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Oil spills are major threat to marine ecosystem and have long-lasting effect on marine life and water quality. In this study, a two-dimension hydrodynamic and oil spill transport model of the Yangtze River Estuary is established based on MIKE21 with a special attention to wind-wave-current interaction (WWCI). The model agrees well with the observed data on water level, current velocity, and the real oil spill event during Typhoon Fongwong. This study is mainly focused on the oil particle trajectory and spread. The model results show: (1) when the oil spill occurs during a typhoon period, the oil film can rapidly deposit under high WWCI, decreasing the swept area to about 20% compared with the normal weather condition; (2) strong current and large wave enlarge the oil film coverage whereas high wind speeds cause the oil particles to deposit in the shallow water area; and (3) the oil particles move farther and the swept area is far greater under the winter wind than under the summer wind, and the two times of the winter wind show the greatest effect on the oil spill. This study considers the drift, dispersion, evaporation, and emulsification of oil during the moving period under different wind, wave and current conditions, providing a good guidance for the oil spill prevention and mitigation in other estuaries. [ABSTRACT FROM AUTHOR]

The theoretical model for group-forced infragravity (IG) waves in shallow water is not well established for nonbreaking conditions. In the present study, analytical solutions of the group-forced IG waves at O(β1) (β1 = hx/(Δkh), hx = bottom slope, Δk = group wavenumber, h = depth) in intermediate water and at O ⁡ (β 1 − 1 ) in shallow water are derived separately. In case of off-resonance [β1μ−1 = O(β1), where μ = 1 − c g 2 / (g h) is the resonant departure parameter, cg = group speed] in intermediate water, additional IG waves in quadrature with the wave group forcing (hereinafter, the nonequilibrium response or component) are induced at O(β1) relative to the equilibrium bound IG wave solution of Longuet–Higgins and Stewart (1962) in phase with the wave group. The present theory indicates that the nonequilibrium response is mainly attributed to the spatial variation of the equilibrium bound IG wave amplitude instead of group-forcing. In case of near-resonance [β1μ−1 = O(1)] in shallow water; however, both the equilibrium and nonequilibrium components are ~ O ⁡ (β 1 − 1 ) at the leading order. Based on the nearly-resonant solution, the shallow water limit of the local shoaling rate of bound IG waves over a plane sloping beach is derived to be ~h−1 for the first time. The theoretical predictions compare favorably with the laboratory experiment by Van Noorloos (2003) and the present numerical model results generated using SWASH. Based on the proposed solution, the group-forced IG waves over a symmetric shoal are investigated. In case of off-resonance, the solution predicts a roughly symmetric reversible spatial evolution of the IG wave amplitude, while in cases of near to full resonance the IG wave is significantly amplified over the shoal with asymmetric irreversible spatial evolution. [ABSTRACT FROM AUTHOR]

• OpenFOAM-based numerical depth-varying wave-current flume is validated against analytical solution and experiment. • Adding vertical shear to uniform current enhances/weakens harmonic wave energy and triad interaction in following/opposing current. • The following current shear may contribute to premature wave breaking at a lower sea state than that with or without uniform current. • Wave steepness at which the current shear starts to affect the crest elevation is greater in deeper water than in shallower water. A Navier-Stokes solver in OpenFOAM® is combined with the Volume of Fluid (VOF) surface capturing method to investigate the wave interaction with depth-varying currents in intermediate and shallow waters. A special attention is paid to the separate effect of vertical current shear on near resonant triad wave interactions. It was found that in the presence of following vertical current shear, the wave exhibits a sharper crest and flatter trough, and the opposite is true in the presence of opposing vertical current shear. Our model results indicate that the wave steepness at which the current shear starts to affect the crest elevation is greater in deeper water than in shallower water. We found that adding vertical current shear to the uniform current further enhances the relative harmonic wave energy and the extent of triad interaction in the following current while weakens them in the opposing current. As a result, following and opposing current shear may cause wave to break at a lower and higher sea state respectively. Due to the increased wave nonlinearity in the presence of a following current shear, a linear superposition of the individual wave and current velocities is no longer adequate to represent the total horizontal velocity close to the free surface. [ABSTRACT FROM AUTHOR]

The fully coupled spectral wave and circulation model SWAN + ADCIRC was applied to investigate tide-surge and wave interaction in the Gulf of Maine during the extratropical storm on Patriot's Day of 2007. Significant tide-surge and wave interaction was found over Georges Bank and in the coastal areas. Over Georges Bank, the wave-induced current reached 0.2 m/s at the storm peak, accounting for 17 % of the total depth-averaged current. In Saco Bay, the current was dominated by wave-induced current with a magnitude up to 1.0 m/s during the storm. Two clockwise circulation gyres were found to form and sustain over a period of 26 hours during the storm in the bay. They were driven by spatial variations of wave height, direction and the resulting wave radiation stress gradient. Wave setup reached 0.2 m at the storm peak along the coast of Saco Bay. In Saco Bay, wave energy dissipation was reduced and wave height increased due to the increased water depth at high tide and surge. Therefore, wave height was modulated by tide and surge accordingly along the coast. As a result, wave setup and wave-induced current in the bay were also modulated by tide and surge. During the tidal cycle at the storm peak, wave setup increased with tidal level and the maximum wave setup coincided with high tide. [ABSTRACT FROM AUTHOR]

