Three-Dimensional Numerical Simulation Of Hydrodynamics And Salinity In The Changjiang Estuary Deepwater Channel

In this thesis, a three dimensional numerical model is established to simulate thehydrodynamics and salinity in the Changjiang estuary deepwater channel by using theFVCOM model. The flow field and salinity distribution in different phases of theChangjiang estuary deepwater channel regulation project are reproduced respectively.Based on the in-situ measured data, the near-bottom sediment transport and thechannel siltation are analyzed in details. The main research contents and conclusionsin this thesis are summarized as follows.1. Using the jetty-spur dike module of FVCOM, the flow field around submergedspur dike is simulated and the numerical results are tested against the experimentaldata of water surface and velocity distribution. The numerical model is verifiedcorrect to describe the overtopping flow over the submerged dike and reproduce thethree-dimensional circulation flow with sufficient accuracy.2. In order to set up the terrain system of the Changjiang estuary deepwaterchannel project more efficiently, a set of algorithm is designed to search the nodes ofsubmerged dike and the corresponding relationship between cells. Besides, theoptimization for the application of the narrow jetty algorithm in the large-scale projectis implemented. Large amounts of field measured terrain data is collected, and all thebase-level of the in-situ terrain data is transformed to the Yellow Sea base-level. Thus,the terrain system in different stages of the Changjiang estuary deepwater channelproject is set up.3. The numerical model is validated against the in-situ measured data of tide,flow velocity, flow direction and salinity at the Changjiang estuary during the floodseason in2012. It is shown that the FVCOM model can accurately reproduce thehydrodynamics and salinity field at the Changjiang estuary.4. Through analyzing the simulated results of the hydrodynamics in differentstages of the Changjiang estuary deepwater channel project, it is found that thehorizontal and vertical circulation flow between the regulation structures and thenear-bottom cross flow on both sides of channel are very remarkable. The complexwater flow may lead to the sediment transport into the channel from shoals on bothsides.5.Throughanalyses of streamline and particle tracking in different workingconditions, it is shown that the ebb-tide at the entrance of the North-South Passageturns southward after the Phase III project, and the diversion ratio of the ebb-tide at North Passage decreases. There may be a certain relationship between the decrease ofdiversion ratio and the overhigh elevation at the current-limiting section of Nanshatouchannel in Xinliuhe submerged dike project.6. Using the flood discharge and tidal elevation boundary conditions, the salinityfields at the Phase I，II, III of the Changjiang estuary deepwater channel regulationproject are simulated respectively. The changes of salinity fields on global-scale, onlocal-scale at the North-South Passage and the vertical salinity distribution along thedeepwater channel are analyzed so as to figure out the changing trend from the PhaseI~III projects.7. Based on the in-situ measured data of the near-bottom suspended sedimentconcentration, the sediment concentration distribution near the bottom of Changjiangestuary deepwater channel is computed. Specifically, the near-bottom sedimenttransport at the bend section of the channel is analyzed. The computed results indicatethat the sediment transported into the channel from the shoals on both sides is asmuch as32million cubic meters (counted by the dredging density of1690kg/m3)forPhase III of the regulation project during the flood season (from May to September),which may be the primary cause for the serious siltation in the Changjiang estuarydeepwater channel.