{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T10:13:06Z","timestamp":1760177586157,"version":"build-2065373602"},"reference-count":58,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2020,7,25]],"date-time":"2020-07-25T00:00:00Z","timestamp":1595635200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia","doi-asserted-by":"publisher","award":["RiverCure PTDC\/CTA-OHR\/29360\/2017"],"award-info":[{"award-number":["RiverCure PTDC\/CTA-OHR\/29360\/2017"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Water"],"abstract":"<jats:p>We address the issue of characterizing experimentally entrainment and disentrainment of sediment particles of cohesionless granular beds in turbulent open channel flows. Employing Particle Image Velocimetry, we identify episodes of entrainment and of disentrainment of bed particles by analysing the raw PIV images. We define a reference velocity for entrainment or disentrainment by space-averaging the flow field in the vicinity of the (entrained or disentrainned) particle and by time-averaging that space-average over a short duration encompassing the observed episode. All observations and measurements took place under generalized movement conditions and in non-controlled geometrical set-ups, resulting in unique databases of conditionally sampled turbulent flow kinematics associated with episodes of particle entrainment and of particle disentrainment. Exploring this database, the objective of this paper is to prove further insights on the dynamics of fluid-particle and particle-particle interactions at entrainment and disentrainment and to polemicize the use of a reference velocity to serve as a proxy for hydrodynamics actions responsible for entrainment or disentrainment. In particular, we quantify the reference velocity associated with entrainment and disentrainment episodes and discuss its potential to describe the observed motion vis-a-vis local bed micro-topography and the type of entrainment or disentrainment event. Entrainment may occur at a wide range of reference velocities, including smaller than mean (double-averaged) velocities. Anecdotal evidence was collected for some typologies of entrainment: (i) momentum transfer from flow to a single particle, (ii) momentum transfer from a perturbed local flow to a single particle, (iii) collective entrainment associated to momentum transfer between a moving and a resting particle and (iv) collective entrainment considered to be a dislodgment of several particles involving momentum transfer from other particles. In some of these cases, e.g., (ii) and (iii), the use of a reference velocity seems inadequate to characterize the entrainment episode. A word of caution about the use of entrainment models based on reference velocities is henceforth issued and contextualized. In the case of disentrainment, a reference velocity seems to constitute a better descriptor of the observed behaviour. The scatter in the observed values seems to express the contribution of bed micro-topography. All particles were found to experience frictional contacts with the resting bed surface particles, but some particles were stopped more abruptly due to the presence of an obstacle along their path. Most disentrainment of particles took place when the near-bed flow was featuring ejection events.<\/jats:p>","DOI":"10.3390\/w12082110","type":"journal-article","created":{"date-parts":[[2020,7,27]],"date-time":"2020-07-27T09:24:49Z","timestamp":1595841889000},"page":"2110","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Kinematics of Particles at Entrainment and Disentrainment"],"prefix":"10.3390","volume":"12","author":[{"given":"Rui","family":"Aleixo","sequence":"first","affiliation":[{"name":"CERIS\u2014Civil Engineering Research and Innovation for Sustainability, Av. Rovisco Pais, 1049-003 Lisboa, Portugal"}]},{"given":"Federica","family":"Antico","sequence":"additional","affiliation":[{"name":"CERIS\u2014Civil Engineering Research and Innovation for Sustainability, Av. Rovisco Pais, 1049-003 Lisboa, Portugal"}]},{"given":"Ana M.","family":"Ricardo","sequence":"additional","affiliation":[{"name":"CERIS\u2014Civil Engineering Research and Innovation for Sustainability, Av. Rovisco Pais, 1049-003 Lisboa, Portugal"}]},{"given":"Rui M.L.","family":"Ferreira","sequence":"additional","affiliation":[{"name":"CERIS\u2014Instituto Superior T\u00e9cnico, Universidade de Lisboa, Av. Rovisco Pais, 1048-001 Lisboa, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2020,7,25]]},"reference":[{"key":"ref_1","unstructured":"Meyer-Peter, E., and M\u00fcller, R. (1948, January 7\u20139). Formulas for bedload transport. Proceedings of the 2nd Meeting of the International Association for Hydraulic Research, Stockholm, Sweden."