Flood control storage substitution from multiple to single-reservoir and storage reservation strategy for hydropower optimization in cascade reservoir systems

Floodwater utilization is critical for balancing flood control and water conservation in multi-reservoir cascade systems, yet conventional reservoir operations often overlook the potential of storage substitution among different reservoirs. This study develops an extended flood control storage substitution model that accounts for both upstream–downstream interactions and intermediate reservoir regulation, thereby enabling a more precise assessment of flood control tasks substitution across multiple reservoirs. Focusing on the Jinsha River cascade and the Three Gorges Project (TGP), we systematically evaluate how additional flood control storage can be substituted and how to reserve storage to maximize hydropower benefits while maintaining flood safety. Results show that upstream reservoirs can collectively substitute as much as 3.3 billion m3 of TGP’s design flood control storage, raising TGP’s operating water level by up to 8 m and boosting system-wide power generation by 2.8 billion kWh. Moreover, strategic initial storage reservation—particularly assigning smaller additional storage to Baihetan and larger to Xiluodu—further enhances hydropower output without increasing flood risk. These findings underscore the importance of coordinated multi-reservoir operations that harness the “substitution effect” to optimize water concervation and electricity generation. By offering a generalizable model for quantifying reservoir substitution and guiding initial storage reservation decisions, this study provides valuable insights into floodwater resource utilization, promoting strategies to optimize water conservation, improve hydropower generation in multiple reservoirs systems.