Linking mesohabitat delineation and landscape metrics to assess the riverscape following multiple dam removals

Abstract

Assessing the riverscape following dam removal requires measurable indicators of physical habitats. We developed and applied a framework for in-stream physical habitat assessment at three reaches of a Nordic lowland river undergoing dam removal and rapids restoration. Flow velocity and water depth were measured with an Acoustic Doppler Current Profiler under comparable pre-and post-restoration discharge. Measurements were interpolated, and spatially contiguous, homogeneous hydraulic patches were delineated using hierarchical clustering. Deterministic patch classification characterised habitat composition, and nine landscape metrics, reflecting hydraulic heterogeneity, spatial connectedness, and diversity, served as proxies for habitat quality. The delineated patches accurately represented spatially explicit hydraulic conditions pre-and post-restoration, and landscape metrics revealed clear restoration effects: incorporating the restored rapids as additional mesohabitat increased values in 25 of the 27 metric–reach combinations, with hydraulic heterogeneity rising 25–47%, and relative richness increasing by þ 0.10 (one additional habitat class) in each reach. These results emphasise the impact of restoring hydraulically diverse habitats. This study advances restoration impact assessment by linking meso-scale habitat delineation with landscape metrics from a riverscape perspective. The framework is transferable to other river environments and flexible in using hydrodynamic model outputs or field data, offering a practical approach for restoration planning and evaluation.