PERSPECTIVE OF COASTAL VEGETATION PATCHES WITH TOPOGRAPHY VARIATIONS FOR TSUNAMI PROTECTION IN 2D - NUMERICAL MODELING

Effectiveness of two types of densely grown coastal vegetation, namely Pandanus odoratissimus and Casuarina equisetifolia were investigated with different ground slopes, against a tsunami event in 2-D numerical simulation. Dimensions of vegetation patches and gap between them were changed rationally in order to represent possible vegetation shapes available on hinterland. Both vegetations showed similar trend of hydraulic properties variations. It was observed that reduction of maximum current velocity is higher than the reduction of maximum water depth behind vegetation patch. Horizontal run-up length is reduced with the patch size increases for very mild ground slope, but when slope becomes steep, gravity effect is dominant than vegetation effect on run-up length. Relatively big patches with narrow gap are identified as destructive forms. In fact maximum current velocity is increased at gap-outlet, gap-inlet and middle of the gap when tsunami flows landward, towards offshore and in both directions respectively compared to the bare land.