Long-term Effects of Detached Breakwaters in Nankoku Beach, Kochi Coast

Abstract

Long-term effects of structures on the beach erosion control were investigated in Nankoku Beach, Kochi Coast from the viewpoint of sediment balance. Monobe River is the main sediment source to the beach though three dams decrease the sediment supply. Construction of 52 detached breakwaters was started in 1973 to prevent beach erosion and completed in 1997. One artificial reef was also constructed in 1999. Effects of the structure were analyzed by the profile data. Results show deposition on the landward side and erosion on the seaward side.It is concluded that breakwaters are effective and decrease longshore transport for the prevention of shoreline retreat though the construction started from up-drift side.