Journal of Geographical Sciences >
Flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam
Hu Yong (1996-), PhD Candidate, E-mail: hooyong@whu.edu.cn |
Received date: 2021-11-15
Accepted date: 2022-03-09
Online published: 2022-12-25
Supported by
National Natural Science Foundation of China(51779185)
National Key Research and Development Program of China(2018YFC0407201)
Since the Three Gorges Dam (TGD) was put into operation, the flood water level at an identical discharge rate has not displayed a decreasing trend along the middle reaches of the Yangtze River (MYR). The flow resistance variations of the channel and bars in response to the operation of the TGD remain poorly understood, despite the importance of understanding these for water disaster mitigation and water environment regulation. Herein, the impacts of the TGD on the downstream flow resistance of the channel and bars in the MYR were analyzed using systematic surveys of hydrological datasets, cross- sectional profiles, sediment datasets, and remote sensing images, during different periods. Under the actual natural conditions in the MYR, a modified semi-empirical formula, which considered the grain, dune resistance, as well as the topographic features of the riverbed, was proposed to predict the channel resistance. Furthermore, the effect of various dam-control flow and sediment elements on the variation in different flow resistance components, and the corresponding relationships among them were investigated. Results showed a decline in the comprehensive, channel, and bar resistances as the discharge increased, whereas there was a slight increase when reaching the bank-full discharges. Notably, the bar resistance occupied 65%, while the channel resistance, in which dune resistance was much larger than grain resistance, contributed 35% to the comprehensive resistance. In addition, while flow resistance rose over time, there was a decline as the distance from the TGD increased. In conclusion, the increased dune and bar resistances, interpreted by the fluctuated channel longitudinal profile and growing vegetated area on bars, were the dominant factors preventing the flood water level from dropping.
HU Yong , DENG Jinyun , LI Yitian , LIU Congcong , HE Zican . Flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam[J]. Journal of Geographical Sciences, 2022 , 32(10) : 2013 -2035 . DOI: 10.1007/s11442-022-2034-1
Figure 1 Sketch map of the study area: (a) Yangtze River Basin, (b) the layout of the remote images, and (c) the middle reaches of the Yangtze River with locations of hydrometric stations, bars, and diversion inlets |
Table 1 Essential information on 18 hydrometric stations, 16 bars and 9 sub-reaches in the middle reaches of the Yangtze River and three operation periods of the Three Gorges Dam |
Station number | Station name | Bar number | Bar name | Channel number | Included reaches | Length | |
---|---|---|---|---|---|---|---|
1 | Yichang | 1 | Yanzhi | Sub-reach 1 | Yichang-Zhicheng | 60.8 km | |
2 | Yidu | 2 | Guan | Sub-reach 2 | Zhicheng-Majiadian | 34.8 km | |
3 | Zhicheng | 3 | Liutiao | Sub-reach 3 | Majiadian-Shashi | 47.9 km | |
4 | Xinjiangkou | 4 | Lalin | Sub-reach 4 | Shashi-Shishou | 88.3 km | |
5 | Shadaoguan | 5 | Tuqi | Sub-reach 5 | Shishou-Jianli | 76.8 km | |
6 | Majiadian | 6 | Ouchikou | Sub-reach 6 | Jianli-Chenglingji | 99.4 km | |
7 | Mituosi | 7 | Wugui | Sub-reach 7 | Chenglingji-Hankou | 251 km | |
8 | Shashi | 8 | Dama | Sub-reach 8 | Hankou-Jiujiang | 270 km | |
9 | Kangjiagang | 9 | Xiongjia | Sub-reach 9 | Jiujiang-Hukou | 25.4 km | |
