Abstract: To explore the coordinated drawdown control strategy for cascade reservoirs in the lower Jinsha River, an optimization model for joint drawdown operation is developed to maximize power generation as the objective. This model integrates those constraints related to power generation, water supply, navigation, and ecology, and uses the Progressive Optimization Algorithm (POA) for model solution. Numerical simulations are conducted for typical inflow scenarios of different frequencies, focusing on quantitative analysis of the compensation benefits of joint operation under the upstream reservoir regulation, and on the drawdown sequence patterns and the optimal control ranges of minimum drawdown water levels under varying inflow conditions. Results show that except for the extreme low-flow scenarios, compensating regulation of the flow－from the Wudongde and Baihetan reservoirs to the Xiluodu and Xiangjiaba reservoirs－enables the cascade system’s total power output to increase by 1.8 - 2.8 billion kW?h (2% - 3%). We recommend that in normal or high-flow scenarios, sequential drawdown should be taken from the upstream to downstream reservoirs, while in low-flow scenarios, the Baihetan reservoir should prioritize drawdown and control the water level dropping as evenly as possible. Except for the extreme low-flow scenarios, the Xiluodu reservoir should maintain high water level to the full, and start a concentrated drawdown in mid-to-late May. We also recommend that the storage in the Wudongde and Baihetan reservoirs should be raised to the flood limited water level in early-to-mid May, be lowered to the lowest in early June, and then start gradual refilling. And the Baihetan reservoir’s lowest drawdown level is 765 - 780 m, with lower drawdown levels in higher flow periods; except for the extreme low-flow scenarios, the Xiluodu reservoir’s lowest drawdown level is 560 m.

Key words: lower Jinsha River, cascade reservoirs, joint drawdown operation, compensation regulation, drawdown sequence