Optimal operation toward energy efficiency of the long-distance water transfer project

•Optimal scheduling of water pumping reduces energy uses of a water transfer project.•Using lateral inflows along the transfer route reduces the water pumping.•Water supplies in the middle section of the transfer route are more vulnerable.•Flexible water pricing is required in the context of hydrological variability. Energy efficiency plays an important role in the sustainable operation of the world's largest water transfer project, i.e., China’s South-to-North Water Transfer Project, by reducing its energy-related operating costs. However, effective energy-saving measures are still under development for the project due to its huge scale and complexity. An optimized operational model was established in this study to reduce the energy use of the eastern route of the South-to-North Water Transfer Project by optimally scheduling the water-pumping process of the different pumps along the transfer route in the context of hydrological variability. The optimized operational rules and recommended operational parameters were obtained. The results show that the proposed operational rules in the form of piecewise functions can reduce the water pumping of the project, thus providing a basis for reducing energy consumption. The energy use of the project’s water pumping could also be reduced in the wet years by using the local water in midstream lakes along the transfer route rather than the pumped water from the Yangtze River at the southern terminus of the route. In addition, it was also found that the initial water storage of the lakes along the southern part of the route has a greater impact on the volume of the water pumping. Raising the water levels of these southern lakes using local runoff at the beginning of a year would help reduce the subsequent water pumping from the Yangtze River and the relative energy use of the project. In addition. the key areas for energy-saving along the eastern route of the South–North Water Transfer Project were identified, providing new insights for understanding the water-energy nexus behaviors of a long-distance water transfer project.