DEVELOPMENT OF TFIE METHOD FOR MAINTENANCE OF WATER ROUTE FRONT OF DISCHARGE GATE LINES ON ARIAKE SEA COAST

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Concerning to maintain the water route in front of discharge gate setting at land reclamation, the effective methods are said to remove the mud deposit by flash water, and/or erode by the screw of the fishing boat. Thus, to obtain the basic aspects for developing the water route maintenance system, the field survey for the mechanism of the mud accumulation was carried out, then the experiments were attempted to analyze following items, 1) the erosional and depositional behaviors of fine sediments, 2) the change of critical erosion rate of mud according to dead weight consolidation and 3) the characteristics of the erosional rate by a screw of boatIn the bottom area of Ariake bay, Nanaura tidal land in Saga prefecture, the deposition rate of mud at water route region was measured as about 5cm/day, when the water was not discharged from the gate.The experiment using Ariake clay with sea water in the annular rotating channel elucidated the change of water contents, the cohesion and the critical erosional rate of the clay during 72hr after the dead weight consolidation occurring. In addition, the vertical distribution of water contents ratio was also revealed in mud area. In this experiment, the progress of consolidation by passing time was obviously shown as the change of water content ratio at 10cm depth from the bottom level; 900% at the beginning time subsequently turning to 540% and 300% after 6hr and 72hr, respectively.The flow characteristics caused by rotating of a screw were accountable with the Jet theory, and revealed its action against the bottom. As the axis velocity of flow was decayed with distance from screw -1 powers, the flow rate on the bottom was widen according to Gaussian distribution.The results obtained in this experiment were new and believed to contribute to develop the water route maintenance system.