Shoreline change caused by the increase in wave transmission over a submerged breakwater due to sea level rise and land subsidence

• Shoreline will retreat approximately 60 m in the next 100-year period.
• The retreat is due to increased incoming wave energy over the submerged breakwater.
• Effect of relative sea level rise on current shoreline change was not confirmed.

Sandy beaches protected by submerged breakwaters, which have crests below sea level, are assumed to be vulnerable to relative sea level rise (SLR). In this study, the shoreline change due to sea level change and land subsidence along the Niigata West coast in Japan, which is protected by submerged breakwaters, was investigated using field data and a shoreline prediction model assuming that the shoreline change is caused by cross-shore sediment transport. The shoreline movement in the past 10 years was not directly caused by sea level change and land subsidence. However, our model predicts that over the next 100 years, the shoreline will retreat 60 m owing to the increase in the energy flux of incoming waves over the breakwater caused by SLR and land subsidence. These results imply that other sandy beaches protected by low-crested breakwaters as well as those behind coral reefs, which are natural submerged breakwaters, would experience non-negligible erosions caused by future relative SLR.