随着人类活动加剧和极端气候事件频发,长江河口面临来沙量锐减、汛期异常干旱以及极端洪潮灾害频发等一系列问题,导致长江口洲滩地貌显著调整。基于1958—2022年长江口水文、泥沙及地形实测资料,系统研究了长江口北支进口段与南支河段河道演变特征及规律,重点分析了北支进口段与南支河段近期河道演变的驱动因素及差异化特征,提出了针对长江口北支与南支河段河道演变特点的治理对策。结果表明:北支进口段近期受圈围等工程和自然淤积等因素影响,淤积趋势明显;南支河段受上游来沙量锐减、径流动力增强及整治工程实施等综合影响,河槽呈冲刷态势,但整体河势基本保持稳定。研究成果为长江口河道的综合治理提供科学依据和技术支撑。

[Objective] Dramatic decline in upstream sediment discharge, abnormal droughts during flood seasons, and recurrent extreme flood and storm surge disasters have triggered pronounced geomorphological adjustments within the Yangtze Estuary. This study aims to systematically investigate the long-term evolutionary characteristics and patterns of the North Branch and South Branch of the Yangtze River Estuary,and also seeks to analyze the driving mechanisms underlying their recent differential evolution and propose scientifically robust management strategies tailored to the distinct evolutionary traits of each branch. [Methods] The hydrological, sedimentological, and topographic datasets spanning from 1958 to 2022 were analyzed, the spatiotemporal variations in channel erosion and deposition were quantified, and the characteristic parameters of these processes were compred. Furthermore, the relationships between these morphological changes and their potential driving factors—including hydro-sediment dynamics, sediment source, and anthropogenic interventions were examined. [Results] The research results reveal significant differences in the evolutionary characteristics of the North and South Branches over the past decades.(1) North Branch: The recent evolution of the North Branch is predominantly characterized by accretion, with the channel progressively narrowing and shrinking annually, accompanied by notable alterations in tidal flat topography. The evolution of its channels and tidal flats is jointly influenced by tidal hydrodynamics and the impacts of reclamation projects. Owing to the combined effects of natural accretion and the reclamation of channels and tidal flats, the channel storage capacity of the North Branch has been continuously decreasing.(2) South Branch: In contrast, the evolution of the South Branch is characterized by alternating erosion and deposition with an overall trend toward stabilization. In recent years, the channel storage capacity of the South Branch has slightly increased, primarily attributed to reduced sediment load, enhanced runoff dynamics, and the effects of engineering measures following the operation of upstream reservoir clusters. Nevertheless, the erosion rate has slowed, and the overall planar morphology of the South Branch has remained generally stable. [Conclusion] This study confirms that the North and South Branches of the Yangtze Estuary are undergoing fundamentally different geomorphological adjustments: the North Branch is in a state of retreat and infilling, while the South Branch is experiencing erosional downcutting. This differential evolution is driven by the complex interplay of multiple factors, including anthropogenic activities (reclamation in the North Branch, regulation works in the South Branch) and changes in upstream boundary conditions (a drastic reduction in basin-derived sediment supply). Based on these findings, we propose differentiated management strategies. For the North Branch, the scale and pace of reclamation should be strictly regulated to avoid excessive land encroachment, and the water-sediment transfer regulation system between the North and South Branches should be optimized. For the South Branch, it is necessary to strengthen watershed ecological management to reduce soil erosion and optimize incoming sediment fluxes, thereby mitigating erosion risks. Additionally, enhanced monitoring, early warning, and emergency response systems are imperative: dynamic monitoring of channel morphology, tidal flat evolution, and flow-sediment regimes in both branches should be intensified to promptly detect changing trends in the riverbed. This study provides scientific and technical support for the integrated management, sustainable development, and disaster risk reduction of the Yangtze Estuary.