Experimental and Numerical Modeling of Tsunami Mitigation by Canals

Many coastal areas have experienced extensive destruction as a result of tsunami waves. The coastal communities in Tohoku, Japan experienced the terrifying effect of giant tsunami waves in March 2011. Tsunami waves triggered by the 2011 Tohoku earthquake swept over existing seawalls and proceeded inland, damaging coastal structures and windbreak forestry. This devastating event demonstrated the need for strong countermeasures in coastal areas to mitigate the impact of huge tsunamis. This paper describes an experimental and numerical study of the tsunami-mitigation capabilities of canals oriented perpendicular to the tsunami motion. First, the use of a canal to reduce the effect of tsunami waves was investigated. Canals can help delay the tsunami arrival time and reduce the tsunami wave velocity and energy; however, the inundation depth may not be sufficiently affected if only canals are used as a countermeasure. An experimental study was then conducted to verify numerical simulations using the improved moving particle semi-implicit (MPS) method, and the experimental and numerical simulation results demonstrated good qualitative and quantitative agreement. A second series of numerical simulations was performed considering combined countermeasures comprising a canal and a dune. Such combined countermeasures have the potential to reduce both the tsunami wave velocity and the inundation depth. Through experiments and numerical simulations, this study examined how canals, individually or coupled with a dune, can play an important role in the mitigation of tsunami disasters.