Hideo Oshikawa

RESPONSE CHARACTERISTICS OF SUSPENDED SOLIDS IN NERITIC REGION IN INNER BAY

In recent years, research on the behavior of suspended solids (: SS) in coastal areas has been carried out. However, physical and chemical characteristics of SS have not been understood sufficiently since such SS consists largely of fine cohesive particles. In order to reveal the properties, effects of surface waves, currents and turbulence on SS were investigated by using in-situ data in the neritic region, Isahaya Bay, Ariake Sea which is a typical enclosed sea in Japan. A multiple regression analysis was performed in order to understand the phenomena affecting SS. In this study, turbidity was used for the analysis instead of SS because it is difficult to measure SS continuously. The multiple regression analysis revealed that wind waves in the bay were extremely important for the turbidity, and turbulent energy, sum of each mean square of velocity fluctuation eliminating surface wave components, and mean velocity or mean sea level variation contributing to tidal current were also slightly related to the turbidity.

Residual Currents Around Plural Asymmetrical Structures in Oscillatory Flow Fields

In the resent years, water deterioration by pollution in a stagnant sea area like a semi-enclosed bay occurs mainly due to the lack of water exchange with the open sea. [KYG97] suggested to use unidirectional residual currents generated by asymmetrical structures which are put on the sea bottom in order to activate substance transport in a tidal field. In addition, [KSK01] also proposed to apply this method to control sediment transport in wave fields. [KHF06] proposed the specific pipe called One-Way Pipe, which can generate residual currents in a wave field by a number of asymmetrical structures set inside the pipe. It is expected to activate water exchange with the open sea by putting a series of One-Way Pipes from the inside end of the bay to the baymouth.

Control of Substance Transport Using Submerged Asymmetrical Structures in Wave Fields

Fairways can be maintained using the “Beach and Navigation Keeper: BaNK system” to cope with shoaling of fairways and beach erosion. The system is a method for controlling sediment transport with plural submerged asymmetrical structures called BaNK blocks that generate residual currents from wave motions. In order to assess effectiveness of the system, its application for a preventive measure against the shoaling of a fairway was tested in a laboratory experiment. In this research, plural half cylinders were used as the BaNK blocks which were set on the bottom of a wave tank, and kaolin was used to create fluid mud. The results of this experiment showed that the BaNK system could reduce 92% of the intrusion of the fluid mud into the fairway on average and, therefore the efficiency of the system to keep the fairway was considerable.

AN OUTLINE OF THE FLOOD DISASTERS IN THE SEADAI RIVER IN JULY 2006 AND THE REVIEW OF FLOOD CONTRORL BY DAM OPERATION

Recently, a heavy rainfall in a short period of time occurs often and causes severe damage from a flood in various regions. The heavy rainfall due to the Baiu front gave severe damage to the southern region of Kyushu Island from July 19 to 23 in 2006. In this paper, an outline of flood disasters for the Sendai river basin in Kagoshima Prefecture from this heavy rainfall was reported. Furthermore, an improvement of the flood control operation of Tsuruda Dam in Kagoshima Prefecture was considered. By introducing the improved operation technique, it is expected that the flood control of Tsuruda Dam works well not only under usual flood conditions but also under unexpected heavy flood conditions.

DEPTH-AVERAGED MODEL OF DIFFUSION AND DEPOSITION OF SETTLING PARTICLES WITH CONSIDERATION FOR TRANSITION OF VERTICAL PROFILE

Diffusion and deposition of sediment in a sea area have caused serious problems in various situations. Thus, it has been required to predict the distribution of the sediment more accurately to takesteps.For horizontally large flow fields having particle sources with well-mixed cross sections, we had proposed the depth-averaged model for diffusion and deposition of settling particles by adopting the result of the numerical research by Jobson and Sayre (1970). In this paper, we improved this model to be adaptable to a flow field having a particle source near a water surface or a bottom region. In addition, the new model was applied to simulate the distribution of the sediment generated by the reclamation in Kawatana Port.As a result of this research, it was confirmed that the present model would make it possible to predict a more accurate distribution of sediment in a nearly-plane sea area.