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1159","DOI":"10.1061\/(ASCE)0733-9429(2006)132:11(1159)","article-title":"Reanalysis and Correction of Bed-Load Relation of Meyer-Peter and M\u00fc ller Using Their Own Database","volume":"132","author":"Wong","year":"2006","journal-title":"J. Hydraul. Eng."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Smart, G.M. (1984). Sediment transport formula for steep channels. J. Hydraul. Eng., 110.","DOI":"10.1061\/(ASCE)0733-9429(1984)110:3(267)"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1264","DOI":"10.1002\/jgrf.20090","article-title":"An analysis of nonlinearity effects on bed load transport prediction","volume":"118","author":"Recking","year":"2013","journal-title":"J. Geophys. Res. Earth Surf."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Bagnold, R.A. (1966). An Approach to the Sediment Transport Problem from General Physics.","DOI":"10.3133\/pp422I"},{"key":"ref_6","unstructured":"Engelund, F., and Hansen, E. (1967). A Monograph on Sediment Transport in Alluvial Stream, Teknisk Forlag."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Rijn, L.C.V. (1984). Sediment transport part I bed load transport. J. Hydraul. Eng., 110.","DOI":"10.1061\/(ASCE)0733-9429(1984)110:11(1613)"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Wiberg, P.C., and Smith, J.D. (1989). Model for calculating bed load transport of sediment. J. Hydraul. Eng., 115.","DOI":"10.1061\/(ASCE)0733-9429(1989)115:1(101)"},{"key":"ref_9","first-page":"167","article-title":"Die eichung des im Rhein verwendeten geschiebefangers (The calibration of bed-load traps used in the Rhine)","volume":"110","author":"Einstein","year":"1937","journal-title":"Schweiz. Bauztg."},{"key":"ref_10","unstructured":"Einstein, H.A. (1950). The Bed-Load Function for Sediment Transportation in Open Channel Flows."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Lakatos, I. (1976). Falsification and the methodology of scientific research programmes. Can Theories Be Refuted?, Springer. Essays on the Duhem-Quine Thesis.","DOI":"10.1007\/978-94-010-1863-0_14"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Engelund, F., and Fredsoe, J. (1976). A sediment transport model for straight alluvial channels. Hydrol. Res.","DOI":"10.2166\/nh.1976.0019"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Cheng, N.S., and Chiew, Y.M. (1998). Pickup Probability for Sediment Entrainment. J. Hydraul. Eng., 124.","DOI":"10.1061\/(ASCE)0733-9429(1998)124:2(232)"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Yalin, M.S. (1972). Mechanics of Sediment Transport, Pergamon Press.","DOI":"10.1007\/978-1-349-00245-0_6"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"402","DOI":"10.1007\/s003489900107","article-title":"The spatial inhomogeneity of turbulence above a fully rough, packed bed in open channel flow","volume":"29","author":"Dancey","year":"2000","journal-title":"Exp. Fluids"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Rowinsky, P., and Radecki-Pawlick, A. (2015). Principles of Bedload Transport of Non-cohesive Sediment in Open-Channels. Rivers-Physical, Fluvial and Environmental Processes, Springer. Chapter 13.","DOI":"10.1007\/978-3-319-17719-9"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"527","DOI":"10.1080\/00221687109500371","article-title":"A stochastic model of bed load transport","volume":"9","author":"Paintal","year":"1971","journal-title":"J. Hydraul. Res."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Schmeeckle, M.W., Nelson, J.M., and Shreve, R.L. (2007). Forces on stationary particles in near-bed turbulent flows. J. Geophys. Res. Earth Surf., 112.","DOI":"10.1029\/2006JF000536"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"42","DOI":"10.1029\/2012JF002354","article-title":"Entrainment of coarse particles in turbulent flows: An energy approach","volume":"118","author":"Valyrakis","year":"2013","journal-title":"J. Geophys. Res. Earth Surf."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"717","DOI":"10.1126\/science.1158954","article-title":"The role of impulse on the initiation of particle movement under turbulent flow conditions","volume":"322","author":"Diplas","year":"2008","journal-title":"Science"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"422","DOI":"10.2136\/sssaj1959.03615995002300060019x","article-title":"Equilibrum of soil grains at the threshold of movement by wind","volume":"23","author":"Chepil","year":"1959","journal-title":"Soil Sci. Soc. Am. J."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"558","DOI":"10.1017\/jfm.2018.522","article-title":"Surface and subsurface contributions to the build-up of forces on bed particles","volume":"851","author":"Leonardi","year":"2018","journal-title":"J. Fluid Mech."