Long-Term Shoreline Changes Over Half Century Since 1964 Along Ibaraki Coast Resulting from Anthropogenic Interventions

The shoreline changes associated with the construction of offshore breakwaters over a half century since 1964 were investigated using aerial photographs of the coast of 12.5 km length between Hitachi Port and Isozaki Fishing Port in Ibaraki Prefecture, Japan. A field observation was also carried out on December 23, 2021. In the study area, significant beach changes occurred after the construction of offshore breakwaters of Hitachi and Hitachi-Naka Ports owing to their wave diffraction effect. In this area, the management of coastal lands is under the jurisdiction of several agencies, such as port, coastal forest, and shore protection Agencies, and the coastal areas are separately managed with minimal cooperation among relevant agencies. Therefore, when beach erosion occurred after the construction of offshore breakwaters, the conventional methods of constructing a seawall and installing concrete blocks along the coast have been adopted in place of the method stabilizing the overall coastline. Thus, the coastline has become an artificially protected coastline. We discussed future measures to prevent the same issues from occurring in other areas.