Hydrodynamic adjustment subject to a submerged canopy partially obstructing a flume: Implications for junction flow behaviour

The scenario of a submerged canopy partially obstructing a channel is common in the natural aquatic flow environment. This study experimentally evaluated the flow adjustment performance and vertical flow structure adaptive to a submerged partially distributed canopy. The experimental results showed that the canopy interior velocity adjustment distance for submerged partially distributed canopies was comparable with that for emergent ones. However, it was smaller than that for submerged fully distributed canopies but comparable with that for emergent fully distributed ones. For the fully developed flow, the neighbouring open waters insignificantly impact the flow structure in the vegetation region (VR), where the mixing‐layer flow behaviour arising from the generation of the vertical coherent vortices was maintained. The vertical mixing‐layer flow behaviour characterised by pronounced vertical Reynolds shear stress transversely extended into the nonobstructed region, suggesting that the canopy‐side waters significantly impacted the neighbouring open flow. This effect decayed in the case of decreasing canopy density and as the location leaving the junction region (JR). Of importance was that near‐bed velocity deflection occurred in the JR and was facilitated by canopy density. Vertically nonuniform distribution of transverse momentum exchange from horizontal coherent vortices due to bed depression can account for the near‐bed velocity deflection. The gained knowledge allowed the development of a phenomenological model for understanding the vertical flow structure in partially vegetated channels.