A reasonable analysis of flood season staging is significant to the management of floods and the alleviation of water shortage. For this paper, the case of the Chengbi River Reservoir in China was selected for study. Based on fractal theory, the flood season is divided into several sub-seasons by using four indexes (multi-year average daily rainfall, multi-year maximum rainfall, multi-year average daily runoff, and multi-year maximum daily runoff) in this study. Also the Benefit-Risk theory is applied to evaluate the effects of staged dispatching. The results show that the flood season of the Chengbi River basin should be divided into the pre-flood season (13 April–6 June), the main flood season (7 June–9 September) and the post-flood season (10 September–31 October). After adjusting the flood limit water level for sub-season and benefit assessment, the probability of exceedance after reservoir flood season operation increases by 0.13×10-5, the average annual expected risk is 0.2264 million RMB, and the average annual benefit increases by 0.88–1.62 million RMB. The benefits obtained far outweigh the risks, indicating the importance of staging the flood season.

A reasonable analysis of flood season staging is significant to the utilization of flood and the alleviation of water shortage. For a case study of the Chengbi River reservoir in China. Based on fractal theory, the flood season is divided into several sub-seasons by using four indexes (multi-year average daily rainfall, multi-year maximum rainfall, multi-year average daily runoff, and multi-year maximum daily runoff) in this study. The Cubic spline interpolation function is then used to determine the flood limit water levels of each sub-season. And the Benefit-Risk theory is applied to evaluate the effects of staged dispatching. The results show that the flood season of Chengbi River basin should be divided into the pre-flood season (13 April-6 June), the main flood season (7 June-9 September) and the post-flood season (10 September-31 October). Adjustment of flood limit water level for sub-season and benefit evaluation. When the risk rate after reservoir flood season operation increases by 0.13×10 -5 , the average annual expected risk is 0.2264 million RMB, and the average annual benefit increases by 0.88-1.62 million RMB. The benefits obtained far outweigh the risks, indicating the importance of staging the flood season.