Cobble-bed concentrations and vegetated banks: effects on flow

The effect of cobble concentration and vegetated banks on the mean flow and turbulence of streams has not yet been investigated. Cobble concentrations ranging from 10 to 30 cobbles/m² were tested by this study. In total, 27 velocity profiles were measured using an acoustic Doppler velocimeter (ADV) at a sampling frequency of 200 Hz. The results show that cobble concentration affects the mean velocity and turbulence intensity profiles close to the vegetated bank, especially near the bed, but does not influence the RS distribution. This experimental study reveals a Z-shaped Reynolds stress (RS) distribution near the vegetated bank without any negative values, but a convex distribution at the centre of flume with negative values near the water surface. Negative RS values are associated with dominant effects of the inward and outward events near the water surface. The effect of cobble concentration on the frequency of bursting events is not considerable, based on the quadrant analysis.