Spatial And Temporal Variation And Transport Characteristics Of Sediment In The Abandoned Yellow River Estuary

Jiangsu coastal waters are composed of Haizhou Bay,the Abandoned Yellow River Estuary,Sheyang Estuary,Huai River Estuary,radial sand ridges and sea waters adjacent to north branch Yangtze River Estuary.There are radial submarine sand ridges which has unique morphology and complex causes.They are affected by ocean hydrodynamic factors,such as runoff,tidal currents and waves for a long time which leads to the extremely complicated motion law.Therefore,its research has been of great concern to oceanographers for many years.The transportation and accumulation of suspended sediments are the important factors to study submerged delta,submarine sand ridges and nearshore shallow.Hence studying on the distribution characteristics of suspended sediment and the controlling factors of sediment transport can not only understand the evolution law about estuary and coast,but also providetheoretical supports to offshore marine engineering construction.Yancheng city is located in the northeast coast of Jiangsu province,with a long coastline and full of shallows and wind energy.In its waters,there are some major estuaries of Abandoned Yellow River,Sheyang River,Huai River and North Jiangsu Irrigation Canal.Ocean wind energy engineering plays a really important role in alleviating the contradiction in the current economic development process of Yancheng,ensuring the rapid development of marine economy and solving the issues of energy shortage and scarcity of land.Since the implementation of the national coastal development strategy,along with the ocean engineering needs in Yancheng waters,such as offshore wind power,port waterways and beach reclamation,researches refer to hydrodynamics,suspended sediment transport and underwater delta evolution in Yancheng coastal waters become more plentiful.This article was based on the fixed hydrologic and sediment observation data at Abandoned Yellow River Estuary in 2014 winter.The combined methods of mathematical statistics,flux mechanism decomposition and sedimentary dynamics were comprehensively used to study the process and mechanism of water delivery and sediment transport in Abandoned Yellow River Estuary.The impact of suspended sediment transport on the erosion-deposition variation of submarine bank slope was discussed as well.This study has scientific significance and application value in further understanding the material transport mechanism of the river bank and revealing the reason of the erosion-deposition variation of submarine bank slope in Abandoned Yellow River,as well as the management and maintenance of the silt shoreline.The survey data showed that each station in the waters of Abandoned Yellow River Estuary would appear 1 to 2 significant peak(s)of suspended sediment concentration at each tide cycle.The number of peaks,time of occurrence and the peak sediment concentration were closely related to the location of each station,fluctuation of dynamic process,saltwater wedge movement and salinity-generated water density stratification.In the salt water convergence zone,salinity distribution could influence the vertical distribution of current velocity during floodtime,and further affect the time change process of sediment concentration.Density stratification could reduce the water turbulence intensity and carrying capacity.And its inhibitory effect on turbulence was the important reason of causing the big difference of tidal cycle sediment concentration in part of the offshore stations during the neap tide.The resuspension of sediments had great impact on sediment concentration during the period between flood and ebb current.The instantaneous material transport decomposition method was used to analyze the hydrologic and sediment observation data obtained from the waters near Abandoned Yellow River and concluded the mechanism of suspended sediment transport in this area.In general,the residual current was mainly Euler residual current,and the current velocity of Stokes residual current was relatively small.Net carrying capacity per unit width in different areas was consistent with the spatial distribution of Euler residual current,so the net carrying capacity per unit width in offshore area was larger,while it was smaller in nearshore area.Besides,the direction of net water transport was also basically the same as Euler residual current.The suspended sediment concentration in nearshore area was relatively larger with an average of 0.988kg/m3,while the concentration was smaller in offshore area with an average of 0.251kg/m3,which was opposite to the spatial distribution of tidal current velocity.The process of suspended sediment transport had significant impact on the erosion-deposition variation of submarine bank slope in the waters of Abandoned Yellow River Estuary.The sediment transport direction in nearshore area was offshore and the direction was instead shoreward in offshore area,but the flux of sediment transport in nearshore area was larger than offshore area.The bottom sediments in nearshore area started and suspended under the action of wave which caused the erosion of underwater delta.