Impact of the operation of a large‐scale reservoir on downstream river channel geomorphic adjustments: A case study of the Three Gorges

Abstract

To evaluate the effects of reservoir construction on the geomorphology of downstream reaches, a case study is performed on the Three Gorges Reservoir (TGR) by comparing data collected before and after impoundment of the reservoir. This study focuses on a 1,183‐km‐long reach downstream from the TGR and investigates the temporal and spatial characteristics and patterns of geomorphic adjustment in the downstream reaches. The amount of erosion in flood plain channels and the annual average intensity of erosion in downstream reaches after 12 years of impoundment are larger than the predicted values before the impoundment of the TGR. The maximum intensity of erosion was found at 410 km from the dam, with an average thalweg incision of 1.5 m, and the main zone of erosion migrated approximately 80 km downstream. At both preimpoundment and postimpoundment, erosion occurred the along beaches and channels in the Yichang–Chenglingji reach. The pattern of erosional channels and depositional river floodplain changed to erosional channels and erosional river floodplain in the Chenglingji–Hankou reach after the trial impoundment stage. In the Hankou–Hukou reach, the erosional channels and depositional river floodplain pattern changed to erosional deep channels, erosional low beaches, and depositional high‐river floodplain during the early impoundment stage. After the trial impoundment stage, erosion continued in the deep channels, but minor deposition occurred on the river floodplain. Moreover, the discharge of clear water increased, and the duration from middle to low‐water levels increased, leading to more concentrated erosion in low‐water channels. The intensity of the erosion along the river floodplain decreased due to the shortened duration of high‐water levels and reduced human activity.

Human impacts on riverbed morphology and hydrology in the lower reaches of the West River, China

“…Such decreases in the sediment load have led to the erosion of many river channels and their subaqueous deltas. For example, the riverbed of the middle and lower reaches of the Yangtze River and its delta were found to be substantially eroded after the construction of the Three Gorges Dam (Dai & Liu, 2013; Yang et al, 2018; Yang, Milliman, Li, & Xu, 2011; Zheng et al, 2018). Twenty‐one rivers in North America exhibited rapid riverbed erosion after dam constructions (Williams & Wolman, 1984).…”

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

“…The cumulative water level drops for Zhicheng, Chenerkou, Maojiahuawu, Yaogang, and Changmenxi were 0.46, 0.59, 0.93, 0.97, and 1.19 m, respectively (Figure 6e). Recently, the intensity of scouring and silting of sand and pebbles on the riverbed has weakened (S. X. Li, Yang, et al, 2021; Y. P. Yang, Zhang, Zhu, et al, 2018; Y. P. Yang, Zhang, Sun, et al 2018). Moreover, coarsening of the riverbed during scouring and silting (Y. P. Yang et al, 2016; Y. P. Yang, Zhang, Sun, Han, et al, 2018) has reduced the downward trend of the water level (Chai et al, 2020; J. Q. Han, Sun, et al, 2017; Y. P. Yang, Zhang, Sun, Han, et al, 2018) to a considerable degree; however, a falling water level is not conducive to a stable waterway depth during low‐water periods (Yan et al, 2019; Y. Yang et al, 2019).…”

“…The complex relationship between changes in the hydrodynamics, sediment transport, and sandbank and tidal flats in the river–lake confluence area is significant, as it is a key river section for waterway management, dredging, and maintenance (Dong et al, 2020). Research has been conducted on erosion and silting (Xia et al, 2017; Y. P. Yang, Zhang, Zhu, et al, 2018), changes in sandbanks and tidal flats (Yang, Zheng, Zhang, Zhu, Zhu, et al, 2021; Zhao et al, 2020), distributary relationships (Hu et al, 2020; L. S. Liu, Li, et al, 2017; H. H. Liu, Yang, et al, 2017; Y. P. Yang, Zheng, Zhang, Zhu, Zhu, et al, 2021), and obstructions to navigation (M. Li, Hu, et al, 2021; Y. Yang et al, 2019) in the confluence area of Dongting Lake and the Yangtze River after the construction of the TGR. The focus has primarily been on water–sediment flux in confluence areas, changing relationships between the river and lake, and utilization of water resources.…”

Simulating Ecological Effects of a Waterway Project in the Middle Reaches of the Yangtze River Based on Hydraulic Indicators on the Spawning Habitats of Four Major Chinese Carp Species

“…Previous studies have focused on characterizing the resources of the FMCCs [7], defining their habitats' hydraulic index suitability curves [8][9][10][11][12][13], revealing the distribution and variations in their spawning sites [14], and determining their spawning times [2,[15][16][17][18][19][20]. Since the operation of the Three Gorges Project, long-distance cumulative scouring has occurred in the middle and lower reaches of the Yangtze River, which has provided favorable conditions for enhancing the waterway depth [21][22][23]. Since 2003, many projects have been implemented to improve the navigation conditions of the main channel of the Yangtze River, covering a variety of categories such as dams, bar protection zones, bottom protection zones, and bank protection.…”