ANNALYSIS OF SEICH IN THE HAKATA BAY AND THEIR FLOODING RISK ON THE COASTAL LAND AREA

Abstract

 From winter to early spring, water surface oscillations called "ABIKI", which is a kind of meteo-tsunami or seich, occur in the west coast of the Kyushu island in Japan. In particular, around the Port of Nagasaki, many studies have been conducted on the secondary vibration phenomenon, because damages due to the higher tide with seich have been often observed. On the other hand, there is information about inundation damage with any higher water event happened near the coast of the Port of Hakata in March of 2019. Although the potential for disasters due to inundation is considered to be extremely large behind the Hakata port area with the population density of more than 10,000 people / km², only a few studies have been conducted for that. Therefore, in this study, we analyzed the observed data including the water levels in the coastal area and precipitation etc. during the event of inundation damage in order to examine the relationship between the high water events with the occurrence of secondary vibration in the Hakata Bay in March 2019.

 As a result of the tide level data analysis, a maximum tidal level rise of 20cm from astronomical tide level was recorded at 22:09 on March 20^th, which was the highest in the month. Correspondingly, the Tatara River, one of the rivers flowing into the Hakata Bay, recorded the water level rise of more than 30cm. The results of the spectral analysis of the time series of the tide level data and corresponding atmospheric pressure fluctuation suggest that the highest tide level event could be owing to the secondary oscillation during the spring tide. In conclusion, it should be noted that there is a risk of flood damage around the bay due to the overlap of the high tide and the secondary vibration in Hakata Bay.