Comprehensive evaluation of environmental flows in the Yangtze River regulated by two large dams

The ecological sustainability of rivers and floodplains depends on their natural flows. Dam construction on rivers has dramatically altered the hydrologic regimes, in turn affecting aquatic ecosystem integrity. The environmental flow components was applied to exam the impacts of the two dams (i.e., the Gezhouba Dam and the Three Gorges Dam) on downstream flows of the Yangtze River, China. Due to the operation of the two dams, the Yangtze River's flow regimes became homogenous through increasing streamflow during the dry season and decreasing streamflow in the flood season. The monthly low flows from January to April significantly increased by 14-31%, while October and November low flows significantly decreased by 18-25%. We observed the decreased duration and frequency of extreme low flows and floods, particularly the disappearance in large floods. These homogenous flows strongly influence the aquatic biodiversity. To alleviate the hydrologic alteration and minimize the negative ecological influence, low flows should be lower and floods should be reestablished as a natural state. The flow characteristics of duration, timing and rate of change should also be incorporated into the environmental flow recommendations. Our results could provide a potential solution to the tradeoffs between water resources exploitation and natural water requirement in the highly regulated rivers.