Three-dimensional habitat suitability index as an ecological indicator for diagnosing dam-regulated fish migration corridor disruption and guiding turbine-level flow management

Dam operations alter the three-dimensional (3D) hydraulic environment of regulated rivers, yet ecological indicators capable of diagnosing how these alterations disrupt fish migration corridors remain lacking. This study develops a 3D habitat suitability index (HSI) as an integrated ecological indicator, coupling computational fluid dynamics with a multi-parameter fuzzy logic model, to diagnose corridor dynamics and guide turbine-level release management. Applied to the Wudongde high-head dam on the upper Yangtze River, with the endangered endemic Leptobotia elongata as target species, the HSI indicator reveals a two-scale diagnostic structure: at the river-channel scale, intermediate total discharge (∼3935 m 3 /s) maximizes high-suitability corridor extent; at the tailrace scale, HSI near the fish-passing facility entrance is governed by individual turbine configuration rather than total discharge — a distinction that conventional discharge-based ecological flow frameworks cannot resolve. An HSI-guided turbine allocation strategy re-established a spatially continuous high-suitability corridor in the model without structural modification, and field hydroacoustic surveys were consistent with the HSI-predicted preferred release conditions at the facility-entrance scale. These findings support the 3D HSI as a scenario-based diagnostic indicator for corridor disruption in regulated rivers. The framework provides a basis for adaptive, turbine-level release management, with full-corridor biological validation identified as a remaining requirement.