Turbulence in a Bend in the Presence of Emergent Vegetation and a 3D Pool Bedform

The interaction of emergent vegetation and three-dimensional (3D) bedforms is essential for understanding turbulent flow dynamics in curved channels. A laboratory investigation can help to collect required data under controlled conditions. Experiments were conducted in a 9.5 m-long, 0.9 m-wide recirculating flume incorporating a 90° bend and a sculpted 3D pool bedform. Artificial rigid vegetation, designed to replicate the hydraulic behavior of natural emergent plants, was installed along both sidewalls. Instantaneous three-dimensional velocities were recorded using an acoustic Doppler velocimeter (ADV) across multiple cross-sections under both bare-bed and vegetated conditions. The results reveal that emergent vegetation markedly increases flow resistance, distorts mean velocity distributions, and suppresses the classical logarithmic velocity profile, particularly within the bend and pool regions. The combined presence of vegetation and the 3D pool bedform amplified turbulence intensity, elevated Reynolds shear stresses, and redistributed turbulent kinetic energy (TKE), which increased by up to sevenfold from the bend entrance to its exit. In vegetated pool sections, Reynolds stresses were approximately 12% greater than under bare-bed conditions, underscoring the synergistic effects of vegetation drag, secondary circulation, and flow separation in producing anisotropic turbulence. These findings highlight the importance of incorporating vegetation–bedform interactions in fluvial modeling frameworks, with significant implications for sediment transport prediction, channel stability evaluation, river restoration, and aquatic habitat design.