Optimal Design of Seasonal Flood Limited Water Levels by Jointing Operation of the Reservoir and Floodplains

Reservoirs play an important role in the exploitation and utilization of water resources, and the flood limited water level (FLWL) is a key parameter to balance flood control and conservation in reservoir operation. This study is aimed at joint operation of the reservoir and floodplains to improve floodwater utilization and enhance economic benefits. The net profits, namely the benefits from power generation and water supply minus the losses from the flood volume diverted to floodplains, are set as the objective function. To maximize the net profits, an optimization model is then proposed. Finally, a nonlinear optimization technique, the complex method, is used to find the optimal seasonal FLWL. The China’s Danjiangkou Reservoir (DR) is selected as a case study. The results show that the joint use of floodplains enables 2.0 m and 0.5 m increment of FLWLs in summer and autumn, respectively, compared to the conventional FLWLs. Since the increment of the FLWL decreases the reservoir flood storage by 0.44 billion m3, the flood volume need to be diverted to floodplains is increased by 0.54 billion m3 per year. Meanwhile, the power generation and water diversion are increased by 0.59% and 2.99%, respectively. The assurance probabilities of power generation, water diversion and minimum flow are also increased by 1.1%, 0.96% and 0.70%, respectively. As a result, the economic benefits can be increased by 0.037 billion USD per year. It is concluded that the reservoir seasonal FLWL can be improved by joint operation of reservoirs and floodplains, which is able to enhance economic benefits without increasing flood risks. Moreover, the increment of economic benefits could be shared by reservoir managers and residents that live in floodplains. This novel operating approach is helpful to the integrated water resources management.