Beach Changes Triggered by Seaward Development of Towns, Expansion of Coastal Forest and Construction of Detached Breakwaters at a Pocket Beach

by Takaaki Uda, Public Works Research Institute, Ministry of Construction, Ibaraki 305-0804, Japan,
Tairyu Takano, Public Works Research Institute, Ministry of Construction, Ibaraki 305-0804, Japan,
Masumi Serizawa, Public Works Research Institute, Ministry of Construction, Ibaraki 305-0804, Japan,
Toshiro San-Nami, Public Works Research Institute, Ministry of Construction, Ibaraki 305-0804, Japan,
Kou Furuike, Public Works Research Institute, Ministry of Construction, Ibaraki 305-0804, Japan,



Document Type: Proceeding Paper

Part of: Sand Rights '99: Bringing Back the Beaches

Abstract: Beach changes triggered by seaward development of towns, expansion of coastal forests and construction of detached breakwaters at a pocket beach were analyzed, taking the Ariake-Ishihama coast located in northern Ibaraki Prefecture as an example. This pocket beach has an approximately 6km-long stretch of coastline. In the northern half of the coast, detached breakwaters were built to protect towns against overtopping of waves. The construction of detached breakwaters, which accelerated sand accumulation behind them, induced erosion along the southern half of the coast. Furthermore, along the southern coast, a coastal dike with a gently sloping revetment had been built against the recent severe erosion in front of the coastal forest. This sea dike was exposed to strong waves because it was built on the eroded beach, and ultimately, it was destroyed. It is concluded that the recent coastal changes of this beach were due to many artificial causes.

Subject Headings: Beaches | Breakwaters | Forests | Ocean waves | Levees and dikes | Erosion | Sea water

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