Impact of upstream reservoirs on geomorphic evolution in the middle and lower reaches of the Yangtze River

Abstract

Intensive human activities in river basins have substantial effects on fluvial hydrological and morphological processes and developmental trends. In this study, we assessed the evolutionary characteristics and developmental trends of the fluvial morphological system of the Three Gorges Dam (TGD) downstream to understand the impacts of human activities on the fluvial hydrological–morphological system of the region. The results indicated that the Three Gorges Project (TGP) and other upstream cascade reservoirs promoted sediment retention, which in turn aggravated the trend of declining sediment load and cumulative scouring over a long distance in the channels downstream of the TGD. Approximately 84% of scouring occurred in the low‐water channels, along with thalweg scouring and riverbank collapse. Notably, extended operation of the TGP and other upstream cascade reservoirs has resulted in gradual changes in the downstream riverbeds. Specifically, we found that the most intensive scouring zone shifted downstream from the near‐dam Yichang–Chenglingji reach (0–408 km) to the Chenglingji–Hankou reach. The scouring–silting distribution in swales has also changed: the scouring of deep swales and silting on floodplains prior to the TGP have been replaced by the scouring of both deep swales and floodplains. The scouring intensity of riverbeds in the Yichang–Hukou reach (954 km) was slightly higher than that forecasted prior to the TGP; the scouring intensities increased significantly during 2013–2021, which could be attributed to the TGP and other upstream cascade reservoirs; river sand mining and waterway dredging are secondary factors. We conclude that, owing to the effects of sediment retention by cascade reservoirs in the upper reaches of the Yangtze River (or Changjiang River), the cumulative scouring intensities of riverbeds in the middle and lower reaches of the Yangtze River will continue to increase in future decades.

Effect of water depth and waterway obstructions on the divergence and confluence areas of Dongting Lake and the Yangtze River after the operation of the Three Gorges Project

“…During the period 1956–2002, Songzikou, Taipingkou, Ouchikou (Guan), and Ouchikou (Kang) were cut off for 81, 83, 95, and 198 days, respectively, whereas during the period 2003–2021, this number increased to 178, 140, 180, and 271 days, respectively, an increase of 97, 57, 85, and 73 days, respectively. After the operation of the TGP, the Jingjiang reach in the middle reaches of the Yangtze River was eroded by the river channel (Yang, Zheng, et al, 2022b; Y. P. Yang, Zhou, et al, 2022), and the flow and low‐water level showed a downward trend (Chai et al, 2020; Y. Yang et al, 2017; Y. P. Yang, Zhang, Sun, Han, et al, 2018). Simultaneously, small‐scale erosion occurred predominantly at the three inlets and flood channels (Wei et al, 2022); however, offsetting the impact of the water level decline of the mainstream was difficult.…”

“…Following the construction of the TGR, the erosion of Dongting Lake led to an increase in the low‐water level and the depth of the waterway (M. Zhang et al, 2015). Subsequently, after the operation of the TGP, the volume of sediment entering the middle reaches of the Yangtze River has significantly reduced (Y. P. Yang, Zheng, Zhu, et al, 2022), causing strong erosion in the Jingjiang reach (Y. P. Yang et al, Zhou, et al, 2022). The first phase of the waterway improvement project in the Jingjiang reach increased the depth of the waterway from 2.9 m in 2002 to 3.5–3.8 m in 2018 (Yan et al, 2019; Y. Yang et al, 2019).…”

Channel-forming discharge based on the extreme value identification of sediment-carrying capacity index

“…With the commissioning of the TGR and a series of cascade reservoirs in the upper Yangtze River, hydrological elements, such as the D f magnitude, temporal and spatial distribution, and the SSC entering the middle and lower reaches of the Yangtze River (MLYR) have changed, resulting in significant changes in the evolution of the riverbed downstream of the reservoirs 45 . The first and foremost change was a reduction in the flood peak.…”

The Migration of the Erosion Center Downstream of the Three Gorges Dam, China, and the Role Played by Underlying Gravel Layer

“…As shown in Figure 2, a big flood occurred in 1998 at the Yangtze River resulting in a significant high sediment load. The sediment load decreased notably after 2013 at Qingxichang as sediment was trapped by cascade reservoirs at the upper Yangtze River and its tributaries (Jiang et al., 2023; Yang et al., 2023). The average trap efficiency of the TGD (i.e., the ratio of sediment trapped in the reservoir to the total sediment inflow) was 78% during 2003–2018 (Liu et al., 2022).…”