Skip to main content Accessibility help
×
Home

Flow separation at convex banks in open channels

  • K. Blanckaert (a1)

Abstract

Laboratory experiments in an open channel bend provide insight into the physics of convex bank flow separation occurring in a variety of channel configurations, including confluences and bifurcations. The edge of the zone of flow separation is characterized by a shear layer, enhanced velocity gradients, tke, turbulent shear stresses and reversal of the streamwise vorticity and vertical velocity. The latter result from turbulence-induced secondary flow near the convex bank. When bankline curvature abruptly increases, flow tends to move away from the convex bank along a straight path, as represented by the inertial forces – including the centrifugal force – in the transverse momentum equation written in curvilinear coordinates. Mass accumulation at the opposite bank leads to a transverse tilting of the water surface, and a pressure gradient towards the convex bank that causes the flow to change direction. The pressure gradient force lags spatially behind the inertial forces, which promotes flow separation. Flow separation typically occurs downstream of the location of maximum change in the bankline curvature, because an abrupt increase in bankline curvature also leads to water surface gradients that cause local flow redistribution towards the convex bank that opposes flow separation. The zone of convex bank flow separation is shaped by the secondary flow induced by streamline curvature and turbulence. The latter is conditioned by the production rate of tke, which crucially depends on the accurate description of the Reynolds stresses. Hydrodynamic, geometric and sedimentologic control parameters of convex bank flow separation are identified and discussed.

