Numerical Studies And Application Of Tidal Dynamics Based On FVCOM In Hangzhou Bay And Adjacent Seas

The Hangzhou bay and adjacent seas are located in the west boundary of East China Sea shelf, South of Shanghai and northeast of Zhejiang province. There are many islands in this region and the coastlines is zigzag. The tidal bore in Qiantang river and the upwelling in Zhoushan Islands, which is very famous, occurs in this region. The ocean dynamics of this region is very complex. The Hangzhou bay and adjacent areas is abundant in natural resources, rich in tourism resources. Ocean engineering is numerous, provide many good harbors and convenient transportation. The cities surrounding this region have a prosperous economy and is densely populated.This article established a tidal dynamics numerical model of the Hangzhou bay and its adjacent seas, which based on the FVCOM ocean model. The model is verified with the measured data, the results show that the model coincides with the trend of the measured data and the error between model result and measured data is small, so the model results is accurate and believable. Based on the results of the numerical simulation, the distribution of the tidal current ellipse, tidal energy flux and the bottom friction dissipation in Hangzhou bay and adjacent seas is claculated.Due to the human activities, especially the built of Lingang new city and continual sea reclamation, the coastline of Nanhui Spit have changed a lot. Based on the model, we dicussed the effect on the Hydrodynamic environment in the Hangzhou Bay and adjacent seas of the Nanhui Spit coastline change. The mode result show that, the external expansion of Nanhui Spit coastline have some effect on the water flux of Hangzhou Bay, about 1% on the total water flux and about 5% on the water flux of the section between Nanhui Spit and Yangshan Island. It also have some effect on the redistribution of water flux in other water channels. The external expansion of Nanhui Spit coastline make the current velocity in the offshore area of Nanhui Spit cape weaken, the current velocity in the north of Hangzhou Bay and the east Nanhui flat strengthen and also have a little effect on Zhoushan Islands seas, have an important influence to the erosion and depositionin Hangzhou Bay. The effect on the Hydrodynamic environment of the external expansion of Nanhui Spit coastline is continual, dut to the continual external expansion result from human activities. For the region of current velocity weakened in the offshore area of Nanhui Spit cape, the tendency of the effect result from human activities is to make the range bigger and the current velocity weaker. but for the Nancao and Jiuduansha regions, the tendency of tidal current velocity changed from becoming lower to becoming higher after the Yantze River Estuary Deepwater Channel Regulation Project. So the effect on the Hydrodynamic environment result from the human activities is not sustained, it is closely related to the plan and actual effect of the ocean engineering. The change of regional coastline may only have a certain effect on the Hydrodynamic environment, but the continual change will have a larger region and higher intensity effect on the Hydrodynamic environment. So we must have an overall and conscious planning when constructing the ocean engineering.Finally, based on the model above, we studied the distribution and characteristics of the vortex produced by the tidal current interact with islands, cape in Zhoushan islands sea area. During the ebb and flood tide, there are widespread fluid separation phenomenon and a lot of vortex in the islands and cape wake zone.There are two main types of its formation mechanism: islands covered shelter and the headlands covered shelter, the vortex produced by islands covered appears in the rear of the island in relation to the direction of the tidal curretn, and the vortex generated by the cape cover appears in the islands side in relation to the direction of the tidal current. The duration of these vortex is shorter, and structural instability, the shape and position always changs. The region around Zhoushan island exists a lot of tidal vortex, and the distribution of tidal vortex in the regions surround ChuShan island and Sijiaoshan Island is relatively sparse. Based on the barotropic model, we built a baroclinic model with the temprature and salinity data averaged by years. The numeric simulation show that: Under baroclinic condition, the number and distribution of the vortex produced by the tidal current interact with islands and cape have no obvious change, the shape and intensity of some vortexs have a certain influence. The rising and falling of water in the Vortex center is relatively weak, and as the structural instability, the position is changed and duration is short, thus the effect to the vertical water exchange is limited.And The rising and falling of water on the vortex edge is relatively stronger, and the scope is bigger, so the water exchange on the vortex edge have a relatively larger contribution. From the point of the whole vertical water exchange, tidal vertox have a certain proportion to the contribution, and has an important role to the sea ecosystem.