PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

The completion and application of the Three Gorges Project has altered the water and sediment conditions of the downstream channel of the reservoir, lowered its water flow and sediment transport capacity and led to channel scour, ultimately impeding flood control. Considering these negative consequences, this study, based on the measured hydrology and river topography data from 1998 to 2021 in Nanjing and its adjacent reaches in the lower reaches of the Yangtze River, statistically analyzed the riverbed scour and deposition changes in the Nanjing reach during the past 20 years after the impoundment of the Three Gorges Dam. The results show that, during 1998-2006, both scour and deposition occurred in the Nanjing reach of the Yangtze River. Afterwards, the overall trend was inclined to scour, which happened at both the floodplain and the main channel. During 2006-2020, the cumulative amount of scour in the bankfull channel was 104.37 million m3, with the annually average scour intensity being 78.1 thousand m3/km. Meanwhile, the scour mainly occurred in the bankfull channel, and the scour amount of the floodplain between the low-flow channel and the flood channel merely accounted for 10%-25%. Between 2006 and 2020, the scour amounts of the low-flow channel and the bankfull channel were 39.18% and 74.22% of that of the flood channel, respectively. Moreover, scour was more intense on the left bank of the Nanjing reach, with the mean value of the annually average scour intensity of each river reach being 1.42 times of that on the right bank. Along the entire Nanjing reach, scour was the most intense at Dashengguan and the left branch of Meizizhou, with the respective annually average scour intensity being 166.8 thousand m3/km and 120.6 thousand m3/km. During 2020-2021, under the effects of severe flooding, significant scour took place at the bankfull channel, and the scour amount reached 28.35 million m3. Based on the trend forecast of the channel scour status of the upstream Ma’anshan reach, it is predictable that the Nanjing reach of the Yangtze River may still be dominated by scouring. Therefore, it is necessary to strengthen the monitoring, especially the left bank, the main stream before the Meizizhou Branch, and the Meizizhou Left Branch and other areas with higher scour intensity. It is imperative to pay attention to this section of the river, and it is also necessary to monitor and analyze the river situation and scouring and silting conditions of the Ma'anshan section upstream of the Nanjing section.

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