Optimized reservoir operation to balance human and environmental requirements: A case study for the Three Gorges and Gezhouba Dams, Yangtze River basin, China

• Four scenarios were established in this paper to find a reasonable method.
• The EDF is first put forward by this paper.
• The RVA is used to evaluate potential hydrologic alterations.
• The EDF is the best way to balance the human and environmental requirements.

After the construction and operation of the Three Gorges and Gezhouba dams, their impacts on hydrologic alterations in the middle and lower reach of Yangtze River are under high attention worldwide, of which the balance between the human and environmental flow requirements is one of the most important issues. This study uses an optimization model for the operation of reservoirs to compare the different environmental flow requirements of river ecosystems. Based on the different environmental flow requirements, four scenarios were established: (1) the no environmental flow case; (2) the minimum environmental flow (MEF) case; (3) the appropriate environmental flow (AEF) case; and (4) the environmental design flow (EDF) case. The EDF case is first proposed in this paper, which considers the reservoir adjustment ability and comprehensively balances the economic, social and ecological benefits. The Range of Variability Approach (RVA) is used to evaluate the potential hydrological alterations of each of the four scenarios. The comparison results of the power production and the degree of hydrological alteration in the four different scenarios, indicate that the system operation under the EDF case imposes the least hydrological alteration while providing adequate power production. The encouraging results demonstrate that this method will be a robust tool for practitioners to better perform reservoir operations in balancing the human and environmental requirements.