[MIS01-P09] Reduction Effect of Tsunami Sediment Transport by Coastal Forest: Numerical Simulation of the 2011 Tohoku Tsunami on Sendai Plain, Japan
Keywords:tsunami simulation, sediment transport modeling, coastal forest, composite equivalent roughness coefficient
To account for varying roughness coefficient in areas of coastal forest, the composite equivalent roughness coefficient was used (e.g., Aburaya and Imamura, 2002, JSCE; Imai et al., 2013, JSCE). Tree occupancy and trunk width are given as 1 %, and 0.15 m, respectively, on the basis of the previous studies (e.g., Harada et al., 2000, JSCE; Imai et al., 2009, JSCE). The area of coastal forest was determined from aerial photographs and land use maps compiled before the 2011 Tohoku earthquake.
Our results revealed that the simulated mean sediment concentration, wave height, flow velocity, and inundation limit were abruptly reduced by the presence of coastal forest. The volumes of net deposition and erosion were reduced to 52-85% of those in the simulation without coastal forest; these reductions were particularly remarkable for fine sand. The maximum extent and thickness of sand layer are also reduced. This evidence of the inhibition of sediment transport by coastal forest suggests that land use conditions and the vegetation environment at the time of a tsunami should be considered in evaluations of historical tsunamis on the basis of geological evidences.