Improved method for determining connecting water level of cascade hydropower stations based on peak regulation operation

The minimum discharge flow is one of the most critical indicators for coordinating the comprehensive utilization of water resources in cascade hydropower stations within basin water resource management. Generally, the implementation conditions of the minimum discharge for cascade hydropower stations are determined by the connecting water level. Existing researches on factors that influence connecting water level determination has primarily focused on cascade reservoir operating water level overlap, river channel water depth between cascade reservoirs, and ecological protection. However, insufficient attention has been paid to the impact of power station peak-shaving operations against the backdrop of frequent extreme high temperatures and the "Double Carbon" goal. Taking the TJZ-SW cascade hydropower stations in the lower reaches of the A River as the research case, this study proposes an improved method for determining the connecting water level of cascade hydropower stations based on peak-shaving operations, aiming to address the collaborative challenge of surging grid peak-shaving demand and river ecological flow protection. A systematic comparative analysis was performed between the proposed method and two traditional approaches, namely the cascade water level overlap method and the downstream river channel water depth method. The research demonstrates that: ① The optimal connecting water level of the TJZ-SW cascade determined by the improved cascade water level connection method based on peak-shaving operations is 430.57 m. The comprehensive peak-shaving amplitudes of the TJZ and SW power stations are increased by 0.2% and 8.8%, respectively, compared with the cascade water level overlap method and the downstream river channel water depth method.② The peak-shaving-oriented connecting water level mechanism maintains the water depth in the cascade power station reach to meet the ecological and environmental needs during low-valley periods. The TJZ and SW power stations improve power generation revenue through "pulse-type" energy storage and water head-flow optimization strategies, respectively, increasing the total cascade revenue by 6.5% and achieving a phased reconciliation of the contradiction between "ecological protection" and "benefit pursuit".③ The improved cascade water level connection method based on peak-shaving operations effectively coordinates multiple objectives such as power generation benefits of cascade power stations, safe grid operation, and river ecological flow protection. The coordination of zero discharge for energy storage of TJZ during low-valley periods and early water storage of SW ensures 100% compliance with ecological flow throughout the entire period while achieving collaborative optimization of peak-shaving and economic benefits, with remarkable ecological, peak-shaving, and power generation benefits. The method proposed in this study provides a new road for resolving the contradiction between "ecological protection" and "peak-shaving emphasis" in the A River Basin and can also serve as a reference for the collaborative optimal dispatching of cascade hydropower stations in the Changjiang River Basin.