Session1: River Engineering and Management
Title: FLOW STRUCTURE AND SEDIMENT TRANSPORT IN ESTUARY: A CASE STUDY OF THE TOJINGAWA RIVER, JAPAN
Ryuichi Hirakawa, Terunori Ohmoto
Observations of suspended sediment concentration, salinity and current were made in the Tojingawa River estuary, Northern Kumamoto prefecture, Japan. The estuarine reaches are approximately 11 km in length, and are formed a compound channel by clay and silt. Flow measurements were undertaken in a straight part to investigate the effect of stratification on secondary flow in well-mixed estuary. Flow velocity was measured using an ADCP. Salinity was also carried out using a water quality monitoring sensor. The sediment concentration goes up on the flood plain in the vicinity of the low waterway shoulder at the ebb though the change in the direction of the crossing is small. The perpendicular direction change in the sediment concentration has become small oppositely high by the vicinity of the surface of the water in the vicinity of the bottom. That is, it is thought that sedimentation on not low-water channel's sedimentation but the flood plain is rolled up, and it is floating in 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 have a sharp inclination than flood tides. The salinity profiles produce an effective transverse flow velocity distribution for natural compound channels.