Improved stagewise trialanderror method for optimal flood control operation of reservoirs with a low regulation capacity
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Abstract:
The storage of a reservoir with low regulation capacity is often small,and the reservoir water level is sensitive to changes in the outflow process.In flood control optimization process operation,small changes in outflows may lead to large variations in the reservoir water level,resulting in the reservoir water level frequently approaches the upper and lower controlled boundaries.To meet the maximum and minimum water level constraints,it will cause severe fluctuations of the reservoir outflow process and affect the operability of the optimal solution. The maximum peak-reduction criterion is taken as the objective function,considering the constraint conditions such as the mass balance,the maximum and minimum water levels,the discharge capacity,the fluctuation of the outflow period,and the return storage level at the end of the operation horizon.The optimized dispatching model is developed for reservoir flood control.Based on the operation process of the realtime flood control operation of the reservoir and the mechanism that the reservoir water levels frequently approach the upper and lower controlled boundaries in the flood control operation,the improved stagewise trialanderror method with low regulation capacity is proposed.The maximization of real-time flood regulation capacity and the operability of the optimal operation solutions is taking into account in this method and proposes the principle of "conceptual" segment.The whole operation period is divided into five stages including the predischarge stage,maintenance stage,flood storage stage,safety drawdown stage,and final drawdown stage.Based on the principle of segmented mass balance,with the principle of homogenizing the outflow process,a segmented trial calculation strategy and implementation process for dynamically determining the start and end times of each stage are proposed using the realtime flooding process of the storage.Furthermore,the uniform outflow process iterative optimization method is proposed. Taking the Fuchunjiang Reservoir as the research subject,the simulation operation of the improved stagewise trialanderror method was carried out.The results were compared with the original stage-wise trial-and-error method and reveal the following: (1) It was found that with the improved stagewise trialanderror method,various constraints are strictly met.However,the original stagewise trialanderror method had a certain deviation from the given water level control conditions.The lowest water level was 0.38 m higher,and the highest water level was lower by 0.2 m,and the adjustable flood control storage capacity was not fully used. (2) From the perspective of the outflow process,the improved stagewise trialanderror method had a regular outflow process with clear stages,and the outflow process at each stage conformed to preexpectations,with reasonable results and strong operability.The "sawtooth" in the outflow process of the original stagewise trialanderror method operation results was more serious,especially in the prerelease stage,where the prerelease period was short and large. (3) Due to the "precision" water level control of the improved stage-wise trial-and-error method and the full utilization of the adjustable flood control storage capacity,the peak reduction rate was 16.2%,which was better than the 14.3% peak reduction rate produced by the original stagewise trialanderror method,and the peak reduction rate was increased by 13.3%. To address the poor performance of the original stagewise trialanderror method applied to reservoirs with low regulation capacity under weekly regulation,an improved stagewise trialanderror method was proposed,which had the following advantages compared with the original one: (1) It could better adapt to the characteristics of reservoirs with small storage and low regulation capacity.It may overcome the shortcoming that the upper and lower limits of reservoir storage capacity and discharge capacity were frequently broken in the original one,which brought a good stability performance to the algorithm. (2) The calculation principle of the improved stagewise trialanderror method was simple,and the segmentation iteration process was complete and clear.A reasonable and operability operation solution could be easily obtained. (3) The case study in Fuchunjiang Reservoir proved that the improved stagewise trialanderror method achieved good application results in the flood control operation.
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