Experimental Study On The Effect Of Coastal Rigid Vegetation On Local Scour Around A Vertical Breakwater Subjected To Solitary Wave

In order to resist the destruction of tsunami on the human life in the coastal areas,vertical breakwater and other coastal protective buildings were constructed.But in fact it often brought immeasurable damage when tsunami occurred.Vegetation revetment method not only benefited to protect bank and damp waves,but also had certain ecological values as a new type of bank revetment.In this paper,the effect of coastal rigid vegetation on local scour around a vertical breakwater subjected to solitary wave was analyzed based on a variety of incident wave heights,cross-shore vegetation width and density,breakwater height.Moreover,the cross-shore wave height variation,wave uprush and backwash over the breakwater,as well as the scour patterns around the breakwater were measured and recorded,and the wave height in front of the breakwater was analyzed to explain the local scour around the breakwater.A series of laboratory experiments was conducted to investigate the relation between dsmax/d or ddmax/d and solitary wave,vegetation,breakwater.Based on a large number of experimental data,the empirical calculation formula was fitted for local scour of vertical breakwater.The wave height in front of the breakwater influenced by factors mentioned above was analyzed to explain the discipline of local scour around the breakwater.Draw the conclusions as follows:(1)When vegetation existed,the maximum local scour depth behind the breakwater reduced significantly;the erosion seabed profile in front of the breakwater appeared to be double-peak shape in contrary to the single-peak L shape eroded profile in absence of vegetation;the erosion in front of the breakwater occurred at the location more close to the vegetation and the extent of the scouring was enlarged as well.Both the maximum local scour depth and deposit height around the breakwater increased notably with the decreasing vegetation width and density when the incident wave height was small.However,the influences of vegetation width and density became insignificant when the wave height increased.(2)The wave height in front of the breakwater increased with the decreasing vegetation width and density.And the higher the incident wave height was,the more the wave height in front of the vertical breakwater was less sensitive to the change of vegetation width and density.The wave height in front of the breakwater decreased with the decreasing of the breakwater height,and the wave height in front of the breakwater was less sensitive to the change of the breakwater height beyond a certain range.Finally,some guidelines were provided in view of the reasonable arrangements of vegetation belt in the practical projects,which had some significances in protecting embankment from erosion and failure.