FIELD MEASUREMENT ON THE TURBIDITY MAXIMUM MOVEMENT IN THE CHIKUGOGAWA RIVER ESTUARY AND THE ARIAKE SEA

Abstract

Intensive field measurements of the turbidity maximum movement were undertaken in the Chikugogawa River mouth estuary and tidal flat. The estuary has two channels - the main channel and a subchannel called Hayatsuegawa. The vertical profiles of the suspended sediment concentration (SSC) and salinity were measured at 20 stations along the Chikugogawa River course. The current profile was monitored by ADCP at six stations. The SSC and salinity are highly correlated; the SSC growup in front of the salt-wedge maximum concentration. A significant relationship is observed between the SSC and bottom shear stress at the upstream stations, but there is no correlation at the downstream stations along the main channel. The suspended sediment loads on the tidal flat and in the upstream channel are much higher during flood tides; on the other hand, the main channel discharges the suspended sediments into the sea. These facts suggest that the turbidity maximum occurs on the tidal flat, and the suspended particles intrude into the Hayatseugawa channel. Further, since these intrusions run up to the upstream channel, the suspended particles settle on the upstream bed as well.