Wave Dynamics And Its Impact On Sediment Transport Under Typhoons In The Changjiang Estuary

The estuary is the strongest area of land-to-sea interaction,which has the most complex environment of hydrodynamic.With the interaction of runoff,current,wave and wind and other dynamic factors,the estuary is affected by the sediment transport processes from both land and sea areas,resulting in the geomorphological characteristics of s spatial and temporal variation.Studying the processes and mechanisms of hydrodynamics,sediment transport and sedimentary features of estuaries is a difficult problem,and it is of great significance to provide sustainable development and utilization of estuary resources for harbor construction,shipping safety,shore protection and utilization of marine resources.During the typhoon,the estuary is subjected to the strong wave effect and deposition-erosion process caused by the storm.The ‘sediment sheared by wave and transported by tide’ is driven by the interaction of the wave-flow interaction,which is an important research point of the sediment transport and sea-bed erosion of the estuary.This is an important scientific basis for marine forecasting,marine engineering,navigation shipping safety,and disaster prevention.However,the previous research on the wave field in the Changjiang Estuary focused on the prediction of storm surge,change of significant wave height,wave surge and the development and application of numerical model.Most of previous studies analyzed the sediment transport driven by wave and tide based the model calculation or observation data,but only a few focused on the evolution of wave dynamic under typhoon and its effect on sediment transport,especially for typhoons in different paths such as remote area,near area and landing type.It is important to study the wave forcing and its decline from deep water to shallow water,sediment erosion and transport caused by wave in morphological evolution.Based on the analysis of hydrodynamic and sediment transport observation data and numerical model during typhoon,this study presents the variation of the typhoondriven wave forcing field in estuary,and discusses the response process of the wave forcing field and wave energy dissipation to typhoons in different paths in the Changjiang Estuary.Further,this study shows the distribution of the erosion pattern caused by wave,discusses the mechanism of sediment transport.Based on the numerical model with typhoon-astronomical tide-wave online coupling,this work presents the function of the tide and wave on the erosion.The results can not only enrich the basic theory of storm surge and its water and sediment transport in the Changjiang Estuary,but also have important application significance for the safety of marine engineering and disaster prevention during typhoon.The main findings are summarized as follows:1.The influence of typhoons in different paths on wave forcing field in the Changjiang Estuary are expounded,and it is pointed out that the 5 to 20 m water is an area where the wave has significant depth-induced transformation,and the wave energy dispersion is the main cause of the change of wave forcing field.2.Swell is the main driving factor caused by sediment erosion during typhoon,and advection effect is the controlling force of suspended sediment transport.The erosion rate induced by wave and current interaction is 2 to 6 times than that of current-induced or wave-induced alone,the averaged suspend sediment concentration is 2 to 9 times than that of current-induced.3.Observation near bottom indicated that typhoon-induced waves are the dominant dynamic factors that cause the bottom shear stress and suspended sediment concentration to increase,the shear stress under wave and current interaction could reach up to 4.9 pa,the suspended sediment concentration was 3 to 4 times than that during normal weather.This study systematically expounds the rule of the variation of wave forcing field in the Changjiang Estuary and adjacent areas under the influence of typhoons with different paths.It reveals the erosion characteristics during typhoon and the hydrodynamic mechanism of the geomorphological erosion.The physical process of the ‘sediment sheared by wave and transported by tide’ is interpreted.The research results make up for the current research on the impact of typhoons on wave forcing field and sediment erosion in the Changjiang estuary,and enrich the quantitative understanding of the process of storm caused erosion/deposition.In addition,it has scientific instructional significance for the coastal disaster prevention and marine engineering construction protection.