# River Discharge and Saltwater Intrusion Level Study of Yangtze River Estuary, China
## 3 Results  
### Changes in the Salinity Levels Caused by the River Discharges  
The model was run for river discharges of 14,832 m\({}^{3}\)/s, 16,331 m\({}^{3}\)/s, 18,112 m\({}^{3}\)/s and 27,856 m\({}^{3}\)/s, respectively, at the Jiangyin boundary. The other conditions did not change. The salinity level changes at a total 14 selected stations (SB1-SB4, NB1, NB2, NC1, SC1, and T1-T6) were analyzed. As can be seen in Figure 1, the SB1 station was located at the upstream of the bifurcation point of the SB and NB; SB2-SB4 was located in the lower reach of the SB; NB1 and NB2 were located in the upper and lower reaches of the NB, respectively; NC1 was located in the middle reach of the NC; SC1 was in the lower reach of the SC; and T1-T6 stations were uniformly located in the offshore area.  
Table 3 and Figure 7(1) show the mean salinity level of the NB with the different river discharges. The overall salinity level of the NB was observed to be in a high state. It was also indicated that the river discharge decreased, while the mean salinity level was generally increased from the upper reaches of the NB to the offshore. Moreover, the amplification in the upper reach was found to be higher than that in the lower reach and offshore. The amplification at station T1 was greater than that at station NB2. This was determined to be due to the fact the salinity level at the NB2 was mainly subjected to the runoff of the NB, the flow spilt ratio of which was observed to be very small at less than 1% [29]. Meanwhile, the salinity level at station T1 was exposed not only to the runoff from the NB, but also the runoff from the SB.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Tidal Station** & **Cmz** & **Lxg** & **Nm** & **Hs** & **Salinity Station** & **Z4** & **Z7** & **Y4** & **Y8** \\ \hline RMSE & 0.51 & 0.56 & 0.61 & 0.54 & RMSE & 0.69 & 0.66 & 0.68 & 0.63 \\ Skill & 0.94 & 0.92 & 0.95 & 0.91 & Skill & 0.71 & 0.81 & 0.79 & 0.77 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Root-mean-square error (RMSE) and skill values of each validation.  
Table 4 and Figure 7(2) present the mean salinity level of the SB under the different river discharges. With the decreasing of the river discharge, the mean salinity level was found to have significantly increased at a rate greater than that of the NB. The salinity of the South Branch was a \"high-low-high\" distribution. This is because the saltwater intrusions have two ways into the SB. One way is affected by the sea tides, and the other is the result of saltwater spilled over from NB. The amplification of the mean salinity level increased along the channel from stations SB1 and SB4 to stations NC1 and SC1. The T3 station was found to be mainly influenced by the runoff from the NC, while station T5 was determined to be obviously subjected to the runoff from the SB. Furthermore, the amplifications of mean salinity levels at stations T3 and T5 were found to be greater than those at stations T4 and T6, respectively, which indicated that there is a good response relationship between the mean salinity levels and river discharges.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{**Station**} & \multirow{3}{*}{
\begin{tabular}{c} **Mean Salinity** \\ **Level with the** \\ **Discharge of** \\ **27/856 m\textasci