In the context of water shortages, environmental flow is the key to alleviating the negative environmental impact of reservoir operation. Environmentally, the suitable stream flow for the survival and reproduction of aquatic organisms is a varying range, although most of studies now give it a fixed value, which leads to unreasonable resource allocations. In this study, we proposed a fuzzy representation of environmental flow by using the fuzzy theory and the ecological hydraulic radius. Furthermore, we used the Three Gorges-Gezhouba cascade reservoirs as a study case and Four Major Chinese Carps as indicator species. In addition, a multi-objective operation optimization model was established, which solved by the Evolver Palisade software, and a multi-objective risk analysis method was proposed based on the design reliability and risk rate of various benefit operations. The results show that: (1) Based on the environmental flow membership function, flow ranges suitable for the aquatic organism survival and reproduction at specific locations can be determined to help guide reservoir discharge.(2) Taking environmental flow membership as an optimization objective rather than a Water Resources Management 2 constraint is conducive to formulating environmentally friendly reservoir operation schemes and make more rational use of water resources. (3) The multi-objective risk analysis can avoid the one-sidedness of a single objective and analyze the risks brought by various benefit operations. Ecological demand has long been a factor considered when formulating reservoir operation schemes. Following the environmentally friendly operation scheme is helpful to protect the environment and maximize the overall benefits of reservoirs.

The risk of flood control in cascade reservoirs reflects the possibility of unforeseen events in upstream reservoirs under certain space-time conditions during the operation of flood control. Using @RISK software and a stochastic simulation model to simulate the inflow flood of cascade reservoirs, the flood routing of cascade reservoirs and the risk analysis of the highest water level were carried out based on the flood regulation rules of Three Gorges-Gezhouba cascade reservoirs. The results of simulation calculations show that the risk rate of the Three Gorges-Gezhouba cascade reservoir is lower than its design flood standard, which can ensure the safety of flood control.

In the context of water shortages, environmental flow is the key to alleviating the negative environmental impact of reservoir operation. Environmentally, the suitable stream flow for the survival and reproduction of aquatic organisms is a varying range, although most of studies now give it a fixed value, which leads to unreasonable resource allocations. In this study, we proposed a fuzzy representation of environmental flow by using the fuzzy theory and the ecological hydraulic radius. Furthermore, we used the Three Gorges-Gezhouba cascade reservoirs as a study case and Four Major Chinese Carps as indicator species. In addition, a multi-objective operation optimization model was established, which solved by the Evolver Palisade software, and a multi-objective risk analysis method was proposed based on the design reliability and risk rate of various benefit operations. The results show that: (1) Based on the environmental flow membership function, flow ranges suitable for the aquatic organism survival and reproduction at specific locations can be determined to help guide reservoir discharge. (2) Taking environmental flow membership as an optimization objective rather than a constraint is conducive to formulating environmentally friendly reservoir operation schemes and make more rational use of water resources. (3) The multi-objective risk analysis can avoid the one-sidedness of a single objective and analyze the risks brought by various benefit operations. Ecological demand has long been a factor considered when formulating reservoir operation schemes. Following the environmentally friendly operation scheme is helpful to protect the environment and maximize the overall benefits of reservoirs.

Flood pulses are closely related to river ecosystem health. Reservoirs bring many benefits to flood control, power generation, shipping etc., but their attenuation effects on the runoff flood pulses should not be ignored. Ecological operation can effectively reduce some negative ecological impacts brought by the reservoir. However, the inability to quantitatively assess ecological effects hinders the promotion of ecological operation in reservoir management. To solve this problem, we proposed 11 flood pulse indicators (FPI), a random simulation method and an ecology-economy coupling model in this study. In addition, we used Four Major Chinese Carps as indicator species and the Three Gorges Reservoir as a case study to test the role of flood pulses in improving the ecological operation effects of the reservoir from the fish protection perspective. The results show that: (1) FPI can be controlled by the reservoir and reflect the flood pulse characteristics of runoff. (2) Random simulation method guides managers to optimize the discharge and formulate eco-friendly operation schemes. (3) Ecology-economy coupling model helps managers analyze the relationship between ecological operation effects and economic benefits. A comprehensive assessment can improve the acceptance of ecological operation, which is conducive to the sustainable development of river ecosystem.