Numerical Simulation Of Pollutant Diffusion In HangZhou Bay

Hangzhou Bay is a typical strong-tide estuary in China.The overall shape of the estuary is trumpet-shaped.The water exchange capacity between the water in the bay and the East China Sea is weak.The plains on both sides of the Hangzhou Bay are low in elevation.The sea level rises and frequent sea levels are affected by the global greenhouse effect.The exchange capacity between Hangzhou Bay and the East China Sea has been further weakened due to factors such as high tide and low tide,which is not conducive to the diffusion of pollutants.The large-scale land reclamation and reclamation activities on both sides of Hangzhou Bay will change the shoreline shape and tidal current field,and then affect the diffusion and transport of pollutants in the bay.Therefore,studying the diffusion characteristics of pollutants on the south and north shores of Hangzhou Bay under the new shoreline conditions after the implementation of the reclamation project and the impact of continuous reclamation projects on the diffusion of major pollutants in Hangzhou Bay can be regarded as Hangzhou Bay The scientific construction of the new area and the formulation of reasonable pollutant discharge measures provide reference value and are of great significance to the protection of the marine environment.Based on the topographical conditions of Hangzhou Bay in 2015,the paper established a two-dimensional plane mathematical model of Hangzhou Bay,and established a water quality model based on the hydrodynamic model.Selecting inorganic nitrogen as a typical pollution factor,the Hangzhou Bay Jianshan,Zhapu and Shangyu were numerically simulated.The dilution and diffusion of pollutants in Yuyao and Cixi areas,focusing on the study of the characteristics of pollutant concentration changes over time in the confluence area in the bay.The simulation results show that the pollutants discharged in Jianshan area on the north bank of Hangzhou Bay spread to the south bank and diluted to 0.5%;the pollutants discharged in Zhapu area on the north bank have no impact on the south bank;the pollutants discharged in Shangyu area on the south bank have a greater impact on the water quality of the north bank than in Yuyao;Cixi discharge Pollutants eventually flow to the sea.The pollutants discharged from Jianshan and Shangyu have a 1:1 impact on the water quality of the junction within the bay;the pollutants discharged from Jianshan and Yuyao have a 2:1 impact on the water quality of the junction within the bay;the pollutants discharged from Zhapu and Yuyao affect the water quality of the junction within the bay.The impact is 2:1;the pollutants discharged by Zhapu and Cixi will not intersect.The research on the response relationship between flow field and pollutant diffusion shows that at high tide,the pollutant concentration rises with the rising tide,and at low tide,the pollutant concentration decreases with the ebb tide;the peak pollutant concentration is negatively correlated with the peak flow velocity of the rising tide.;The relationship between the valley of the pollutant concentration and the flow velocity of the ebb tide varies according to the area where the pollutant is discharged.The paper selects 1997,2007,and 2015 as the representative years,and uses the corresponding year's terrain to modify the mathematical model to simulate and analyze the impact of the change of the Hangzhou Bay coastline on the inorganic nitrogen transport of typical pollutants in the bay in two stages: 1997-2007 and 2007-2015.The influence of the law and characteristics of change.Research shows that: in general,the area of pollutant diffusion before and after the reclamation project is slightly reduced,but there are differences in the changes in the diffusion of pollutants in the bay from the north and south shore reclamation: the north shore reclamation will cause a more significant area of pollutant diffusion The impact of the south bank reclamation on the diffusion of pollutants showed a phased change,that is,the previous stage(1997-2007)the south bank reclamation caused a slight increase in the pollutant diffusion area,and the diffusion change range was significantly smaller than that of the north bank reclamation.In the first stage(2007-2015),with the increase of the reclamation area on the south bank and the displacement of the shoreline,the overall diffusion area of pollutants showed a decreasing pattern.In addition,the article also discusses the impact of reclamation projects on both sides of Hangzhou Bay on the exchange capacity of Hangzhou Bay water body.The results show that the cumulative reclamation of tidal flats in the two stages of 1997-2007 and 2007-2015 has a positive effect on the dilution of pollutants in the bay water.