Saltwater intrusion of the Nandu River under the changing environment in China

Saltwater problems in the Nandu River have gradually intensified in recent years. The effect of runoff variability (RV) on saltwater intrusion has not yet been fully revealed. Long-term trends in runoff and sea level (SL) were analyzed using the Mann-Kendall test and Theil-Sen estimation, and salinity exceedance rates (Ps) were calculated based on MIKE 11 and daily runoff distributions. As RV increased, Ps decreased the most at 16.0 km (6.7 %) and increased the most at 23.2 km (5.3 %). SL increased by 0.4 m and Ps increased the most at 20.5 km (11.7 %). Constant Ps is projected to move downstream by the 2060s and 210 s, with maximum increases in Ps of 6.2 % and 10.1 %, respectively. The ratio of changes in Ps due to changes in RV and SL is about 0.85. Constant Ps sections can be used to assess the risk of saline intrusion in some of the world's estuaries.