Mechanism of Flow in Patchy Gravel and Vegetated Beds

Velocity and turbulence measurements were performed in an open channel with patchy gravel and vegetated beds in order to further understand the transport processes and flow regimes that exist in open channels. The results of laboratory experiments that describe the mechanisms and transport features of heterogeneous flexible and rigid strip vegetation flow interaction with gravel roughness are presented. The paper examines the shear layers and momentum transport that arise as a result of a particular type of patchy roughness distribution. It is shown that relative to a gravel bed, the vegetated section of the channel generally resembles a free shear layer. The resistance within the vegetation porous layer reduces the velocity and creates a sharp transition across the interface at the top of vegetation; of primary importance is the shear layer at the top of the vegetation which influences and dominates the overall momentum transport. At the boundary between the gravel and vegetated section, the lateral momentum transportis observed to be a maximum. The Sweep motions are more significant near bed while Ejections dominates the flow at the upper region of the flow.