A comparative study of turbulent flow fields in the wake of an isolated boulder, vegetation patch, and wooden log

Over the past three decades, large roughness elements (LREs) have been widely used as instream habitat structures and playing a crucial role in the restoration and management of aquatic ecosystems. Understanding their influence on river dynamics is crucial for their effective implementation. Analyzing turbulence variations around LREs is key to quantifying their impact on flow and sediment dynamics, thereby informing the design of habitat structures, and improving water quality. In this study, we explored the comparative variations in turbulence parameters (e.g., turbulent intensity, turbulent kinetic energy, energy dissipation rate, and integral length scale profiles) in the wake of three submerged LREs: an isolated boulder, a vegetation patch, and a wooden log. Velocity time series measurements were conducted using a Vectrino Plus (Nortek) Acoustic Doppler Velocimeter (ADV) to estimate these turbulence parameters. The findings of this study highlight the complex interaction between LRE geometry, submergence ratios, and turbulence generation. Notably, vegetation patches exhibit a distinct dual-layer turbulence structure, with reduced turbulence within the canopy and elevated levels at the vegetation–water interface. Boulders and wooden logs generate high turbulence due to shear layer separation and vortex formation. The presence of LREs disrupts the expected turbulence decay patterns, leading to enhanced turbulence production, elevated energy dissipation rates, and complex, three-dimensional flow fields downstream. The study could provide valuable insights for hydraulic modeling and river restoration strategies by improving our understanding of how large natural roughness elements influence river dynamics.