# River Discharge and Saltwater Intrusion Level Study of Yangtze River Estuary, China
## 5 Conclusions  
In this study, the effects of river discharges on the saltwater intrusions in the YRE were explored. The effects were examined using a hydrodynamic and salinity transport numerical model with high-resolution unstructured grids, and spatial variabilities in bottom roughness. The 25%, 50%, and 70% frequencies of the river discharges during the dry seasons were determined to be 18,112, 16,331, and 14,832 m\({}^{3}\)/s, respectively, and the multi-year averaged river discharge was 27,856 m\({}^{3}\)/s. These river discharge values were used to simulate the salinity level changes caused by the different river discharges. The main findings of this study are summarized as follows. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Station**} & \multicolumn{5}{c}{**Mean Salinity Level with Different Tide Range (\%c)**} \\ \cline{2-7}  & **\textless{1.5 m (\%c)**} & **1.5–2 m (\%c)** & **2–2.5 m (\%c)** & **2.5–3 m (\%c)** & **3–3.5 m (\%c)** & **\textgreater{3.5 m (\%c)**} \\ \hline SB1 & 0.070 & 0.101 & 0.198 & 0.343 & 0.412 & 0.445 \\ SB2 & 0.301 & 0.610 & 1.307 & 2.324 & 2.610 & 2.870 \\ SB3 & 0.098 & 0.170 & 0.475 & 0.778 & 0.868 & 1.072 \\ SB5 & 0.230 & 0.279 & 0.949 & 1.320 & 1.740 & 1.810 \\ NC1 & 0.231 & 0.321 & 1.140 & 1.560 & 1.800 & 2.100 \\ SC1 & 0.310 & 0.532 & 1.310 & 2.230 & 2.570 & 2.780 \\ \hline \end{tabular}
\end{table} 
Table 10: Mean salinity level of the SB in different tidal range under average river discharge of dry season. Figure 13: Mean salinity level of the selected stations in different tidal range. The salinity levels of the selected stations in the NB showed slowly decreasing trends from the upstream to the downstream, and the salinity was maintained above 20%. The salinity of the SB was distributed as \"high-low-high\", and the changes in the salinity levels were greatly affected by the river discharges. When compared with the average river discharge scenario, the increases in the salinity under the other flow conditions were determined to be above 60%. The salinity levels rose as the river discharges decreased, and the amplification line of the SB was greater than that on the NB. The salinity levels displayed very good positive correlations with the river discharges in the YRE, with a correlation coefficient range of between 0.971 and 1. When the river discharge was 27,856 m\({}^{3}\)/s, the standard rate of salinity was exceeded. However, in the SB, it was found to be always lower than 10% regardless of the tide levels. The SB was impacted less by the salt water intrusions. However, when the runoff was reduced to 16,331 m\({}^{3}\)/s, the standard salinity rate became exceeded in the SB, and reached more than 50%. At this point, the saltwater intrusion was considered to be at a serious level. The mean salinity inside the SB rapidly increased when the river discharge decreased. The amplification line of 0.2% continued to shrink, and the amplification lines of 0.45% and 2% gradually expanded. In the areas far away from the river's entrance to the sea, the effects of runoff were weak, such as the amplification lines became gradually reduced. The changes in the river discharges were found to have significant impacts on the freshwater reservoir water withdrawal. The salinity levels at the Dongfeng Xisha Reservoir were mainly affected by the salinized water spilling over from the NB. The amplifications of the monthly mean salinity at the Dongfeng Xisha Reservoir were observed to be larger than at the Chenhang, Baogang, and Qingcaosha Reservoirs in the three river discharge scenarios of this study. When the river discharge was maintained at 27,856 m\({}^{3}\)/s, the salinity levels of the Baogang, Chenhang, and Qingcaosha Reservoirs all remained below 0.45%. The salinity levels at the four reservoir locations were observed to have exceeded the drinking water standard for more than 23 days in the 14,832 m\({}^{3}\)/s river discharge scenario, which potentially negatively affected the drinking water of the population living near the YRE. Conceived the study, Z.X.