Author(s): Abul Bm Baki; Hasan Zobeyer; Md Aminul Islam Shagor; Haitham Ghamry; Christos Katopodis; Tom A. Langen

Linked Author(s): Haitham Ghamry, Christos Katopodis, Abul Baki

Keywords: Fish suitability index (FSI); Habitat-scale hydrodynamic complexity metrics; Instream boulders; River2D model; Weighted usable area (WUA)

Abstract: Nature-based instream habitat structures (IHSs) enhance hydraulic and ecological complexity, yet most suitability assessments rely on simplified hydraulics and hydrology alone. This study integrates the Habitat- scale Hydrodynamic Complexity Metrics (HHCMs) framework into a validated River2D physical-scale model derived from the Ecohydraulics Flume at Clarkson University for an instream boulder-dominated channel. Flow scenarios spanning low (SR < 1.0), medium (SR = 1.5, 2.5), and flood (SR = 3.5) submergence, and boulder densities (λ = 0–8.3%) were simulated. HHCMs were synthesized into a bounded Fish Suitability Index (FSI; 0–1) and spatially aggregated as Weighted Usable Area (WUA). Preliminary results indicate that the uniform bed (no-boulder) condition produced substantially lower weighted usable area (WUA), whereas the introduction of boulders have increased WUA by creating hydraulic refugia and wake zones. Among the tested configurations, moderate boulder densities showed the most favorable balance between habitat availability and flow connectivity. Results confirm that hydrodynamic refuge and layout, not density alone, govern reach-scale suitability, establishing HHCM-based FSI as a predictive ecohydraulics restoration design tool.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.244

Year: 2026