Deriving reservoir operating rules considering ecological demands of multiple stations

Reservoirs play important roles in hydropower generation, flood control, water supply and navigation. However, the regulation of reservoirs is challenged due to their adverse influences on river ecosystems. In this study, 'Ecoflow' was used as an ecological indicator for reservoir operation to indicate the extent of natural flow alteration. Three reservoir optimisation models were established to derive ecological operating rule curves (ORCs). Model 1 only considers maximisation of average annual hydropower generation (AAHG) and the assurance rate (AR) of hydropower generation. Model 2 incorporates ecological objectives and constraints. Model 3 not only considers the hydropower objectives but also simulates runoff and calculates the ecological indicator values of multiple downstream stations. The three models were optimised using a simulation-optimisation framework. Reservoir ecological ORCs were derived for a case study of China's Three Gorges reservoir. The results provided feasible schemes for reservoir operation by considering both hydropower and ecological demands. The AAHG and AR of the preferred optimised scheme for model 3 were increased by 1.06% and 2.50%, respectively. Furthermore, the ecological benefits of three hydrologic stations were also improved. In summary, the ecological indicator Ecoflow and optimisation models could be helpful for reservoir ecological operations.