Behavior of fine sediment and its effect on the formation of hypoxia in estuaries.

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In conventional manuals for river improvement works, in which ordinary river channels are taken as a standard object of planning, do not refer to the special aspects of the estuarine part of downstream reaches. In this research, aiming the future reform of the standard of river improvement works, hydraulic factors related to the fine sedimentation in estuaries are investigated in downstream reaches of some rivers whose hydraulic characteristics are different from one another.In Tone River Estuary, suspension of fine sediment was measured in the salt wedge by using some up-to-date measurement techniques including acoustic turbulence measurement, and the effect of fine sediment on the formation of hypoxia in the head of salt wedge was estimated. In Oppa Bay, where Kitakami River flows in, the deterioration of bay water by the effect of river freshets containing a lot of fine sediment was investigated through field observation and satellite image analysis. In Takase River Estuary, the effect of bed topography, especially of shallow area made by the deposition of fine sediment, on the salt water intrusion was estimated by field measurements and numerical simulation.