Abstract: To investigate the impact of one-sided floodplain vegetation on secondary flow in meandering channel, we designed meandering compound channels with smooth floodplains and one-sided vegetated floodplains in a generalized manner, and measured the cross-sectional instantaneous velocities using an Acoustic Doppler Velocimeter (ADV). The experimental results revealed that the formation of main vortexes in a single bend is solely influenced by centrifugal force, whereas the formation of main vortexes in the experimental meandering compound channel is closely associated with flow exchange between the floodplains and the main channel. When the relative water depth is 0.15, compared to the situation under smooth floodplain conditions, the secondary flow intensities at the apex sections with the narrowest vegetated floodplain and in crossover areas exhibit larger attenuation, but there is no apparent difference for the secondary flow intensity at apex section with the widest vegetated floodplain. For the relative depth of 0.35, the secondary flow intensity at each cross section in the meandering channel is enhanced, with the secondary flow intensity under one-sided vegetated floodplain conditions being smaller than the corresponding value under smooth floodplain conditions. In the case of one-sided vegetated floodplain conditions and the same relative depth, the secondary flow intensities in the crossover areas with a smooth upstream floodplain are notably larger than the corresponding values in crossover areas with a vegetated upstream floodplain. Under the smooth floodplain conditions, the “island center” of the cross-sectional contours of Reynolds stress R_vw can indicate the rotational center of the main vortex. The positive or negative sign of the Reynolds stress R_vw at the “island center” can reflect the rotational direction of the main vortex. Conversely, under the one-sided vegetated floodplain conditions, the R_vw contours in the cross-sectional middle parts appear disordered and do not demonstrate the aforementioned characteristics, with the absolute values of Reynolds stress R_vw being noticeably smaller than the corresponding values under smooth floodplain conditions.

Key words: meandering compound channel, one-sided floodplain vegetation, secondary flow, relative intensity, curl