EXPERIMENTAL STUDY ON THE RESISTANCE BY MANGROVE UNDER THE UNSTEADY FLOW

摘要

This paper presents the resistance model by the hydraulic experiment to understand the dynamic and unsteady behavior of a tsunami passing through a green-belt (mangrove) forest and the effectiveness of such a tsunami control forest in reducing its impact. A mangrove with a complex system consisting leaves, trunks and roots is simplified to the artificial model in the hydraulic experiment and put in an open channel. The water level, current and pressure at front and rear of the model are measured to clarify change of tsunami propagation due to the existence of a mangrove forest. Furthermore, the force act on the model was calculated by using the measured pressure. The drag coefficient, C_D, and the inertia coefficient, C_M, averaged over the model are estimated by using the Morison's equation and separating the experimental data to the quasi-steady and the un-steady flow section. We find that the drag coefficient is proportional to essentially the volume occupied ratio. In the other experimental case, the results of numerical model for the tsunami propagation with the resistance model show good agreement with the measured wave profile at front and rear of the mangrove model, which shows that the effect on Tsunami of mangrove forest could be evaluated quantitatively by the resistance model depending on volume occupation ratio. It can make possible to calculate a tsunami inundation area in consideration of the mangrove green belt, which provides information on the mitigation plan and land-use management for reducing tsunami disaster without artificial constructions.