Abstract
The sediment regime in the Jingjiang river reach of the middle Yangtze River has been significantly changed from quasi-equilibrium to unsaturated since the impoundment of the Three Gorges Dam (TGD). Vertical profiles of suspended sediment concentration (SSC) and sediment flux can be adopted to evaluate the sediment regime at the local and reach scale, respectively. However, the connection between the vertical concentration profiles and the hydrologic conditions of the sub-saturated channel has rarely been examined based on field data. Thus, vertical concentration data at three hydrological stations in the reach (Zhicheng, Shashi, and Jianli) are collected. Analyses show that the near-bed concentration (within 10% of water depth from the riverbed) may reach up to 15 times that of the vertical average concentration. By comparing the fractions of the suspended sediment and bed material before and after TGD operation, the geomorphic condition under which the distinct large near-bed concentrations occur have been examined. Based on daily discharge-sediment hydrographs, the reach scale sediment regime and availability of sediment sources are analyzed. In total, remarkable large near-bed concentrations may respond to the combination of wide grading suspended particles and bed material. Finally, several future challenges caused by the anomalous vertical concentration profiles in the unsaturated reach are discussed. This indicates that more detailed measurements or new measuring technologies may help us to provide accurate measurements, while a fractional dispersion equation may help us in describing. The present study aims to gain new insights into regime change of sediment suspension in the river reaches downstream of a very large reservoir.
Highlights
Characteristics of the sediment regime are one of the most important factors that control the processes in the transportation and sedimentation zones of a fluvial system [1]
The sediment regime of a river reach can be expressed as the suspended sediment load
Regarding the physical processes of suspension on a local scale, they may be related to the vertical profiles of suspended sediment concentration (SSC), which are essential for estimating sediment flux, and numerical simulation [2]
Summary
Characteristics of the sediment regime are one of the most important factors that control the processes in the transportation and sedimentation zones of a fluvial system [1]. Changes in the sediment regime cause varied fluvial evolution processes and the inner physical processes of sediment suspension. The sediment regime of a river reach can be expressed as the suspended sediment load (sediment flux). Regarding the physical processes of suspension on a local scale, they may be related to the vertical profiles of suspended sediment concentration (SSC), which are essential for estimating sediment flux, and numerical simulation [2]. A large number of researchers have paid, and are paying, attention to the vertical concentration profiles.
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