Analysis of Shoreline Response to Large-Scale Breakwaters Based on Physical and Field Studies

This study investigates the erosion and accretion characteristics of the surrounding coastline during the installation of an approximately 1.5 km-long impermeable slit caisson breakwater on the east coast of Korea. Three-dimensional physical model tests were conducted to predict morphological changes and to clarify sediment transport mechanisms with and without the breakwater. Submerged breakwaters were employed at critical points prone to erosion, and their coastal protection effectiveness was assessed using 11 different spatial configurations. Experimental waves were chosen to represent erosion-inducing conditions (Hs: 3 m, Ts: 10 s) prevalent at the study site. The results revealed that the breakwater generated strong diffracted waves in the sheltered area, promoting erosion, while the effectiveness of submerged breakwaters depended on installation conditions. In all cases, shoreline retreat was observed behind the opening and at the ends of the submerged breakwater. Field surveys over five years since 2020 confirmed pronounced erosion and accretion behind the submerged breakwaters, attributed to a single 600 m-long, zero-opening configuration that reduced flow velocity behind the submerged breakwater causing accretion and intensified diffracted wave-induced erosion at both ends.