Three-dimensional Numerical Simulation On The Tidal Current Characteristics Of Fresh And Salt Received Water Area

The mixing phenomenon of salt and fresh water is a common natural hydrological phenomenon.Fresh water flowing into rivers and seawater with higher salinity are mixed with each other under the influence of tidal currents in estuaries,and it is traced along the estuary when the tide rises,thus forming saltwater intrusion.This phenomenon is more pronounced with the decrease of fresh water runoff,and has a relatively large impact on residents' living,industrial production and agricultural irrigation.Therefore,it is of great significance to the rational development of water resources and environmental impact assessment that we study the spatial and temporal distribution of salinity in saline and freshwater confluence waters.And it has high academic value.According to the research results of physical model experiment,it used the ECOMSED hydrodynamic model to simulate the water flow and salinity of the salt and fresh water in the estuary area of a generalized estuarine area,and analyzed the salinity distribution affected by the tidal power,river runoff andriver water depth.The specific research contents and results are as follows:(1)Through consulting the relevant literature of tidal current and saltwater intrusion,the present research situation and methods in this field at home and abroad are systematically expounded.And make a comprehensive understanding of the relevant work done in the previous physical model test,and deal with the existing data.(2)Combined with the research content,we carefully study,modify and debug the source code of ECOMSED model,so as to establish a three-dimensional numerical model for the water area.(3)According to the 2 experimental group including spring and neap tides in the physical model,the numerical simulation of tidal current and salinity field is carried out.The results of tide level,velocity and direction,and salinity of the corresponding measuring point are in good agreement with the physical model test data.(4)Based on the good results of the model,the numerical simulation of flow field and salinity field was carried out for 8 groups with different tidal range,different runoff and different downstream water depth.The temporal and spatial distribution of salinity under different conditions is given.(5)The brine is reciprocating under the action of tidal currents.The salinity distribution in the flume decreases from the downstream to the upstream.The surface salinity is less than the bottom salinity on the vertical.There are varying degrees of salt wedge in the calculation of the group.In the flat,the horizontaldistribution of salinity is basically uniform.In the flexural section,the salinity in the right bank side is larger than that of the left bank.(6)In the simulation range,relatively speaking,the tidal range has little effect on the distribution of salinity.With the decrease of the tidal range,the distance of saltwater intrusion is slightly reduced,the mixing capacity of salt and freshwater decreased,the vertical stratification is more obvious than that of spring tide.(7)In the range of simulation,with the increase of runoff,Fresh water on salt dilution and blending increased,and the length of brine wedge decreased gradually.When the runoff increases from 1 L/s to 4 L/s,the length of the brine wedge decreases from 46 m to 28 m.(8)In the range of simulation,when the water depth of the downstream increases,the salt and fresh water stratification phenomenon is more obvious,and the distance of brine rising is increasing.When the water depth in the lower reaches increased from 10 cm to 13 cm,the length of the saltwater wedge increased from 32 m to 53 m.(9)The calculation results show that the ECOMSED model can reflect the characteristics of water flow after the intrusion of saltwater in unsteady waters,and can be used to further analyze the mechanism of salt transport and to predict the distribution of salinity.