Copyright

Corresponding author

Email address for correspondence: koen.blanckaert@epfl.ch

References

Hide All
Abad, J. D. & Garcia, M. H. 2009 Experiments in a high-amplitude Kinoshita meandering channel: 1. Implications of bend orientation on mean and turbulent flow structure. Water Resour. Res. 45, W02401.
Bagnold, R. A.1960 Some aspects of the shape of river meanders. US Geological Survey Professional Paper 282-E, US Geological Survey, Washington, DC.
Batchelor, G. K. 1970 An Introduction to Fluid Dynamics. Cambridge University Press.
Best, J. L. & Reid, I. 1984 Separation zone at open-channel junctions. J. Hydraul. Engng ASCE 110 (11), 15881594.
Biron, P. M., Lane, S. N., Roy, A. G., Bradbrook, K. F. & Richards, K. S. 1998 Sensitivity of bed shear stress estimated from vertical velocity profiles: the problem of sampling resolution. Earth Surf. Process. Landf. 23 (2), 133139.
Biron, P. M., Robson, C., Lapointe, M. F. & Gaskin, S. J. 2004 Comparing different methods of bed shear stress estimates in simple and complex flow fields. Earth Surf. Process. Landf. 29 (11), 14031415.
Blanckaert, K. 2009 Saturation of curvature-induced secondary flow, energy losses and turbulence in sharp open-channel bends. Laboratory experiments, analysis and modeling. J. Geophys. Res. 114, F03015.
Blanckaert, K. 2010 Topographic steering, flow recirculation, velocity redistribution and bed topography in sharp meander bends. Water Resour. Res. 46, W09506.
Blanckaert, K. 2011 Hydrodynamic processes in sharply-curved river bends and their morphological implications. J. Geophys. Res. 116, F01003.
Blanckaert, K., Duarte, A., Chen, Q. & Schleiss, A. J. 2012 Flow processes near smooth and rough (concave) outer banks in curved open channels. J. Geophys. Res. 117, F04020.
Blanckaert, K., Kleinhans, M. G., McLelland, S. J., Uijttewaal, W. S. J., Murphy, B. J., van de Kruijs, A., Parsons, D. R. & Chen, Q. 2013 Flow separation at the inner (convex) and outer (concave) banks of constant-width and widening open-channel bends. Earth Surf. Process. Landf. 38, 696716.
Blanckaert, K. & Lemmin, U. 2006 Means of noise reduction in acoustic turbulence measurements. J. Hydraul Res. IAHR 44 (1), 317.
Blanckaert, K. & de Vriend, H. J. 2004 Secondary flow in sharp open-channel bends. J. Fluid Mech. 498, 353380.
Blanckaert, K. & de Vriend, H. J. 2010 Meander dynamics: a 1D flow model without curvature restrictions. J. Geophys. Res. 115, F04011.
Boyer, C., Roy, A. G. & Best, J. L. 2006 Dynamics of a river channel confluence with discordant beds: Flow turbulence, bed load sediment transport, and bed morphology. J. Geophys. Res. 111, F04007.
Bulle, H. 1926 Untersuchungen über die Geschiebeableitung bei der Spaltung von Wasserläufen. Forsch. Gebiete Ing. 282, 5784; (in German).
Burge, L. M. & Smith, D. G. 2009 Confined meandering river eddy accretions: sedimentology, channel geometry and depositional processes. In Fluvial Sedimentology VI (ed. Smith, N. D. & Rogers, J.), Special Publication of Internat, Association of Sedimentologists, vol. 28, pp. 113130. Blackwell Science.
Chow, V. T. 1959 Open Channel Hydraulics. McGraw-Hill.
Constantinescu, G., Kashyap, S., Toyay, T., Rennie, C. D. & Townsend, R. D. 2013 Hydrodynamic processes and sediment erosion mechanisms in an open-channel bend of strong curvature with deformed bathymetry. J. Geophys. Res. 118 (2), 480496.
Constantinescu, G., Miyawaki, S., Rhoads, B., Sukhodolov, A. & Kirkil, G. 2011 Structure of turbulent flow at a river confluence with momentum and velocity ratios close to 1: insight provided by an eddy resolving numerical simulation. Water Resour. Res. 47, W05507.
Crosato, A.2008 Analysis and modelling of river meandering. PhD thesis, Delft University of Technolgy.
Dargahi, B. 2004 Three-dimensional flow modelling and sediment transport in the River Klaralven. Earth Surf. Process. Landf. 29, 821852.
De Serres, B., Roy, A. G., Biron, P. M. & Best, J. L. 1999 Three dimensional structure of flow at a confluence of river channels with discordant beds. Geomorphology 26, 313335.
Dietrich, W. E. & Whiting, P. 1989 Boundary shear stress and sediment transport in river meanders of sand and gravel. In River Meandering (ed. Ikeda, S. & Parker, G.), Water Resour. Monogr. Ser., vol. 12, pp. 150. AGU.
Duarte, A.2008 An experimental study on main flow, secondary flow and turbulence in open-channel bends with emphasis on their interaction with the outer-bank geometry. PhD thesis, no 4227, Ecole Polytechnique Fédérale Lausanne.
Engel, F. L. & Rhoads, B. L. 2012 Interaction among mean flow, turbulence, bed morphology, banks failures and channel planform in an evolving compound meander loop. Geomorphology 163–164, 7083.
Engelund, F. 1974 Flow and bed topography in channel bends. J. Hydraul. Div. ASCE 100 (HY11), 16311648.
Ferguson, R. I., Parsons, D. R., Lane, S. N. & Hardy, R. J. 2003 Flow in meander bends with recirculation at the inner bank. Water Resour. Res. 39 (11), 13221333.
Frothingham, K. M. & Rhoads, B. L. 2003 Three-dimensional flow structure and channel change in an asymmetrical compound meander loop, Embarras River, Illinois. Earth Surf. Process. Landf. 28 (6), 625644.
Hardy, R. J., Lane, S. N. & Yu, D. 2011 Flow structures at an idealized bifurcation: a numerical experiment. Earth Surf. Process. Landf. 36 (15), 20832096.
Hickin, E. J. 1974 The development of meanders in natural river-channels. Am. J. Sci. 274 (April), 414442.
