Changes in the coastline after the construction of submerged breakwaters: a case study of the Hasidong area in Gangneung, South Korea

Numerous artificial structures have been constructed to address coastal erosion along the east coast of South Korea. Submerged breakwaters are intended to reduce erosion in the short term; however, they can also have adverse effects, such as shifting erosional hotspots. This study examines changes in the coastline and sandy beaches over the past three years, from December 2021 to December 2023, focusing on the submerged breakwater built on the beach in Hasidong-ri, Gangneung-si, Gangwon State, completed in 2022. Following its construction, the total beach area increased by approximately 27%; however, erosion has intensified in certain sections. Notably, the coastline has retreated by as much as 80 meters at both ends of the submerged breakwater, with some areas experiencing an annual retreat of over 10 meters. Additionally, seasonal changes of beach has decreased, leading to a coastline that has become less flexible and more fixed compared to the past. The changes observed in the coastline appear to result from these artificial structures rather than natural factors such as sea level rises.