BEACH CHANGES TRIGGERED BY SEAWARD DEVELOPMENT OFTOWNS, EXPANSION OF COASTAL FOREST AND CONSTRUCTIONOF DETACHED BREAKWATERS AT A POCKET BEACH

摘要

Beach changes triggered by seaward development of towns, expansion of coastalrnforests and construction of detached breakwaters at a pocket beach were analyzed, takingrnthe Ariake-Takahama and Ishihama coasts located in northern Ibaraki Prefecture as anrnexample. This pocket beach has an approximately 6-km-long stretch of coastline. In thernnorthern half of the coast, detached breakwaters were built to protect towns against overtoppingrnof waves. The construction of detached breakwaters, which accelerated sand accumulationrnbehind them, induced erosion along the southern half of the coast. Furthermore, alongrnthe southern coast, a coastal dike with a gently sloping revetment had been built against thernrecent severe erosion in front of the coastal forest. This sea dike was exposed to strongrnwaves because it was built on the eroded beach, and ultimately, it was destroyed. It is concludedrnthat the recent coastal changes of this beach were due to many artificial causes.