Influences of increasing water release of the Three Gorges Reservoir during dry season on water regimes of downstream lake

The severe and frequent drought in Poyang Lake, the largest freshwater lake in China, has seriously affected the local water resources security and wetland ecological security. Especially, the impoundment of the Three Gorges Reservoir (TGR) in the Yangtze River further aggravated the drought in lake. To explore the approaches to alleviate drought in Poyang Lake, this study simulated and quantified the influences of increasing water release of the TGR during the dry periods on water regimes of Poyang Lake, including the lake water level, duration of low water, flow velocity, flow field of lake, as well as potential suitable habitat area of migratory birds, based on a hydrodynamic model. Major results showed that the increase of water release of the TGR raised the lake water level, especially in the northern lake area, with the average lake level increase of 0.2-1.08 m and the lowest lake level increase of 0.16-0.68 m. Meanwhile, the duration of low water was significantly shortened, from 127 days to 87-116 days (threshold lake level of 12.0 m) at Xingzi station. In addition, the hydrodynamic simulations revealed that the increasing water release of the TGR reduced the lake flow velocity and discharge of Poyang Lake, which decreased the outflow of lake by 1.66-17.87 x 10(8) m(3), accounting for about 0.47%-5.11% of the total outflow in the dry season. Finally, the potential suitable habitat area with 0.2-0.6 m water depth increased by 1.7-27.9 km(2) in December-February, and showed a significant expansion trend in the central area of Poyang Lake. Outcomes of the study are useful for understanding the influences of water release of the TGR on water regimes of downstream lakes, and can provide valuable references for mitigating lake droughts in complex river-lake system.