Effect of Runoff Variability and Sea Level on Saltwater Intrusion: A Case Study of Nandu River Estuary, China

Abstract

AbstractSaltwater intrusion exits in estuary areas. Significant change in runoff variability (RV) has been detected in many basins, but limited research has investigated this change's effect on downstream saltwater intrusion. Using measured time series, this study has statistically detected a significant trend of increased RV and sea level (SL) rise in Nandu River Estuary, China, and analyzed their effect on the saltwater intrusion combining the Finite Volume Community Ocean Model and Monte Carlo method. The Mann‐Kendall test and Theil‐Sen estimator show that the yearly variance of the log‐transformed runoff and mean SL have significantly increased and are expected to increase by approximately 50% and 0.2 m by the 2060s, respectively, and 101% and 0.4 m by the 2100s. SL rise increases the salinity‐exceeding rate (salinity > 0.45‰, the standard for drinking water), and the increase in middle channels are higher than that of upstream and downstream channels. With an increased RV, the model‐predicted salinity‐exceeding rate decreases at downstream and increases at upstream channels, respectively. In our specific site, the location with a constant salinity‐exceeding rate is predicted to move downstream, and the maximum increase of salinity‐exceeding rate will reach 13.3% and 19.1% in the 2060s and 2100s, respectively, at the middle channel section. The results are validated in Yangtze River Estuary and are generalized to other estuaries to determine the change pattern of salinity‐exceeding rate. Moreover, a lower RV helps to extend the channel length with fresh water available and can be used as a management tool.