Stage-wise optimizing operating rules for flood control in a multi-purpose reservoir

- We present release rules for a single reservoir during three flood stages.
- The rules aim to regulate reservoir to the target levels in the end of stages.
- An efficient algorithm is used to stage-wise optimize parameters in the rules.
- The deviation to the target level in the end of each stage is minimized.
- The results satisfy dam safety, flood mitigation, and sufficient final storage.

SummaryThis paper presents a generic framework of release rules for reservoir flood control operation during three stages. In the stage prior to flood arrival, the rules indicate the timing and release discharge of pre-releasing reservoir storage to the initial level of flood control operation. In the stage preceding the flood peak, the rules prescribe the portion of inflow to be detained to mitigate downstream flooding, without allowing the water surface level of reservoir to exceed the acceptable safety level of surcharge. After the flood peak, the rules suggest the timing for stepwise reduction of the release flows and closing the gates of spillways and other outlets to achieve the normal level of conservation use. A simulation model is developed and linked with BOBYQA, an efficient optimization algorithm, to determine the optimal rule parameters in a stage-wise manner. The release rules of Shihmen Reservoir of Taiwan are established using inflow records of 59 historical typhoons and the probable maximum flood. The deviations from target levels at the end of different stages of all calibration events are minimized by the proposed method to improve the reliability of flood control operation. The optimized rules satisfy operational objectives including dam safety, flood mitigation, achieving sufficient end-of-operation storage for conservation purposes and smooth operation.