抄録
Beach erosion of the Shimosakurai coast located in the north part of Ibaraki Prefecture and facing the Pacific Ocean were investigated on the basis of the aerial photographs and field observation. In February 2007, extraordinary oblique waves attacked this coast, resulting in collapsing of the seawall. The direct cause of the collapsing of the structures is due to the attack of the storm waves, but the decrease in the ground level is the indirect cause which was caused by the development of the southward longshore sand transport under the condition that detached breakwaters were installed and waves were incident obliquely. The shoreline next to the detached breakwaters significantly retreated, and the seawall was severely damaged.
