Abstract
The Three Gorges Project (TGP) is the world’s largest water conservation project. The post-construction low-flow water level at the same discharge below the dam has declined, but there remains disagreement over whether the flood level has increased. Measured water levels and upstream and downstream flow data from 1955 to 2016 show that, post-construction: (1) the low-flow water level at the same discharge decreased, and the lowest water level increased due to dry-season reservoir discharge; (2) the decline of the low-flow water level below the dam was less than the undercutting value of the flow channel of the river; (3) the flood level at the same discharge below the dam was slightly elevated, although peak water levels decreased; (4) flood characteristics changed from a high discharge–high flood level to a medium discharge – high flood level; and (5) an expected decline in the flood level downstream was not observed. Channel erosion and the adjustment of rivers and lakes tend to reduce flood levels, while river bed coarsening, vegetation, and human activities downstream increase the flood level. Although the flood control benefits of the Three Gorges Dam (TGD) and the upstream reservoirs are obvious, increased elevation of the downstream flood level remains a concern.
Highlights
With the decline of the low-flow water level downstream of the world’s other large reservoirs[6,7]
There is no common understanding of the variation in the downstream flood level before and after construction of the Three Gorges Dam (TGD), and it is not certain whether data show a decrease in the downstream flood level14,a small or non-significant increase[15], or a rising trend[16,17]
During July 2016, flood control water levels were exceeded at the lower sections of Jianli Station in the middle and lower reaches of the Yangtze River, and at Dongting Lake and Poyang Lake
Summary
Yunping Yang[1,2], Mingjin Zhang[1], Lingling Zhu[3], Wanli Liu[1], Jianqiao Han4 & Yanhua Yang[1]. After construction of the Three Gorges Reservoir (TGR), a consensus was reached that the lowest water level at the same discharge had decreased It remains controversial whether the flood level has increased, it is necessary to study the characteristics, regularity, and genesis of the changes of the flood level downstream of the TGD. Following construction of the TGR, the erosion downstream of the dam intensified[22], and the impact of factors, such as the coarsening of the river bed[23,24], the variation in the number of days of floodplain inundation[23], and the effects of human activities[25,26], on the flood level is apparently increasing. The TGR reduces the peak flow so that the corresponding flood level decreases, while allowing an increase in the low-flow water level during the dry season[27,28]
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