Effects of tide-surge interactions on the temporal distribution of the peak residual in Hangzhou Bay, China

Abstract

Hangzhou Bay has a trumpet-shaped geometry and is known for its extremely large tidal range. Understanding tide-surge interactions is essential for coastal defence applications during storm events. Analysis of long-term hourly sea level observation data at three sites and numerical experiments show that a remarkable cluster of peak residuals occurs 4 h before the high tide inside Hangzhou Bay (Zhapu and Ganpu Sites), while a weaker cluster occurs around the low tide outside the bay (Shengshan Site). Further analysis of various sea levels in Hangzhou Bay revealed that the non-linear level inside the bay was greater than that outside the bay, leading to the observed difference in frequency distributions between them. To understand the underlying mechanism, the contributions of each non-linear interaction factor to the tide-surge interactions were distinguished. It was found that quadratic bottom friction is the dominating factor inside Hangzhou Bay, which always peaks approximately 4 h before high tide due to wave deformation. Whereas, outside Hangzhou Bay, advective term and quadratic bottom friction are the main forces, which are much larger than wind stress, and they tend to have peaks around low tide. It is indicated that peak residual arrives synchronously with the peak non-linear interaction term.