Flow Pattern and Sediment Transport in the Tojingawa River Estuary

Suspended solids concentration, salinity, and velocity were observed in the Togami River estuary in northern Kumamoto Prefecture, Japan. The length of the estuary is about 11 km, and a compound channel made of clay and silt has been formed. Flow measurements were undertaken in a straight channel to investigate the effect of stratification on secondary flow in a well-mixed estuary. Flow velocity was measured using an ADCP. Salinity measurement was also carried out using a water quality monitoring sensor. The sedimentation density goes up on the flood plain in the vicinity of the low waterway shoulder at the ebb through the change in the direction of the crossing is small. The vertical direction change in the sedimentation density has become small oppositely high by the vicinity of the surface of the water in the near bottom. In other words, it is thought that floodplain sediments, not low channel sediments, are being rolled up and floating on the surface of the water. It is understood that the sedimentation transportation in the direction of the crossing is predominant in the cross-section. The measured data shows that the position of maximum flow velocity in the low-water channel convected downward on flood tides. Suspended sediment concentration profiles were very well-mixed both vertically and laterally. Salinity profiles showed a cross-channel salinity gradient has a sharp inclination than flood tides. The salinity profiles produce an effective transverse flow velocity distribution for natural compound channels.