Impact of anthropogenic drivers on subaqueous topographical change in the Datong to Xuliujing reach of the Yangtze River

Changes of subaqueous topography in shallow offshore water pose safety risks for embankments, navigation, and ports. This study conducted measurements of subaqueous topography between Datong and Xuliujing in the Yangtze River using a SeaBat 7125 multi-beam echo sounder, and the channel change from 1998 to 2013 was calculated using historical bathymetry data. The study revealed several important results: (1) the overall pattern of changes through the studied stretch of the river was erosion–deposition–erosion. Erosion with a volume 700×10⁶ m³ occurred in the upper reach, deposition of about 20⁴×10⁶ m³ occurred in the middle reach, and erosion of about 60²×10⁶ m³ occurred in the lower reach. (2) Dunes are the most common microtopographic feature, accounting for 64.3% of the Datong to Xuliujing reach, followed by erosional topography and flat river topography, accounting for 27.6% and 6.6%, respectively. (3) Human activities have a direct impact on the development of the microtopography. For instance, the mining of sand formed holes on the surface of dunes with lengths of 20–35 m and depths of 3–5 m. We concluded that the overall trend of erosion (net erosion volume of 46⁸×10⁶ m³) occurred in the study area mainly because of the decreased sediment discharge following the closure of the Three Gorges Dam. However, other human activities were also impact factors of topographic change. Use of embankments and channel management reduced channel width, restricted river meandering, and exacerbated the erosion phenomenon.