Mechanism of suspended sediment variation during a landing typhoon in the Yangtze River Estuary

Abstract

Hydrodynamic variations and suspended sediment concentration (SSC) dynamics under typhoon conditions are critical to understanding sediment transport processes in the Yangtze River Estuary (YRE). Strong winds, waves, and currents during typhoons alter water levels, flow velocities, and SSC distribution patterns, significantly affecting estuarine stratification. This study employs a validated three-dimensional coupled hydrodynamic-salinity-sediment transport model integrated with wave dynamics to investigate storm surge characteristics and SSC variations during Typhoon Muifa (September 2022). The mechanisms driving SSC changes were analyzed through wave effects and bottom shear stress (BSS). Key findings include: 1) Storm surge evolution during Typhoon Muifa transitioned from positive to negative storm surge due to the typhoon's southeast-to-northwest path, with a declining trend post-landfall. 2) Peak BSS values at NC2 (outer North Channel) reached 9.0 Pa, five times higher than normal conditions, while the maximum bottom-layer SSC at NB2 (outer North Branch) exceeded 15 kg/m³. 3) Nonlinear wave-current interactions modulated BSS magnitudes and SSC distribution. These interactions enhanced BSS in outer estuarine regions, suppressed tidal forces, and promoted sediment deposition, ultimately reducing SSC across all study sites. The results highlight distinct SSC responses to typhoon-induced dynamics, underscoring the need for further research on wave-sediment interaction mechanisms.