Case Study of the Storm Surges in the Seto Inland Sea Caused by Typhoon Chaba

Abstract

Typhoon Chaba hit southeastern Kyushu and passed through Chugoku (western part of Japan's main island) on August 30, 2004, causing large storm surges in the Seto Inland Sea (SIS). Record-high storm tides were recorded at tide stations in Takamatsu and Uno Ports. We analyzed the tidal data and simulated this case with numerical storm surge models.

The results revealed that the wind setup basically played a key role in causing the large storm surges. Since the time of the maximum storm surge (MSS) approximately corresponded to the time of high spring tide in Takamatsu, a record-breaking storm tide was observed there. However, the MSS occurred not when the typhoon was closest to the city but two hours later. We also investigated the mechanism and the degrees of contribution of the two main factors of storm surges, the inverse barometer effect and the wind setup, in each local area. The results revealed that the peak time of each effect was influenced by geographical features, as well as the wind field and the typhoon position, and had different characteristics in these areas. They also revealed that the Kanmon Strait, which is very narrow and supposed to be negligible in effect, had an important role in sea water inflow into the SIS.

Keywords:

• Topographic effect
• wind setup
• numerical simulation
• TY Chaba

Acknowledgements

The authors express their sincere gratitude to Dr. Ohno, the Director of the Takamatsu Local Observatory, for his helpful comments and continuous encouragement. Some of the data used in this research have been collected in the “Urgent research about typhoons that made landfall on Japan in 2004” of MRI, and the authors also thank the organizations that provided data.