Bedload Transport and Its Implication on Bed Morphology at a River Confluence

Abstract

River confluences are the key elements within fluvial systems, where three-dimensional flow fields and sedimentation patterns can have a substantial effect on the hydraulics, bed morphology of stream courses, and environments. The present study is configured to realize the alterations in bedload transportation and in bedform at confluence channel in relation to particular hydrological occurrences. It is anticipated that the patterns of the flow attributes following the confluence to be different from those in the conditions reported in other publication. Therefore, this article concisely reports the various flow aspects, examines the corresponding river bed patterns, and provides a brief description of the different flow properties. On the basis of field findings in response to fluctuation in the flow of contributory tributaries, the recorded morphological and sedimentological changes are explained. To accomplish this, bedload transport, bed surveys, and particle size distribution measurements were carried out at the study site during different hydrological seasons at intervals of two months from January 2018 to March 2019. The three major goals of this work were to comprehend the symmetry between two confluence channels, estimate bedload transport, and investigate the consequences of net fluvial behavior on bedform dynamics. The short-term impacts of stream flow irregularity on channel morphology and particle structures were discovered by repeated transect studies and bed material sampling at a small asymmetrical river junction. Results show that the confluence involves the shifting in the scour region, frequent erosion and deposition of sediments, and bar development at the downstream confluence as flow rate fluctuates following the hydrological changeability in the confluence channels. The average bedload at the confluence appears to be irregular in favor of the tributary, since two-thirds of the total bedload was carried across the shallow zone of the cross-section. A high speed digital camera was used to detect sand ripples, and video technique was utilized to obtain statistics on the presence of ripple geometries. Asymmetric two-dimensional ripples were observed in relatively calm weather conditions and in moderate winds. It was discovered that ripples generated by the two-dimensional flow were supplanted by flatbed circumstances and the normal two-dimensional wash-out ripples after the medium wind periods, demonstrating that the presence of a combined flow increases the induced bed shear stress.