Bottom fine sediment boundary layer and transport processes at the mouth of the Changjiang Estuary, China

SummaryImproved understanding of fine sediment transport processes within turbid estuaries has been of interest to both the coastal engineer and coastal oceanographer. The continuous measurement of fine suspended sediment concentration profiles is central to the study of transport processes. With this in mind, we utilise acoustic backscatter measurements to infer continuous vertical profiles of suspended sediment concentration. The acoustic profiling method has the advantage that it senses suspended sediment concentrations remotely and non-intrusively with a high degree of temporal and spatial resolution. Observational studies were undertaken to obtain more insight into the importance of bottom fine sediment boundary layer and transport processes to the seaward part of the North Passage in the Changjiang Estuary, China. Field measurements were made in October 1994 during spring, moderate and neap tides, respectively. Time series data of tidal elevations, current speed, and directions were measured. Vertical profiling of fine suspension concentration was made hourly by an acoustic suspended sediment monitor. Three dominant physical processes were identified: (1) the near-bed periodic resuspension by the tidal currents via tidal pumping; (2) the asymmetric stratifications due to fine suspension; and (3) the exchange of sediment between the bed and water column. The study also has its regional significance in estuarine morphodynamics, regulation of navigational channel, and water quality at the North Passage in the Changjiang Estuary.