# River Discharge and Saltwater Intrusion Level Study of Yangtze River Estuary, China
## 3 Results
### Influences of the River Discharges on the Four Reservoirs in the YRE  
It has been determined that the four freshwater reservoirs in the YRE are often affected by saltwater intrusions, especially during the dry seasons. The saltwater intrusions in the SB were mainly \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Discharge (m\({}^{3}\)/s)** & **Total** & **A (0.2–0.45\%)** & **B (<0.2\%)** & **C (0.2–0.45\%)** & **D (0.45–2\%)** & **E (>2\%)** \\ \hline
18,112 & 113.27 & 24.96 & 27.94 & 8.63 & 18.05 & 33.69 \\
16,331 & 115.26 & 29.20 & 17.31 & 11.33 & 20.22 & 37.20 \\
14,832 & 116.19 & 33.60 & 6.00 & 14.57 & 22.59 & 39.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The length of salinity amplification in the SB and offshore (unit: km). Figure 11: Differences of salinity level between different river discharges and multiyear river discharge in the dry season: (**a**) Q = 18,112 m\({}^{3}\)/s; (**b**) Q = 16,331 m\({}^{3}\)/s; (**c**) Q = 14,832 m\({}^{3}\)/s; A, B, C, D and E are the length of salinity amplification (unit: km). caused by two factors: saltwater spilled over from the NB to the SB; and the occurrences of saltwater intrusions during the periods of low levels of river discharge. Due to the reduction in runoff during dry seasons, and the increased human water usage, the low river discharges aggravated the saltwater intrusions, and negatively influenced the effective operations of the reservoirs. In the study, the salinity change process of four reservoirs under different flow rates through the model was simulated. Figure 12 shows that as the river discharges decreased, the salinity of the reservoir exceeded the standard. The changes in the salinity levels in the Dongfeng Xisha Reservoir displayed large fluctuations, and at times exceeded the standard. In comparison with the Dongfeng Xisha Reservoir major fluctuations, the salinity of the other reservoirs changed relatively slowly. When the river discharge was 27,856 m\({}^{3}\)/s, part of the Dongfeng Xisha Reservoir exceeded time limit. However, the salinity levels of the remaining three reservoirs were found to be below 0.45%, and were not affected by the salt water intrusions. This was due to the fact that the Dongfeng Xisha Reservoir was located at the junction of the SB and NB. In this location, interactions occurred between the highly concentrated saltwater and the river water as it entered the sea. Therefore, the salinity levels fluctuated greatly. Figure 12: _Cont._  
Table 8 presents the monthly mean percentages of the salinity increases in the discharges of the three rivers compared with the average annual river discharges. The Dongfeng Xisha Reservoir was located farthest away from the open sea, and was found to be dominated by the saltwater spilling over from the NB to the SB. Since the Dongfeng Xisha Reservoir was located at the junction of the SB and NB, the interactions between the highly concentrated saltwater and the river as it entered the sea resulted in major fluctuations in the salinity levels. The salinity amplification at the Dongfeng Xisha Reservoir was approximately twice that of the Chenhang and Baogang Reservoirs. The Baogang and Chenhang Reservoirs were located close to each other, and the salinity increasing percentages were observed to be similar. Due to its closeness to the sea, it was found that the Qingcaosha Reservoir's increasing percentage was relatively small. In Table 9, it can be seen that the increasing percentage totals and the longest successive times of the salinity exceeded 0.45% at the four examined freshwater reservoirs during the river discharges in a typical month (31 days or 745 h).