Generalized instream habitat models

Conventional instream habitat models (e.g., the physical habitat simulation system) predict the impact of regulation on the habitats of freshwater taxa. They link a hydraulic model with microhabitat-suitability models for taxa to predict habitat values at various discharge rates. Their use requires considerable field effort and experience. Recent analyses performed in France suggested that comparable results could be achieved using simplified hydraulic data. We tested this approach for 99 stream reaches and nine aquatic taxa in New Zealand. The resulting generalized habitat models predict habitat values similar to those predicted by conventional models from simplified hydraulic data (depth-discharge and width-discharge relationships, average particle size, and mean annual discharge). As in France, within-reach changes in habitat values were linked to the specific discharge of reaches, while between-reach changes depended mainly on the Froude number at mean annual discharge. The generalized models perform well outside their calibration range. Models previously developed in France perform well in New Zealand. Such generalized models contribute to identifying the key hydraulic variables for freshwater taxa and should facilitate habitat studies worldwide.