Hinze, J. O. 1975 Turbulence. McGraw-Hill.
Hooke, J. 2003 River meander behaviour and instability: a framework for analyses. Trans. Inst. Brit. Geogr. 28 (2), 238253.
Hurther, D. & Lemmin, U. 1998 A constant beamwidth transducer for three-dimensional Doppler profile measurements in open channel flow. Meas. Sci. Technol. 9 (10), 17061714.
Jamieson, E., Post, G. & Rennie, C. D. 2010 Spatial variability of three dimensional Reynolds stresses in a developing channel bend. Earth Surf. Process. Landf. 35, 10291043.
Jin, Y.-C. & Steffler, P. M. 1993 Predicting flow in curved open channels by the depth-averaged method. J. Hydraul. Engng ASCE 119 (1), 109124.
Kim, S. C., Friedrichs, C. T., Maa, J. P. Y. & Wright, L. D. 2000 Estimating bottom stress in tidal boundary layer from Acoustic Doppler Velocimeter data. J. Hydraul. Engng ASCE 126 (6), 399406.
Kleinhans, M. G., Ferguson, R. I., Lane, S. N. & Hardy, R. J. 2013 Splitting rivers at theirs seams: bifurcations and avulsion. Earth Surf. Process. Landf. 38, 4761.
Kleinhans, M. G., Schuurman, F., Bakx, W. & Markies, H. 2009 Meandering channel dynamics in highly cohesive sediment on an intertidal mud flat in the Westerschelde estuary, The Netherlands. Geomorphology 105, 261276.
Koken, M., Constantinescu, G. & Blanckaert, K. 2013 Hydrodynamic processes, sediment erosion mechanisms, and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry. J. Geophys. Res. 118, 117.
Leeder, M. R. & Bridges, P. H. 1975 Flow separation in meander bends. Nature 253 (5490), 338339.
Leite Ribeiro, M., Blanckaert, K., Roy, A. G. & Schleiss, A. J. 2012 Flow and sediment dynamics in channel confluences. J. Geophys. Res. 117, F01035.
Lemmin, U. & Rolland, T. 1997 Acoustic velocity profiler for laboratory and field studies. J. Hydraul. Engng ASCE 123 (12), 10891098.
Markham, A. J. & Thorne, C. R. 1992 Geomorphology of gravel-bed river bends. In Dynamics of Gravel-Bed Rivers (ed. Billi, P., Hey, R. D., Thorne, C. R. & Tacconi, P.), pp. 433456. Wiley.
Nanson, R. A. 2010 Flow fields in tightly curving meander bends of low width-depth ratio. Earth Surf. Process. Landf. 35 (2), 119135.
Neary, V. S. & Odgaard, A. J. 1993 3-Dimensional flow structure at open-channel diversions. J. Hydraul. Engng ASCE 119 (11), 12231230.
Nelson, J. E.1988 Mechanics of flow and sediment transport over nonuniform erodible beds, PhD dissertation, University of Washington, Seattle, WA, p. 277.
Nezu, I. & Nakagawa, H. 1993 Turbulence in Open-Channel Flows, IAHR-Monograph. Balkema.
Ottevanger, W.2013 Modelling and parameterizing the hydro- and morphodynamics of curved open channels. PhD thesis, Delft University of Technology.
Rhoads, B. L. & Kenworthy, S. T. 1995 Flow structure at an asymmetrical stream confluence. Geomorphology 11 (4), 273293.
Rhoads, B. L. & Massey, K. 2012 Flow structure and channel change in a sinuous grass-lined stream within an agricultural drainage ditch: implications for ditch stability and aquatic habitat. River Res. Appl. 28 (1), 3952.
Rhoads, B. L. & Sukhodolov, A. N. 2001 Field investigation of three-dimensional flow structure at stream confluences: 1. Thermal mixing and time-averaged velocities. Water Resour. Res. 37 (9), 23932410.
Rozovskii, I. L. 1957 Flow of Water in Bends of Open Channels. Acad. Sci. Ukraine. SSR; Israeli. Progr. Sci. Transl; 1961.
Schnauder, I. & Sukhodolov, A. N. 2012 Flow in a tightly curving meander bend: effects of seasonal changes in aquatic macrophyte cover. Earth Surf. Process. Landf. 37 (11), 11421157.
Sime, L. C., Ferguson, R. I. & Church, M. 2007 Estimating shear stress from moving boat acoustic Doppler velocity measurements in a large gravel bed river. Water Resour. Res. 43 (3), W03418.
Simpson, R. L. 1989 Turbulent boundary-layer separation. Annu. Rev. Fluid Mech. 21, 205234.
Simpson, R. L. 1996 Aspects of turbulent boundary-layer separation. Prog. Aerosp. Sci. 32, 457521.
Sukhodolov, A. N. 2012 Structure of turbulent flow in a meander bend of a lowland river. Water Resour. Res. 48, W01516.
Sukhodolov, A., Thiele, M. & Bungartz, H. 1998 Turbulence structure in a river reach with sand bed. Water Resour. Res. 34 (5), 13171334.
Termini, D. & Piraino, M. 2011 Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend. Earth Surf. Process. Landf. 36, 244256.
Van Balen, W., Blanckaert, K. & Uijttewaal, W. S. J. 2010 Analysis of the role of turbulence in curved open-channel flow at different water depths by means of experiments, LES and RANS. J. Turbul. 11, Art. No. N 12.
de Vriend, H. J. 1977 A mathematical model of steady flow in curved shallow channels. J. Hydraul. Res. IAHR 15 (1), 3754.
Wilcock, P. R. 1996 Estimating local bed shear stress from velocity observations. Water Resour. Res. 32 (11), 33613366.
Yang, Q. Y., Wang, X. Y., Lu, W. Z. & Wang, X. K. 2009 Experimental study on characteristics of separation zone in confluence zones in rivers. J. Hydrol. Engng 14 (2), 166171.
Zeng, J., Constantinescu, G., Blanckaert, K. & Weber, L. 2008 Flow and bathymetry in sharp open-channel bends: experiments and predictions. Water Resour. Res. 44, W09401.
Zinger, J., Rhoads, B. L., Best, J. L. & Johnson, K. K. 2014 Flow structure and channel morphodynamics of meander bend chute cutoffs: a case study of the Wabash River, USA. J. Geophys. Res. 118 (4), 24682487.
MathJax
MathJax is a JavaScript display engine for mathematics. For more information see http://www.mathjax.org.

JFM classification

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed