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The massive earthquake with a magnitude of 9.0 occurred at 14:46 on March 11, 2011, with an epicenter 130 km offshore from the Oshika Peninsula in Japan’s northeastern Miyagi Prefecture. After the earthquake, large tsunamis were generated owing to abrupt crustal subsidence and uplift, which inundated Japan’s eastern Pacific Ocean coastline. We carried out field observations to investigate the deformation of a previous river-mouth bar by comparing oblique photographs, and investigated the damage to seawalls and the tsunami inundation depth on the Iwama-Sanuka coast, located north of the Same River in southern Fukushima Prefecture. Here, the results of the field observations on the deformation of the sandy beach and the inundation of the Iwama-Sanuka coast are reported.

Sand movement in the field experiment of beach nourishment offshore of south Kujukuri Beach was numerically simulated using the BG model, given the wave field predicted by an angular spreading method of irregular waves on the basis of wave data measured at Choshi. The effectiveness of the model was confirmed, and then numerical simulation of the recovering effect of sandy beach in full-scale beach nourishment was carried out under the conditions that the artificial headlands have the present shapes, they are half and fully extended. It is found that although the best one is the shape fully extended, significant effect can be expected in artificial headland with a half length.

The bathymetric changes and changes in longshore sand transport passing through the tip of the headland were investigated using the contour-line-change model, while changing the shape and scale of the artificial headland. The maximum shoreline recession and eroded area downcoast of the headland, and rate of decrease in longshore sand transport were compared each other. It is concluded that the groin part of the headland must be extended first to reduce longshore sand transport off the artificial headland.