Sediment Dynamics and Siltation Pattern in a Macrotidal Bay: A Case Study of Wuyuan Bay, China

Siltation in semi-enclosed basins is commonly ascribed to the combined action of horizontal entrainment, tidal filling/emptying, and density flow, yet the interplay among these processes complicates a mechanistic understanding of siltation in artificially modified macrotidal bays. In this study, Dyer’s decomposition method for suspended sediment flux (SSF) and end-member analysis (EMA) were applied, combined with in situ hydrodynamic, suspended sediment concentration (SSC), and surface sediment grain-size measurements. Using Wuyuan Bay (Xiamen, China) as a case study, we examined its sediment dynamics and siltation patterns from a tidal-cycle perspective. Results show that the contribution of density flow is negligible. A recirculating gyre, formed during flood and suppressed during ebb, creates flood–ebb velocity asymmetry and net landward sediment transport, producing a central siltation body (CSB) that accounts for 45% of the total deposition. Near the entrance, Eulerian residual transport (gyre advection) dominates, with a notable contribution from tidal pumping. Further landward, tidal pumping weakens and gyre-induced Eulerian transport prevails. Grain-size analysis and EMA decomposition reveal uniform sedimentary dynamic conditions in this zone, with flood-phase deposition averaging 83% of the total siltation.