Turbulent bursting and sediment resuspension in hyper-eutrophic Lake Taihu, China

Abstract

Turbulent bursting plays a crucial role in sediment resuspension and transportation in many shallow lakes. This study analyzed the relationships between coherent structures and sediment resuspension in regions with and without intense wind waves in Lake Taihu. Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) were used to measure field data sets including flow velocities and intense wind waves respectively. The results showed that the intermittent bursting events contributed significantly to the processes of momentum and sediment exchanges. Turbulent bursting effectively controlled the three patterns of sediment suspension during the 512 s observation period. In the windy region, the bursting motions, i.e. “ejection” and “sweep” events mainly accounted for the Reynolds stress generation and made major contribution to sediment resuspension. While in the current-dominant region, turbulent mixing from inward and outward interactions overwhelmed other processes. The vertical sediment fluxes reduced by an order of magnitude due to the less effect of wind waves and the lack of upwelling currents. It is therefore important to study turbulent coherent structures and sediment resuspension to understand the spatio-temporal and frequency characteristics of bursting events.