Enhanced hysteresis of suspended sediment transport in response to upstream damming: An example of the middle Yangtze River downstream of the Three Gorges Dam

Abstract

The peak in sediment transport in alluvial rivers generally lags behind the peak in discharge. It is thus not clear how the hysteresis in the sediment/discharge relationship may be impacted by damming, which can fundamentally alter the water and sediment regimes in the downstream reaches of the river. In this study, a total of 500 flood events in the Yichang–Chenglingji Reach (YCR) of the Middle Yangtze River immediately downstream of the Three Gorges Dam (TGD) are analysed to study the impacts of dam operations on the hysteresis of suspended sediment transport. Sediment rating curves, hysteresis patterns, as well as lag times, are investigated to determine the relationship between suspended sediment concentration (SSC) and flow discharge (Q) at different temporal scales, from inter‐annual to individual flood events, for the pre‐ and post‐TGD period from 1992 to 2002 and from 2003 to 2017, respectively. The results showed that the TGD operation decreased the frequency and magnitude of floods. The decrease in peak flow and increase in base flow weakened the flood contribution to the annual discharge by nearly 20%. However, the relative suspended sediment load contribution during flood events was much higher than the discharge contribution, and was little impacted by the dam. At seasonal and monthly scales, more than 80% of the suspended sediment was transported by ~65% of the water discharge in the summer and early autumn. The monthly SSC–Q relationship changed from a figure‐eight to an anti‐clockwise pattern after the construction of the TGD. For single flood events, the TGD operations significantly modified the downstream SSC–Q hysteresis patterns, increasing the frequency of anti‐clockwise loops and the lag time between peak Q and peak SSC. These adjustments were mainly caused by differences in the propagation velocities of flood and sediment waves and the sediment ‘storage–mobilization–depletion’ process, whereas the influence of lateral diversions was small. © 2020 John Wiley & Sons, Ltd.

Propagation characteristics of the flow and suspended sediment peaks in the three gorges reservoir, China: Insight from numerical simulations and measured data

“…In general, Q peak is characterized by flood waves while SSC peak is associated with flow velocity (Lyu et al, 2020). As shown in Figure 14, in the near‐dam region (the Miaohe Station) almost all the flood events are characterized by “ SSC peak lagging behind Q peak ”.…”

Effect of the Three Gorges Reservoir on vertical distribution of suspended sediment concentration and estimation accuracy of depth‐average concentration in downstream reaches

“…For a long time, the downstream channel was basically a dynamic balance of sediment before the impoundment of the TGR. Therefore, the long-term average annual sediment concentration corresponding to each discharge before impoundment can be approximated as the saturated sediment concentration under this flow (Lyu et al, 2020), as shown in Figure 5e. The ratio of the sediment concentration investigated in Table 1 and the saturated sediment concentration is approximately taken as the sediment saturation degree (ξ), as shown in Figure 5f.…”

Mechanisms Controlling Water‐Level Variations in the Middle Yangtze River Following the Operation of the Three Gorges Dam

“…The jacking force is an interactive force in that the lakes create a backwater effect on the Yangtze River and in turn, the Yangtze River has a block effect on the outlet of lakes. The MYR is a predominately meandering channel with many floodplains, and a riverbed composition that tends toward finer grain sizes downstream (He et al., 2021; Lyu et al., 2020).…”