Differentiating the effects of advection and resuspension on suspended sediment concentrations in a turbid estuary

Suspended sediment concentration (SSC) has a significant impact on the estuarine environment and its morphological evolution. At any given location, the temporal variability of depth-averaged SSC is due to a combination of two processes: horizontal advection and local resuspension. In this study, we investigated the sediment dynamics at three anchored monitoring stations close to the maximum turbidity zone of the Changjiang Estuary, and developed a box model to differentiate the effects of advection and resuspension. Further, settling velocities were estimated using the ADV Reynolds flux method, excluding the advection SSC component. We found that predicted changes in advection- and resuspension-induced SSCs were consistent with the bottom shear stress and accretion/erosion observations. The combination of observed bed accretion/erosion changes and the predicted advection-induced SSCs indicates that the advective transport of suspended sediment is an important process in accelerating persistent erosion at the monitoring stations. Although SSC variations due to advection and resuspension are of similar magnitudes, our model results indicate that if resuspension dominates, the resuspension-induced component can reach up to twice the magnitude of the advection-induced component. We conclude that the box model is a valuable tool for evaluating subaqueous delta accretion/erosion in response to sediment reduction caused by upstream dam construction and climate change.