Optimized scheduling of medium and small floods in reservoirs considering resources and safety: A case study of Miyun Reservoir

Abstract

[Objective] Miyun Reservoir, as the core strategic water reserve for the Beijing-Tianjin-Hebei region, has current scheduling rules that exhibit limitations in handling medium and small floods, such as insufficient refined regulation and control, as well as water levels at the end of the main flood season often falling below the reservoir's restricted levels for the post-flood period. This result in compromised storage benefits, and the constrained dynamic regulation capacity of water resources makes it difficult to balance flood control and storage benefits. To enhance both safety and resource utilization efficiency in medium and small flood scheduling, it is necessary to extract and optimize the scheduling rules. [Methods] A scheduling model for medium and small floods based on model predictive control(MPC) was constructed. For four flood magnitudes, 11 graded release strategies were designed as scheduling rules, and 44 scenarios were simulated and compared to identify the optimal scheduling scheme. Additionally, simulations for the probable maximum flood(PMF) and a 10 000-year return period flood were performed to validate the model's applicability under extreme conditions. [Results] The result showed that for a 2-year return period flood, retaining the entire flood volume was sufficient. For a 5-year return period flood, the maximum outflow decreased from 554 m³/s under the original rules to 244 m³/s, representing a reduction of 56%. The number of gate operations decreased from 82 to 19, a reduction of 76.8%. For the 10-year and 20-year return period floods, optimization was achieved to varying degrees. On average, for floods with return periods of 5 years and above, the maximum outflow was reduced by 25%~30%, the final water level stabilized within the target range of 154±0.1 m, the comprehensive evaluation score improved by 15%~30% compared with the original rule, and the number of gate operations decreased by over 60%. [Conclusion] While adhering to existing scheduling principles, optimized scheduling of small and medium floods can be achieved through model-based simulation. This approach strikes a balance between flood control and water utilization, while effectively reducing the operation and maintenance costs for management units. The findings provide a reference for optimizing flood scheduling in similar reservoirs with large storage capacities and significant differences in scheduling tiers.

Keywords

medium and small floods / MPC method / scheduling rules / graded release control / storage-release balance / Miyun Reservoir / prediction model / influencing factors