Bed evolution characteristics and influencing factors of the South Passage of the Yangtze Estuary (1998–2023)

As a inlet of the Yangtze Estuary, the bed evolution dynamics of the South Passage have attracted widespread attention. Based on long-term underwater topographic and sediment data, along with large-scale water-related engineering implementation since 1998, this study analyzes the recent bed erosion and deposition processes of the South Passage. The characteristics and influencing processes of bed evolution are discussed from two aspects: watershed sediment reduction and engineering construction. The results indicate that over the past 25 years, the bed evolution of the South Passage has shown a three-stage change pattern: "slow erosion–approaching equilibrium–accelerated erosion." The first stage of "slow erosion" was primarily influenced by engineering construction, while watershed sediment reduction is one of the main factors driving the "accelerated erosion" in the third stage. In the future, under conditions of a stabilized riverbed boundary and lower sediment concentration, the South Passage is likely to continue the erosion trend in the short term until a new equilibrium is reached.