Does reservoir always decrease flood risk? A case study of the Three Gorges Reservoir for middle Yangtze River

Abstract:

This study is aimed to quantify the effects of the hydrologic alteration of the middle Yangtze River due to the operation of the Three Gorges Reservoir (TGR), the largest dam in China. The streamflows of three downstream stations, Yichang, Shashi and Luoshan are studied to quantify the effect of TGR. Three schemes, including without TGR operation, with conventional and optimal TGR operating rules respectively, are compared of the Yichang station. The multi-input single-output systems models (MISO) are used to simulate the streamflows at Shashi and Luoshan stations with three different inputs of Yichang station, respectively. These streamflows are then analyzed by using the Indicators of Hydrologic Alteration (IHA) and the Range of Variability Approach (RVA) to evaluate the hydrologic changes associated with TGR operation. Results indicate that: (1) The 1-day maximum flows of Yichang and Shashi stations are decreased significantly, while their 1-day minimum flows are increased with TGR operation. (2) On the contrary with the maximum flows at Yichang and Shashi stations, the 1-day maximum flow of Luoshan station can be increased caused by encountering between the intervening flood and the post-flood release of the TGR. These findings are beneficial to evaluate the hydrologic systems in the middle Yangtze River after the TGR construction, and provide a scientific foundation for deriving the TGR flood control rules.