Study On Impacts Of Offshore Artificial Islands Cluster's Construction On Scouring-Deposition Features In Longkou Bay

With the rapid development of local economy, Longkou City has been playing a leading role in the county-level economy in Shandong Province. However, because of the highly density of industries in the industrial region nearby the port and the limitation of land area, the sustainable development of regional economy is severely restricted. Therefore, an offshore artificial Islands cluster is to be constructed to enlarge the developing space and ensure the continual increase and sustainable development of the economy.The construction of the Islands cluster will definitely cause changes in the flow field as well as scouring-deposition features in Longkou Bay, and hence a new cycle of geomorphic evolution. In this paper, to scientifically predict the impacts of the construction on the scouring-deposition features and geomorphic evolution in the bay so as to provide some theoretical bases for planning and design of similar engineering projects, the flow field in Longkou Bay and adjacent sea area was established to carry out simulation calculation on the characteristics of flow field before and after the construction and the characteristics of scouring-deposition features under various typical wind conditions. In the calculation, MIKE 21 numerical model was applied on the basis of the past data of water depth, topography, hydrology, meteorology, sediment, wind, etc, in the Bohai Sea Area and Longkou Bay. As the result of the numerical calculation, the evolution of seabed topography due to construction of artificial Islands cluster was analyzed. The CERC formula recommended in "Shore Protection Manual"(SPM)of USA was applied to calculate the variation in long-shore sediment discharge rate in the southeast of the artificial Islands cluster, and furthermore the evolution of coastal topography due to construction of artificial Islands cluster was also analyzed.The numerical model of flow field established in the paper proved consistently matched with actually-measured data. After the construction of artificial Islands cluster, the tendency of food tide and ebb tide is consistent with the current situations on the whole, but the current velocity and direction in the adjacent sea area of the artificial Islands cluster varied to different degrees. In the north of the sea area, they varied the most significantly; in the southwest and northwest of the sea area, they varied relatively significantly; in Longkou Harbour, they varied insignificantly.According to the results of the numerical simulation, after the construction of the artificial Islands cluster, deposition will increase under various typical wind conditions in the northern sea area, especially along the southwestern side of the principal channel; due to actions of trajectory flow, the western sea area will be severely eroded at that time instead of being slightly deposited or slightly eroded for the time being; deposition will increase considerably under the calm wind condition, remain basically the same as the current situation under the northwestern wind condition, and increase relatively severely instead of being eroded for the moment under the southwestern wind condition.After the construction, the submarine geomorphic evolution in Longkou Bay can be listed as follows:a scouring area will be formed in the western sea area with annual erosion maximum depth of about 0.3 meters; four deposition areas will be formed in the northern and southwestern sea areas as well as the artificial waterway openings with annual maximum deposition thickness of above 0.05 meters; the primitive isolated reef in the sea area will disappear subsequently. The coast geomorphic evolution can be listed as follows:the northern section of artificial Islandss will reach an equilibrium state; the artificial waterway section between Islandss and mainland will be in a strong deposition state; in the south coast of the Jie River, the section which state in the wave shadow area, its degree of erosion will be greatly eased, while the section state out of the wave shadow area, its degree of erosion will be increased to some extent.