As a typical ecological engineering structure, oyster reefs can weaken wave energy while providing ecological restoration functions, serving as an important component of nature-based coastal protection solutions. This study systematically investigated the wave attenuation characteristics of two types of oyster reefs—hemispherical and cage structures—through physical model experiments in a wind-wave-current flume. A total of 43 test conditions were designed for the hemispherical reef experiments to analyze the influence of relative crest freeboard, wave steepness, and reef width on the transmission coefficient. Results showed that the transmission coefficient decreases as the relative crest freeboard increases. When wave steepness exceeds a certain threshold, the transmission coefficient becomes more sensitive to changes in wave steepness. Based on the experimental data, an empirical transmission coefficient formula for hemispherical oyster reefs under regular waves was fitted. For the cage reef experiments, the empty flume control method was employed to analyze the spatial wave height variation under different filling rates. It was found that, under the deeply submerged condition, higher filling rates result in more significant wave attenuation, and the roughness dissipation effect of the reef structure is more pronounced under the deeply submerged condition than under the shallowly submerged condition. The research findings can provide experimental evidence for the configuration selection and parameter optimization of wave attenuation units at the front of coastal ecological seawalls.

The nonlinear interaction between storm surge and astronomical tide controls coastal flood levels in macrotidal regions, but the effect of tidal phase on the surge of a given typhoon is rarely quantified. Using a high-resolution MIKE 21 FM model of the East China Sea forced by ERA5, we hindcast the storm surge of super typhoon Bebinca (2024), which made landfall at Shanghai. Tidal RMSE at four gauges is 0.11–0.37 m and surge RMSE is 0.11–0.24 m. The surge evolved from pressure-dominated offshore setup to wind-dominated nearshore setup and then to slow shallow-water decay, reaching 2.0–2.5 m in the Yangtze River Estuary and northern Hangzhou Bay. Keeping the typhoon forcing identical, we shifted the open-boundary tide by ±6 h. The two shifted cases differed by 0.5–0.9 m in total water level at landfall, but by less than 0.1 m in surge, so that difference was the tide itself. Relative to the baseline, in which landfall nearly coincided with high water, both shifted cases lowered the landfall surge by about 0.9 m on the northern coast of Hangzhou Bay and by about 0.7 m at the Yangtze River Estuary peak. Between the shifted cases, surge differed appreciably only at the bay head, by up to about 1 m before landfall.

Artificial seawater lakes constructed in estuarine environments are highly susceptible to the intrusion of water containing high concentrations of suspended sediment, which can degrade water quality and threaten ecosystem stability. To clarify the settling mechanisms and sedimentation efficiency under high-turbidity conditions, this study investigated the Baishawan Artificial Lake in the Jiaojiang Estuary, eastern China, through field observations, controlled still-water sedimentation experiments, and a multi-particle size sedimentation efficiency model. Field measurements revealed significant spatiotemporal variability in suspended sediment concentration (SSC), with higher SSC during spring tides than neap tides and a spatial gradient decreasing from the near-estuary zone to the artificial lake and offshore waters. Grain-size analysis showed that suspended sediment was dominated by clay and silt (>98%). Laboratory experiments indicated a two-stage settling process characterized by rapid initial sedimentation followed by gradual stabilization; under high concentration (1.32 kg/m³), SSC decreased by about 85% within 40 min due to concentration-enhanced flocculation, whereas under low-concentration conditions (0.24 kg/m³) approximately 14 h were required to reach the target concentration of 0.01 kg/m³. Model validation demonstrated that the multi-component sedimentation model effectively reproduced the temporal attenuation of SSC. Model application further suggested that when the initial SSC was 0.70 kg/m³ and the water depth was 5.7 m, the sedimentation tank could reduce the SSC to 0.01 kg/m³ within about 16–17 h, with an estimated annual sedimentation volume of ~65,000 m³ and a recommended dredging interval of five years. These results provide quantitative guidance for sedimentation tank operation and sediment management in estuarine artificial lakes and other high-turbidity coastal environments.