Deltaic channels, as the essential part in system of river deltas where river and ocean connect, are influenced profoundly on its deposition and erosion processes, by changes of riverine sediment due to human activities from catchment to mouth of large rivers and sea-level rise worldwide. Here, based on a series of hydrological, sedimentary and morphological records in the main outer channel South Passage (SP) of the river-tide dominant Changjiang (Yangtze) Delta (CJD) for more than half a century, regional deposition–erosion process and the implication mechanism were examined. The results showed that fluvial sediment supply declined by over 70% stepwise during the past decades and local suspended sediment concentration in the SP reduced by half within recent years. Correspondingly, three distinct stages of morphodynamic process came out one after another, which were phases of rapid deposition (1959–1979), moderate deposition (1979–1997) and dramatic erosion (1997–2021), respectively. Channel and shoal had asynchronous performance during this deposition–erosion transition, especially after 1979, when channel entered a rapid erosion period earlier after a stable volume period, while shoal suffered slow erosion after high-speed deposition. Moreover, the current erosion phase was furtherly explained as two main modes by the Empirical Orthogonal Function analysis, accounting for 61% and 14%, respectively. The dominant mode describes the continuous scouring in channel contributed by transfer in riverine sediment regime, consisting of the reducing upstream sediment, local increasing flow diversion, dredging activities and sea-level rise. The second mode suggests decadal shift from deposition to slight erosion of shoal zones, which was also adjusted to episodic events and local engineering projects like shoal embankment and reclamation. It’s predictable that the SP would constantly suffer long-term erosion under riverine sediment reduction, sea-level rise and artificial waterway regulation, together with aggradation of the fringing shoals by reclamation. This highlights channels in the river deltas are faced with the erosion risk caused by anthropogenic activities, which calls for compelling attention.

三角洲河道作为河流与海洋相连的河流三角洲系统的重要组成部分，其沉积和侵蚀过程受到深刻的影响，人类活动导致的河流泥沙从大河集水区到河口的变化以及全球海平面上升. 在这里，基于潮汐主导的长江（长江）三角洲（CJD）的主要外河道南通道（SP）半个多世纪的一系列水文、沉积和形态记录，区域沉积-侵蚀过程和对蕴涵机制进行了检查。结果表明，在过去几十年里，河流泥沙供应逐步减少了 70% 以上，近几年 SP 的局部悬浮泥沙浓度减少了一半。相应地，相继出现了三个不同的形态动力学过程阶段，分别是快速沉积（1959-1979）、中等沉积（1979-1997）和剧烈侵蚀（1997-2021）阶段。在此沉积-侵蚀转换过程中，河道与浅滩呈现不同步表现，尤其是1979年以后，河道在容积稳定期后较早进入快速侵蚀期，而浅滩在高速沉积后遭受缓慢侵蚀。此外，经验正交函数分析进一步将当前侵蚀阶段解释为两种主要模式，分别占61%和14%。主导模式描述了由河流泥沙转移引起的河道持续冲刷，包括上游泥沙减少，局部增加流量分流，疏浚活动和海平面上升。第二种模式表明浅滩区从沉积到轻微侵蚀的年代际转变，这也被调整为偶发事件和当地工程项目，如浅滩堤防和填海。可以预见，随着河道减沙、海平面上升、人工航道整治，再加上围填海加剧岸滩，SP将长期遭受侵蚀。这凸显了三角洲河道面临人为活动侵蚀的风险，需要引起高度重视。可以预见，随着河道减沙、海平面上升、人工航道整治，再加上围填海加剧岸滩，SP将长期遭受侵蚀。这凸显了三角洲河道面临人为活动侵蚀的风险，需要引起高度重视。可以预见，随着河道减沙、海平面上升、人工航道整治，再加上围填海加剧岸滩，SP将长期遭受侵蚀。这凸显了三角洲河道面临人为活动侵蚀的风险，需要引起高度重视。