| China's largest group of islands-Zhoushan Islands,located in the southeast coast of China,is China's largest archipelago.The construction of Zhoushan Continental Island Project,constructed an all-weather channel to connect Zhoushan and the mainland,so that Zhoushan and the mainland into one has a far-reaching significance for Zhoushan.Since 1999,five Bridges have been built,crossing four islands and crossing five waterways.Rising sea levels will harm people living in coastal areas.Strengthening marine power,weakening the ability of coastal protection dykes,increasing the difficulty of engineering construction,large-scale bridge construction and sea level changes will change the hydrodynamic environment.This paper was studied the impact of Island-Land Project and sea level rise on Zhoushan sea area,and the hydrodynamic mathematical model under each situation was established by using Mike 21 software.After the comparison and verification with the measured data,the hydrodynamic environmental characteristics of Zhoushan sea area were analyzed.On this basis,the changes of hydrodynamic sediment erosion and deposition environment in Zhoushan sea area under the condition of continuous Island-Land Project phase 3(Zhoudai Bridge)and sea level rise of 0.5 m,1.0 m and 2.0 m are analyzed.The main effects are as follows:(1)The influence of Zhoudai Bridge project on the sea area of Zhoushan is mainly concentrated in the water area within a distance of 15 km where the bridge is located,which blocks and weakens the tidal power from the sea area.On the side near the mainland,the tidal current velocity decreases and the tidal range decreases.In the position of pile foundation,there is obvious cylindrical flow around,and the flow velocity decreases and the tide level increases at the surface of the pile foundation.The changes on the ocean side show a fluctuation change,and the most obvious change is at the distance of 2-3 km from the bridge.The influence on suspended sediment is mainly reflected in the improvement of the sediment carrying capacity caused by the rising velocity.These influences decrease with the extension of the distance from the axis of pile foundation layout,so that the sediment that would have been deposited near the bridge is deposited in a further place and has a long-term impact.(2)The sea level rise mainly affects the coastal sea area and the estuary area,which greatly increases the tidal power in the estuary area.In the coastal open sea area and the estuary waterway area,the impact of sea level rise is almost completely opposite.In the open sea area,with the rise of sea level,the tidal range decreases,the tidal current velocity decreases,the concentration of suspended sediment decreases,and the deposition increases.In offshore islands sea area,as a result of the existence of islands,the region especially among channel islands area,due to the water flow convergence between the channel,the effects of rising sea levels and coastal open area,water level change and the open area is the same but in tidal current velocity and suspended sediment concentration,in contrast to the open area on the deposition conditions change.The influence of sea level rise has been reduced in the water area where Zhoudai Bridge is located,which is embodied in the decrease of tidal current velocity and sea level rise amplitude in the water area where the bridge is located. |
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