抄録
Large-scale beach erosion and accretion triggered by the construction of an offshore breakwater on the Ajigaura and Naka coasts in Ibaraki Prefecture was investigated through field observation and analysis of aerial photographs.The shoreline retreated largely outside the wave shadow zone, leaving gravels on the foreshorezone by selective erosion of bed materials and devastating famous bathing beach of mild slope. In contrast, in the wave shadow zone, a large amount of fine sand accumulated. The measured shoreline configuration was well predicte by the Hsu model to forecast a stable shoreline. On the Naka coast, the same phenomenon was occurred and seawall was heavily damaged.
