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.
Similar content being viewed by others
REFERENCES
Aagaard, T., Hughes, M., Baldock, T., Greenwood, B., Kroon, A., and Power, H., Sediment transport processes and morphodynamics on a reflective beach under storm and non-storm conditions, Marine Geol., 2012, vol. 326–328, p. 154–165.
Ashmore. P. and Gardner, J.T., Unconfined confluences in braided rivers, River Confluences, Tributaries and the Fluvial Network, 2008, Chichester: John Wiley and Sons, pp. 119–147.
Balouchi, B. and Shafai Bejestan, M., The effect of bed load on maximum scour depth at river confluence, J. Ecol. Environ. Conserv., 2012, vol. 18, no. 1, pp. 157–164.
Balouchi, B., Nikoo, M.R., and Adamowski, J., Development of expert systems for the prediction of scour depth under live-bed conditions at river confluences: Application of ANNs and the M5P model tree, 2015, Applied Soft Comput., 34, 51−59.
Best, J.L., Sediment transport and bed morphology at river channel confluences, 1988, Sedimentol., vol. 35, pp. 481–498.
Best, J.L. and Rhoads, B.L., Sediment transport, bed morphology and the sedimentology of river channel confluences, River Confluences, Tributaries and the Fluvial Network, 2008, Rice, S.P., Roy, A.G., Rhoads, B.L. (Eds.), Chichester: John Wiley and Sons, UK, pp. 45–72.
Biron, P., Roy, A.G., Best J.L., and Boyer, C.J., Bed morphology and sedimentology at the confluence of unequal depth channels, Geomorphol.,1993, vol. 8, pp. 115–129.
Biron, P., Best, J.L., and Roy, A.G., Effects of bed discordance on flow dynamics at open channel confluences, J. Hydraul. Eng., 1996, vol. 122, no. 12, pp. 676–682.
Biron, P.M., Richer, A, Kirkbride, A.D., Roy, A.G., and Han, S., Spatial patterns of water surface topography at a river confluence, Earth Surf. Processes Landforms, 2002, vol. 27, 913–928.https://doi.org/10.1002/esp.359
Biron, P.M. and Lane, S.N., Modelling hydraulics and sediment transport at river confluences, River Confluences, Tributaries and the Fluvial Network, S.P. Rice, A.G. Roy, and B.L. Rhoads, Eds., 2008, pp. 17–43.
Borghei, S.M. and Jabbari Sahebari, A., Local scour at open channel junctions, J. Hydraul. Res., 2010, vol. 48, no. 4, pp. 538–542.
Boyer, C., Roy, A.G., and Best, J.L., Dynamics of a river channel confluence with discordant beds: flow turbulence, bed load sediment transport, and bed morphology, J. Geophys. Res., 2006, vol. 111, F04007. https://doi.org/10.1029/2005JF000458
Bradbrook, K.F., Lane, S.N., and Richards, K.S., Numerical simulation of three-dimensional time-averaged flow structure at river channel confluences, Water Resour. Res, 2000, vol. 36, no. 9, pp. 2731–2746.
Bradbrook, K.F., Lane, S.N., Richards, K.S., Biron, P.M., and Roy, A.G., Role of bed discordance at asymmetrical river confluences, J. Hydraul. Eng., 2001, vol. 127, no. 5, pp. 351–368.
Canelas, O.B, Ferreira, R., Guillen-Ludeia, S., Alegria, F., and Cardoso, A., Three-dimensional flow structure at fixed 70° open-channel confluence with bed discordance, J. Hydraul. Res., 2020, vol. 58, no. 3, pp. 434–446. https://doi.org/10.1080/00221686.2019.1596988
De Serres, B., Roy, A.G., Biron, P.M., and Best, J.L., Three-dimensional structure of flow at a confluence of river channels with discordant beds, Geomorphol., 1999, vol. 26, no. 4, pp. 313–335.
Dumas, S., Arnott, R., Southard, J.B., Experiments on oscillatory-flow and combined-flow bed forms: implications for interpreting parts of the shallow-marine sedimentary record, J. Sediment. Res., 2005, vol. 75, no. 3, pp. 501–513.
Ghobadian, R. and Shafai Bejestan, M., Investigation of sediment patterns at river confluence, J. Applied Sci., 2007, vol. 7, no. 10, pp. 1372–1380.
Leeder, M.R., Sedimentology and Sedimentary Basins: From Turbulence to Tectonics, 2011, Wiley, U.K.
Leite Ribeiro, M., Blanckaert, K., Roy, A.G., and Schleiss, J., Flow and sediment dynamics in channel confluences, J. Geophys. Res., 2012, vol. 117, F01035. https://doi.org/10.1029/2011JF002171
Liu, T.H., Chen, L., and Fan, B.L., Experimental study on flow pattern and sediment transportation at a 90° open-channel confluence, Int. J. Sediment Res., 2012, vol 27, pp. 178–187.
Monsalve, A., Yager, E.M., Turowski, J.M., and Rickenmann, D., A probabilistic formulation of bed load transport to include spatial variability of flow and surface grain size distributions, Water Resour. Res, 2016, vol. 52, pp. 3579–3598.
Nargess Amini, Behnam Balouchi, Mahmood Shafai Bejestan, Reduction of local scour at river confluences using a collar, Int. J. Sediment Res., 2017, vol. 32, no. 3, pp. 364-372. https://doi.org/10.1016/j.ijsrc.2017.06.001
Parsons, D.R., Best, J.L., Lane, S.N., Orfeo, O., Hardy, R.J., and Kostaschuk, R., Form roughness and the absence of secondary flow in a large confluence-diffluence, Rio Paraná, Argentina, Earth Surf. Processes Landforms, 2007, vol. 32, pp. 155–162. https://doi.org/10.1002/esp.1457
Passchier, S. and Kleinhans, M., Observations of sand waves, megaripples, and hummocks in the Dutch coastal area and their relation to currents and combined flow conditions, J. Geophys. Res. Earth Surf., 2005, p. 110.
