Integrated Modeling of Typhoon Damrey's Effects on Sediment Resuspension and Transport in the North Passage of Changjiang Estuary, China

摘要

A typhoon is one of the major factors that often cause sediment transport and bed erosion in estuarine navigational channels. A 12.5-m deepwater navigational channel (DNC) is located in the north passage of the Changjiang Estuary. Because it acts as the entrance navigation waterway of the Changjiang River, it is important to investigate the impact of typhoons on sediment suspension and transport in the navigation channel. In this study, a previously calibrated hydrodynamic and sediment transport model [shallow-water equation model (SWEM)] was integrated with a storm wind model [weather research and forecasting (WRF)] and a wave model [simulating waves nearshore (SWAN)] to investigate the effect of Typhoon Damrey on the navigation channel in 2012. The typhoon produced a weak storm surge but significant wave heights in the Changjiang Estuary. By comparing bottom shear stress induced by current and wave, numerical modeling results indicated that the increase of sediment concentration in the navigation channel during Typhoon Damrey was mainly caused by sediment transport fluxed into the channel from shallow-water areas outside the channel, where wave-induced bottom shear stress during Typhoon Damrey caused sediment resuspension. The high sediment flux overtopping from the south dike into the channel was the important sediment source for the navigation channel. During the passage of Typhoon Damrey, there was a convergence area of sediment flux between the upstream seaward sediment transport and the lateral transport of sediment flux overtopping from the south dike at the middle-lower reach of the north passage. Near the outlet of the north passage, the near-bottom residual transport of sediment was in the upstream direction against the seaward sediment transport from the river. The convergences of sediment flux produced the high-turbidity maximum zone at the lower reach of the north passage, where in situ bathymetric surveys within the DNC before and after Typhoon Damrey showed the sediment deposition area in the channel.