Author(s): Naima Reggad; Abul Bm Baki; Christos Katopodis; Haitham Ghamry; Hasan Zobeyer

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

Keywords: Instream boulders; Stream restoration; Computational Fluid Dynamics (CFD); Habitat complexity metrics

Abstract: Instream boulder placement is a common river restoration technique that significantly alters wake zones, mean and turbulent flow characteristics, and sediment transport processes , thereby shaping instream habitat quality and availability. This study applied Computational Fluid Dynamics (CFD) modeling to investigate the mean and turbulent flow fields and their corresponding habitat -scale hydrodynamic complexity metrics (HHCMs) within a boulder-dominated channel under varying flow regimes. Th e CFD model is developed and validated using controlled laboratory experiments in the Ecohydraulics Flume at Clarkson University, where high-resolution Digital Elevation Models (DEMs) of the channel geometry were generated through the Structure-from-Motion (SfM) photogrammetry technique. A detailed sensitivity analysis comparing multiple turbulence closure models (k–ε, k–ω , and RSM) against ADV measurements of velocity magnitude and turbulent kinetic energy (TKE) was performed to identify the most reliable turbulence formulation. The k–ω model was selected for the mean flow, while the Reynolds Stress Model (RSM) was selected for turbulence due to its superior predictive capability. Analyses focused on patterns and variability in HHCMs, including energy gradients, turbulent kinetic energy, turbulent energy dissipation rates, Reynolds shear stresses, and vorticity, reveal distinctive patterns across different arrangements of boulders and lead to novel relationships between HHCMs and flow regimes. These findings highlight the role of boulder -induced flow complexity in driving habitat diversity, offering predictive tools for ecohydraulic stream restoration. The integration of CFD with high -resolution bathymetry advances the design of restoration interventions that balance hydraulic and ecological goals.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.140

Year: 2026