Ecological scheduling of cascade hydropower stations on middle and lower Hanjiang River for four major Chinese carps

The successive completion of cascade hydraulic hubs in the middle and lower Hanjiang River has inevitably obstructed the natural river flow. To address the impaired hatching of drifting-egg fish species, this study quantifies the required eco-hydrological threshold indices for spawning using the ROC model, and combines the SWAT semi-distributed hydrological model and the MIKE11 one-dimensional hydrodynamic model to draft scheduling schemes under different scenarios. The results indicate that: ① the eco-hydrological thresholds for drifting-egg fish reproduction are a water level rise duration ≥3 days and a daily water level increase ≥0.3 m (P < 0.1, AUC>0.95). ② Model calculations determine the triggering conditions as: flow ≥1 200 m³/s at Huangzhuang Station (Hanjiang mainstem) and flow ≥100 m³/s at Dongpo Station (Tangbai River). Under three combined conditions-Tangbai River (Dongpo) ≥600 m³/s and Hanjiang (Huangzhuang) ≥2 100 m³/s, or Tangbai River (Dongpo) ≥300 m³/s and Hanjiang (Huangzhuang) ≥1 200 m³/s, or Tangbai River (Dongpo) ≥100 m³/s and Hanjiang (Huangzhuang) ≥1 200 m³/s-the coordinated open-discharge scheduling of the Yakou, Nianpanshan, and Xinglong hubs can satisfy the spawning and reproduction needs of the four major Chinese carps in the middle-lower Hanjiang River mainstream to varying degrees.