Analysis of the evolution of the current estuarine geomorphology of the Yellow River under 20 years of water and sediment regulation

The development of river deltas possesses considerable economic and ecological benefits. Both geomorphology and ecology of the Yellow River estuary have undergone significant changes since the diversion project of Qing8 (Q8) in 1996. Since 2002, the implementation of the Water and Sediment Regulation Scheme (WSRS) in the Yellow River Basin has inevitably affected the sediment transport and geomorphology of the Yellow River estuary. In this study, Google Earth Engine (GEE) was used to automatically extract the coastline of the current estuary of the Yellow River for different times, and the relationship between land accretion-erosion and the runoff and sediment load of the Yellow River was discussed. The development of the current estuary delta of the Yellow River has experienced four different stages since the diversion of Q8: rapid erosion (1996-2001), rapid accretion (2002-2007), slow erosion (2008-2011) and slow fluctuating accretion (2012-2021). During WSRS period, runoff, sediment transport and sediment-runoff ratio jointly control changes in river delta accretion area. Sediment-runoff ratios greater than 9 kg/m3 will result in overall proliferation while those below it will result in erosion. After 20 years of WSRS, the downstream channel shifted from high to low scouring efficiency around 2007. Over time, the WSRS gradually refined the particle size of the suspended sediment entering the sea and reduced the sedimentation rate. If the current WSRS is maintained, the rate of land accretion in the estuarine delta will gradually slow down or even erode. Our research provides scientific ideas for sustainable development and WSRS scheduling in the Yellow River Delta.