Numerical Investigation of the Effectiveness of Vegetation-Embankment Hybrid Structures for Tsunami Mitigation Introduced after the 2011 Tsunami

As a mitigation measure against tsunami inundation, vegetation-embankment hybrid structures received attention after the 2011 Great East Japan Tsunami, and some have already been constructed or are under construction in Japan. The present study conducted series of numerical simulations using system comprised an artificial structure (an embankment, moat) natural component (vegetation) that was experimentally proposed previous studies as effective for mitigation. After validating model published data, this investigated differences performance by changing period height characteristics tsunami-like surge-type flow. result, delay arrival time (ΔT) not affected wave structures. Among structures, Case Ve40ME (where Ve40, M, E represent vegetation, moat, respectively, order from seaward) showed maximum ΔT. reductions overflow volume (ΔQ), fluid force index (RFI), moment (RMI) declined during period. effect is closely related to relationship between development times backwater rise, hydraulic jump, ΔT, ΔQ, RMI. EMVe40 especially RFI. When short, water level at shoreline starts decrease before full jump generated system. Thus, landward decreases, effects increase. long, receding phenomenon peak does affect values, thus become smaller compared with short However, superiority other maintained seaward vegetation respectively.