A model for calculating the erosion distance of soft sea cliff under wave loading
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A model for calculating the erosion distance of soft sea cliff under wave loading CHANG Fangqiang1*, SHU Zhonglei1 1 Faculty of Civil Engineering, Huaqiao University, Xiamen 361021, China
Received 14 March 2017; accepted 9 October 2017 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
A model for calculating the erosion distance of soft sea cliff under wave loading is established based on the erosion mechanism of soft sea cliff under wave loading and for considering wave hydrodynamic and sea cliff material parameters. The model is verified, and the parameters are regressed using an indoor flume experiment. The erosion distances of the sea cliff in the northeast of the Pingtan Island are calculated by the model, and the results are compared with the measured data. The maximum erosion occurs in static water level, the location of the maximum erosion moves up as the wave continues, and the erosion stops when the wave lasts for a period of time. The erosion does not occur until the wave height exceeds a critical value; however, the contribution of large waves to the erosion is not relatively substantial. The calculated erosion distances at two places in the northeast of Pingtan Island are 0.32 m and 0.26 m. Key words: wave, soft sea cliff, erosion Citation: Chang Fangqiang, Shu Zhonglei. 2018. A model for calculating the erosion distance of soft sea cliff under wave loading. Acta Oceanologica Sinica, 37(7): 69–77, doi: 10.1007/s13131-018-1245-x
1 Introduction Sea cliffs suffer severe erosion and retreat worldwide, particularly on the east coast of England, the Baltic, the southern North Sea, north of Lake Great Britain, the west coast of Cape Cod, California and the Denglou Cape, southwest of the Leizhou Peninsula of China; the maximum retreat rate is approximately 1–2 m/a (Sunamura, 1992; Lee, 1997; Lee et al., 2001; Wang et al., 2002). Severe erosion also occurs in the provinces of Zhejiang, Fujian, Guangdong, Zhuang Autonomous Region of Guangxi, and Hainan in China and leads to gradual decrease in land areas. Retreat is a threat to the security of local engineering facilities; sea cliff erosion intensifies with annual increase in global warming and sea levels, thereby prompting the local government to build breakwaters or other protective measures (Trenhaile, 2010). Understanding sea cliff erosion rates and its position in the following years are important for implementation of protective sea cliffs and land use planning. In engineering design lifetime, sea cliff erosion should not be a threat to the engineering security on the top of the cliff. Moreover, determining the protection time is necessary for facilities facing threats of erosion. Most theoretical works, including studies on an erosion rate and an erosion distance, have focused on erosion and retreat because of severe erosion of sea cliffs. The increase in sea level promotes cliff erosion. Bray and Hooke (1997) proposed a semi-empirical method for calculating the retreat rate. Most predictive mode
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