Sediment dispersal and accumulation off the present Huanghe (Yellow River) subdelta as impacted by the Water-sediment Regulation Scheme

Hydrographic surveys conducted simultaneously at stations along three transects emanating off the river mouth during the man-made flood in 2013 were used to investigate the dispersal and accumulation of the Huanghe sediment off the present Huanghe subaqueous delta. During the WSRS period, the diluted water from the Huanghe covered all over the study area via the surface layer, whereas high-concentrated sediment was found in the bottom layers and limited in nearshore area shallower than 12 m, indicating that the buoyant hypopycnal plume was the main sediment dispersal pattern during the WSRS. At the early stage of the WSRS when large amount of ‘clear’ water was released from the Xiaolangdi Reservoir, sediment eroded from the riverbed in the lower reaches increased the median grain size of surface sediment off the river mouth. During the second stage when water discharge was reduced but sediment discharge was dramatically increased, the fine-grained sediment derived from the Xiaolangdi Reservoir mixed with the previously deposited coarser surface sediment, leading to the decreasing median grain size of surface sediment that approached to be poorly sorted. After the physical sorting of the winter storms, the distribution of surface sediment varied regularly with water depth. As the median grain size of suspended sediment discharge to the sea has been significantly increased due to the WSRS, more sediment accumulated in the nearshore area, which effectively extended the subaerial delta and steepened the subaqueous slope off the present river mouth.