Saltwater Intrusion Function based on the Interaction Principle between the Accumulation of Energy and the Impedance: A Case Study of Yangtze River Estuary, China

Saltwater intrusion is a major hazard to coastal communities as it causes degradation of fresh water resources. In recent years, the issues related to saltwater intrusions have received increased attention, due to the fact that these intrusions have shown increased levels and frequencies. In this research study, a saltwater intrusion function was constructed based on the theory of the interactions between energy accumulation and impedance. A MIKE21 model was used to simulate the hydrodynamics of Yangtze River Estuary (YRE). Then, through the analysis of the relationships between the river discharge conditions, tidal ranges, and saltwater intrusions, it was determined that under certain river discharge conditions, the tidal ranges and salinity levels at the stations in the southern branch (SB) of the YRE conformed to S-shaped curve characteristics. Also, the tidal ranges and salinity excess area rate (SEAR) displayed similar characteristics. Furthermore, the river discharge conditions were also found to match the S-curve characteristics between the two aforementioned relationship features. Therefore, the saltwater intrusion function of the YRE was constructed based on the previously mentioned development rules. Also, the applied quantification method was elaborated, and the values of the parameters were determined. As a result, the two critical inflows to the sea (more than 10,000 m³/s) were obtained, which could withstand large-scale saltwater intrusions. When the river discharge was greater than 30,000 m³/s, the area was considered to be basically without salt water intrusions, and the estuarine ecology was in an optimal state. These findings have important reference value for future water scheduling during the dry seasons in the upper and middle reaches of the YRE.