Controls on channel morphodynamics in the Yellow River Estuary: Insights from a multi-method assessment under an evolving multi-channel regime

The Yellow River Estuary (YRE) in China has transitioned to a complex multi-channel regime since 2013, making understanding terminal channel morphodynamics crucial for effective water and sediment management. The current study investigates the controls on channel evolution in both non-estuarine and estuarine reaches of YRE, differentiated by bifurcation locations, using a multi-method approach. For the non-estuarine reach, wavelet analysis was applied to satellite-derived river centerlines (2003–2022) to quantify channel migration and its relation with fluvial forcing. In the estuarine reach, the interplay between fluvial and marine processes and their influence on channel migration were assessed. The analysis was complemented by scaled physical modeling experiments. The results indicate that in the non-estuarine reach, the erodibility of the channel, primarily governed by the median grain size of the bed material, exerts a dominant control on channel migration, with higher discharge consistently enhancing mobility by providing the necessary erosive energy. The concentration of incoming suspended sediment plays a secondary role, as much of it can be transported through the reach without causing significant local morphological change. The estuarine reach exhibits three distinct morphological states: limited mouth oscillation, minor bifurcation, and major bifurcation/avulsion. River discharge is the primary driver of these changes, while marine forces exert a stabilizing influence. Crucially, both physical modeling and field data indicate that local bed material characteristics—shaped by selective sediment transport and deposition—significantly influence estuarine morphodynamics, more so than upstream sediment supply parameters alone. Effective management of the YRE requires an integrated approach considering the spatial variability of bed material and the temporal dynamics of hydraulic conditions. The current study emphasizes the importance of distinguishing between bed material properties and suspended load characteristics for predicting morphodynamic responses in sediment-rich, highly managed river systems.