Reduction of wave overtopping by Vetiver grass

In this research Vetiver grass is investigated as outer slope protection in order to reduce wave overtopping discharges. In consequence sea dike crest can be reduced. Beside it, this research also focuses on addressing the hydraulic effects of flow and Vetiver hedges. Physical model is conducted full-scale of Vetiver grass and wave parameters in front of the hedge. Mature Vetiver grasses are used for testing and wave is simulated by dam-break method. Experimental results have shown that resistance between flow and Vetiver hedge depends on grass density. In this research, Mannings coefficient is used to describe the resistance; it varies with the changing of flow depth. One interested characteristic of Vetiver grasses showed in this experiment is that its ability to withstand flow of backwater which reaches depths up to nearly 0.4m. The reduction of wave overtopping of more than 60% is measured. The roughness coefficient of Vetiver grass that depends on grass density is found to be varying between 0.33 and 0.41.