Sediment Transport in Meandering Streams: New Insights Based on a Large Width-to-depth Ratio Laboratory Experiment

The coupling between meandering flow, sediment transport and bed morphology is investigated. For this purpose, detailed flow velocity measurements and particle tracking were carried out in a sine-generated channel with a flat bed; the stream sinuosity and flow width-to-depth ratio were equal to 1.5 and 17.4, respectively. The results were analyzed in view of the bed topography produced in previous mobile bed experiments conducted in a similar channel and conveying a nearly identical flow. It is found that the process of bed deformation, and especially the location in flow plan of the point bars, was primarily driven by the convective acceleration-deceleration of flow. Cross-circulatory motion was found to contribute to the process of bed deformation primarily by determining the ultimate shape of the bars. The experiment in this paper is the first to provide factual evidence for previous anedoctal observations that point bars in meandering rivers and streams do not necessarily emerge as the result of cross-circulatory motion transporting the material across the channel from the outer to the inner bank around the apex.