Second-order analytical solutions are constructed for various long waves generated by a gravity wave train propagating over finite variable depth h( x) using a multiphase Wentzel-Kramers-Brillouin (WKB) method. It is found that, along with the well-known long wave, locked to the envelope of the wave train and traveling at the group velocity Cg, a forced long wave and free long waves are induced by the depth variation in this region. The forced long wave depends on the depth derivatives hx and hxx and travels at Cg, whereas the free long waves depend on h, hx, and hxx and travel in the opposite directions at . They interfere with each other and generate free long waves radiating away from this region. The author found that this topography-induced forced long wave is in quadrature with the short-wave group and that a secondary long-wave orbital velocity is generated by variable water depth, which is in quadrature with its horizontal bottom counterpart. Both these processes play an important role in the energy transfer between the short-wave groups and long waves. These behaviors were not revealed by previous studies on long waves induced by a wave group over finite topography, which calculated the total amplitude of long-wave components numerically without consideration of the phase of the long waves. The analytical solutions here also indicate that the discontinuity of hx and hxx at the topography junctions has a significant effect on the scattered long waves. The controlling factors for the amplitudes of these long waves are identified and the underlying physical processes systematically investigated in this presentation. [ABSTRACT FROM AUTHOR]

The impacts of large-scale coastal structures on tidal dynamics have been studied extensively over the past decades, but the relevant mechanisms are not fully understood. In this study, a two-dimensional Delft3D barotropic tidal model is applied to investigate the tidal dynamic changes induced by the large-scale sequential constructions of Huanghua-Binzhou Harbor in the northeastern China during year 2003–2016. It was found that the predominant M 2 tide is increased on the stoss side and decreased on the lee side of the harbor by 2–6 cm due to the harbor constructions. This feature is due to 1) the increased and decreased potential tidal energy on the stoss and lee side, respectively, by the harbor structures; 2) the structure-induced changes in momentum flux is balanced by pressure gradient, and thus leads to a larger tidal range on the stoss side and a smaller tidal range on the lee side. The sensitivity studies on nonlinear M 4 tide demonstrate that it is generated locally by M 2 self-self interaction, which is not only related to M 2 tidal energy but also nonlinearity. Consequently, M 4 tide increases towards the shore on the tidal flat with natural slope due to enhanced nonlinearity by decreasing water depth, but is proportional to M 2 tide on the tidal flat with a constant water depth, where local nonlinearity is nearly the same in space. In addition, the energy transfer from M 2 to M 4 is affected by the structure-induced changes in nonlinearity, resulting in different responses of M 2 and M 4 tide to the coastal structure. • Numerically investigate the tidal dynamics changes induced by the large-scale sequential constructions. • Predominant M 2 tide increased on the stoss side and decreased on the lee side of the harbor jetties. • Structure-induced changes in current acceleration is balanced by the changes in pressure gradient. • M 4 tide is generated locally by M 2 self-self interaction, which is relative to M 2 tidal energy and local nonlinearity. • Three prominent separated bands of tidal energy density appear in the third harbor construction phase. [ABSTRACT FROM AUTHOR]

A mobile-bed sandbar-lagoon model was employed in a series of flume experiments to investigate the influence of vegetation with different densities over the sandbar on wave attenuation and bed profile evolution. Nineteen flume tests were carried out for the same sandbar-lagoon model under different conditions. Extensive analyses were conducted on the profile evolution and the wave parameters along the profile of the sandbar-lagoon system. Based on the weighted vegetation density by the canopy width, a new empirical relationship was established between wave attenuation and vegetation density, water depth and sandbar freeboard. It was found that wave attenuation increases with the rise of sandbar freeboard and weighted vegetation density, and decreases with the fall of incident wave height. The collision (s-shaped scarp) and overwash (upward concave scarp) types of fore-dune morphological evolution were observed in the experiments. The maximum erosion thickness of dune follows a quadratic polynomial relationship with vegetation density, indicating that too sparse vegetation cover may lead to more erosion. It follows that an optimal vegetation density may lead to the least wave reflection due to the quadratic polynomial relationship. However, when the maximum erosion thickness of fore-dune is small, the quadratic polynomial relationship becomes linear. Furthermore, the experimental results indicate that wave height, water depth, sandbar freeboard and vegetation density are all important contributing factors to the morphodynamic evolution of sandbar-lagoon system with emergent vegetation. These relationships promote the development of wave-vegetation-sediment mechanics and provide a scientific guide to carry out coastal ecological restoration projects, especially in the sandbar-lagoon system. • A new empirical linear wave decay model is developed for a vegetated sandbar-lagoon system. • A quadratic polynomial relationship between wave reflection and vegetation density is shown. • A linear dependence of wave transmission or wave dissipation on vegetation density is depicted. • Two regimes of dune erosion are identified, collision and overwash. • A quadratic polynomial model for the maximum erosion thickness of fore dune is presented. [ABSTRACT FROM AUTHOR]