Typhoon‐Influenced Formation and Dissipation of Fluid Mud in the Changjiang Estuary

ABSTRACT Fluid mud (FM) is a transient high‐concentration sediment layer commonly observed in highly turbid estuaries, exerting significant influences on sediment transport, channel evolution, and navigation conditions. However, the formation and dissipation mechanisms of FM under extreme weather conditions remain poorly constrained due to the limited availability of field observations during storm events. Here, an event‐oriented field observation programme was conducted in the North Passage of the Changjiang Estuary following two typhoon events, In‐Fa (202106) and Chanthu (202114), to investigate the evolution of FM under typhoon‐induced hydrodynamic forcing. The observations revealed rapid variations in FM thickness, density structure, and spatial distribution following both storms. After Typhoon In‐Fa (202106), extensive FM developed along the middle and lower reaches of the navigation channel, reaching a maximum thickness of 2.4 m, whereas the FM response following Typhoon Chanthu (202114) was weaker, with a maximum thickness of 1.5 m. The FM density generally increased toward the estuary mouth, while sediment grain‐size characteristics exhibited limited spatial variability, suggesting that hydrodynamic processes rather than sediment properties dominated the observed FM evolution. Based on the field observations, a conceptual framework is proposed in which typhoon‐generated waves trigger sediment resuspension, tidal currents regulate sediment transport and redistribution, and channel morphology enhances sediment retention and accumulation. These findings provide new field‐based insights into storm‐driven FM dynamics and improve understanding of sedimentary responses in tide‐dominated estuarine navigation channels.