DENSITY-STRATIFIED FLOW OF XIANGXI BAY AT THREE GORGES RESERVOIR BASED ON THE TRACER PRINCIPLE OF INORGANIC ION

The Three Gorges Dam,the largest hydroelectric dam in world currently,is located at Sandouping of Yichang City,Hubei Province.While it has brought far-reaching economic and other benefits in flood control,hydroelectric power,and greater navigation access to the Yangtze River in central China,it also has many negative impacts on ecology and environment.Since the initial filling of Three Gorges Reservoir(TGR),eutrophication and algal bloom have been observed in some tributaries,which arouse the attention from the scholars both home and abroad,and have been carried out a large number of researches.Since the initial filling of TGR,the hydrodynamics of the Xiangxi Bay(XXB)has also been changed.Regulation of water level in reservoir and the physical and chemical difference of water in XXB and steam stream,cause the frequent water exchange between steam stream and tributaries in the TGR.The hydrodynamics of the XXB could be generalized as a density-stratified flow,and could not be simply simulated by one-dimension model.The upstream water mainly flowed out of the bay in a process of downslope-bottom density current,meanwhile,the TGR mainstream water flowed into the XXB in a flowed reverse density current.SO42-,Cl-,Na+,Ca2+,Mg2+,K+,F-are constant ion in water.The content of some ions in the water is relatively stable,which have chemical conserved.In this paper,XXB was as the study location.On September 26 th,2012,hydrodynamics and inorganic ion were measured in XXB,the largest tributary bay in the TGR,to study hydrodynamic characteristics of XXB at TGR.Based on the tracer principle of inorganic ion,spatial distribution of inorganic ion in XXB suggest that inorganic ions in XXB exist gradient trend.The concentration of Mg2+is low in downstream and high in upstream in space,the concentration of Na+is contrary,and they form wedge-shape while diffused to upstream.The wedgeshape is the same with that of the velocity distribution profile diagram.The water is from the steam stream,and it back flows into XXB.It verified the stratified density currents in XXB.Velocity distribution profile diagram in XXB suggests that the water back flows into XXB in the middle of the estuary,which is the middle density currents;while the water in the upstream flow into XXB at the bottom,which is the upstream slope density current.Stratification movement of the water in XXB is obvious.Finding out the hydrodynamics in XXB is a basic work to solve eutrophication.