| Estuaries are one of the most important components of the coastal zone and an important area where land and sea materials meet and where currents and runoff interact.There are many and complex types of estuaries in China,and the estuarine areas are economically developed,densely populated,with dense docks and developed shipping.Sediment transport causes shore beach scouring,shoreline deformation,channel siltation and other effects,and plays an important role in the continuous evolution of coastal topography and the transport of pollutants into the sea.Therefore,the study of sediment transport in estuaries and the investigation of its movement laws are of great significance to the rational use and development of marine resources and the prevention and control of marine pollution.The Yangtze estuary is the largest estuary in China,carrying a large amount of sediment when entering the sea,and is the main source of land-derived material in the East China Sea.Therefore,many studies have been conducted by previous authors on the sediment transport mechanism of the Yangtze River estuary and adjacent waters.However,under the influence of typhoons,the weather is more severe,and it is difficult to obtain hydrological sediment information,so previous studies on sediment transport under typhoon weather are still relatively few.China is one of the countries most affected by typhoons,and typhoons are also one of the natural disasters that occur frequently on estuarine coasts.China’s coastal areas are often hit by typhoons,and under the action of typhoon waves,water turbulence is enhanced,flow velocity increases,and scouring of the submarine bed is enhanced,at which time the sediment that requires a larger scouring force to start occurs in suspension,leading to an increase in the concentration of suspended sand,so typhoon waves have a significant impact on estuarine coastal sediment transport,estuarine Typhoon waves play an important role in coastal sediment transport,estuarine migration,coastal erosion and channel siltation.The study of sediment transport in typhoon weather is of great importance.This paper mainly uses MIKE21 software to build a numerical model of the Yangtze River estuary and Hangzhou Bay waters with the premise of collecting hydrological data.The modeling of the hydrodynamics of the study area under normal weather conditions was firstly carried out and verified using the measured data,and the results showed that the simulated values were in good agreement with the measured values.After determining the feasibility of the model,the study area was modelled under typhoon "fireworks" and the tidal characteristics under typhoon conditions were analysed.The wind field was reconstructed using an empirical wind field model with the background wind field from the reanalysis data,as the reanalysis data did not accurately describe the strength and location of the typhoon.For the calculation of waves under typhoon conditions,the SW module of the MIKE software was used.In the ocean,residual currents are crucial for pollutant transport,sediment transport,and temperature and salinity field analysis.Therefore,on the basis of the residual current analysis,the hydrodynamics under normal weather and typhoon weather are analysed.Under typhoon conditions,the residual flow characteristics of the study area change under the influence of strong wind and waves.In Hangzhou Bay the main direction is from the outer sea towards the inner bay and the flow velocity is also relatively high.In normal weather,the residual flow in Hangzhou Bay is mainly from the inner to the outer bay,with an overall easterly-northerly direction,while a coastal flow exists on the north shore towards the bay.On the basis of the hydrodynamic model,sediment transport models were developed for normal weather and typhoon conditions respectively,using the MT module in MIKE.The sediment transport characteristics were analysed under different weather conditions.In normal weather,sediment transport is mainly influenced by the tide,and the maximum turbidity zone is near the south sink mouth,and the position is shifted with high and low tides.This is because,in the bottom bed,part of the sediment needs a large critical initiation force to be in suspension,when the tide increases,this part of the sediment occurs in suspension,the sediment initiation,re-suspension and transport diffusion all need a time process,this is the main reason that makes the peak sediment concentration lags behind the peak of the flow velocity.Under the influence of the typhoon,the sediment concentration values are high and different from the spatial distribution of sediment concentration in normal weather,the area of high suspended sand concentration has been expanded,at the time of typhoon landfall,the highest value of suspended sand concentration is distributed in the middle of the bay mouth,the concentration reaches 6.8kg/m~3.In the area of high suspended sand concentration the bottom bed was washed away and there were varying degrees of siltation and scouring in the bay. |
