Floodwater utilization for cascade reservoirs based on dynamic control of seasonal flood control limit levels

Reservoirs play an important role in flood control and conservation, in which the flood control limit level (FCLL) is the most significant parameter of the tradeoff between flood control and comprehensive utilization of water resources. This study was aimed at constraining the seasonal FCLL for cascade reservoirs to obtain more economic benefits without reducing the original flood prevention standards. Based on flood initiation and ending times during the flood season, fuzzy set theory was used to build the experiential and theoretical membership function of each day, which clarified the relationship between the seasonal FCLL and the designed FCLL, and then the total flood season was divided into sub-seasons. The seasonal FCLL was revised by analyzing numerous flood control operation schemes of cascade reservoirs to satisfy a given flood prevention standard. Using the case study of ShiQuqn and XiHe cascade reservoirs in the Hanjiang River, the proposed method was demonstrated to provide an effective design for the seasonal FCLL, which increased the FCLL in the pre-flood and post-flood seasons. Forty-five operation schemes with different combinations of ShiQuqn and XiHe reservoir’s FCLLs under five flooding frequency scenarios were evaluated to revise the seasonal FCLL. An optimization model with real-coded genetic algorithm was proposed to maximize hydropower generation by dynamic control of the FCLL. The results show that compared with the traditional operation, joint operation based on dynamic control of FCLL can generate 0.23 × 108 kWh (3.18%) more hydropower for the cascade reservoir system during the flood season without increasing the flood risk.