| Long-term effects of structures on the beach erosion control were investigated inNankoku Beach, Kochi Coast Japan, 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. In this study we looked at the long-term coastal protection effects of detached breakwaters on Nankoku Beach from the viewpoint of shoreline changes and sand movement, based on actual measurements such as work records, aerial photographs, surveying results and grain diameter surveys. 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 long shore transport for the prevention of shoreline retreat though the construction started from updrift side. |
