WAVE OVERTOPPING REDUCTION THROUGH VETIVER GRASS

In a number of tropical countries Vetiver grass (Vetiveria zizanioides) is well-known as bioengineering. Recently, Vetiver grass has been planted on outer slope as sea dike protection. However the understanding of the processes and properties between waves and Vetiver grasses are still limited. More insight on affection of Vetiver grass to reduce wave overtopping discharges will be carried out. Physical model is conducted full-scale of Vetiver grass and wave parameters around the hedge. 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. An example with the use of Vetiver grass on a sea dike in Vietnam is worked out, by use of the results from the physical model. This example shows that a reduction of 0.5m of the crest height is feasible for upgrading the present sea dike. It corresponds with a reduction of 12,6% of the costs in case of two Vetiver hedges are planted on the outer slope. This case shows that Vetiver grass is a good solution for sea dike in order to reduce wave run-up on the outer slop and decreases the cost for upgrading sea dike.