Effects of the Three Gorges Dam on Yangtze River flow and river interaction with Poyang Lake, China: 2003–2008

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Summary The Three Gorges Dam (TGD) has been in operation since 2003. Over the operation period from 2003–2008, data have been collected for preliminary evaluations of actual effects of the TGD on the Yangtze River flow and river interactions with downstream lakes and tributaries. These effects are examined in this study, after the climate influence was minimized by comparing hydrological changes between years of similar climate conditions before and after the operation of the TGD. Major results show that the TGD operation has affected the Yangtze River discharge and water level. The significance of these effects varies seasonally and with different locations along the river. The seasonal variation follows the TGD’s seasonal impounding and releasing of water. The magnitude of the effects is dependent on the impounding/releasing rate and the seasonal flow of the river. The most significant effects are confined in the river reach near the TGD and are as great as five times those of sections downstream. The weakening and diminishing of effect of the TGD is primarily because of “dilutions” to the effect by inflows to the Yangtze River from downstream tributaries. Changes in the Yangtze River discharge caused by the TGD have further altered the interrelationship between the river and Poyang Lake, disturbing the lake basin hydrological processes and water resources. A major consequence of such changes has been a weakening in the river forcing on the lake, allowing more lake flow to the river from July–March. This effect of the TGD may partially fulfill the TGD’s mission to mitigate flood risks in the lake basin, especially during the peak wet season of the Yangtze River basin from July–September. In the 6 years since the TGD operation began the annual average number of severe outflow events of rates of ⩾3000 m 3 s −1 from the lake in July–September has increased by 74. It has also resulted in reduction of water storage in Poyang Lake. Results of this study point to strong needs for working strategies to balance the TGD impacts on flood control and water resources as well as their societal and ecological consequences in the Poyang Lake basin. Meanwhile, in the context of studies of impacts of large dams this study shows an example of extending the previous studies in the dam–river setting to a new dam–river–lake construct.