Suspended sediment carrying capacity of lightweight model sediments under the influence of tidal currents

Numerous scholars have investigated suspended sediment carrying capacity (SSCC) formulas under the influence of tidal currents. However, lightweight model sediment, which is commonly used in physical estuarine models, is incompatible with traditional SSCC formulas under tidal currents due to its low density and low settling velocity. Furthermore, for estuarine areas with periodic tidal variations, existing formulas inadequately account for the dynamic variations in suspended sediment concentration (SSC) and hydrodynamic parameters. To address these issues, this study conducted a series of flume experiments on the SSCC of lightweight model sediment under tidal currents, accompanied by theoretical analysis and formula derivation. The results indicate that the suspension parameter of the plastic sediment ranged from approximately 0.6 to 0.8, demonstrating a strong flow-following capability. The optimal hysteresis time of SSC relative to current velocity was approximately 100 s; this hysteresis is jointly controlled by advective transport and local nonequilibrium adjustment, the latter referring to the finite-time response of processes such as sediment resuspension, settling, and vertical mixing near the measurement point. Based on the energy balance theory, an SSCC formula under tidal currents suitable for lightweight model sediment was derived. The SSCC was innovatively decomposed into a background SSCC and a dynamic SSCC: the background SSCC is maintained by the tidal-cycle-averaged hydrodynamics, whereas the dynamic SSCC adopts the half-tidal-cycle average as the dynamic equilibrium period to fully reflect the dynamic response between SSC and hydrodynamic parameters. The corresponding coefficients were calibrated using the flume experimental results, yielding a good correlation between the calculated and measured values.