Abstract
The current pattern and suspended sediment dynamics in the meandering channel of the Chikugogawa estuary were investigated. A secondary current was observed in the upstream region of the curve when the turbidity maximum migrates landward during a flood tide, and the suspended sediment concentration near the bottom increases at the inside of the curve. A fluid mud layer with a maximum velocity of 0.4 m/s was formed at the inside of the curve. The maximum thickness of the mud layer increased to 1.3 m during a flood tide, and it remained 0.2 m after three tidal cycles. Because the settling velocity of the suspended particles, as estimated by the Rouse equation, was higher than the theoretical velocity for a single mineral, particles collide and flocs are formed. The relationship between the pick-up rate of the bottom sediment and the shear velocity indicates reduced sediment erodibility during an ebb tide. Fine sediment processes in an estuarine channel could be explained as follows: suspended sediment is transported to the inside of the curve and settled sediments form fluid mud during a flood tide, following which the particles consolidate over the course of several hours and the pick-up rate reduces during an ebb tide; the morphological evolution of the river bed occurs at a semi-diurnal scale.
