In Osaka prefecture, the artificial reefs with a stirring and enhancement of feed culture function were located in the sea bottom to promote vertical mixing and attempting to reduce the occurrence of hypoxic water mass. Those artificial reefs were verified their current control function. Also, the extent of occurrence of upwelling, eddy current and biological effect have been quantitatively evaluated in actual marine area. In this research, we focused on the spread of turbidity with occurrence of upwelling and eddy by artificial reefs which have a controllable function against the flow from multiple directions. In order to verify the current control function of artificial reefs, we attempted a new observation method of the two-dimensional cross-stion which combines the turbidimeter and ADCP.
 We visualized the turbidity distribution around the artificial reefs using that method. Also, we have conducted the field research of fish aggregation and fouling of prey abundance around the artificial reefs. The result of that, it was confirmed a group of Japanese horse mackerel (Trachurus japonicas), Chicken grunt (Parapristipoma trilineatum) and Japanese anchovy (Engraulis japonicus) on the in the rear (downstream side) of the artificial reefs. Also, by continuing the investigation, the quantity of fish aggregation and adhered prey abundance were increased and stabilized.
 This current control function would contribute importantly to provide preferable habitat for marine resources by improving marine environment.

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 Numerical analysis of flow field during the drop of a sealed bucket in dredging works were carried out using a numerical model that can compute dynamic interaction between the flow and bucket to demonstrate its predictive capability against experimental results and determine the optimal operation of the bucket for reducing the generation of turbidity. Numerical results showed that suspending the drop operation can reduce the effect of a vortex formed over the bucket, and a decrease in the drop speed after the suspension can reduce the velocity of jet flow under the tip of the bucket. From these results, it was found that the suspension of the drop operation and the decrease in the following drop speed can reduce the maximum bottom flow velocity and thus would be effective to reduce the generation of turbidity.

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 Introduction of the renewable energy needs to be strongly carried out, in order to avoid too much dependency on nuclear power generation, and to promote for discharge reduction of greenhouse gas. As Japan has large ocean exclusive economic zone (EEZ) compared to small land area, Japanese ocean renewable energy potential is important. Up to present, among various ocean renewable energy potential, ocean wind-generated electricity is supposed to be the most practical one to be realized in near future. This session introduced various field study in Japan aiming for offshore wind farm construction, and discussed on future problems to be solved.

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 A huge tsunami generated by the Great East Japan Earthquake caused drastic changes of coastal environments and ecosystem. It is necessary to clarify the long-term trends of water quality and ecosystem in coastal areas after the above huge tsunami. For this, the special session titled “Variations of coastal environments due to the Great East Japan Earthquake” was held to discuss field studies for the variations of coastal environments and ecosystem due to the tsunami. Importance for continuous and long-term monitoring of coastal environments and advanced numerical models for bed deformation are discussed.

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