Author(s): Kerstin Schlobies; Erik Van Rooijen; Davide Vanzo; Eliisa Selina Lotsari

Linked Author(s): Davide Vanzo

Keywords: Habitat delineation; Hydraulic units (HUs); Dam removal; River restoration; Hydroacoustics; ADCP

Abstract: Restoring rivers through dam removal can substantially alter fluvial mesohabitat composition, providing insights into how restored river reaches evolve. Our case study is the Nordic Hiitolanjoki River, the most important landlocked salmon river in Finland, where three dams were removed and replaced with restored rapids between 2021 and 2023. We collected thousands of hydroacoustic measurements using an Acoustic Doppler Current Profiler (ADCP) downstream of the removed dams before and after the dam removal under comparable discharge conditions. These datasets were used to delineate hydraulic units (HUs). To do so, we developed PatchBuilder, a Python -based tool that performs fast hierarchical clustering with a spatial contiguity constraint to delineate mesohabitat patches based on interpolated water depth and depth-averaged flow velocity from field data. In a further step, we applied deterministic classification to group the delineated HUs into overarching habitats of similar hydraulic characteristics. Our findings indicate a shift in the high -velocity core in two of the three studied reaches following dam removal and rapids restoration. The approach demonstrates the potential of hierarchical clustering for mesohabitat delineation to assess river restoration outcomes. Furthermore, this framework supports the assessment of habitat composition, thereby contributing to strategies aimed at mitigating habitat loss in aquatic ecosystems.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.215

Year: 2026