RESEARCH ON THE HYBRID METHOD FOR TSUNAMI-MITIGATION BY ADDING AN EMBANKMENT AND MOAT IN FRONT OF THE EXISTING COASTAL FOREST

Abstract

 After the Great East Japan Tsunami, tsunami mitigation method by strengthening the existing coastal forests were considered in Hokkaido. Effectiveness of tsunami energy reduction by the hybrid structures using an embankment, moat and vegetation from the seaside was tested using surge-type flow by quicky opening gate, and by numerical simulation in the real topography. The inflow volume to inland and the delay in tsunami arrival were measured, and fluid force index was estimated by the measured data. The effectiveness of the hybrid structures for tsunami energy reduction has clearly been shown. Especially, the collision to the ground utilizing the difference of height between embankment and moat, and the vegetation resistance were effective for reducing fluid force index in the experiment. Inundation area, the delay in arrival time and fluid force index were also compared in numerical simulation under different arrangement of hybrid structures in real topography. The effectiveness of the hybrid structure in the order of an embankment, moat and forest from the seaside for tsunami energy reduction is also shown. The importance to the countermeasures on the tsunami inundation through a river was also demonstrated as the tsunami arrival was more rapid and fluid force index was higher than the tsunami inundation through the hybrid structures.