Development Of Hydrodynamic And Water Quality Model Of Shenzhen Bay Based On Delft3D

Based on the Delft3D hydrodynamic and water quality model,this paper establishes and validates the three dimension hydrodynamic and water quality model of Shenzhen Bay,’and illustrate the numerical principle and modeling process of the model.In the hydrodynamic model,this paper verifies the water level,water temperature and salinity of Shenzhen Bay,the results are acceptable.The hydrodynamic model show that the changes in water temperature of Shenzhen Bay are greatly affected by the air tem,perature,and the salinity is evenly distributed in the plane.The flow direction is basically influenced by the tidal.The velocity in the mouth of the bay is bigger than in the top of the bay,and the water flow is reciprocally flowed.The beach at the top of the bay is dry out during tide ebb,and submerged during tide rise.Based on the verification of the hydrodynamic model,the water quality coupled model of Shenzhen Bay was established to simulate the DO、NH4 and BOD.The results are close to the observations data.As for the simulation results,Shenzhen Bay’s dissolved oxygen is low,with an annual average value of 6 mg/L,and the annual mean value distribution gradually decreases from the mouth of the bay to the top of the bay.The distribution of NH4 and BOD are different with dissolved oxygen,which concentration in the top of the bay is significantly higher than other area.The average annual concentration of BOD in the top of the bay is about 3 to 5 mg/L,and the NH4 is about 2 to 3 mg/L.The water quality belong to poor grade IV,the concentration of BOD and NH4 are gradually decreased from the top of the bay to the mouth of the bay.Based on the well verified hydrodynamic water quality model,this paper combined with the background of climate change,changing the input condition:the temperature was increased by 2℃ without changing the boundary conditions,and three scenarios were designed:1 normal pollution discharge,2 doubled pollution discharge.and 3 half pollution discharge,to test the stability of the water quality model.The results were in line with the expectation,showed that the increase of temperature caused the NH4 and BOD are decreased compared to before,but the changing was not significant.Get the conclusion is the impact of air temperature to water quality is weaker than the impact of changing discharge scenario.The three-dimensional hydrodynamic water quality model of Shenzhen Bay in this paper has certain reference for the decision to Shenzhen Bay’s water environment problem,and also has certain reference for the modeling of other areas.