Flow resistance in open channels with leafed flexible vegetation and large-scale bedforms

Vegetation is a ubiquitous feature of river systems affecting flow and sediment transport processes and being of importance for many engineering and ecological applications. The hydraulic resistance of vegetated channels depends on many factors including form drag due to the presence of the plants, as well as the roughness of the channel itself. In case bedforms are present, an additional hydraulic resistance must be considered depending on bed form drag. Many open questions arise regarding how these multiple and interconnected roughness scales can be adequately characterized. This paper investigates the applicability of the linear superposition principle of the hydraulic resistance in vegetated channels with a mobile bed characterized by large-scale bedforms, a bed configuration that for example, can be found in floodplains or drainage ditches. The results of this study therefore reveal the need to revise the models to estimate flow resistance in river environments.