Rhoads, B.L., Mean structure of transport-effective flows at an asymmetrical confluence when the main stream is dominant, Coherent Flow Structures in Open Channels, Ashworth, P., Bennett, S.J., Best, J.L., and McLelland, S., Eds., 1996, Chichester: Wiley, pp. 491–517.
Rhoads, B.L. and Kenworthy, S.T., Flow structure at an asymmetrical stream confluence, Geomorphol., 1995, vol. 11, pp. 273–293.
Rhoads, B.L. and Kenworthy, S.T., Time-averaged flow structure in the central region of a stream confluence, Earth Surf. Process. Landf., 1998, vol. 23, no. 2, pp. 171–191. https://doi.org/10.1002/(SICI)1096-9837(199802)23:2b171:AID-ESP842N3.0.CO;2-T
Rhoads, B.L. and Sukhodolov, A.N., Field investigation of three-dimensional flow structure at stream confluences: 1. Thermal mixing and time-averaged velocities, Water Resour. Res, 2001, vol. 37, pp. 2393–2410.
Rhoads, B.L. and Sukhodolov, A.N., Spatial and temporal structure of shear layer turbulence at a stream confluence, Water Resour. Res., 2004, vol. 40, W06304. https://doi.org/10.1029/2003WR002811
Rhoads, B.L. and Sukhodolov, A.N., Lateral momentum flux and the spatial evolution of flow within a confluence mixing interface, Water Resour. Res., 2008, vol. 44, W08440. https://doi.org/10.1029/2007WR006634
Rhoads, B.L., Riley, J.D., and Mayer, D.R., Response of bed morphology and bed material texture to hydrological conditions at an asymmetrical stream confluence, Geomorpho., 2009, vol. 109, pp. 161–173. https://doi.org/10.1016/j.geomorph.2009.02.029
Riley, J.D. and Rhoads, B.L., Flow structure and channel morphology at a natural confluent meander bend, Geomorpho., 2012, vol. 163–164, pp. 84–98. https://doi.org/10.1016/j.geomorph.2011.06.011
Sadeghi, S.H.R. and Kheirfam, H., Temporal variation of bed load to suspended load ratio in Kojour River, Iran, Clean: Soil, Air, Water, 2015, vol. 43, no. 10, pp. 1366–1374.
Schneider, C.A., Rasband, W.S., and Eliceiri, K.W., NIH image to ImageJ: 25 years of image analysis, Nature Methods, 2012, vol. 9, no, 7, pp. 671–675. https://doi.org/10.1038/nmeth.2089
Shafai Bejestan, M. and Hemmati, M., Scour depth at river confluence of unequal bed level, 2008, J. Applied Sci., 2008, vol. 8, no. 9, pp. 1766–1770.
Soulsby, R., Dynamics of Marine Sands: A Manual for Practical Applications, 1997, Thomas Telford.
Southard, J.B., Experimental determination of bed-form stability, Annu. Rev. Earth Planet. Sci., 1991, vol. 19, pp. 423–455.
Sukhodolov, A.N., Julian Krick, Sukhodolova, T.A., Zhengyang Cheng, Rhoads, B.L., and Constantines-cu, G.S., Turbulent flow structure at a discordant river confluence: asymmetric jet dynamics with implications for channel morphology, JGR Earth Surface, 2017, vol. 122, no. 6, pp. 1278–1293.
Van Rijn, L.C., Principles of Sediment Transport in Rivers, Estuaries and Coastal Seas, 1993, Amsterdam: Aqua Publications.
Van Rijn, L.C., Unified view of sediment transport by currents and waves. i: initiation of motion, bed roughness, and bed-load transport, J. Hydraul. Eng., 2007, vol. 133, no. 6, pp. 649–667.
Wyss, C., Rickenmann, D., Fritschi, B., Turowski, J., Weitbrecht, V., Boes, R., Measuring bed load transport rates by grain-size fraction using the Swiss Plate Geophone signal at the Erlenbach, J. Hydraul. Eng., 2016, vol. 142, no. 5, 04016003-1–04016003-11.
Xia Shen, Ran Li, Huanjie Cai, Jingjie Feng, Hang Wan., Characteristics of secondary flow and separation zone with different junction angle and flow ratio at river confluences, J. Hydrol., 2022, vol. 614, Part B, 128537. https://doi.org/10.1016/j.jhydrol.2022.12853722
Zhang, X., Y Ji, Yang, Z., Wang, Z., Liu, N., and Jia, P., End member inversion of surface sediment grain size in the South Yellow Sea and its implications for dynamic sedimentary environments, Sci, China Earth Sci., 2015, vol. 59, pp. 258–267.
Zhang, Z. and Lin, Y., An experimental study on the influence of drastically varying discharge ratios on bed topography and flow structure at urban channel confluences, Water, 2021, vol. 13, no. 9, 1147. https://doi.org/10.3390/w13091147
Funding
The authors acknowledge the Science and Engineering Research Board (SERB), Ministry of Science and Technology, Government of India for the financial support (Grant no. EMR/2016/005371).
Author information
Authors and Affiliations
Corresponding authors
Ethics declarations
The authors of this work declare that they have no conflicts of interest.
Additional information
Publisher’s Note.
Pleiades Publishing remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Khanam, N., Biswal, S. Bedload Transport and Its Implication on Bed Morphology at a River Confluence. Water Resour 51, 110–126 (2024). https://doi.org/10.1134/S0097807823601310
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1134/S0097807823601310