Field methods of a near-bed suspended sediment experiment in the Yangtze River, China

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ORIGINAL PAPER

Field methods of a near-bed suspended sediment experiment in the Yangtze River, China Caiwen Shu 1 & Guangming Tan 1 & Yiwei Lv 1 & Quanxi Xu 2 Received: 6 September 2019 / Accepted: 6 October 2020 # The Author(s) 2020

Abstract Using experimental data of near-bed suspended sediment concentrations at five typical hydrometric stations of the Three Gorges Reservoir at the early reserving stage, the differences were investigated between the common method and improved method during flood seasons and non-flood seasons. The impact of taking measurements below 0.2 times the water depth on the results was discussed. The results show that the average discharges and velocities at each station calculated by the common method were slightly larger than those calculated by the improved method. Regarding the suspended sediment concentration at each station, the errors in the reservoir and downstream channels in dynamic equilibrium state were small, and the largest errors occurred where the river bed was strongly scoured in the downstream reach below the large dam. There was no significant relationship between water discharge and flow velocity, and the missed measurement phenomenon also occurred. The sediment discharge error was affected by the suspended sediment concentration, implying that errors usually occurred in channels with serious erosion during flood seasons. The correction coefficients (R2) of sediment discharge at each station were given during the experiment, which showed that the sediment discharges at the hydrometric stations where a large amount of sediment transport occurred near the river bottom, needed to be modified. Furthermore, the test methods proposed in this study were applied to calculate the sediment discharges of three rivers, and the results indicate that this method can narrow the gap between bathymetric comparisons and sediment load measurements. Keywords Near-bed suspended sediment experiment . Measurement error . Sediment discharge . Correction coefficient

Introduction It has long been known that the sediment placed into suspension by flow-induced bottom shear stresses achieves a vertical distribution, which essentially represents a balance between the upward turbulent diffusion and the downward settling of sediment particles (O’Brien 1933; Cacchione et al. 2008; Responsible Editor: Stefan Grab * Caiwen Shu [email protected] * Yiwei Lv [email protected] 1

State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, Hubei, China

2

Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China

Yuan et al. 2017). The process of near-bed sediment transport can be considered as dynamic feedback interactions among the bed, flow, and mobile sediments. According to the “Code for measurement of suspended sediment in open channels” (GB/T 50159-2015) and “Measurement of liquid flow in open channels—Methods for measurement of characteristics of suspended sediment” (ISO 4363:2002), common measurements of suspended sediment (such as

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