Numerical Simulation On Impacts Of Coastline Changes On Hydrodynamics In Hangzhou Bay

Hangzhou Bay has large reclamation in the last several decades.According to the remote sensing data,the width of Hangzhou Bay shrinks by approximately 15 km from 1974 to 2005 and by up to 7.8 km from 2005 to 2016 near the bay head.To ascertain the accumulate influences of these engineering projects upon the tidal dynamics of the funal-shaped,macro-tidal system,this study uses FVCOM(Finite Volume Community Ocean Model)to firstly investigate the characteristics of tides,flow asymmetries and tidal energy density of the bay,and secondly examine the long-term variations of hydrodynamics caused by the coastline changes.(1)Based on historical data,the hydrodynamic model of Hangzhou Bay was established by using the FVCOM numerical model,with high-resolution topographic grids and diverse bottom friction parameters.After verifying the numerical result with the measured water level and velocity data,the model can accurately reproduce the hydrodynamic characteristics of Hangzhou Bay.Model results show that the amplitude of M2 in the Hangzhou Bay gradually increases from the mouth to the top of the bay.M4 amplitude gradually decreases from the head to the mouth of the bay.The system in Hangzhou Bay is flood dominant,and the tide energy could be concentrated in the north channel from Jinshan to Zhapu.(2)Sensitivity tests show that the maximum tidal range,the M2 amplitude and the M4 amplitude slightly increase from 1974 to 2016.The flood dominance increases at the head of the bay,subsequently.The tidal energy density decreases.The narrowed coastline changes the shoaling effect and the bottom dissipation,and impacts the tidal amplitudes and phases,the tidal asymmetry and energy density.(3)The sketched-geometry numerical model indicates that the reduction of the water depth and the bottom slope would reduce the M2 consitituent amplitude,increase the M4 consitituent amplitude,strengthen the flood dominance and change tidal energy density.