Variations of Water and Sediment Flux from the Yellow River Estuary over Decades and Estuarine Dynamic Erosion and Accumulation Shifts

Since the 1950s, the inflow of water and sediment from the Yellow River (YR) into the Bohai Sea has significantly diminished, leading to pronounced coastal erosion. In this study, the temporal variations of water and sediment flux from the YR to the sea during 1950–2021 and their impact on the erosion and accumulation of the estuary are examined making use of the complex Morlet wavelet analysis and mathematical statistical analysis. The results showed that the annual runoff and sediment load had a stepwise reduction trend and changed abruptly in 1974 and 1985, respectively. From 1987 to 2021, the average annual runoff and sediment discharge were 175×108 m3 and 2.45 ×108 t, respectively, representing a 57.52% and 76.10% decrease compared to the period of 1950–1986. The water and sediment transport into the sea from the YR show significant correlation and synchronicity. On the interannual scale, the water-sediment sequence of the YR exhibits multi-timescale periodicity. The runoff exhibits an average cycle of 15 years at 23a time scale, while sediment transport has an average cycle of 14 years at 18a time scale. Forecasting indicates a continuous downward trend over the next seven years from 2021, transitioning from a state of abundance to dryness. The areal variations in the estuary correspond closely to the periodic changes in sediment flux, showing decreasing trends in sedimentation for active estuary and erosion for abandoned estuary. The center of accumulation shifted from a northeastward direction in 1997–2004 to a northward direction in 2004–2012. The results contribute to a deeper understanding of water and sediment transport in the lower reaches of the YR and provide a scientific basis for coastal wetlands protection and estuarine ecology maintenance.