsunami wave. The seawall and vegetation belt properties in the mitigation system were varied and subjected to different tsunami periods and beach slopes to reflect a New Zealand context. The modelling results suggest that larger seawalls in the mitigation system reduced tsunami inundation lengths thus run-up heights, and damage forces considerably more than smaller seawalls. Vegetation belts in the system did not contribute to reducing tsunami inundation lengths. Longer vegetation belts did however reduce the damage force of the tsunami. Individually, the seawall structure played a more significant role than the Pohutukawa vegetation belt in the mitigation system.