The Effect Of Deep Waterway Project On Current And Salinity In Changjiang Estuary

Changjiang estuary has the geomorphological pattern of "3 bifurcations and 4 outlets" into the inner shelf of East China Sea. The character of current and salinity distributions in the river mouth is complicated for the horizontal and vertical distributions and its variations. With the rapid economic and social development of Shanghai City, more hydrodynamical constructions were built in the recent decade in the Changjiang Estuary resulting with the flow pattern and salinity distributions been effected. This thesis studies the characteristics and variations of current and salinity distribution under the impact of the Deep Waterway Project by using a 3D numerical model. The main works in this thesis are listed as follows:1) Based on the observed data around the river mouth of the Changjiang estuary, vertical distribution of current and salinity are analyzed and discussed. These data shows there exists stronger vertical stratification in the North Channel and relatively weaker in the South Passage. The minimum value of horizontal velocity occurred at the 0.8-depth layer in the vertical column during the flood tide. The velocity difference between the flood and ebb tidal currents is not so significant in North Passage.2) The hydrodynamic impacts of the Deep Waterway Project on local circulations around the North Passage and adjacent waters has been simulated and analyzed with the three-dimensional Finite-Volume Coastal Ocean Model (FVCOM). The modeling results reveals that original rotational currents in the North Passage had been changed to the alternating patterns due to the constructions of dikes and groynes. The dikes had significantly blocked the water transports from the Jiuduansha Shoals into the North Passage during the high tide of flood cycle. Small-size eddies, located in the groyne-blocked regions, are generated with the spatial dimension as the scale of nearest groyne. The velocities are increased along the lower part shipping channel from the middle to bottom layers at maximum flood tide. The maximum value of the ebb tide current remains unchanged at the maximum ebb tide, but its spatial coverage increased.3) The salinity distributions have significant variations during the several phases of the DWP constructions. After the Phase III completed, the saltwater intrusion along the shipping channel, however, aren't significantly changed. On the otherhand, the spatial coverage of the high-salinity water is extended upon the upper part of the North Passage. And the saltwater intrusion had minor increasing due to the deepened bathymetry at the eastern part of North Passage. The vertical mixing been weakened within the North Passage, especially during the flood tide when high stratification occurred.