The 12th International Conference on Scour and Erosion (ICSE 2025)

143 / 2025-10-08 12:50:49

Variation of suspended sediment concentration under tidal bore in the Qiantang River Estuary

Qiantang Estuary,Suspended sediment concentration,Tidal bore

Suspended sediment concentration (SSC) plays a critical role in estuarine sediment transport, morphodynamic evolution and ecological processes. While hydrodynamic measurements in estuaries are routinely conducted, gaps remain in understanding river–tide–sediment dynamics, especially in macrotidal estuaries influenced by tidal bores. Utilizing an extensive dataset comprising over 180 tidal cycles of SSC measurements (April, July and November 2018) alongside concurrent hydrographic and bathymetric surveys, we investigate seasonal SSC variations in the upper Qiantang Estuary, a macrotidal system in China with active morphological changes. The results show that the observed SSC exhibits distinct seasonal patterns superimposed on tidal fluctuations. SSC demonstrates strong positive correlation with tidal range during large tidal range conditions but weak correlation during small tidal range conditions. Summer SSC values exceed those in spring and winter by 2–3 times, indicating seasonal migration of the turbidity maximum zone. Three distinct hydro-sedimentary regimes have been identified: winter–spring quiescent phase, high-discharge erosion phase and summer –autumn tidal dominance phase. Tidal bores, confirmed through Froude number analysis, occur predominantly during spring tides in the tidal dominance phase. The system exhibits moderate flood–ebb SSC asymmetry under normal conditions but extreme flood dominance during tidal bore events. Notably, high river discharges can reduce SSC by 50% through dilution effects while simultaneously inducing bed erosion, increasing tidal amplification, and subsequently elevating SSC in following months. These findings improve our understanding of sediment dynamics in tidal bore-affected estuaries and provide valuable insights for tidal bore forecasting, water resource management, and sediment transport modeling.