Temporal and spatial variations of erosion and accumulation off the Qingshuigou mouth of the Yellow River

The deltaic river course of the Yellow River was diverted artificially northward at the Qing8 of the Qingshuigou channel to the current channel. The channel shift resulted in a decrease or cutoff in the sediment supply from the river. However, the response of the tempo-spatial variation in erosion and accumulation off the abandoned Qingshuigou mouth to the channel shift has not been well studied. Based on multi-years bathymetric data and Landsat satellite remote sensing images off the Yellow River Delta, the tempo-spatial variations of erosion-accumulation off the abandoned Qingshuigou mouth were analyzed comprehensively. In the early stage of the Yellow River diversion (1996—2002), the seafloor erosion rate in the study area was relatively fast, and the average annual seafloor erosion rate was about 0.03-0.05 km³/a. From 2002 to 2007, the value was significantly reduced to about 0.02 km³/a. During 2007—2010, as the Yellow River mouth diverted northward again in 2007, the average annual seafloor erosion increased to about 0.26 km³/a. In the years of 2010—2015, the value reduced to about 0.01 km³/a again, which was much lower than the level at the initial stage of the Yellow River artificial diversion in 1996. Meanwhile, the tidal regime changes and its response to tempo-spatial variation of erosion-accumulation off the abandoned Qingshuigou mouth were simulated using the Delft-3D model. The results indicated that waves and currents played significant but different roles in the erosion and accumulation of seabed in the study area. On one hand, The high bed shear stress area formed by the tidal current and wave on the slope of the delta front caused the area to be severely eroded after the Yellow River rerouted. In addition, as the abandoned Qingshuigou mouth gradually eroded landward and water depth at the slope continuously increased, the influence of tidal current and wave to seafloor decreased gradually. Finally, the erosion rate of seabed continuously decreased in the study area in recent years. The wave-induced high-bottom shear stress zone mostly resulted in the different erosion on both sides of the mouth and the formation of erosion center in the nearshore area. Meanwhile, the interactions between hydrodynamics and delta erosion played an important role in the erosion-accumulation evolution pattern of the subaqueous delta off the abandoned Qingshuigou mouth of the Yellow River.