Comparative analysis of modeled and measured vegetative Chézy flow resistance coefficients in a drainage channel vegetated by dormant riparian reed

Field hydraulic experiments have been conducted in an abandoned drainage channel colonized by dormant Phragmites australis (common reed) riparian plants. Hydrodynamic measurements (3D water flow velocity fields and water level at bankfull) were taken under stationary hydraulic conditions for a partial reed coverage scenario. Reed canopy cover has been characterized through field vegetation measurements (i.e. stem diameters, reed heights and density, expressed as the number of plants for unit bed surface area). Then, global flow resistance was determined during a real-scale experiment carried out under steady flow conditions. Two vegetative flow resistance models, respectively combined with four distinct composite cross section methods and the divided channel method, were evaluated in comparison with the global flow resistance retrieved by the hydrodynamic field measurements. The global flow resistance was expressed in terms of vegetative Chézy flow resistance coefficients. The model proposed by Baptist et al. combined with the Yen composite cross section method resulted to be the most accurate.