Optimizing multi-objective operation of cascade reservoirs to enhance hydropower generation and fish spawning demand synergies during the pre-flood drawdown period

The middle reaches of the Jinsha River, China. The construction and operation of reservoirs have modified streamflow regimes, resulting in river fragmentation, and adversely affecting riverine functions, particularly fish spawning activities. This study proposes a novel pre-flood multi-objective drawdown operation (PFMODO) framework with the advantages of dynamically configuring ecological optimization objectives in combination with the variability of streamflow to optimize the synergistic benefits of hydrologic and ecological objectives through drawdown operation during pre-flood periods. Based on the relationship of the fish rising processes for fish spawning, the reservoir inflow, and regulation capacity, the study identified three scenarios with distinct optimization objectives set for each scenario. A competitive relationship between the objective of hydropower generation and the objective of fish spawning demand and natural flow restoration was found. The corresponding recommended operation scheme (ROS) was proposed to increase the hydropower generation in cascade reservoirs (with the maximum improvement rate of 2.66 %) for each scenario. At the same time, fish spawning was stimulated (with the maximum objective improvement rate of 81.6 %), compared to the standard operation policy (SOP). This study provides an innovative approach to optimizing drawdown operation for the synergies of fish spawning stimulus and hydropower generation in cascade reservoirs, thereby offering scientific guidance for environmentalists and decision-makers in sustainable water resources management. • A novel PFMODO framework is proposed for boosting synergies of hydroelectricity and ecology. • Ecological optimization objectives can be dynamically configured with streamflow regimes. • Identify relationship of hydropower generation, fish spawning and natural flow restoration. • The ROS for specific streamflow scenarios can increase hydropower generation while stimulating fish spawning.