针对枯水期干支流梯级最小下泄流量保障与发电调峰需求难以兼顾，且缺乏干支流双向回水顶托作用下衔接水位研究的问题，本文以酉水干流石堤水电站、支流三角滩水电站及下游石堤控制断面为研究对象，基于地形测量、水文原型观测与一维水动力学模拟，构建了干支流梯级尾水双向顶托作用下的衔接水位判别方法、梯级最小下泄流量日均或瞬时泄放条件，模拟并验证了基于干支流梯级日内交替发电的水资源调度方案。结果表明：石堤和三角滩水电站的衔接水位分别为248.0m和248.33m；当两电站分别按不低于118m³/s和39m³/s发电泄流时，即可在对方停运期间保障坝下河段不脱水及基本生境需求，并满足下游控制断面的最小下泄流量要求；与常规运行调度相比，日内交替调度使下泄流量保障率提高约30%，综合发电效益提升约9%。研究表明，基于干支流梯级双向回水顶托的日内交替发电调度在严守生态底线的同时，实现了与发电效益的协同优化，为山区干支流梯级水库生态调度提供了可行的技术路径。

[Objectives]Current water resources management generally determines the implementation conditions for the minimum discharge of cascade hydropower stations based on the connecting water levels between upstream and downstream reaches.However, research on connecting water levels affected by backwater surcharge from the operation of cascade projects on main and tributary rivers remains insufficient. Aiming at the difficulty in simultaneously meeting the minimum discharge requirements and peak-load regulation demands for power generation of cascade reservoirs on main and tributary rivers during dry seasons, this study takes Shidi hydropower Station on the main stream of the Youshui River, Sanjiaotan hydropower Station on the Meijiang Tributary, and the controlled section at the downstream Shidi hydrological Station as the case study, and investigates the connecting water levels and the intra-day alternate water resources dispatching mechanism under the bidirectional backwater surcharge of main and tributary rivers.

[Methods]Based on topographic survey downstream of dams, prototype observations of the the water-level-discharge relationship, and one-dimensional hydrodynamic simulation, a discrimination method for connecting water levels was established to guarantee the hydraulic habitat of the main and tributary river channels as well as the minimum discharge at the controlled sections. The daily average and instantaneous discharge conditions for the minimum discharge under mutual tailwater surcharge of the two hydropower stations were analyzed. Combined with the inflow conditions and regulation capacities of the cascade projects, an intra-day alternate dispatching scheme for water resources of the mainstream-tributary cascade projects was proposed. The scheme is validated through dispatching simulation using daily inflow data from the past decade.

[Results] The results show that the connecting water levels at the tailwater sections of Shidi and Sanjiaotan hydropower Stations are 248.00m and 248.33m respectively. When the two cascade stations discharge for power generation at 118m³/s and 39 m³/s, respectively, the river reaches downstream of each dam can be prevented from drying up, with basic hydraulic habitats maintained while the counterpart station is shut down. In addition, the control index of minimum discharge at the Shidi Section can be satisfied. Simulation results indicate that, compared with the conventional operation mode, the intraday alternate dispatching increases the guarantee rate of minimum discharge for the two cascade stations and the Shidi Section by approximately 30%, and improves the comprehensive power generation benefit of cascade projects by about 9%.

[Conclusions]The intra-day alternate dispatching of water resources for cascade projects considering the bidirectional backwater surcharge of main and tributary rivers realizes the collaborative optimization of minimum discharge guarantee and power generation benefit improvement under the strict constraints of ecological red lines. This study provides a practical technical approach for ecological flow dispatching of cascade reservoir groups in mountainous mainstream-tributary river systems.