10 | Guanjiapu | 10 | Zhong | ||||
11 | Shishou | 11 | Fuxing | ||||
12 | Jianli | 12 | Hankou | ||||
13 | Chenglingji | 13 | Tianxing | ||||
14 | Luoshan | 14 | Dongcao | ||||
15 | Xiantao | 15 | Daijia | Period number | Impounded water level (m) | Included years | |
16 | Hankou | 16 | Zhangjia | 1 | - | Before 2002 | |
17 | Jiujiang | 2 | 135.0-139.0 144.0-156.0 145.0-172.8 | 2003-2005 2006-2007 2008 | |||
18 | Hukou | 3 | 145.0-171.4 145.0-175.0 | 2009 2010-present |
Table 2 Sources of measurements |
Data type | Number (station/bar/channel) | Period of record | Sources |
---|---|---|---|
Daily discharge | Stations 1-18 | 1991-2015 | CWRC |
Daily water level | Stations 1-18 | 1991-2015 | CWRC |
Daily sediment concentration | Stations 1-18 | 1991-2015 | CWRC |
Surveyed profiles | Sub-reaches 1-9 (450 cross-section profiles per year) | 2004, 2006, 2009, 2012, 2015 | CWRC |
Surveyed terrains | Sub-reaches 1-9 (two-dimensional terrain) | 2015 | CWRC |
Medium diameters of bed load | Stations 1, 3, 8, 12, 14, 16 | 2003-2019 | CWRC |
Landsat images | Bars 1-16 | 1993, 2002, 2006, 2009, 2015 | USGS |
Figure 2 The variation of the comprehensive (n), channel (nc), and bar (nb) resistances as the (1) discharge, (2) time, and (a‒i) space changes. The ratio (3) of channel and bar resistances in different sub-reaches. |
Figure 3 The accumulative erosion volumes of the channel and bars (a), the variations of dune roughness heights in different reaches (b), variations of the dune resistance growth rate as a function of the dune roughness height growth rates (c), and the dune resistance growth rates for periods 2-3 in different sub-reaches (d) |
Figure 4 Variation of the medium diameters of bed load with the Three Gorges Dam operation periods at different hydrometric stations (a-f), and the growth rate of the grain resistance during periods 2-3 in different sub-reaches (g) |
Figure 5 Variation of the bar submerged frequency with the Three Gorges Dam operation periods in different sub-reaches |
Figure 6 Variations of the vegetated area on 16 bars with the Three Gorges Dam operation periods |
Table 3 Comparison of calculated vegetated areas through Landsat-8 OLI and two-dimensional (2D) terrain in 2015 |
Bar number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
---|---|---|---|---|---|---|---|---|
Calculated vegetated areas through Landsat-8 OLI (km2) | 2.23 | 2.55 | 1.68 | 6.19 | 7.15 | 7.87 | 8.98 | 8.62 |
Calculated vegetated areas through 2D terrain (km2) | 2.15 | 2.31 | 1.81 | 5.88 | 6.96 | 7.93 | 9.05 | 8.51 |
Bar number | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
Calculated vegetated areas through Landsat-8 OLI (km2) | 8.45 | 10.55 | 10.17 | 9.89 | 16.83 | 19.95 | 17.41 | 80.13 |
Calculated vegetated areas through 2D terrain (km2) | 8.22 | 10.63 | 10.22 | 9.71 | 16.66 | 20.01 | 17.55 | 79.95 |
Figure 7 Fitting lines among the growth rate of bar resistance, vegetated area, and bar submerged frequency during periods 2-3 |
Figure 8 Stage and discharge relationships at stations 1 (Yichang), 3 (Zhicheng), 8 (Shashi), 12 (Jianli), 14 (Luoshan), 16 (Hankou), and 17 (Jiujiang) in 2003 and 2014 |
Figure 9 Temporal changes of the cross-section profiles of four typical sections in the middle reaches of the Yangtze River |
Figure 10 The relative flood water level influenced by the flow resistance and riverbed erosion along the middle reaches of the Yangtze River |
Figure 11 Engineered banks at Bar 4 (Lalin): (a) planar graph; (b) cross-sectional drawing |
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