Siltation Characteristics and Prediction for Continuous Pile-Supported Marginal Wharves in a Tide-Dominated Estuary

This study addresses the severe siltation issue prevalent at continuous pile-supported marginal wharves constructed in tide-dominated estuaries. By integrating multi-decadal measured bathymetric data with a high-resolution two-dimensional hydrodynamic-sediment numerical model, we systematically investigate the siltation characteristics, spatial distribution patterns, and underlying mechanisms. The results indicate that between 1998 and 2019, the volume of the deep channel in the South Port increased by over 20%. Concurrent northward migration of the main channel axis led to a 15%-20% reduction in nearshore flow velocity, significantly diminishing the flow's sediment transport capacity and establishing a hydrodynamic setting conducive to deposition. Following the wharf's construction, the dense pile clusters produced a pronounced flow-blocking effect, substantially reorganizing the velocity field within the harbor basin and adjacent waters. A widespread decrease in flow velocity was observed, with local reductions exceeding 0.8 m/s during peak ebb periods due to combined tidal dynamics and pile-induced resistance, directly triggering intense localized siltation. Spatially, siltation exhibited significant non-uniformity: along the wharf front, intensity followed a "high at both ends, low in the middle" pattern, while in the cross-shore direction, the area behind the wharf structure and in front of the mooring pontoon formed the core deposition zone, with an average annual siltation rate of approximately 1.7 m. Furthermore, slope instability of the excavated basin during the project's initial phase and the influx of near-bed high-concentration sediment induced by upstream dredging activities jointly exacerbated siltation. Monitoring data revealed that within three months after a dredging operation, the average siltation thickness in the basin reached 1.8-2.0 m, with a maximum exceeding 4 m. This study elucidates the complex siltation mechanisms associated with pile-supported wharves in tidal environments and provides a solid scientific basis for siltation prediction, mitigation planning, and maintenance strategy development for similar estuarine engineering projects.