Impact of the Three Gorges Dam Overruled by an Extreme Climate Hazard

While it is generally difficult to separate the impact of extreme climate events on river catchment conditions from that of human activities, there are unique data available to document this for the catchment area of the Yangtze in the years that the Three Gorges Dam (TGD) started to have an impact. During the second impoundment phase in 2006, the suspended sediment discharge (SSD) and water stored behind the TGD was 23 x 10(6) t and 11 x 10(9) m(3), respectively, which is only 18% of the total SSD reduction and about 1% of the water discharge (901x10(9)m(3)) in 2005 at Datong. The total SSD and water discharge into the Yangtze Estuary in 2006 was 60 and 24% less than those in 2005, respectively. It can be quantified that the contribution of the extreme climate (drought) on discharge and SSD reduction was 95 and 82% of the total in 2006, respectively. In addition, it was found that the periods of high salinity (>250 and 400 mg/L) at Haimen that happened during the second impoundment phase accounted for 25 and 23% of the total occurrences in 2006, respectively. This analysis shows that the impact of extreme climate conditions can overrule the human interference, even for the largest dam, the TGD. DOI: 10.1061/(ASCE)NH.1527-6996.0000081. (C) 2012 American Society of Civil Engineers.