China is one of the countries that is most seriously affected by storm surges. In recent years, storm surges in coastal areas of China have caused huge economic losses and a large number of human casualties. Knowledge of the inundation range and water depth of storm surges under different typhoon intensities could assist predisaster risk assessment and making evacuation plans, as well as provide decision support for responding to storm surges. Taking Pingyang County in Zhejiang Province as a case study area, parameters including typhoon tracks, radius of maximum wind speed, astronomical tide, and upstream flood runoff were determined for different typhoon intensities. Numerical simulations were conducted using these parameters to investigate the inundation range and water depth distribution of storm surges in Pingyang County considering the impact of seawall collapse under five different intensity scenarios (corresponding to minimum central pressure values equal to 915, 925, 935, 945, and 965 hPa). The inundated area ranged from 103.51 to 233.16 km² for the most intense typhoon. The proposed method could be easily adopted in various coastal counties and serves as an effective tool for decision-making in storm surge disaster risk reduction practices.

Results are presented from a numerical simulation to investigate the vertical buoyant wall jet discharged into a linearly stratified environment. A tracer transport model considering density variation was implemented. The standard $k\text{-}ϵ$ model with the buoyancy effect was used to simulate the evolution of the buoyant jet in a stratified environment. Results show that the maximum jet velocity trend along the vertical direction has two regions: acceleration and deceleration. In the deceleration region, jet velocity is reduced by the mixing taking place between jet fluid and ambient lighter fluid. Jet velocity is further decelerated by the upward buoyant force when ambient fluid density is greater than jet fluid density. The normalized peak value of the cross-sectional maximum jet velocity decreases with $\lambda$ (the ratio between the characteristic momentum length and the buoyancy length). When $\lambda <1$ , the dimensionless maximum penetration distance (normalized by the characteristic buoyancy length) does not vary much and has a value between 4.0 and 5.0, whereas it increases with increasing $\lambda$ for $\lambda \ge 1$ . General good agreement between the simulations and measurements was obtained, indicating that the model can be successfully applied to investigate the mixing of buoyant jet with ambient linearly stratified fluid.

This study evaluates the effectiveness of artificial Kandelia obovata forests in wave attenuation through physical model experiments conducted in a wave flume. The experiments meticulously replicated real-world hydrodynamic conditions and mangrove movement responses using the principles of gravitational and motion similarity, with a scaled 1:10 model of Kandelia obovata. Our approach included comparative experiments against a 1:100 gradient concrete slope to isolate the effects of seabed friction and flume wall reflections. The wave height was measured using strategically placed wave gauges. The findings indicated that the artificial Kandelia obovata forests significantly attenuated waves, with a decrease in the total attenuation capacity as the water depth increased from 2.75 m to 3.28 m under both regular and irregular waves. The elastic mangrove model with a canopy effect led to a 15% increase in wave attenuation over cylindrical models. Predictive models using multivariate nonlinear regression and back propagation neural networks showed that the latter provided a superior accuracy in estimating wave transmission coefficients

Salt marshes are declining due to the dual pressures of coastal erosion and land reclamation. However, there remains a lack of quantitative analysis regarding this reduction process and its driving mechanisms. This study examines the dynamics and influencing factors of salt marsh vegetation along the eroding coastline of Sheyang County, Jiangsu Province, China, between 1985 and 2020, using remote sensing to analyze changes in artificial coastlines, water boundaries, vegetation front edge, and its topography. Our results showed an extensive seaward movement of artificial coastlines due to reclamation, coupled with severe reductions in salt marsh area and width. Coastal erosion further caused a 10.5% decline in vegetation elevation and a 46.7% increase in slope steepness, amplifying vulnerability to wave action. Native species were largely replaced by Spartina alterniflora, reducing ecological diversity. Currently, human pressure on the landward side has been alleviated; thus, addressing coastal erosion is vital to preventing the further loss of salt marshes. Sediment retention engineering and native vegetation restoration efforts can gradually facilitate the recovery of salt marshes. This study provided critical insights for sustainable coastal management under bidirectional pressures.

The coupling interactions between flood propagation, sediment transport, and river morphology in alluvial rivers are mathematically described by the high-order dynamic wave model. The coupling capability of currently used dynamic wave models is systematically conducted. The results indicate that the propagation of a dynamic flood wave only depends on the Froude number, but is independent of the coupling of sediment transport and river mobility. Furthermore, based on the continuum hypothesis, the dynamic equations describing the motion of the active bed layer are obtained. A renewed dynamic wave model is established. Four families of asymptotic solutions to the eigenvalues of the renewed four-order hyperbolic system are obtained by means of the singular-perturbation technology. The results demonstrate that the interactions between flood propagation, sediment transport, and riverbed mobility are coupled. Propagation of the main dynamic flood wave and the dynamic sediment wave will be slower with the increasing deposition rate, but will be faster when the erosion intensity is enhanced. These mainly occur in the lower flow regime. In the process of deposition, the second dynamic flood wave and the dynamic bed wave will propagate both upward and downstream. Besides, the dynamic bed wave will propagate downstream and the second dynamic flood wave will only propagate upstream, regardless of the flow regime.