Riverbed Adjustments in Gravel–Sand Reaches Immediately Downstream of Large Reservoirs

Sixuan Li, Lingling Zhu (), Jing Yuan, Bingjiang Dong, Chaonan Lv and Chenggang Yang
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Sixuan Li: Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China
Lingling Zhu: Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China
Jing Yuan: Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China
Bingjiang Dong: Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China
Chaonan Lv: China Three Gorges Corporation, Yichang 443100, China
Chenggang Yang: Bureau of Hydrology, Changjiang Water Resources Commission, Wuhan 430010, China

Sustainability, 2024, vol. 16, issue 24, 1-23

Abstract: The operation of large reservoirs significantly modifies flow–sediment regimes, and the reaches immediately downstream of the dams are the first to undergo responsive channel adjustments. Considering that the geomorphological responses are directly related to the flood control safety, channel stability and other sustainable functions of rivers, this paper explores the similarities and dissimilarities of the channel adjustments in the two reaches with gravel–sand beds immediately downstream of the Xiangjiaba reservoir and the Three Gorges Dam, respectively. The results show that major erosion primarily occurred during the initial years of reservoir impoundment. And then with the prominent reduction in washable sediment on the riverbed, the erosion intensity further weakened. It takes 6 to 13 years for the two reaches to reach a new state of relative equilibrium. In comparison, after the equilibrium state has been achieved, the reach with significant tributary sediment inflows exhibits alternating erosion and deposition dynamics, while the other remains relatively stable. The tributaries that transport a large amount of sediment during floods are the main sources of sediment deposition in the downstream reaches of the Xiangjiaba reservoir. However, the tributary inflow of the Qing River with low sediment concentrations has little impact on the riverbed evolution of the reaches from Yichang to Zhicheng immediately downstream of the Three Gorges Dam. These findings contribute to a deeper understanding of geomorphic adjustments near dams in response to upstream damming.

Keywords: riverbed adjustments; immediately downstream of the dam; influencing factors; tributary inflows; bed material coarsening (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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