EFFECT OF UNDERWATER DEEP TRENCH FORANIMMERSED TUNNEL ON HYDRODYNAMICS ANDSALINITY TRANSPORT IN PEARL RIVER ESTUARY

摘要

The deep dredged trench for immersed tunnel engineering in estuary area significantly influences the hydrodynamics and salinity transport, which mayaffect not only the marine environment but also the installation process of tubes element. To understand the hydrodynamics and salinity transport in the trial dredged trench of Shenzhen-Zhongshan Link project,a three-dimensional nonhydrostatic numerical model is set up based on SUNTANS, an unstructured-grid ocean and coastal simulator. The predictions of water surface elevation, current velocities and salinity are in good agreement with field observations in June 2016. The simulated results reveal that mean veloc- ity reduces dramatically in the deepest area of trial dredged trench, and the current velocities in the bot-tom layers at the trench center are quite smaller than those in the top layers. Salinity in the trench changes periodically with the tide, with saline water concen-trating in bottom layers at the trench center at most of the time. These variation of hydrodynamics andsalinity may increase the probability of sediment deposition in the trench. At the end of flood towards higher high tide, the intrusion of the saline water in the bottom layers into the trench leads to a cyclone style vortex in the west part of the trench, and a vor- tex is formed above the south slope, which make the hydrodynamics more complicated to some extent.