Sediment budget and riverbed deformation in the uppermost part of the lower Yangtze River, China

The Yangtze River (YR), similar to most large rivers in the world, has experienced significant changes in its depositional environment due to anthropogenic disturbances and climatic influences in recent decades. However, knowledge of how the river channel and bed deformation respond to these changes in the uppermost part of the lower YR, a 200-km-long branched channel, is limited. In the current study, historical bathymetric data collected from 1992 to 2013 and high-resolution multibeam echo sounder (MBES) data obtained from 2015 to 2016 were analyzed to address the changes in the depositional environment. The results indicate that the whole riverbed in the Hukou to Datong reach (HDR) has been scouring over the past two decades and this trend is expected to continue in the future due to decreasing sediment supply from the upper watershed. The amount of net erosion from the HDR during 1992–2013 approximately accounted for 7.2% of total sediment load in the Yangtze River (5.02 billion metric tons at Datong). The evolution of the riverbed is trending towards stabilization even though the patterns of erosion and/or deposition in the HDR have dramatically changed in the last two decades. The part of the channel from the upper 100 km to Datong was found to be a sensitive reach that first showed erosion from 1992 to 2003 and showed deposition during 2003–2008, and then mild erosion during 2008–2013 in response to environmental changes. Thus, the findings indicate that riverine channel deformation in response to anthropogenic disturbance and climate influence is dynamic in different reaches, and this finding has both scientific and practical significance in terms of understanding channel stability and its response to external stressors.