Abstract
The aim of this study is to clarify mechanism of rainfall inundation caused by the 2019 Typhoon Hagibis in Iwate prefecture coastal zone, Japan, using probable 1-hour rainfalls estimated for the 2 periods of 1976-2005 and 1989-2018.
The differences between rainfalls by the 2019 Typhoon Hagibis and 10 year return level of 1-hour rainfall (P10) of 1976-2005, which is generally assumed as discharge standard of drainage system in Japan, at Fudai village, Iwaizumi town, Miyako city, and Yamada town were ranged 40.7-106.6 mm for maximum 3-hours rainfall during the 2019 Typhoon Hagibis, and the estimating gigantic rainfall inundations.
On the other hands, gigantic rainfall inundations were observed at Kamaishi city, where the amount of overflow from the existing drainage system was only 3.5 mm for maximum 3-hours rainfall during the 2019 Typhoon Hagibis, by rainfall inundations obstructed the huge sediment and woody debris produced landslides at narrow sections in the streams and drainage systems, and by coastal embankments for Tsunami.
In addition, P10 at all study areas were increased in 8-24 % from 1976-2005 to 1989-2018, which were corresponded with increasing frequency of P10 of 1976-2005 in 1.4-2.1 times. Namely, increasing frequency of rainfall inundations in Iwate prefecture coastal zone was expected in the future.
