Fluid Force on Vegetation Due to Tsunami Flow on a Sand Spit
One of the features of the 1998 Papua New Guinea tsunami is that a maximum tsunami height of 14.8 m was observed on the vegetated sand spit of Sissano lagoon that faced the tsunami source. This tsunami caused a large number of human casualties. The coastal vegetation in the western Pacific Ocean countries attracts attention from an economical and environmental point of view as a tool of tsunami countermeasures. Fluid force on vegetation mainly consists of drag force F D , inertia force F M , and linear wave making resistance force F W . In this paper, the ratios of these forces and corresponding coefficients are examined. It is clarified that F M reaches 50 % of the maximum drag force F Dmax at the early stage of inundated flow, and that F D and F W are dominant at the quasi-steady state after the early stage. The drag coefficient C D is found to be 0.9–1.5, the mass coefficient C M is 1.5–2.5, and the linear wave making resistance coefficient θ' is 0.02–0.07. C D and C M change with the same tendency as those of group of piles in open channel flows, and they decrease as vegetation density κ increases.
KeywordsDrag Force Linear Wave Tsunami Source Fluid Force Inundation Depth
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