Numerical simulation of bar and bank erosion in a vegetated floodplain: A case study in the Otofuke River

• Morphodynamics, chute cutoff and bar/channel coevolution were reproduced.
• Sand bar growth and discharge unsteadiness were key factors in meandering increase.
• Vegetation reduced channel width, resulting in a single-thread meandering channel.
• No vegetation changed the pattern from a single-thread to a multi-thread channel.
• Braided channel could be a moderately meandered channel by presence of vegetation.

Recent studies suggest that braided river could be single-thread channel by colonization of riparian vegetation; however, this kind of mutual interactions between physical and ecological processes in rivers are still poorly understood. Here we investigate the development of meandering channel in a river, which was originally braided and currently vegetated, the Otofuke River in Japan. The significant morphological processes of this river during a destructive flood event was studied using a two-dimensional morphodynamic model. Using well-calibrated parameters, this model qualitatively reproduced observed morphological changes such as the co-development of sand bars, bar-induced meandering and a chute cutoff. We find that for vegetated channels, meandering could maintain moderate sinuosity; in contrast, in the absence of riparian vegetation, bar-induced meandering channels could become braided. This suggests that distinct meandering channels could be a fundamental channel morphology in the originally braided, but currently vegetated river; however, the simultaneous occurrence of the chute cutoff and meandering indicates that this channel could not be a fully-developed high amplitude meandering channel.