Author(s): Nathalie Friese; Kate L. Mathers; Christine Weber; Diego Tonolla; Nico Batz

Linked Author(s):

Keywords: Hydropeaking; Macroinvertebrates; Habitat response; Patch-scale hydraulics; Habitat modelling; River managemen

Abstract: Flow pulses generated by on-demand hydropower (i.e. hydropeaking) strongly affect riverine benthic communities by causing macroinvertebrate drift. Because benthic community composition is inherently patchy, macroinvertebrate drift responses are therefore also likely to be habitat specific. We investigated how patch-scale hydraulic processes mediate macroinvertebrate drift during short -term flow pulses using an in-situ portable flume. The flume allowed simulation of rapid flow pulses on 45 patches characterized by either slow (< 0.5 m s⁻¹) or fast (> 0.5 m s⁻¹) current velocity within a pre-alpine river reach supporting an unimpacted macroinvertebrate community. This in-situ approach bridges the gap between controlled laboratory flumes and observational studies in regulated rivers. In patches with slow current, drift intensity was primarily influenced by absolute current velocity (V40) and current velocity rise rate (V40rate), whereas in patches with fast current, the relative change in current velocity (V40%) was more influential. Moreover, V40% significantly shaped drift composition in slow- current habitats. These results demonstrate that flow-pulse-induced drift arises from patch-scale hydraulic stress rather than being uniform across the reach. Incorporating such habitat-specific processes into ecohydraulic models can improve the assessment of drift risk, identify vulnerable areas, and guide targeted mitigation strategies to reduce flow pulse induced hydraulic stress in sensitive habitats.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.153

Year: 2026