CHALLENGES OF RESTORING AND REHABILITATING SEWER SYSTEMS DAMAGED BY THE GREAT EAST JAPAN EARTHQUAKE AND TSUNAMI

摘要

This is a review of the restoration and rehabilitation of sewer systems damaged by the Great East Japan Earthquake and Tsunami. The disaster caused serious damage to sewer systems, amounting to approximately 470 billion JPY. The damage was mainly caused by the tsunami, but the damage due to liquefaction was also serious. The tectonic activity caused additional discharge loads to municipalities in coastal areas. The nuclear accident at Fukushima Daiichi Nuclear Power Plant also affected sewer systems in such forms as radio-contamination of sewage sludge and reduction of power supplies. In addition, migration of users of sewer systems took place. In the restoration activities, sewage treatment plants (STPs) were restored step-by-step, and guidelines were developed to strengthen STPs against tsunamis. The effectiveness of different countermeasures against earthquakes and liquefaction were examined, and new countermeasures were proposed. Software measures such as the introduction of business continuity plans and information technologies are recognized as effective measures for overcoming disasters. In particular, the sewer systems in Sendai City have been successfully restored and rehabilitated after the disaster, with different hardware and software measures. In contrast, sewer systems in small municipalities seriously damaged by the tsunami are still taking time to rehabilitate.