Presenter
Dr. Zican He, Changjiang River Scientific Research Institute
Co-author(s)
Dr. Zhaohua Sun, Wuhan University
Dr. Geng Qu, Changjiang River Scientific Research Institute
Dr. Hualong Luan, Changjiang River Scientific Research Institute
Dr. Wentao Lei, Changjiang River Scientific Research Institute
Sub-theme
4. Supporting Aquatic Ecosystem Health and Functions
Topic
4-3. Protection and management of major rivers and lakes, from headwaters to estuaries
Body
Human activities have increased rapidly in recent decades and introduces changes to the flow-sediment regime, particularly the sediment supply, in the downstream reach, inevitably influencing the evolutionary processes of the gravel-sand transition. The Yangtze River, the third-largest river in the world, appears to represent a field example of a GST with strong human interference. Since 1975, the sediment transport in the Yangtze River has been frequently disturbed by human activities, whereas there is no systematic study on the migration characteristics and its inner mechanisms of the gravel-sand transition. Based on topographic data and bed material information, our work has accurately identified the location of the gravel-sand transition in the Yangtze River by three identification methods from different angles, analyzed the factors affecting its stability, and predicted its future trend. The results showed that (1) from the bed material perspective, the transition was stable in Yichang-Jiangkou Reach during 1970~2002, and then its onset and end migrated 49.5 km and 10 km downstream from 2003~2015, respectively; From morphology and hydrodynamics perspective, the transition was stable in Zhicheng-Chenjiawan Reach with a length of about 70 km over the period 1970~2015. (2) The location of the gravel-sand transition in the Yangtze River was dominated by the combination of channel width and tributaries rather than the longitudinal bed profile. The variation of the shear stress across the gravel-sand transition had two abrupt decreases at Zhicheng and Chenjiawan, which were caused by geomorphology and sedimentary characteristics under the joint action of natural and long-term human factors. This phenomenon would not change in a short time. (3) The downstream migration of the GST in the Yangtze River reflected by the bed material perspective resulted from the dramatic reduction in suspended-load supply. As the low sediment supply continues, the GST position is expected to progress downstream, but its onset and end are unlikely to move over Zhicheng and Chenjiawan, respectively. Our results provide not only a theoretical basis for channel adjustment prediction but also a powerful reference for channel regulation along the Yangtze River.