The Failure of the Kamaishi Protection Breakwater

Abstract

Kamaishi is a small city located in the Iwate Prefecture on the East coast of Japan. Historically, Kamaishi was famous as a city for its steel production, but more recently is known for its fishing and shellfish production. In March of 2009, construction was completed on the world’s largest breakwater within Kamaishi Bay. The completion of the breakwater was the result of over 30 years of research and construction, and was recognized by Guinness World Records as the world’s deepest breakwater at 63 meters deep and 1950 meters long. The design intention of the breakwater was to protect Kamaishi Bay from the threat of tsunamis and other significant wave action. Two years later, Japan was devastated by the Tohoku earthquake; the most powerful earthquake known to have struck Japan and the fifth largest recorded earthquake to date at a 9.0 magnitude. An accompanying tsunami struck the breakwater at Kamaishi, where waves as tall as 4.3 meters surmounted the breakwater and proceeded to submerge the city center. The failures of this and other breakwaters on the coast of Japan have forced officials to rethink the effectiveness of the structures. The following paper will highlight the research undertaken for the design of the breakwater, challenges met during construction, and the failure of the breakwater. In addition, this paper will address the issue of the effectiveness of breakwaters in areas known to have high seismic activity.