Impacts of Tide–Surge Interaction on Sediment Dynamics During Typhoons

Extreme weather conditions dominate sediment transports and thus determine morpho-dynamic evolution in coastal zones. Tide–surge interactions during extreme weather conditions modulate surge, and thus impact storm tides and sediment dynamics, especially in macro-tidal turbid estuaries. In this study, the macro-tidal turbid Hangzhou Bay (HZB) is selected as an example. A three-dimensional numerical model combining tide, wave, surge, and sediment was established in HZB and validated using field data. The effects of the tide–surge interaction and their impact on suspended sediment dynamics are investigated using numerical experiments. The tidal components influence the storm tides and sediment characteristics through amplitudes and phases during the typhoon. Semi-diurnal tidal components have the largest effect on the storm tides and sediments in the bay during the typhoon, followed by diurnal tidal components and shallow water tidal components. The tidal amplitudes and phases determine the water level, which positively influences the wave height in the shallow areas where waves are depth-limited. In HZB, the nonlinear interaction promotes/inhibits the suspended sediment concentration (SSC) at high/low water levels. However, the semi-diurnal tide–storm surge interaction mainly inhibits SSC, and the promotion effect is not obvious. With an increase in tidal amplitude, the impact of tide–surge interaction on SSC is further enhanced. The suspended sediment flux (SSF) is mainly controlled by Eulerian transport and sedimentation and incipient motion hysteresis during typhoons. Semi-diurnal/diurnal tide interactions with surge mainly decrease the potential/kinetic energy, but the former increases the potential energy in the bay head and tidal flat. The findings from this study shed lights on the correlation between tide–surge interactions during typhoons and sediment fluxes in macro-tidal turbid estuaries.