A reservoir ecological flow optimization framework for multiobjective fish conservation under multipoint water...

Large-scale water diversion projects mitigate water scarcity but often involve diversions at multiple points, degrading hydrological regimes and threatening downstream fish habitats. To mitigate these impacts, an integrated framework was developed for allocating and optimizing ecological flows for multiobjective conservation. The framework is first used to identify critical habitats through a spatial overlay analysis of hydrological and ecological sensitivities. Then, species-specific flow requirements are quantified by integrating two-dimensional hydrodynamic modeling with habitat suitability criteria under the Instream Flow Incremental Methodology (IFIM). Finally, a novel Hydrological Connectivity-Habitat Function (HC-HF) coupled model is introduced to resolve flow conflicts and optimize releases for upstream and downstream habitats. The framework was demonstrated in the Dadu River headwaters, a key source area for China's South-to-North Water Diversion Project, where critical spawning grounds of three endemic fish species (Hucho bleekeri, Schizothorax davidi, and Schizothorax prenanti) were identified. Species-specific ecological flow requirements during spawning periods were quantified, with optimal flows of 70 and 21 m³/s determined for H. bleekeri. The application of the HC-HF model significantly improved the comprehensive habitat quality by 22.8 %, as measured by the weighted useable area (WUA). The optimized coordinated reservoir releases were determined to be 47.0 and 6.4 m³/s, representing 98 % and 31 % of the multiyear average flows, respectively. This study provides a robust and transferable framework for managing ecological flows in complex river systems affected by multipoint water diversions, offering a pragmatic pathway to balance human water security and ecosystem conservation goals.