Abstract: The design rule curves are used to simulate reservoir operation to verify the design values and obtain a benchmark for comparative study. Joint and multi-objective optimal operation models are developed for the lower Jinsha-Three Gorges-Gezhouba cascade reservoirs. We solve the optimal model and its Pareto frontier using a parameterization-simulation-optimization framework based on the Gaussian radial basis functions and a Borg many-objective evolutionary algorithm. Comparative study reveals that the design values of annual hydropower generation are reasonable and reliable, and the joint operation of cascade reservoirs must consider the backwater effect of downstream reservoirs. Compared to the rule curve scheme, the joint (optimal) operation scheme reduces water spillage by 20.38% (30.44%) and increases annual hydropower generation by 4.01% (5.45%), with significant increases in the generation by the reservoirs of Xiluodu, Xiangjiaba, and Gezhouba. Generally, a conflict between hydropower generation and impoundment efficiency occurs, and the Three Gorges Reservoir will be faced with a challenge in dry years if it starts impoundment on the tenth of September. We suggest that the Three Gorges Reservoir should optimize further its flood-limited water level and consider an earlier start of impoundment.

Key words: cascade reservoirs, rule curves, joint operation, multi-objective optimization, radial basis function, lower Jinsha River, Three Gorges Reservoir