Experimental analysis of vegetation heterogeneity on flow characteristics and bed morphology in partially vegetated channels

Abstract This study investigated the effects of varying vegetation heights and partial coverage on turbulent flow and bed morphology in a laboratory sand‐bed channel with an aspect ratio of 4.615. Vegetation was distributed to represent 33.3% emergent, 33.3% just submerged and 33.3% fully submerged plants (16 cm, 12 cm and 8 cm). Velocity measurements were made using a 5 cm down‐looking micro ADV, and bed morphology was surveyed with a Bosch GLM 400 Laser Distance Measurer after 24 hours of continuous flow. Results showed that while vegetation stabilizes riverbanks and beds, it also intensifies erosion in non‐vegetated zones. Streamwise velocity decreased by 20–40% downstream of vegetated areas and increased by 25–40% in non‐vegetated areas. Higher turbulent intensities were observed at the vegetated/non‐vegetated interface, while weaker intensities occurred within vegetated zones. The strength of streamwise‐vertical Reynolds shear stress is close to zero with negative magnitude in the shorter vegetation (8 cm) region, while higher with negative magnitude in taller vegetation (16 cm) at the interface of the vegetation region indicated helical flow due to the intermixing of different flow velocities. This research enhances understanding of the effects of heterogeneous vegetation on flow dynamics and sediment transport, offering insights for riverbank and riverbed restoration efforts.