Survey on February 2009 Abiki Disaster in Urauchi Bay, Kamikoshiki Island

Abstract

Field surveys were conducted around Urauchi Bay in Kamikoshiki Island to examine damage due to the secondary undulation, which is called 'abiki', in February, 2009. Eight fishing boats capsized at Oshima fishing port, where the occurrence time is supposed to be around when the low tide appeared because of the overlap of the spring tide and the long-period oscillation. Eight houses were flooded under floor level due to the long-period waves which propagated upstream on a river and overflowed nearby the residential area. The water level reached a maximum about three meters at Oshima fishing port. According to both the observed and simulated data, the predominant oscillations are the first and second modes, the last of which is peculiar to T-type bays. The damping processes of these modes were also numerically simulated.