Design floods and flood control water levels during operation period of cascade reservoirs in lower Jinsha River

The joint operation of upstream reservoirs has altered the natural inflow and sedimentation conditions of the cascade reservoirs in the lower Jinsha River.Consequently, the original design floods and flood limited water levels no longer meet the demands of flood and drought prevention and the efficient utilization of water resources in the new era.To quantify the impact of upstream reservoir regulation, the Most Likely Flood Regional Composition (MLFRC) method and the Most Unfavorable Flood Regional Composition (MUFRC) method were modified based on the Vine Copula.The design floods for the cascade reservoirs in the lower Jinsha River were estimated and compared with the non-stationary flood frequency analysis (NFFA) method.Furthermore, the flood control water levels (FCWL) and hydropower generation benefits were reevaluated.The results indicate that: ① The regulation of upstream cascade reservoirs has significantly reduced the design floods.For the operation period of the Xiangjiaba Reservoir, the 1000-year design peak discharge and the 3-day, 7-day, 15-day, and 30-day flood volumes decreased by approximately 40.7%, 37.8%, 33.9%, 24.4%, and 13.2%, respectively, compared to the natural design values.② Maintaining the original flood control standards unchanged, the FCWLs of the Wudongde, Baihetan, Xiluodu, and Xiangjiaba reservoirs can be raised to 958.56 m, 794.67 m, 568.75 m, and 373.42 m, respectively, resulting in additional power generation of 2.43 billion kW·h from June to September.③ The results obtained from the MLFRC and MUFRC methods show no significant difference from those of the NFFA method, but they can reflect the flood control and dispatch of upstream reservoirs in greater detail.This research can provide theoretical and technical support for the operation of cascade reservoirs in the lower Jinsha River and contribute to the realization of flood resource utilization.