The Impact of Sluice Construction in the North Branch of the Changjiang Estuary on Saltwater Intrusion and Freshwater Resources

Estuarine projects can quickly change the estuarine topography and influence the hydrodynamics and saltwater intrusion. The Changjiang Estuary is a multiple-bifurcation megaestuary, and the outstanding feature of the saltwater intrusion is the saltwater spillover from the North Branch (NB) into the South Branch (SB). In this study, the improved ECOM-si model was adopted to numerically experiment with the impact of the sluices that are planned for construction in the upper, middle, and lower reaches of the NB on the saltwater intrusion and freshwater resources. The simulation results show that, on the one hand, sluice construction can eliminate the saltwater spillover from the NB into the SB; on the other hand, sluice construction makes water enter the NB from the SB, and the runoff discharging into the sea in the SB decreases. The water intake time of the Qingcaosha Reservoir (QCSR) increases by 3.2 days for sluice construction in the upper reaches of the NB and decreases by 0.97 and 0.94 days for sluice construction in the middle and lower reaches of the NB, respectively. Considering the impact of sluice construction in the NB on the saltwater intrusion and freshwater resources, the construction of sluices in the upper reaches of the NB is recommended.