Identifying the pattern of delta morphological change under decreasing sediment flux due to dam construction is essential for sustainable management in such densely populated coastal areas. In this study, we investigated the morphological processes of the Yangtze mouth bar and prodelta based on bathymetric data on a decadal-interannual scale (1958, 1978, 1997, 2002, 2007, 2010, 2013 and 2015). We found that strong accretion (205.1 Mm³ yr⁻¹) occurred during 1958–1978, when a high sediment load (465 Mt yr⁻¹) was supplied by the Yangtze. Afterwards, the net accumulation rate decreased to 31.9 Mm³ yr⁻¹ in 1978–1997 and 114.6 Mm³ yr⁻¹ in 1997–2002 as a result of riverine sediment loads decreasing to 390 Mt yr⁻¹ and 314 Mt yr⁻¹, respectively. Surprisingly, the net accumulation rate increased to 130.8 Mm³ yr⁻¹ in 2002–2007, though the sediment load sharply decreased to 177 Mt yr⁻¹. This anomaly was attributed to the construction of training walls within the mouth bar area, which induced significant accretion in groyne-sheltered areas and nearby regions. Along with a further decrease in sediment load, the entire study area converted to net erosion of −200.4 Mm³ yr⁻¹ in 2007–2010 and −152.2 Mm³ yr⁻¹ in 2010–2013. Stronger erosion in the former period was partly caused by intensive dredging activities in the mouth bar area. The critical sediment discharge for the Yangtze mouth bar and prodelta to retain net accretion was estimated to be ca. 218 Mt yr⁻¹. If deducting the impacts of estuarine engineering projects on accretion/erosion during 1997–2010, the critical sediment discharge is adjusted to ca. 234 Mt yr⁻¹. In combination with previously reported accretion-erosion conversion elsewhere in the Yangtze Delta, we inferred that most portion of the subaqueous delta has most likely converted from net accretion to net erosion in response to fluvial sediment decline, and the mouth bar area showed the latest conversion among portions of the delta. Integrated assessment and adaptive strategies are urgently required for the Yangtze Delta to survive the coming erosional stage.

在这种人口稠密的沿海地区，可持续的管理至关重要的是，要确定由于大坝建设而导致的泥沙流量减少下的三角洲形态变化模式。在这项研究中，我们基于年代际尺度（1958、1978、1997、2002、2007、2010、2013和2015）的测深数据，研究了长江口mouth和三角洲的形态过程。我们发现，强增生（205.1毫米³ 年^-1）在1958一1978年，当高输沙量（465万吨年发生^-1）由长江供给。此后，净积累率在1978-1997 年降至31.9 Mm ³ yr ^-1和114.6 Mm ³  yr ^-1由于河流沉积物负荷分别降低到390 Mt yr ^-1和314 Mt yr ^-1，因此在1997–2002年期间。出人意料的是，净积累率提高到130.8毫米³ 年^-1在2002- 2007年，虽然输沙量急剧下降到177万吨年^-1。此异常现象归因于口巴区域内训练墙的构造，该训练壁在防波堤保护区和附近区域引起大量积聚。随着泥沙量的进一步减少，整个研究区域在2007–2010 年转换为净侵蚀量分别为-200.4 Mm ³ yr ^-1和-152.2 Mm ³  yr ^-1在2010–2013年。前期侵蚀加剧，部分是由于口岸地区的密集疏activities活动造成的。据估计，扬子河口坝和三角洲保持净积聚的关键沉积物排放量约为。218 Mt yr ^-1。如果扣除1997-2010年河口工程项目对增生/侵蚀的影响，则关键沉积物的排放量应调整为约5％。234 Mt yr ^-1。结合以前在长三角其他地区报道的吸积-侵蚀转换，我们推断出，由于河流沉积物的减少，水下三角洲的大部分地区很可能已从净吸积转化为净侵蚀，而口条区域显示了最新的转换。在部分三角洲之间。长江三角洲迫切需要综合评估和适应性策略，以度过即将来临的侵蚀阶段。