Abstract: This paper analyzes the bathymetric characteristics and the evolution processes affected by human activities in recent years at the bifurcation of the South and North Passage in the Yangtze River Estuary. A high-resolution FVCOM model is used to investigate the impact of the diversion project, the direction of submerged dike and the bathymetric change of Ruifeng Shoal on the ebb flow diversion ratios of the South and North Passage. The results show that the construction of the submerged dike at the bifurcation head has limited influence on the ebb flow diversion ratio of the North Passage. The ebb flow diversion ratio of the North Passage decreases when the submerged dike deflects northward and vice versa; however, the influence of the southward deflection is greater than that of the northward deflection. Scouring of the middle and lower Ruifeng Shoal and the northward shift of the mainstream are favorable for the flow entering the North Passage, which increases the flow diversion ratio of the North Passage in the upstream cross-section. Due to adjustment of the water flux in HengSha channel, the flow diversion ratio of the North Passage is slightly increased in downstream cross-section.

Key words: flow diversion ratio, FVCOM, submerged dike, Ruifeng Shoal