Multi-objective model and decision-making method for coordinating the ecological benefits of the Three Gorger Reservoir

Abstract

The operation of the Three Gorges Reservoir (TGR) has changed the original flow regimes in the reservoir area, as well as middle and lower reaches of the Yangtze River, which may lead to algal blooms in the tributaries of TGR, changing conditions in the downstream of TGR for fish spawning and breeding, and saltwater intrusion in water sources area of Yangtze estuary. In this study, a multi-objective model is developed to improve the environmental issues both upstream and downstream of TGR by trading off the contradiction between the ecological benefits and the power generation considering these environmental problems mentioned above caused by the operation of TGR. Solving the multi-objective model with the non-dominated sorting genetic algorithm III (NSGA-III), the non-inferior solutions are obtained. And then the concept of subjective trade-off rate (STOR) is introduced to measure the level of preference of the decision-makers for each objective. Combining the STOR method and ecological risk analysis, a decision-making method is proposed to select the most suitable alternative. As a case study, the operation process of TGR in 2015 on a daily scale is simulated with the multi-objective model, and the most suitable operation rule is selected by decision-making method within the interval ranges for decision-makers’ preference. Analyzing the effect of different trade-off rates combinations on the level of objectives in the suitable alternative, and the result indicates that when the trade-off rates in the combinations increase, the power generation increases but the ecological benefits reduce. Considering this relationship and the trade-off rate ranges both determined to be [1,1.5] with a step of 0.05, some schemes are established. And then the most suitable solution is selected from these schemes, whose power generation is 1.74% less than the maximum and its ecological risk probability is optimal. The most suitable operation rule derived by the multi-objective model and decision-making method provides an operational reference for decision-makers to coordinate the water conflict between ecological benefits and power generation.