Characterization of spatial and temporal evolution of saltwater intrusion in the Qingnian reservoir of Pinglu Canal

Abstract

After the construction of the Pinglu Canal, the operation of the ship lock induces saltwater intrusion into the Qingnian Reservoir, threatening the drinking water supply of Qinzhou City. Despite its significance, studies on the dynamics of low?salinity and non?tidal saltwater intrusion in large artificial canal?reservoir systems remain limited. This study therefore establishes a three?dimensional hydrodynamic and salinity transport numerical model validated against field measurements and laboratory experiments, with discrepancies of less than 0.05 m for water levels and 4% for salinity transport, to systematically investigate the spatiotemporal evolution of saltwater intrusion in the Qingnian Reservoir.This work provides novel insights by quantifying the relationship between upstream inflow and intrusion distance, and by deriving specific operational criteria for drinking-water safety based on stratification analysis.The results show that saltwater intrusion displays a distinct salt?wedge pattern, with the bottom saline layer intruding up to 7.54?km. The maximum intrusion distance is positively correlated with the salinity boundary at the upstream approach channel and negatively correlated with upstream inflow. Specifically, a 411% increase in runoff (from 21.8 to 111.3 m³/s) reduces the intrusion distance by 70% (5.36 km), indicating that higher upstream discharge effectively suppresses the upstream advance of saltwater.Density?driven vertical salinity stratification develops, with the stratification coefficient increasing along the intrusion path. Specifically, safety?margin analysis confirms that under upstream salinity?boundary conditions of 1‰ to 3‰, the use of surface water intakes can reliably maintain output salinity within permissible limits. The research results provide a theoretical basis and technical support for the water resource safety of large?scale estuarine canal projects.