The Time Delay of Flow and Sediment in the Middle and Lower Yangtze River and Its Response to the Three Gorges Dam

Abstract

AbstractAs the largest hydropower project in the world, the Three Gorges Dam (TGD) has drawn extensive concern in terms of its impact on downstream areas. In this study, an improved time delay estimation and wavelet analysis were used to investigate the influence of the TGD on the streamflow and sediment in the middle and lower Yangtze River, using time series of the daily discharge and sediment concentration data from three hydrological stations downstream of the dam. The results indicated that all of the time series at the three stations have prominent annual cycles, but the cycle of daily mean sediment concentration was nearly nonexistent after the impoundment of the TGD. Changes in discharge and sediment between the Yichang and the Hankou stations are larger than those between the Hankou and the Datong stations, which is mainly attributed to the streamflows of tributaries and Dongting Lake and the flood diversion area of Jingjiang. The transmission time of discharge for the whole Yichang?Datong river section is approximately 6 days. In addition, the attenuation of discharge from the Yichang station to the Datong station is 20%?30%. In contrast, the transmission of suspended sediment is slower than that of discharge, which takes 7?7.5 days to move from the Yichang station to the Datong station. The attenuation of sediment is approximately 30% in the Yichang?Datong river section and shows a clear increasing trend after 2006, mainly because a large amount of sediment was trapped by the TGD, and the dynamic balance of sediment was disturbed.