Acoustic profiling of fine suspension concentration in the Changjiang Estuary

Vertical profiles of suspended fine sediment concentration, tidal current v elocity, and salinity were measured in May 1994 in the Changjiang Estuary. High resolution concentration profiles were obtained by using a 0.5-MHz aco ustic suspended sediment monitor. High temporal and spatial resolution acou stic profiling of fine suspension concentration provides both the instantan eous vertical profile of concentration, and information on the continuous d ynamic processes of fine sediment erosion, transport, and deposition. Calib rated acoustic images revealed 1) highly stratified suspensions, 2) resuspe nsion of the cohesive mud bed, and 3) re-entrainment of the near-bed high c oncentration suspensions by turbulent shear flow. Within the near-bed high concentration su!;pensions, two different frequencies of highly episodic re suspension processes were identified: high frequency resuspension, lasting a few seconds; low frequency resuspension, lasting a few minutes. The highe st concentrations, associated with low velocity and high salinity, were fou nd close to the cohesive mud bed. Lutoclines were persistent features durin g the measurements.