Study on the risk and characteristics of rip currents over sandbars at South China’s recreational beaches

Zhang Yao; Liu Xu’nan; Liu Qiang; Wang Bin; Hong Xiao; Zhou Shuihua; Zhang Juan; Meng Xiaojie; Li Rui; Tao Jinbo; Wang Gang

doi:10.3969/j.issn.0253-4193.2020.09.002

Volume 42 Issue 9

Nov. 2020

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Zhang Yao，Liu Xu’nan，Liu Qiang, et al. Study on the risk and characteristics of rip currents over sandbars at South China’s recreational beaches[J]. Haiyang Xuebao，2020, 42(9)：9–21 doi: 10.3969/j.issn.0253-4193.2020.09.002

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Study on the risk and characteristics of rip currents over sandbars at South China’s recreational beaches

doi: 10.3969/j.issn.0253-4193.2020.09.002

1.
National Marine Hazard Mitigation Service, Ministry of Natural Resources, Beijing 100194, China
2.
South China Sea Prediction Center, State Oceanic Administration, Guangzhou 510260, China
3.
Engineering College, Ocean University of China, Qingdao 266100, China
4.
North China Sea Marine Forecasting Center, State Oceanic Administration, Qingdao 266061, China
5.
College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, China

Received Date: 2019-06-14
Rev Recd Date: 2019-10-16

Available Online: 2021-04-21

Publish Date: 2020-09-25

Abstract

Abstract

In responding to deadly drowning accidents, China's first operational attempt on the rip current hazard prevention for coastal tourism was carried out by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches in South China are found developing littoral sand bars and rip currents. Present paper, which is part of the nation-wide work, investigate the mechanism, characteristics, and evolution sandbar-induced rip current at three most visited beaches employing multi-techniques as complementary tools. The alongshore sandbar morphology, shorelines, and rip currents are highly dynamic with seasonal variations evidenced by the morphodynamic calculation and the satellite image interpretation. Unconventional contrary seasonal evolution of the rip current is identified at Qing’ao Bay with higher risk in cooler seasons. The rip current shows high sensitivity to the sandbar group pattern, the wave height, and the incident direction according to the phase-resolving hydrodynamic modelling. The wider rip channel between sandbars generated larger rip size compared to narrower gaps, but is not necessarily accompanied by stronger flow velocity. The rip current might be totally absent in small channels when majority of water flows out through neighboring broader pathways. The flow velocity is demonstrated proportional to the wave height and inversely proportional to the incident angle. Alongshore currents dominated over rip currents as the wave incident angle reached 10°−30° in the numerical simulation. It is verified in the field observation that the rip current is most hazardous at low tide when shallower water depth intensifies the topographic effect on waves and currents. The study result provides useful reference for the engineering mitigation and public warning of beach rip hazard. In near future, long time observation for specific sections of shoreline would be conducted to accumulate enough statistics for the rip current prediction and risk governance.
- rip current,
- sandbar,
- wave,
- morphodynamics,
- numerical modelling,
- marine hazard

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References(46)

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