Research on minimum discharge flow protection scheduling strategies in flow-reduced reaches of Yalong River based on ecological security

Abstract

[Objective] To explore scheduling strategies for ensuring minimum discharge flow in flow-reduced reaches of the Great Bend of the Yalong River, thereby safeguarding aquatic ecosystem health. [Methods] The Mann-Kendall(M-K) test was used to detect non-stationarity in runoff series. A joint probability distribution model was established for mainstream and tributary inflows of the Luning cross-section of the Yalong River using the Copula function to analyze the wet-dry encounter characteristics of mainstream and tributary runoff. Subsequently, a strategy for ensuring minimum discharge flow at the Luning cross-section under inconsistent runoff conditions was proposed. A joint scheduling model for cascade reservoirs was established to analyze schemes for ensuring minimum discharge flow at the Luning cross-section and scheduling strategies for cascade hydropower stations under normal and extremely dry scenarios in the mainstream and tributaries. [Results] The result showed that an abrupt change in runoff occurred at the Jinping-II dam site around 1989. Both pre-and post-change periods exhibited low probabilities of wet-dry or dry-wet encounters in mainstream and tributary inflows. Compensation water releases from the Jinping cascade were necessary to maintain minimum discharge flow at the Luning cross-section. Under normal and dry scenarios of mainstream and tributary inflows, Jinping-II gate site required additional compensation water releases of 0 to 18.2 m³/s and 11 to 48 m³/s, respectively, beyond the ecological base flow. During intraday no-load operation of the Jinping cascade, the hydraulic connectivity between upstream and downstream reservoirs was leveraged to enhance the regulation capability of Jinping II. Joint scheduling of mainstream and tributaries was implemented to achieve the goal of minimum discharge flow at the Luning cross-section. [Conclusion] The M-K method effectively identifies abrupt change points in runoff at the Jinping-II dam site. The joint probability distribution model based on Copula function accurately describes the dependency between mainstream and tributary runoff. The proposed scheme for ensuring minimum discharge flow and scheduling schemes for cascade hydropower stations under different scenarios can effectively ensure the minimum discharge flow in flow-reduced reaches of the Great Bend of the Yalong River, thereby preserving aquatic ecosystem health.

Keywords

wet-dry encounter / Copula function / cascade reservoir / minimum discharge flow / scheduling strategy / Yalong River / influencing factor