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Rubey, W.W. (1938). The Force Required to Move Particles on a Stream Bed, Professional Papers.","DOI":"10.3133\/pp189E"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"476","DOI":"10.1029\/WR020i004p00476","article-title":"Bed Load Grain Velocities and Sediment Transport Rates","volume":"20","author":"Bridge","year":"1984","journal-title":"Water Resour. Res."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"369","DOI":"10.1061\/(ASCE)0733-9429(2002)128:4(369)","article-title":"Stochastic incipient motion criterion for spheres under various bed packing conditions","volume":"128","author":"Papanicolaou","year":"2002","journal-title":"J. Hydraul. Eng."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"W03518","DOI":"10.1029\/2009WR008007","article-title":"A comparison between flume and field bed load transport data and consequences for surface-based bed load transport prediction","volume":"46","author":"Recking","year":"2010","journal-title":"Water Resour. Res."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2529","DOI":"10.1002\/2014JF003421","article-title":"Stochastic interpretation of the advection diffusion equation and its relevance to bed load transport","volume":"120","author":"Ancey","year":"2015","journal-title":"J. Geophys. Res. Earth Surf."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Furbish, D.J., Fathel, S.L., and Schmeeckle, M.W. (2017). Particle Motions and Bedload Theory. Gravel-Bed Rivers: Processes and Disasters, Wiley.","DOI":"10.1002\/9781118971437.ch4"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/ncomms7527","article-title":"Onset of sediment transport is a continuous transition driven by fluid shear and granular creep","volume":"6","author":"Houssais","year":"2015","journal-title":"Nat. Commun."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1017\/S0022112007008774","article-title":"Entrainment and motion of coarse particles in a shallow water stream down a steep slope","volume":"595","author":"Ancey","year":"2008","journal-title":"J. Fluid Mech."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"06016021","DOI":"10.1061\/(ASCE)HY.1943-7900.0001224","article-title":"Statistical Description on theRole of Turbulence and Grain Interference on Particle Entrainment from Gravel Beds","volume":"143","author":"Cecchetto","year":"2017","journal-title":"J. Hydraul. Eng."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1002\/esp.2096","article-title":"Fluvial dunes: Initiation, characterisation, flow structure","volume":"36","author":"Coleman","year":"2011","journal-title":"Earth Surf. Process. Landf."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Furbish, D.J., Haff, P.K., Roseberry, J.C., and Schmeeckle, M.W. (2012). A probabilistic description of the bed load sediment flux: 1. Theory. J. Geophys. Res. Earth Surf., 117.","DOI":"10.1029\/2012JF002352"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"364","DOI":"10.1080\/00221686.2012.689682","article-title":"Dam-break flows over mobile beds: Experiments and benchmark tests for numerical models","volume":"50","author":"Canelas","year":"2012","journal-title":"J. Hydraul. Res."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"94","DOI":"10.1017\/jfm.2011.386","article-title":"Bedforms in a turbulent stream: Ripples, chevrons and antidunes","volume":"690","author":"Andreotti","year":"2011","journal-title":"J. Fluid Mech."},{"key":"ref_36","unstructured":"Daubert, A., and Lebreton, J.C. (1967, January 11\u201314). \u00c9tude \u00e9xperimentale et sur modele mathematique de quelques aspects du calcul des processus d\u2018erosion des lits alluvionaires en regime permanent et non permanent. Proceedings of the 12th Congress of IAHR, Fort Collins, CO, USA."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"113","DOI":"10.1080\/00221688909499247","article-title":"Spatial lag effects in bed load sediment transport","volume":"27","author":"Phillips","year":"1989","journal-title":"J. Hydraul. Res."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"55","DOI":"10.1017\/S0022112004001028","article-title":"Erosion and deposition of particles on a bed sheared by a viscous flow","volume":"519","author":"Charru","year":"2004","journal-title":"J. Fluid Mech."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"392","DOI":"10.1080\/00221686.2013.798891","article-title":"Two-dimensional depth-averaged modelling of dambreak flows over mobile beds","volume":"51","author":"Canelas","year":"2013","journal-title":"J. Hydraul. Res."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"36","DOI":"10.1016\/j.advwatres.2015.05.016","article-title":"Stochastic-deterministic modeling of bed load transport in shallow water flow over erodible slope: Linear stability analysis and numerical simulation","volume":"83","author":"Bohorquez","year":"2015","journal-title":"Adv. Water Resour."