Downstream geomorphic impact of the Three Gorges Dam: With special reference to the channel bars in the Middle Yangtze River

Li, Dongfeng; Lu, Xixi; Chen, Li; Wasson, Robert J.

doi:10.1002/esp.4691

Cited by 56 publications

(27 citation statements)

References 66 publications

(151 reference statements)

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“…Meanwhile, the migration of bedforms becomes inactive so that the form‐induced resistance decreases, which further promotes bed erosion. Bed degradation can be widely found in rivers with sediment deficits because of upstream dam construction (Li et al, 2019; Mei et al, 2018). For the tributary, the bed topography is less impacted by the change in sediment supply of the main channel.…”

Section: Resultsmentioning

confidence: 99%

Numerical assessments of bed morphological evolution in mountain river confluences under effects of hydro‐morphological factors

Yan

Duan

Yang

et al. 2022

Hydrological Processes

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Understanding hydro‐morphological characteristics in mountain river confluences is significant in flood disaster mitigation and mountain river restoration, which is still poorly explored. This study employed a 2D hydro‐morphological model based on the finite element method to simulate the major bed morphological features in a mountainous‐type flume confluence and evaluate the effects of main controlling factors on these features. The modelling results show that the dominant bed morphological features in mountain river confluences can be well produced by the 2D model. Five controlling factors including downstream water level (H), branch discharge ratio (Qr), main channel sediment supply ratio (ψ), tributary slope (St) and confluence angle (α) reflecting different flow‐sediment‐geometry scenarios were adopted into a sensitive study. The upstream reach of the main channel is controlled by H and ψ and their decreases lead to bed degradation. The increase in Qr, St, and α mainly results in bed aggradation and steepening in the tributary, attaining a higher sediment transport rate. This contrasts the existing experimental results, due to the difference in sediment feeding. The size of the bank‐attached bar is promoted by the increase in Qr, St, and α and the decrease in H and ψ. A quantitative analysis shows that the water surface slope well correlates with various dimensions of the scour hole and bar morphology (correlation = 0.58–0.8). Meanwhile, the bank‐attached bar displays a strong self‐similarity (correlation = 0.84–0.98) regarding its geometric dimensions. This study provides new insights into the existing knowledge of the hydro‐sediment‐morphodynamics of mountain river confluences obtained from laboratory studies and field investigations.

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Section: Resultsmentioning

confidence: 99%

Numerical assessments of bed morphological evolution in mountain river confluences under effects of hydro‐morphological factors

Yan

Duan

Yang

et al. 2022

Hydrological Processes

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“…The Three Gorges Project (TGP), one of the largest hydropower projects in the world, is located at the immediately upstream of the MYR. It serves the comprehensive functions of flood control, hydropower generation, navigation, utilization of water resources in the Yangtze River basin (Fang et al, 2012; Li et al, 2019). With the TGP operation, the flow and sediment regime in the MYR has been altered drastically, with a sudden decrease in suspended sediment concentration, which resulted in severe channel degradation and bed material coarsening.…”

Section: Study Area and Data Collectionmentioning

confidence: 99%

A new formula for predicting movable bed roughness coefficient in the Middle Yangtze River

Liu

Xia

Deng

et al. 2021

Progress in Physical Geography: Earth and Environment

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Computing movable bed roughness plays an important role in the modeling of flood routing and bed deformation, and the magnitude of movable bed roughness is closely associated with complex bedform configurations that change with the sand wave motion. The motion of sand wave is dependent on the incoming flow and sediment conditions and channel boundary. After the operation of the Three Gorges Project, the flow and sediment regime changed remarkably in the Middle Yangtze River (MYR), followed by significant channel adjustments. A dramatic decrease in sediment concentration caused continuous channel degradation and significant variations in cross-sectional profiles of the MYR. These adjustments in the channel boundary influence the motion of sand wave, which can further affect the magnitude of movable bed roughness. A new formula for predicting the movable bed roughness coefficient is developed, which can be expressed by a power function of both Froude number and relative water depth. The proposed formula was first calibrated using 1266 datasets of measurements at five hydrometric stations in the MYR during 2001–2012. A back-calculation process shows that the roughness coefficients calculated by the proposed formula agree well with the observations, with the determination coefficient being equal to 0.88. The proposed formula was further verified using 651 datasets of measurements at these hydrometric stations during 2013–2017. Furthermore, four common roughness formulas selected from the literature were tested for comparison. The results indicate that the calculation accuracy of the proposed formula is significantly higher than that of the previous formulas, and the Manning roughness coefficients predicted by the proposed formula have the errors less than ±30% for 96% of the datasets. Therefore, the new bed roughness predictor proposed in this study can accurately calculate the roughness coefficients straightforwardly without iterative solution and graphical interpolation, and the parameters required in the roughness predictor are easily obtained from the hydrometric observations.

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“…They are commonly present in various sized rivers around the world [2,3]. As a typical fluvial landform, MCBs are often focused on by engineering projects, such as maintaining channel stability and navigation safety [4,5]. In recent decades the ecological functions of MCBs have been gradually recognized thanks to their characteristics of isolation and edge effects [6,7].…”

Section: Introductionmentioning

confidence: 99%

Impacts of Dam Operation on Vegetation Dynamics of Mid-Channel Bars in the Mid-Lower Yangtze River, China

et al. 2021

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Vegetation dynamics on mid-channel bars (MCBs) is essential for supporting ecosystem functions and associated services in river systems, especially in dammed large rivers. Generally, there are two possible changing patterns that vegetation of MCBs downstream a dam would experience. On one hand, the vegetation area may shrink because of a decrease in the MCB area in the post-dam period, which has been observed in many rivers around the world. On the other hand, the MCB vegetation area may expand because flood disturbances would be weakened by dam operation. However, little evidence has been reported to clarify such confusion. Therefore, vegetation dynamics of MCBs in the mid-lower Yangtze River downstream the Three Gorges Dam (TGD; the world’s largest dam) is selected as a case study to address the issue. Using long-term (1987–2017) Landsat archive images, this study reveals the spatiotemporal variations of vegetation area change intensities (VACIs; indicated by dynamic trends) on MCBs in the mid-lower Yangtze River. Results show that an overall VACI in the post-dam period (2003–2017) is about three times faster than that in the pre-dam period (1987–2002). In other words, the rate of vegetation colonization accelerated after the TGD operation began in 2003. Moreover, the VACIs in the post-dam period are size dependent, where large size MCBs are likely to gain higher VACIs: Small-sized MCBs (0.33 km2/yr), medium-sized MCBs (1.23 km2/yr), large-sized MCBs (1.49 km2/yr). In addition, VACIs of individual MCBs in the post-dam period are distance dependent, where the further a MCB was from the TGD, the higher the VACI. It is also suggested that the weakened flood disturbances in the post-dam could explain the rapid vegetation growth and colonization. This work is not only beneficial for managing and protecting MCBs downstream the TGD after its operation, but is also helpful in understanding vegetation dynamics of MCBs in other dammed river systems around the world.

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Downstream geomorphic impact of the Three Gorges Dam: With special reference to the channel bars in the Middle Yangtze River

Cited by 56 publications

References 66 publications

Numerical assessments of bed morphological evolution in mountain river confluences under effects of hydro‐morphological factors

Numerical assessments of bed morphological evolution in mountain river confluences under effects of hydro‐morphological factors

A new formula for predicting movable bed roughness coefficient in the Middle Yangtze River

Impacts of Dam Operation on Vegetation Dynamics of Mid-Channel Bars in the Mid-Lower Yangtze River, China

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