Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 13 11 2009 10.5194/hess-13-2253-2009 http://www.hydrol-earth-syst-sci.net/13/2253/2009/ http://www.hydrol-earth-syst-sci.net/13/2253/2009/hess-13-2253-2009.html http://www.hydrol-earth-syst-sci.net/13/2253/2009/hess-13-2253-2009.pdf 2253 2264 2009-11-26 Sedimentation in the Three Gorges Dam and the future trend of Changjiang (Yangtze River) sediment flux to the sea Bangqi Hu Zuosheng Yang zshyang@mail.ouc.edu.cn Houjie Wang Xiaoxia Sun Naishuang Bi Guogang Li College of Marine Geosciences, Ocean University of China, 238 Songling Rd., Qingdao 266100, China Key Lab of Submarine Sciences & Prospecting Techniques (KLSSET), Ministry of Education, 238 Songling Rd., Qingdao 266100, China North China Sea Branch of the State Oceanic Administration, 22 Fushun Rd., Qingdao 266033, China The Three Gorges Dam (TGD) on the upper Changjiang (Yangtze River), China, disrupts the continuity of Changjiang sediment delivery to downstream and coastal areas. In this study, which was based on 54 years of annual water and sediment data from the mainstream and major tributaries of Changjiang, sediment deposition induced by the TGD in 2003–2008 was quantified. Furthermore, we determined the theoretical trapping efficiency of the cascade reservoir upstream of the TGD. Its impact on Changjiang sediment flux in the coming decades is discussed. Results show that about 172 million tons (Mt) of sediment was trapped annually by the TGD in 2003–2008, with an averaged trapping efficiency of 75%. Most of the total sediment deposition, as induced by the TGD (88%), accumulated within the region between the TGD site and Cuntan. However, significant siltation (12% of the total sediment deposition) also occurred upstream of Cuntan as a consequence of the upstream extended backwater region of the TGD. Additionally, the Changjiang sediment flux entered a third downward step in 2001, prior to operation of the TGD. 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