Abstract
The Yangtze River Estuary (YRE) is the largest estuary in China. Recently, due to the increase of extent and frequency, saltwater intrusion has received more and more attention. In this paper, with the adoption of hydrodynamic and salinity transport mode, quantitative research of the influence of river discharge to the North Branch (NB) of the Yangtze River on the saltwater group migration law is conducted. Tide and salinity data are used to validate the model effectively. In different paths, the changes in flow and the movement of the saltwater group are similar. The saltwater group starts to move downward from the sixth day. In the staged downward movement, the larger the runoff volume, the further the distance of the core of the saltwater group, and converges to around 90 km gradually. At different flow rates, the relationship between the average location of each waterway saltwater group core tide cycle and time is consistent with the Gompertz model, and its parameters had a nonlinear relationship with the flow rate. A function is constructed to calculate the length and time of the saltwater group migration. As the flow rate increases, the faster the core of the saltwater group reaches the entrance. The downwards movement takes 3–8 days. Quantitative research on the influence of the saltwater spilling from NB to the three major reservoirs in the South Branch (SB)is conducted. The simulation results are consistent with the function calculation. River discharge has a direct impact on saltwater transport and diffusion in the YRE.
Highlights
The estuary is where the seawater and freshwater meet
The calculation length of each flow value at the upstream of Jiangyin was always consistent with the control mode, and both were one month
In the case of a high flow rate (Q > 10,000 m3 /s), as the core of the saltwater group will move beyond the exit in the later period, the lateral diffusion of the saltwater group was intensified, and the concentration decrease rate of the saltwater group increased significantly, because it was not constrained by the land boundary
Summary
The estuary is where the seawater and freshwater meet. Different forms of estuaries, different tides and runoff intensities will have an important impact on the mixing type of saltwater and freshwater, whereas different mixing types of saltwater and freshwater will have a significant impact on saltwater transport. N.D. et al [7] used a three-dimensional numerical model of the estuary to simulate and analyze the effects of changes in water volume and sea level on estuarine saltwater intrusion. Wu Hui [27] used the ECOM-si model to study the quantitative relationship between saltwater spillover, runoff and tidal range in the NB of the Yangtze River estuary. Qiu Chen et al [30] did quantitative research on the changes of saltwater intrusion characteristics in the Yangtze River estuary after sea level rises in the future. This paper combines the measured data, builds a MIKE21 model, which simulates the movement of spillover saltwater group and salinity variation, under the influence of NB of Yangtze River estuary alone, and discusses the effects of factors, such as runoff, tidal current and wind on the activity and concentration of the saltwater group
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