Numerical Investigation On Hydrodynamic Characteristics Of Plant-seawall Combined System Under Wave Action

With global climate change and increases in sea level,the erosion rate of the coast is greatly accelerated,it is necessary to implement protection engineering in coastal areas,coastal hard protection combined with soft protection is usually applied to achieve the best effect of coastal protection.With the promotion of the concept of ecological revetment,the combination of coastal vegetation and seawalls becomes an up-and-coming coastal protection measure.The hydrodynamic characteristics of waves interacting with seawalls after passing through the vegetation zone are different than those without plants,it is necessary to carry out research on wave hydrodynamic characteristics of the "plant-seawall" system and the findings can provide reference for the construction of coastal projects.In this paper,the nonhydrostatic model NHWAVE is used to systematically study the effects of emergent rigid vegetation patch on hydrodynamic characteristics of seawall under wave action.The main results are as follows:With regard to the hydrodynamic characteristics of the "plant-seawall" system under the action of regular waves,this section focuses on wave height attenuation induced by vegetation patch,the flow characteristics around the vegetation zone and the wave run up influenced by emergent vegetation.When Stokes wave interact with vegetation patch,the normalized wave height attenuation follows the laws proposed by Dalrymple,but the actual value of the damping factor is larger compared with the result calculated by linear theory due to wave nonlinearity.Boundary effects of the vegetation belt reinforced with the increase of incident wave height and vegetation density.The maximum wave run up increases with the incident wave height and wave period,but the sensitivity of the maximum run-up influenced by the increase of wave height reduces due to more energy dissipated in the vegetation zone.With regard to the hydrodynamic characteristics of the "plant-seawall" system under the action of solitary waves,this section focuses on the waveform characteristics,the energy of the water body and spatial distribution characteristics of the overtopping flow on the crest of the seawall.Results indicate that the wave energy attenuation rate increases with vegetation density and width.The overtopping layer thickness and flow velocity on the crest of seawall vary monotonically with the vegetation density and width.As wave nonlinearity increases,influence of vegetation density and width on the overtopping layer thickness is gradually enhanced at the frontal side of the seawall,but weaken at the rear side.The maximum overtopping layer thickness on the rear side of the crest is almost half of the frontal side.For large incident wave height,although the influence of vegetation on the relative velocity distribution of overtopping flow is limited,the relative current velocity is greater than that without vegetation.Meanwhile,the maximum current velocity on the rear side of the crest is about 1.6 times of the frontal side.