This study developed a novel framework integrating UAV-derived orthophotography, deep learning-based substrate classification, two-dimensional hydraulic modeling, Froude number (Fr) analysis, and multispecies habitat suitability assessment to evaluate the effects of channel modification and precipitation on fish habitats in Gaoliao Creek, eastern Taiwan. Habitat changes under baseflow and rainfall-induced high-flow conditions were quantified using Fr-based hydraulic habitat availability and Habitat Suitability Index (HSI)- and Combined Habitat Suitability Index (CHSI)-based habitat suitability. Channel modification transformed the channel from a deep and slow-flowing system into a shallower and faster-flowing environment. Under baseflow conditions, the proportion of available habitat meeting the adopted hydraulic criteria decreased from 81.6% to 73.9%, whereas the CHSI-derived proportion of weighted usable area (PUA) increased from 0.300 to 0.323 due to favorable substrate composition. During rainfall events, habitat availability and suitability declined markedly during peak flows and recovered as discharge receded. Compared with the pre-engineering channel, the modified channel exhibited greater sensitivity to short-term hydrological fluctuations but effectively prevented overbank flooding during the selected extreme rainfall event. These findings highlight the trade-off between flood-control benefits and ecological resilience and emphasize the importance of maintaining habitat heterogeneity in river management. Because the analyses were based on a single typhoon-related rainfall event and lacked direct biological validation, the results should be interpreted as event-specific predictions requiring further verification.
Hu et al. (Mon,) studied this question.