Infragravity wave dynamics on Seisho Coast during Typhoon Lan in 2017

ABSTRACT

The extreme typhoon Lan caused devastating damage to the Seisho Coast of Japan in 2017. This study presents nearshore wave measurements conducted at different locations along the shore and numerical hindcasts to elucidate the extreme wave field during the typhoon focusing on infragravity wave dynamics, which was comparable in magnitude to incident short waves in shallow water. During the peak of the typhoon, there was a significant wave height of ~8 m, and the infragravity wave height exceeded 2 m at a 14 m depth. The measurement data suggest that infragravity waves developed as bound waves from incident wave groups and partially dissipated during the typhoon peak in the surf and swash zones through their energy transfer to high-frequency waves. Numerical wave hindcasting models successfully reproduced the measured extreme wave field and indicated that the wave refraction over Oiso Spur caused an incident wave concentration in the severely damaged area where high waves collapsed a seawall during the typhoon. Moreover, infragravity waves also exhibited significant alongshore variation, which was due to the different bottom slopes and incident short-wave properties. This study identifies several key features that may have caused the localization of significant damage along the Seisho Coast.

KEYWORDS:

• Infragravity waves
• extreme waves
• nonlinear interactions

Acknowledgments

We would like to extend our appreciation to the Kanto Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Japan, who offered us the wave data. The bathymetry data shown in Figure 1 and used in the wave hindcasts conducted with WAVEWATCH III were generated from the GEBCO_2014 Grid, version 20150318, available at (http://www.gebco.net). The typhoon tracking data on Typhoons Fitow and Lan are available on the Digital Typhoon Database (http://agora.ex.nii.ac.jp/digital-typhoon/index.html.en). The offshore wave data used to validate the wave hindcast are available at NOWPHAS (http://www.mlit.go.jp/kowan/nowphas/index_eng.html). The weather reanalysis data used as the wind input are available at the GPV Data Archive (http://search.diasjp.net/en/dataset/GPV). This study was supported by JSPS KAKENHI (Grant No. JP18J21135) and the JSPS-STINT Japan-Sweden Bilateral Joint Research Project. It is conducted as a research activity of “Enhancement of National Resilience against Natural Disasters”, a cross-ministerial Strategic Innovation Promotion Program (SIP), under the supervision of the NIED. The program was supported by the Council for Science, Technology, and Innovation (CSTI).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Council for Science, Technology and Innovation [Enhancement of National Resilience against Natural Disasters]; Japan Society for the Promotion of Science [JP18J21135]; Japan Society for the Promotion of Science [Japan-Sweden Bilateral Joint Research Project].