Author(s): Takehito Zaha; Norio Tanaka; Yuya Kimiwada
Linked Author(s): Norio Tanaka
Keywords: No Keywords
Abstract: After the Great East Japan tsunami, a compound defense system comprising of an existing coastal forest, a new moat and a new embankment from the seaside was proposed and constructed in Hokkaido Prefecture to strengthen the tsunami mitigation effects. A flume study using surge-type flow by quickly opening a gate was conducted to consider the effectiveness of tsunami energy reduction by the compound system changing the order of the three defense components. The overflow volume to inland side, the tsunami arrival time, the fluid force index and the moment index were measured, and the tsunami reduction effect was compared with the other compound defense layouts/arrangements. The compound defense system in the order of a vegetation, a moat and an embankment (Case VME) from the seaside shows the highest reduction in overflow volume, moment index and tsunami delay effect. In terms of the fluid force index, Case VME performed the best up to a certain tsunami height. For the higher tsunami heights, the compound system in the order of a vegetation, an embankment and a moat from the seaside (Case VEM) performed better in reducing maximum fluid force index compared with Case VME, due to the greater reduction of flow velocity by an inland side of the moat.