Tide-surge interaction and its impact on coastal inundation: a case study of super typhoon Meranti

Typhoon-induced storm tides can cause severe coastal inundation hazards in low-lying lands. The extreme water levels can be significantly modified by the nonlinear tide-surge interactions. To explore the impact of these interactions on coastal inundation on Xiamen Bay and its adjacent low-lying coastal regions during Super Typhoon Meranti (1614), a series of numerical experiments utilizing a high-resolution FVCOM model were conducted. The results show that tide-surge interaction is extremely strong in Xiamen Bay, with relative intensity of 0.1 to astronomical tides and over 0.3 to the practical surges across most area of the bay. The nonlinear interaction tends to decrease the peak water levels across the bay but elevates peak surges in most parts of it. There are two peaks in the surges. The former peak occurs around mid-rising tide, and can mainly attribute to the nonlinear tide-surge interaction, while the latter mid-falling peak is resulted from the combined action of the strong wind and tide-surge interaction. The momentum balance analysis revealed that nonlinear transformations in local acceleration and advection terms are remarkable throughout the bay, and the nonlinear transformations in surface wind stress and bottom friction are significant in the shallow Jiulong River Estuary and the waters around Dadeng Island. During this storm, tide-surge interactions led to a significant reduction in inundation area, inundation depths, and inundation duration, by about 24%, 16%, and 10%, respectively. This study highlights the importance of considering tide-surge interactions in the assessment of coastal inundations risks.