Optimization scheduling of cascade reservoirs under an ecological approach: a case study

Abstract

The Yalong River Basin is a significant hydropower base and a crucial component of the global biodiversity hotspot, Mountains of Southwest China. There are five key cascade reservoirs in the lower reaches of Yalong River. The current optimal operation focuses on power generation and flood control, which alters the natural flow regime and adversely affects the river ecosystem. To address the lack of ecological flow considerations in this basin, a study on optimal dispatching of cascade hydropower stations with minimum ecological flow requirements incorporated was conducted. First, based on hydrological variations in the study area, the Improved Ten-day Frequency Method (ITFM) is used to calculate the minimum ecological flow requirements. Second, a medium- and long-term multi-objective optimization model balancing power generation and ecological objectives was established, which aimed to maximize power generation and minimize the sum of ecological alteration degrees for the cascade hydropower stations, and was solved using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). Subsequently, ecological scheduling schemes for cascade reservoirs in various typical years are determined. The results show that the hydrological change point of the Yalong River Basin occurred in 1992, with the runoff differences before and after this point are significant. Compared to conventional scheduling schemes, under the ecological-prioritizing scheme, the proposed ecological scheme achieved reductions in ecological alteration degrees of 37.74%, 19.84%, and 58.6% in the three typical years of wet, normal, and dry, which shows a significant increase in ecological benefits. This approach demonstrates the significant role of ecological regulation in facilitating the restoration of river ecosystems and provides a valuable reference for reconciling the conflict between reservoir power generation and downstream ecological water use.