Numerical Study For Wave And Wave-induced Current In Vegetation Waters By The Boussinesq Equation

When Waves and current act directly on the beach,they may cause beach erosion or even threat coastal buildings and people's lives and property.At present the beach protection mainly take two methods,the traditional engineering revetment and plant revetment.The traditional engineering revetment generally uses concrete,riprap,masonry and other material,so it will cause a certain degree of damage,affecting the coastal ecological environment.As a new way of revetment,plant revetment can not only eliminate wave blocking,product silt beach,but also maintain the balance of ecosystems and hydrodynamic systems to improve the coastal ecological environment.Wave can be attenuated and wave energy can be reduced in the coastal vegetation waters,due to the dissipation of vegetation.And plant can reduce the impact of broken waves;at the same time,when the waves are broken,vegetation will be a certain degree on the reduction of offshore wave-induced flow intensity,playing an important role on siltation revetment.Therefore,it is of great significance to study the propagation and deformation of waves in coastal vegetation waters.In the paper,vegetation effects on coastal wave propagation are numerically studied by using fully nonlinear Boussinesq Model.The model is based on the implementation of drag resistances due to vegetation in the fully nonlinear Boussinesq equation where the drag resistance is provided by the Morison's formulation for structures induced drag stresses.The model was used to test the effects of vegetation parameters,water depth,incident wave parameters and submergence degree on wave attenuation.Then we concluded as follows.(1)With the increase of incident wave height,relative wave height values decrease approximately in a negative logarithmic form.But when the incident wave height is very small,the wave height change is no longer obvious.(2)The wave height attenuation due to vegetation for wave with smaller period increases with the increase of wave period,but as incident period increases to a certain value,this shows a reverse trend for wave with bigger periods.In a word,the effect of wave period on wave energy attenuation due to vegetation is complicated and not a simply monotonic relation.(3)With the wave period constant,the wavelength becomes larger when the water becomes deeper.The effect of vegetation in wave energy dissipation on the longer wave is significantly less than that of the shorter wave.And with the decrease of origin water depth,relative wave height value decreases mainly in the negative exponential form.(4)The attenuation effect of the whole vegetation is the best,but the discontinuous vegetation field for the same number of plant,the attenuation effect of the wave is close to the whole vegetation.The vegetation patches on the back and sides of the discontinuous vegetation model will increase the decay effect of wave to a certain extent.(5)The main effect of the vegetation is to provide increased energy dissipation through the plants.That can also act as a blockage to the swash flow over the mounds.This damping and blockage Effect influenced the mound–channel interaction,which affected the wave transformation and recirculation currents over the domain.