Ecological Scheduling of Middle and Lower Reaches of Han River for Drifting Egg Fish Species

With the successive completion of the cascade hubs in the middle and lower reaches of the Han River, the natural flow of the river has inevitably been hindered. To solve the problem of blocked spawning of drift-spawning fish, this study quantifies the ecological and hydrological threshold values required for spawning based on the ROC model, and combines the SWAT semi-distributed hydrological model and the MIKE11 one-dimensional hydrodynamic model to study and formulate different dispatching schemes under various scenarios. Results demonstrate that the eco-hydrological thresholds for drifting-egg fish reproduction require water level rise duration ≥3 days and daily water level increase ≥0.3m (P<0.1, AUC>0.95). Model simulations established triggering conditions when flow rates reach ≥1200m³/s at Huangzhuang Station (Hanjiang) and ≥100m³/s at Dongpo Station (Tangbai River). Furthermore, under three operational conditions with flow rates ≥1200m³/s and 2100m³/s at Huangzhuang Station, combined with ≥300m³/s and 600m³/s at Dongpo Station, the proposed coordinated sluice-opening schemes among cascaded projects can simultaneously satisfy both reservoir recharging requirements and spawning habitat restoration objectives across different reproduction zones.