Velocity distribution for open channel flows with suspended vegetation

Suspended vegetation in open channels retards flow, which, as a result the vertical distribution of streamwise velocities, will deviate from the classic logarithmic law. To clearly understand the hydraulic properties of turbulent flow in an open channel with suspended vegetation, we analyzed hydraulic mechanisms by vertically dividing the flow region into three parts extending from the channel bed to the water surface: a basal non-vegetated layer, an internal vegetation layer and an upper vegetation layer. For each layer, the streamwise velocity was obtained by mathematically solving the momentum equations. Mixing length theory was adopted to determine the shear stress in the internal and non-vegetation layers, and some parameters were determined using published data from Plew’s detailed laboratory measurements. The good agreement between the analytically and experimentally predicted vertical distributions of streamwise velocity indicated that the three-layer model is both applicable and reliable.