This paper analyzes the complex relationship among flood control, power generation and ecological maintenance for the four cascade reservoirs located on the lower reaches of the Jinsha River, China. A weighted flood control index is incorporated and a constraining method consisting of the combination of a constrained corridor and a penalty function is proposed. A comprehensive utilization model is established in this paper based on the objectives of flood prevention, power generation, and ecological maintenance of the downstream cascade reservoir group of the Jinsha River during flood season. In addition, based on the coalescent selection of reference points and vector angles, an optimized non-dominated sorting genetic algorithm (VA-NSGA-III) is proposed. The algorithm is applied to the constructed model to define the cooperative competition mechanisms among these three targets, resulting in a set of non-inferior scheduling schemes with more uniformity and better convergence acquired with VA-NSGA-III. The scheduling program shows that there is a non-linear competitive relationship between the power generation and ecological effects of the cascade reservoirs during flood season, and the competitiveness weakens as the power generation increases. Furthermore, when the flood control is at low risk, there exists a complex coupling relationship between competition and coordination of the flood control, power generation, and ecological maintenance. While the risk appears high, there is a competitive relationship between flood control and power generation, with flood control being in synergy with ecological maintenance.

To promote ecosystem protection in the Wujiang River, this paper proposes a practical approach for calculating the environmental flow. The proposed approach combines the idea of the “guarantee rate” of the flow duration curve (FDC) method and the grading idea of the Tennant method. A daily flow series of the Wujiang River was compiled from 1956 to 2019 and used to compare the effect of the proposed approach versus the traditional approaches in four selected sections along the river. The results show that the environmental flow of the Wujiang River can be divided into five levels by the T-FDC method, with a level-by-level disparity, and all levels can capture the temporal and spatial variability of river flow. Additionally, the calculated basic environmental flow process ranges between the historical minimum and second minimum monthly average flow, and the threshold width of the optimal flow is more reasonable than the Tennant method. The T-FDC method can provide technical support for Wujiang River ecosystem management and sustainable development.

The multi-objective optimal operation and the joint scheduling of giant-scale reservoir systems are of great significance for water resource management; the interactions and mechanisms between the objectives are the key points. Taking the reservoir system composed of 30 reservoirs in the upper reaches of the Yangtze River as the research object, this paper constructs a multi-objective optimal operation model integrating four objectives of power generation, ecology, water supply, and shipping under the constraints of flood control to analyze the inside interaction mechanisms among the objectives. The results are as follows. (1) Compared with single power generation optimization, multi-objective optimization improves the benefits of the system. The total power generation is reduced by only 4.09% at most, but the water supply, ecology, and shipping targets are increased by 98.52%, 35.09%, and 100% at most under different inflow conditions, respectively. (2) The competition between power generation and the other targets is the most obvious; the relationship between water supply and ecology depends on the magnitude of flow required by the control section for both targets, and the restriction effect of the shipping target is limited. (3) Joint operation has greatly increased the overall benefits. Compared with the separate operation of each basin, the benefits of power generation, water supply, ecology, and shipping increased by 5.50%, 45.99%, 98.49%, and 100.00% respectively in the equilibrium scheme. This study provides a widely used method to analyze the multi-objective relationship mechanism, and can be used to guide the actual scheduling rules.

The lower reaches of Jinsha River host the richest hydropower energy sources in China. With the construction of Wudongde and Baihetan, the multi-objective optimization for cascade reservoirs (along with Xiluodu and Xiangjia Dam) in the lower reaches of Jinsha River will create significant benefits. This paper focuses on the competitive relationship between flood control and power generation, and attaches attention to the measurement of different objective functions and their competitive relationship. With observations of the flood in 1974, 1981, and 1985, a 100-year return period flood with peak-3d volume pair as different inputs for the optimal model is approached by NSGA-II. Different flood seasons divided by flood feature is applied to figure out specific competitive relationship. The results can be concluded as the following: (1) Strong competitive relationship mainly occurs in pre-flood season. (2) Whether it shows a strong competitive relationship depends on the amount of discharge. If the turbine is set to full capacity, power generation is fulfilled certainly, which means that there exists a weak competitive relationship between multi-objectives. (3) The different processes of floods have an effect on the duration of a competitive relationship. A flood with a late peak causes the extension of strong competition in the pre-flood season, which lends itself to a strong competition relationship in the post-flood season. (4) The intensity of competition in the pre-flood season is higher than that in the post-flood season because it has a larger range.

Climate change has far-reaching impacts that have created new challenges for water resource management. As an important measure to coordinate the relationship between society, economy, and environment, reservoir scheduling can reduce the future impact of climate change. It is, therefore, important to investigate the impacts of scheduling on reservoir operation. In this study, a reservoir system in the Pearl River Basin was selected to explore these impacts. Results show that the basin temperature significantly and abruptly increased in 2000, and precipitation and streamflow changed abruptly in 1983 and 1992. Historically, climate change has increased power generation, increased the risks to water supply security and ecological protection, and altered the relationship between power generation and ecological protection objectives. Based on 28 global climate models, the rank scoring method, Delta statistical downscaling, and the SWAT model, three emission scenarios (RCP2.6, RCP4.5, and RCP8.5) in CMCC-CM were evaluated to assess the climate change impact. In the future, the temperature will continue to exhibit an increasing trend, and the amount and distribution of streamflow will be altered. Although climate change will increase power generation in the dry season, it will also bring about new challenges for ecological protection and water supply security. Accordingly, the Datengxia Reservoir operating rules may require significant amendments.

There is a conflict between the hydropower benefit of hydraulic engineering and other functions such as ecological protection, water supply, flood control, etc. Deciding on an appropriate scheme to balance the interests among multiple objectives is a crucial issue in hydropower operation management. The Pareto set is the carrier and embodiment of a multi-objective mutual feedback relationship. It has a constant increasing or decreasing tendency, and most distribute unevenly, meaning different change rates and sensitivities are embedded. Based on this understanding, a new idea of "profit/loss ratio" is obtained, which constructed the average change rate of each neighbouring non-inferior solution on the Pareto frontier. Processed dimensionless, a new non-dominated subset of Pareto non-inferior solutions is filtered out according to the dominance relationship to limit scheme selection scope. On this basis, a method for calculating the "bias degree" of each Pareto non-inferior solution relative to different objective functions is proposed, which leads to the quantitative evaluation of Pareto solutions and provides quantitative support for decision-makers select operation schemes according to their preferences. Taking the cascade reservoirs in the lower reaches of the Jinsha River Basin in China as a case, the trade-off between the two objectives of hydropower generation and ecological protection is investigated, and the feasibility and effectiveness of the methodology are verified.