Impacts of change of river discharge and sea level on estuarine turbidity maximum zone

Using the improved ECOM model and coupling the sediment transpor tequation,the impacts of change of river discharge and sea level on estuarine turbidity maximum zone are studied.The estuarine turbidity maximum zone locates at the stagnation point.Both the upper-stream and lower-stream residual currents at low layers convey sediments to the stagnation point that induces the convergence of sediments,and the upwelling current induced by the convergence of flow field makes sediment difficult to settle down near the stagnation point.Because higher salt water brought by the saltwater intrusion lies in the bottom layer of the north coast,its baroclinic effect induces the transverse current at bottom layer flows from north to south which advects horizontally the high concentration sediments from north to south coast,it makes the turbidity maximum zone lie in the bottom of south coast.It is necessary for using a three dimension sediment transport model to study estuarine turbidity maximum zone.In the case of river discharge increase,compared with the case of control experiment,the land-ward density induced current at bottom layer reduces,the stagnation point moves downstream that makes the turbidity maximum zone move down-stream.The suspended sediment concentration at the center of the turbidity maximum zone and near the sand bar tends to increase because of the sediment addition from upstream.In the case of river discharge decrease,the variation tendencies of estuarine circulation,saltwater intrusion and turbidity maximum zone are in contrast with the results of river discharge increase.In the case of rise of sea level,the land-ward density induced current near sand bar enhances,the stagnation point moves upstream that makes the turbidity maximum zone move upstream.The sediment concentrations of turbidity maximum zone tends to be higher,but the sediment concentration at sand bar tends to be lower.The variations of change of river discharge and sea level have obvious impact on the turbidity maximum zone.