Flow dynamics and turbulence patterns in a drainage channel colonized by common reed (Phragmites australis) under different scenarios of vegetation management

Drainage channels are a widespread component of agricultural and urbanized lowland landscapes. Management of instream and riparian vegetation along drainage channels must be planned by reconciling the need to ensure channel hydraulic efficiency with the need to preserve the riparian habitat. The present paper reports the experimental results of a study conducted on a drainage channel colonized by Phragmites australis in undisturbed natural conditions. The impacts of common reed on flow resistance, flow velocity distribution and turbulence parameters were examined with different discharges under three different scenarios of channel vegetation, which were obtained by means of machineries traditionally used in land reclamation areas. Removing either totally or partially the channel vegetation had great effects on streamwise velocity distribution and turbulence patterns, with small differences in global flow resistance. The experimental results suggest that clearing the channel vegetation just in the center of the cross section can improve the channel conveyance to values close to those obtained with the total removal of the vegetation, while maintaining relatively high levels of turbulent intensities.