The need for operational models describing the friction factor f in streams remains undisputed given its utility across a plethora of hydrological and hydraulic applications concerned with shallow inertial flows. For small-scale roughness elements uniformly covering the wetted parameter of a wide channel, the Darcy-Weisbach f= 8 (u*/U b) 2 is widely used at very high Reynolds numbers, where u* is friction velocity related to the surface kinematic stress, U b= Q/A is bulk velocity, Q is flow rate, and A is cross-sectional area orthogonal to the flow direction. In natural streams, the presence of vegetation introduces additional complications to quantifying f, the subject of the present work. Turbulent flow through vegetation are characterized by a number of coherent vortical structures:(i) von Karman vortex streets in the lower layers of vegetated canopies,(ii) Kelvin-Helmholtz as well as attached eddies near the vegetation top …