Abstract
Understanding the sediment transport processes, especially the formation and maintenance of the estuarine turbidity maximum (ETM) in estuaries is essential for dealing with harbour siltation and the related estuarine environmental issues. To gain insight into the mechanism of sediment dynamics and ETM formation in the Yongjiang estuary (YE), which is well-mixed and features abundant suspended sediment sourced from the adjacent sea area, field observations were conducted in June 2015. The flow velocity, salinity, and suspended sediment concentration (SSC) were synchronously measured over a 25-h tidal cycle along the YE and its adjacent sea area. Observations showed that there was abundant suspended sediment exchanging between the YE and its adjacent sea area. In particular, there existed an obvious difference in the single or twin peak SSC signals in different stations during a semi-diurnal tidal cycle, especially between the inner-estuary and outer-estuary regions. Detailed analyses on the processes of sediment transport showed that, in the outer sea area, the tidal-driven advection of suspended sediment was dominant to the temporal distribution of SSC, which was featured by a single peak signal in a semi-diurnal tidal cycle. For the estuarine channel, the landward transport of high-concentration suspended sediment by the flood current from the sea region was the major inducement of peak SSC signals in the lower reach of the YE, while the effect of bed sediment resuspension was mainly responsible for the peak signals during the ebb period. Unlike the formation of ETM in highly stratified or partially mixed estuaries, the ETM in the YE, which is located approximately 7 km upstream from the estuary mouth, was mainly controlled by the effect of tidal asymmetry, together with the contributions made by local resuspension of bed sediment and possible fluid mud. Some other possible factors, such as deflocculation, may also impact the formation and maintenance of the ETM in the YE, but further study is needed in the future.
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