},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Cecchetto, M., Tait, S., Tregnaghi, M., and Marion, A. (2016, January 12\u201315). The mechanics of bedload particles deposition over gravel beds. Proceedings of the International Conference On Fluvial Hydraulics (River Flow 2016), St. Louis, MO, USA.","DOI":"10.1201\/9781315644479-120"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"18","DOI":"10.1080\/00221686.2019.1702595","article-title":"Bedload transport: A walk between randomness and determinism. Part 2. Challenges and prospects","volume":"58","author":"Ancey","year":"2020","journal-title":"J. Hydraul. Res."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"873","DOI":"10.1061\/TACEAT.0004652","article-title":"Sand mixtures and sand movement in fluvial model","volume":"100","author":"Kramer","year":"1935","journal-title":"Am. Soc. Civ. Eng."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"125305","DOI":"10.1088\/0957-0233\/27\/12\/125305","article-title":"A particle counting system for calculation of bedload fluxes","volume":"27","author":"Mendes","year":"2016","journal-title":"Meas. Sci. Technol."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1016\/j.advwatres.2014.10.004","article-title":"The von K\u00e1rm\u00e1n constant for flows over rough mobile beds. Lessons learned from dimensional analysis and similarity","volume":"81","author":"Ferreira","year":"2015","journal-title":"Adv. Water Resour."},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Dwivedi, A., Melville, B.W., Shamseldin, A.Y., and Guha, T.K. (2011). Analysis of hydrodynamic lift on a bed sediment particle. J. Geophys. Res. Earth Surf., 116.","DOI":"10.1029\/2009JF001584"},{"key":"ref_47","unstructured":"Antico, F. (2019). Laboratory Investigations on the Motion of Sediment Particles in Cohesionless Mobile Beds under Turbulent Flows. [Ph.D. Thesis, Instituto Superior T\u00e9cnico, Universidade de Lisboa]."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1017\/S0022112077001554","article-title":"Prediction of the contributions to the Reynolds stress from bursting events in open-channel flows","volume":"80","author":"Nakagawa","year":"1977","journal-title":"J. Fluid Mech."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"803","DOI":"10.1061\/(ASCE)HY.1943-7900.0000738","article-title":"Spatially averaged flows over mobile rough beds: Definitions, averaging theorems, and conservation equations","volume":"139","author":"Nikora","year":"2013","journal-title":"J. Hydraul. Eng."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"417","DOI":"10.1063\/1.869889","article-title":"Very large-scale motion in the outer layer","volume":"11","author":"Kim","year":"1999","journal-title":"Phys. Fluids"},{"key":"ref_51","doi-asserted-by":"crossref","unstructured":"Schoklitsch, A. (1962). Handbuch des Wasserbaues, Springer.","DOI":"10.1007\/978-3-642-52043-3"},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1080\/00221688909499244","article-title":"The different ripple formation mechanisms","volume":"27","author":"Gyr","year":"1989","journal-title":"J. Hydraul. Res."},{"key":"ref_53","doi-asserted-by":"crossref","unstructured":"S\u00e9chet, P., and Guennec, B.L. (1999). Bursting phenomenon and incipient motion of solid particles in bed-load transport. J. Hydraul. Res.","DOI":"10.1080\/00221689909498523"},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"2071","DOI":"10.1029\/95WR00976","article-title":"Role of near-bed turbulence structure in bed load transport and bed form mechanics","volume":"31","author":"Nelson","year":"1995","journal-title":"Water Resour. Res."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"011302","DOI":"10.1103\/PhysRevE.74.011302","article-title":"Statistical description of sediment transport experiments","volume":"74","author":"Ancey","year":"2006","journal-title":"Phys. Rev. E"},{"key":"ref_56","doi-asserted-by":"crossref","unstructured":"Valyrakis, M., Diplas, P., Dancey, C.L., Greer, K., and Celik, A.O. (2010). Role of instantaneous force magnitude and duration on particle entrainment. J. Geophys. Res. Earth Surf., 115.","DOI":"10.1029\/2008JF001247"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"193","DOI":"10.1017\/S0022112088001831","article-title":"Bedload transport of fine gravel observed by motion-picture photography","volume":"192","author":"Drake","year":"1988","journal-title":"J. Fluid Mech."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"061307","DOI":"10.1103\/PhysRevE.69.061307","article-title":"Fluctuations of the solid discharge of gravity-driven particle flows in a turbulent stream","volume":"69","author":"Ancey","year":"2004","journal-title":"Phys. Rev. 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