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Proper operation of gated spillways, which plays an important role in safety of dams during flood event, remains as a prominent challenge. Although telecommunication networks used in flood warning systems facilitate flood management by dams to some certain level but accurate prediction of both the magnitude and timing of peak flood flows with few days of lead time is not still possible. Therefore, operation of gated spillways may mostly benefit from the observed reservoir water level and observed flood discharges in the upstream gagging stations. In Iran, many of river-reservoir systems face severe floods every year. Most of these reservoirs are operated based on engineering judgments of dam personnel and static policies such as rule curves, which are not proper formulated for flood events with various return periods. In this study, we proposed a rule curve for operation of gated spillways using sequential approach and its performances was compared with previously developed operation policies. For this purpose, nine stages as critical control levels were assigned and spillway gate openings associated with each critical level were determined for Mahabad Dam, located in northwest of Iran, as the case study of this research. Each control level was related to given percentage of the design flood volume. When using the proposed rule curve, as a critical control level is reached, the discharge through the spillway and related opening of its gate are accordingly increased. The gate openings associated with each critical water level were optimized using a real coded Genetic Algorithm (GA). This attitude or policy of nine -stage operation includes an appropriate algorithm for determining critical levels, development of operational models spillway gates, calculation of gate opening in each stage, and applying the model to the case study of Mahabad dam. This study adopts the nine stages approach for which nine control levels and gate openings are determined by GA. As it mentioned before, the nine critical levels should be placed in flood retention reservoir between initial water surface elevation and maximum water surface elevation. So, it will have crucial role to determinate gate opening spillway during flood events, and increase of flood storage in the flood retention reservoir. This model was employed to route a flood with the same return period of design spillway flood through Mahabad reservoir. The performance of the proposed rule curve was then assessed by determining the amount peak flow discharge reduction. The results of the case study shows superiority of the proposed rule curve over previously developed operation policies for flood control in Mahabad Dam. One of the main advantages of the proposed methodology is that for using the proposed rule curve not flood forecast data is needed and therefore, it can be considered as a reliable tool for operation of gated spillways when there is no flood warning system in the upstream basin. The future studies can be focused on testing the proposed algorithm on other reservoirs. In the cases of dams with large flood control volumes, critical control levels can also be considered as decision variables of the GA optimization model.

Keywords: Genetic Algorithm, Flood Control, Gated Spillway, Operation Policy, Flood Hydrograph.

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