# River Discharge and Saltwater Intrusion Level Study of Yangtze River Estuary, China
## 3 Results
### Spatial Distribution of the Salinity in the YRE and Its Offshore Areas  
The current study continued to carry out research on the spatial distribution of the salinity in the YRE and its offshore areas in order to better study the relationship between the changes in salinity and the river discharge. This part analyzes the salinity distribution, the change of salinity excessive area, and salinity amplification lines under different conditions in the YRE. The Chinese drinking water standard requires that the salinity of raw water should be less than 0.45%. The Chinese drinking water standard requires that the salinity of raw water should be less than 0.45%. Figure 9 illustrates the space distribution of the salinity during the spring tides. The salinity of the NB was observed to have a high concentration. Also, it was observed that under the spring tide conditions in the SB, when the discharge was 27,856 m\({}^{3}\)/s, the salinity of the SB was lower than 0.45%, and no saltwater instrusion was evident. However, as the runoff decreased, the salinity standard was gradually exceeded in the SB, and the influence of the saltwater intrusions gradually became aggravated. The driving force in the tide under the action of the saltwater intrusion that can cover the area gradually increases with the increase of tidal strength, and the river discharge has played an important role in the resistance to saltwater intrusion. The saltwater intrusion is the process of interaction between a driving force (tide level) and impedance resistance (river discharge), and the process conforms to the principle of volume energy accumulation and impedance [1]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Station** & **Coefficient A** & **Coefficient B** & \(\mathbf{R^{2}}\) \\ \hline NB1 & \(-1.382\) & 25.697 & 0.973 \\ NB2 & \(-0.671\) & 25.426 & 0.996 \\ T1 & \(-1.384\) & 27.307 & 0.992 \\ T3 & \(-0.307\) & 27.849 & 0.992 \\ SB1 & \(-0.049\) & 0.204 & 0.973 \\ SB2 & \(-0.377\) & 1.402 & 0.996 \\ SB3 & \(-0.317\) & 1.246 & 0.992 \\ SB4 & \(-0.317\) & 1.246 & 0.992 \\ NC1 & \(-0.365\) & 1.475 & 0.928 \\ SC1 & \(-0.393\) & 1.532 & 0.983 \\ T3 & \(-2.150\) & 9.216 & 0.983 \\ T4 & \(-1.471\) & 27.196 & 0.983 \\ T5 & \(-4.371\) & 23.871 & 0.971 \\ T6 & \(-1.910\) & 27.571 & 0.999 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistics of coefficients in the linear expression of fitting curve in the NB and SB. Figure 10 shows the trends of the salinity changes in the YRE and its offshore areas at the neap tide, which were similar to those detailed in Figure 8. Furthermore, under the same discharge conditions, the excess areas of salinity during the spring tide periods were larger than those during the neap tide. Since the tides are the driving force of the salt water intrusions, it was found that the more intense the tides, the more severe the salt water intrusions. It was also observed that when the runoff decreased, the saltwater became backdropped in the NB, which resulted in increased saltwater intrusions in downstream areas. The excess salinity areas in the upper reaches of the SB, as well as in the downstream sections of the area, continuously increased and expanded into the middle reach region. Figure 10: _Cont._  
Figure 9: The space distribution of salinity in the spring tide: (**1**) Q = 27,856 m\({}^{3}\)/s; (**2**) Q = 18,112 m\({}^{3}\)/s; (**3**) Q = 16,331 m\({}^{3}\)/s; (**4**) Q = 14,832 m\({}^{3}\)/s. Since the intakes of the Three Great Reservoirs (Changxing Reservoir, Qingcaosha Reservoir, and Dongfeng Xisha Reservoir) in the YRE are all on the south branch [16], and the north branch is in high salinity for a long time, this part analyzes the salinity changes of the south branch of the YRE. Since the intakes of the Three Great Reservoirs (Chenhang Reservoir, Qingcaosha Reservoir, and Dongfeng Xisha Reservoir) in the YRE are all on the South Branch [16], and the North Branch is in high salinity for a long time, this part focuses on analyzing the distribution of salinity in the SB.