福島県勿来海岸における東北地方太平洋沖地震津波による大規模土砂移動と海岸地形変化

Abstract

Large-scale sand movement due to the 2011 Tohoku Tsunami was investigated for the Nakoso Coast, Fukushima Prefecture, by using analysis of bathymetry surveys combined with beach deformation simulation. SignificantLarge beach deformation was observed in the north area where many seawalls were destroyed. In contrasts, the sand movement due to tsunami was small in the south area, where the coast is protected by shore-parallel detached breakwaterstructures, although successive storm waves developed subsequent significant erosion by northward longshore transport. The offshore sand loss was foundconsidered to be small since the sand movement due to tsunami was mostly confined in the nearshore area shallower than the closure depth. The total sand loss on the Nakoso Coast was found to be estimated by the co-seismic tectonic subsidence of the order of 40 cm. However, a non-negligible loss of sand was found in the sand transport to the riverland and to the seaA non-Unnegligible loss of sand was found, however, by the sand transport to the land and to the river.