Deltaic engineering-induced accumulation hides erosion in response to fluvial sediment decline in the Yangtze submarine shoal

Worldwide river deltas are impacted by human activities and climatic change, but it has been challenging to quantify their contributions due to nonlinear natural processes and a lack of long-term geomorphological data. Time-series bathymetric data were collected at submarine Hengsha Shoal in the Yangtze Delta during 11 repeat surveys over 60 yr. Our results show that the minimum riverine sediment supply to maintain the shoal's morphology was 229–258 Mt yr⁻¹. Without human impacts, it would have been experiencing net erosion since the operation of the Three Gorges Dam in 2003. However, this shoal has been growing in certain periods. Specifically, the accumulation/erosion during the project's period was much stronger than those during the pre- and post-projects periods. Morphological change due to deltaic engineering was as high as 19 times of that induced by sediment decline. For future research, it is critical to quantify the impact of deltaic human activities during the Anthropocene Epoch.