Longitudinal Mean Velocity and Turbulent Kinetic Energy Within an Emergent Canopy in Nonuniform Flows

Abstract Vegetation‐induced drag generates nonuniform water surface profiles through flow disruption, creating complex hydrodynamic conditions characterized by enhanced turbulence and energy dissipation. This study investigates the longitudinal velocity and turbulent kinetic energy (TKE) dynamics in emergent canopies under streamwise varying flow conditions. Laboratory flume experiments systematically examined four vegetation densities and two flow discharge scenarios. The results indicate that the time‐mean longitudinal velocity and the TKE both enhance significantly downstream along the emergent canopy. Based on TKE budget, an analytical model to predict the longitudinal TKE evolution within the emergent canopy was developed. Compared to uniform flows in a vegetated channel, the flow nonuniformity gives rise to distinct terms including the streamwise‐position dependent mean velocity , water surface gradient , and Froude number Fr( x ). The model reveals an effective power‐law exponent of 2/3 between longitudinal TKE and mean velocity, rather than the canonical value of 2, attributed to residual energy contributions from the water surface gradient. These results provide a mechanistic framework for predicting the streamwise turbulence evolution in vegetated floodplain flows, addressing a critical gap in ecohydraulic modeling.