EP012-0022
Poyang and Dongting Lakes, Yangtze River: Tributary Lakes Blocked by Main-stem Aggradation

Tuesday, 8 December 2020
Poster
Chenge An1, Hongwei Fang1, Li Zhang1, Xinyue Su1, Xudong Fu2, He Qing Huang3, Gary Parker4, Marwan A Hassan5 and Guangqian Wang6, (1)Tsinghua University, Beijing, China, (2)Tsinghua University, Department of Hydraulic Engineering, Beijing, China, (3)Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing, China, (4)University of Illinois at Urbana Champaign, Urbana, IL, United States, (5)Univ British Columbia, Vancouver, BC, Canada, (6)Tsinghua University, State Key Laboratory of Hydroscience and Engineering, Beijing, China
Abstract:
During its 6300-km course from the Tibetan Plateau to the ocean, the Yangtze River encounters two large lakes: Dongting Lake and Poyang Lake. We explain why these lakes exist. Holocene deglaciation forced a sea level rise of ~ 120 m over ~ 12,000 years. This resulted in a wave of rising water surface elevation and concomitant bed aggradation upstream. While aggradation attenuated upstream, the low bed slope of the Middle-Lower Yangtze River (~ 2x10-5 near Wuhan) made it susceptible to sea level rise. The main stem, sourced at 5054 m above sea level, had a substantial sediment load to “fight” against water surface level rise by means of bed aggradation. The tributaries of the Middle-Lower Yangtze have reliefs ~ hundreds of meters, and did not have had enough sediment supply to fill the “hole” along the main stem. Therefore, as the main stem has aggraded, the river bed itself has formed a dam that blocks the tributaries and creates lakes. We further derive a dimensionless number capturing the incipient condition for the blockage of tributary blocked valley lakes.
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