Deriving the optimal refill rule for multi-purpose reservoir considering flood control risk

• A new method is developed to derive the optimal refill rules for multi-purpose reservoir.
• The refill of TGR begins on Sept. 1 with storage level reaching 160 m on Sept. 30 linearly.
• The proposed method can increase hydropower generation by 7.19% for TGR reservoir.

For most multi-purpose reservoirs, there is a conflict between the flood control and refill operations. Refill before the end of the flood season is a valuable and effective solution to the conflict. In this paper, we present a method to derive the optimal refill rule for multi-purpose reservoir considering flood control risk. The paper begins with an investigation of the temporal trends of historical reservoir inflow series during refill period by the methods of linear regression, Mann–Kendall and Spearman's rho test. Six refill rules are then proposed. A procedure to couple a flood control risk module with utilization benefits analysis module is then developed to derive the optimal refill rule. China's Three Gorges Reservoir (TGR) is selected as a case study. The application results show that the optimal refill rule is that refill begins on September 1 with storage level reaching 160 m on September 30 linearly. Compared with the original rule, the optimal refill rule can increase hydropower generation by 7.19%, decrease spilled water by 25.07%, and improve the fullness storage rate to 95.35%, without increasing flood control risk.