Responses of tidal modification and nonlinearity to large-scale sequential harbor constructions in the northeastern China

Abstract

The impacts of large-scale coastal structures on tidal dynamics have been studied extensively over the past decades, but the relevant mechanisms are not fully understood. In this study, a two-dimensional Delft3D barotropic tidal model is applied to investigate the tidal dynamic changes induced by the large-scale sequential constructions of Huanghua-Binzhou Harbor in the northeastern China during year 2003–2016. It was found that the predominant M2 tide is increased on the stoss side and decreased on the lee side of the harbor by 2–6 cm due to the harbor constructions. This feature is due to 1) the increased and decreased potential tidal energy on the stoss and lee side, respectively, by the harbor structures; 2) the structure-induced changes in momentum flux is balanced by pressure gradient, and thus leads to a larger tidal range on the stoss side and a smaller tidal range on the lee side. The sensitivity studies on nonlinear M4 tide demonstrate that it is generated locally by M2 self-self interaction, which is not only related to M2 tidal energy but also nonlinearity. Consequently, M4 tide increases towards the shore on the tidal flat with natural slope due to enhanced nonlinearity by decreasing water depth, but is proportional to M2 tide on the tidal flat with a constant water depth, where local nonlinearity is nearly the same in space. In addition, the energy transfer from M2 to M4 is affected by the structure-induced changes in nonlinearity, resulting in different responses of M2 and M4 tide to the coastal structure.