Numerical Simulation Of The Influence On Water Environment Of The Proposed Artificial Island In Shenzhen Bay

In the past 30 years,due to high-speed urbanization in Shenzhen,human activities such as the fast-growing population,land reclamation and so on have caused a lot of environmental problems.For example,the sedimentation rate and the tidal-flat in Shenzhen Bay are increasing,which have resulted the sediment odor and water quality deteriorating.Thus,the regulation of Shenzhen bay is urgent.Engineering means is proposed in this thesis to improve the hydrodynamic condition in Shenzhen Bay,in order to slow down the status of siltation rate,which can provide guidance to the governance and planning of Shenzhen Bay.In this paper,the hydrodynamics,the water quality,the silt and sediment deposition of Shenzhen Bay were analyzed and reviewed.According to the topography and siltation situation of Shenzhen Bay,the plan that the area near Dasha River can be dredged locally wherever is silted up severely and the dredging sludge can be used to build a triangle-shape artificial island near the mouth of Dasha River is proposed,which aims to improve the hydrodynamics,and slow down or improve the state of sedimentation.The area of the island is about 2.2 km² with its western and northern boundaries being parallel to the shoreline,and the width of the channels both sides is about 800 m.The proposal of island scheme is evaluated by the water environment model.The hydrodynamic modeling was developed for Shenzhen Bay and partial Pearl River using Delft3d software,and the model was validated with observation data.The average errors of high and low water levels are 0.05 and 0.06 m,respectively,and the errors of velocity magnitude and direction are 0.07 m/s⁰.11 m/s and 27.6°³3.0°,respectively;and the errors of salinity are 2.9%⁴.1%.Results show that this model can well simulate the flow field and pollutant diffusion of Shenzhen Bay.The average velocity of flood tide is 0.29 m/s,and the average salinity is 21.97 ppt,while the velocity of ebb is 0.38 m/s,and the average salinity is 19.82 ppt.The tidal volumes in flood and ebb are about 150 and 152 million m³ during spring tide,respectively.The model was used to simulate the situation with/without island scheme so as to discuss the changes of hydrodynamic condition and pollutant diffusion.The model results show that,the average velocities will increase on both channels of the island with the corresponding velocities in the North-South and East-West channels by 60.0%and 27.7%,respectively.The average velocities of the section near the mouth of the Bay and the middle section of the Bay will decrease by 2.4%and 4.6%compared to the present situation.The velocity of the southwest side of the artificial island section will increase by 11.1%and the average velocity of the upper section of the Shenzhen Bay will increase by 0.1%.The increase of velocity in the main tide channel helps to scour sediment and slow down siltation.The calculation results of 15-day continuous tide show that,the average net tidal volume increases 34 thousand m³ for the island scheme.Moreover,the average ebb duration extended 1.4 min under the condition of artificial island.The more net tidal volume and the longer during in ebb will help to take away more sediment,so as to improve the status of sediment condition.Based on the proposal of the artificial island,the concentration of pollutants near the mouth will decrease,while that within the Bay will increase.In the channel of the west side of island,the concentrations of TIN and PO₄^3-will decrease about 0.800 and 0.0400mg/L,respectively.And in the channel of the north side of island,TIN and PO₄^3-will increase about 0.200 and 0.0020 mg/L,respectively.In all,the scheme has little impact to the pollutant diffusion in Shenzhen Bay.