| Abstrakt: |
Patterns of grain sorting and migration of a river channel bar have been studied and compared with an experimental channel bar generated in a laboratory flume. The influence of boundary effect on sand transportation vis-a-vis changing patterns of textural parameters has been observed from upstream to downstream ends of the bars. Results indicate that the effect of shearing and friction at the boundary walls/edges causes aperiodic sand movement influencing the textural parameters. In the channel's central part, such effects are least causing relatively free sediment transportation downstream. As a result, the grain sorting pattern changes from initial polymodality to unimodality at the central part. The central part apparently migrates faster than its lateral counterparts with the development of projection of patches of finer sediments at the bar toe. Correspondingly, low depressed areas are developed adjacent to boundary walls, which are gradually filled up by the bed materials with the migration of the bar. Morphologically, it appears that the bar migrates in large-scale mega-bed forms with consecutive crests and successive troughs. This study provides insights into the channel bar sedimentation and its migration pattern from the perspective of grain sorting. An integrated approach that considers lateral facies trends, sedimentary structures, and bar morphology allows for more robust paleoenvironmental reconstructions from these deposits. The findings validate the utility of scaled experiments to model natural sorting and migration processes in fluvial bars. |
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