Sedimentological study of sedimentation and dispersion processes of red soils in coastal areas of the Okinawa Island.

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Sedimentation and dispersal behaviors of terrigenous red soils were investigated in both east coast and west coast of the Okinawa Island to study the method to prevent the soil pollution of coral reefs. Spatial observation of dispersal patterns in over-lying waters and bottom sediments was made. Also, time-series observation, using a mooring system of current meter, turbidity meter, and sediment traps, were made particularly in the estuary area adjacent to coral reefs. Measurements of in situ settling velocity of red soils were attempted using a special device of measurement equipment using turbidity meter. Results show that the in situ settling velocity becomes faster with the increasing salinity due to the flocculation effects of fine-grained red soils.