Effects of the Three Gorges Dam on the downstream streamflow based on a large-scale hydrological and hydrodynamics coupled model

The Yangtze River basin, China. In this study, a large-scale coupled model of hydrological and hydrodynamic processes was developed via the Distributed Time Variant Gain Model and the hydrodynamics-operation coupled model. Two scenarios including operated by the Three Gorges Dam (TGD) and natural condition hypothesis without the reservoir construction, were analyzed based on the coupled model to investigate the effects of TGD operation on the streamflow from 1970 to 2018. Results exhibited that the annual average relative deviation of flow operated by the TGD was approximately 24% compared with the natural state at Yichang, while the value of Chenglingji, Hankou, Hukou and Datong were 8.5~12.8%. During water supply period, the TGD operation increase the streamflow by 33% at Yichang, and the streamflow in downstream can gain about 6–17%. For impounding process, except Hukou, the others showed a decreasing trend, and the reduction ranged from about 7–20%. For flood season, the dam operation mainly intercepts high flood peaks while the average streamflow changes a little. The high flood peaks at Yichang can be reduced by 20%, and the changes of high flood peaks in downstream reduce to no more than 10% due to the influence of interval inflow. The deviations during drawdown period are almost below 10%.