Experimental investigation into the effects of strong winds on the transport of overtopping water mass over a vertical seawall

ABSTRACT

Hydraulic experiments using a wave flume with a wind tunnel at a scale of 1/40 were carried out to investigate the effect of wind on wave overtopping of a vertical seawall. To ascertain the possible effects of wave breaking, incident waves with various wave steepness (0.0102 to 0.0371) and three kinds of wind forcing (0 m/s, 6.84 m/s, 10.04 m/s) were used. The authors found that winds significantly increased the overtopping rate in general, and that there is a clear relationship between the overtopping rate and the wave steepness. Velocity fields obtained from PIV analysis revealed that the onshore winds directly enhanced the transport of overtopping water mass. The influence of the wind on the wave hydrodynamic processes that indirectly have an effect on the overtopping rate (such as the formation of a partially standing wave, breaker location, and breaker type) is also discussed. The perspective of treating wave overtopping as a transport of water mass could provide a novel understanding of complex fluid behavior, which would help to formulate countermeasures against future disasters influenced by intensive wind forcing.

KEYWORDS:

• Wave overtopping
• wind effect
• vertical seawall
• wind-wave flume
• transport of water mass

Acknowledgments

The present work was financially supported by Japan Science and Technology Agency (JST) as a part of the Belmont Forum, Re-Energize DR3 project, Grant Number JPMJBF2005, and by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number 20KK0107 and 21J20393. The work was also performed as a part of the activities of the Research Institute of Sustainable Future Society, Waseda Research Institute for Science and Engineering, Waseda University.

The authors gratefully acknowledge the support of students in Niigata University for performing the experiments: Tamaki Kanemura, Koji Bushimata, Yuki Obara, Ari Toyama, Yudai Aoki, Shin Yazaki, Yuma Sato, Kohei Nishida, Yudai Shimura, Ryota Takayama, Yusei Miyashita, Daichi Katayama, and Masaki Kabasawa.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Notes

¹ This “overshooting” was defined as the water volume blown off the water surface by the wind. See De Chowdhury et al. (2021).

Additional information

Funding

This work was supported by the Japan Science and Technology Agency [JPMJBF2005]; Japan Society for the Promotion of Science [21J20393]; Japan Society for the Promotion of Science [20KK0107].