Tsunami hazards: impact mitigation characteristics of coastal vegetation

Abstract

In the aftermath of the Indian Ocean tsunami in 2004 the protection offered by coastal vegetation became evident in many countries affected and the role of coastal green belts in mitigating tsunami impacts has now been clearly recognized. Coastal green belts also attract attention as an environmental friendly and cost effective measure of impact mitigation. In this study, expanding the previous works conducted, further experiments were conducted to assess the energy dissipation and impact mitigation characteristics of coastal vegetation in detail. The resistance offered towards the flow which depends on the characteristics of individual plants and characteristics of the vegetation as a whole were assessed. Tests were conducted in a hydraulic flume in which vegetation was represented by geometrically similar small scale models. The energy dissipation of flow through vegetation was determined under steady flow conditions and reduction in inundation extent was assessed under unsteady flow conditions. Energy dissipation levels up to 48 % and inundation reduction levels up to 35 % were obtained in the experiments which clearly indicate the effectiveness of coastal green belts in tsunami impact mitigation. The dependence of the level of inundation reduction on the level of energy dissipation was also investigated.