Numerical Modelling Of Sediment Transport In An Artificial Reef Area

As an important part of modern marine pasture construction,artificial reefs will have a certain impact on the natural sea area current field environment,and will also change the erosion and deposition process of the bottom bed sediment.It is of great significance to study the current field environment and the effect of seabed scour and deposit in the artificial reef area under natural sea conditions to analyze the physical stability and ecological effects of artificial reefs.Based on the unstructured grid,the three-dimensional ocean numerical model FVCOM and its sediment model using the finite volume method are used to study the east China Sea tidal current numerical model with the artificial reef area of Ma?an archipelago as the main research area.The grid is well represented in the model grid with a higher resolution.The effect of the artificial reef on the current field and sediment activity in the surrounding sea area was calculated by the method of approximating the reef to a closed,non-permeable solid,and subtracting the water depth of the corresponding reef height.Besides,experimentally simulated the artificial reef hill and it's application.The tidal level and current velocity and directions and the sediment concentration data of several observation sites in the Ma?an archipelago are used to verify the calculation results of the model tidal current field.The verification results show that the tidal level verification accuracy is higher,the flow direction verification result is better than the flow velocity value,and the precision is good,can be used as the basis for the calculation of the sediment field.Through the determination and test of the sediment parameters in the model,the suspended sediment concentration of the five sites was measured during the period of spring and neap tides,in surface layer,0.6H and the bottom layer.The average value of the relative error is less than 15%,indicating that the simulation of the sediment field reaches a certain precision.According to the model calculation results,the difference between the surface and the bottom current velocity distribution of the artificial reef area during the period of spring and neap tide,and the comparison of the presence or absence of artificial reefs were analyzed.The results of tidal field,suspended sediment concentration,seabed thickness analysis indicate that the sediment transport in the artificial reef area of Shengshan and the artificial reef hill of Huangjiao are mainly affected by the tidal current.The difference of suspended sediment concentration caused by artificial reef is within ±0.015 g/l,the thickness of the bed is varied within ±1 m.The impact of artificial reefs on seabed erosion and deposit ranges from 30 to 100 m,and is basically unaffected by more than 100 m away from the reefs area.For the construction of marine pasture in artificial reef areas,the current field changes caused by artificial reefs and sediment erosion,suspension,transport,deposition and other processes are local processes,and for larger areas around the sea,within the longer time range,the influence range of the erosion and deposition is relatively small,and the thickness of the seabed layer will also tend to be stable.