The narrow flume: a tool for studying steep-slope bedload transport

During intense precipitations, bedload sediment transport becomes a potential hazard. In steep mountain streams, the volumetric sediment rate of transported material can reach as much as 20% of the water discharge. For this reason, a torrential flood can cause significant modification of the bed, sometimes leading to a massive deposit of sediment on the surrounding land.

A typical example of a major flood was the Saltine Flood (Canton du Valais in witzerland which occurred in 1996, and resulted in 2 deaths in Brig. In order to properly protect mountain populations, it is therefore important to understand the processes of bedload transport.

Scientific objectives

In-depth understanding of bedload sediment transport (beyond a mere description of the problem) poses serious difficulties. Semi-empirical formulae often become inaccurate once the flow approaches the transport threshold. This is especially true for poorly sorted materials. The main reason for these difficulties is that bedload is a multi-scale problem. Sometimes the problem must be analysed in a discrete manner, for example, during the incipient motion stage, whereas in other cases, continuum mechanics approaches are efficient. In order to better understand these processes, a narrow flume has been designed specifically to study (at the particle scale) the complex interactions between particles in movement on a mobile bed and the flow of water.

Experimental device

This device consists of a 2 m long flume with a variable width and bed. It is composed of aluminium beams between which two glass plates are affixed. These glass plates have a height of 20 cm and a thickness of 1 cm. The gap between the 2 plates can vary between 3 to 25 mm.

A vertical-guide system is used to adjust the slope to a value between 0 and 20 degrees. The bed is removable and interchangeable and it is possible to use a fixed bed (with different sizes and shapes and degrees of roughness) or a mobile bed composed of solid particles (driven by the water flow).
This flume is fed with water and glass beads. It can be used to study two-dimensional flows where the flume width is equal to the bead diameter. The regularity of the flow rate is ensured by using a constant head reservoir. Two glass-bead distributors provide a large range of constant sediment rate (typically from 5 to 30 beads/s) and diameters allowing us to study size segregation.

An image-processing system (backlight, high-speed camera, WIMA software) was developed in collaboration with the Hubert Curien laboratory at University of St Etienne to determine hydrodynamic parameters and the trajectories of solid particles (PhD of H. lafaye de Micheaux),Experiments have addressed  first  the study of a single rolling or saltating bead (F. Bigillon PhD), then  the motion of a set of particles on a mobile bed (T. Böhm PhD). And  the study of  two-size mixtures (V. Hergault PhD).More recently, the  Infiltration of fine sediment into a coarse mobile bed was studied depending on the size ratio and the percentage of fine material (PhD of A. Dudill  co-tutelle with M. Church, University of British Columbia, dept of Geography, Vancouver, Canada).

 

 

Figure 1: The experimental narrow flume with particle distributors used in the study of bedload at the particle scale (Böhm, modified by Hergault)
Figure 2: Observing steep-slope bedload transport at the particle scale – photo by Hubert Raguet
Figure 3: Segregation obtained with a two-size mixture (4 and 6 mm diameters, 10% slope, 6.5 mm width) - photo by Hubert Raguet

Projects (on-going)

ANR project (P.I P. Frey):  Size Segregation in sediment transport
 

Collaborations

Publications (Selection)

Based on data obtained in the narrow flume

 

  • Dudill, A., Lafaye de Micheaux, H., Frey, P., Church, M., in press. Introducing finer grains into bedload: the transition to a new equilibrium. Journal of Geophysical Research: Earth Surface, doi:10.1029/2018JF004847.
  • Lafaye de Micheaux H, Ducottet C, Frey P. 2018. Multi-model particle filter-based tracking with switching dynamical state to study bedload transport. Machine Vision and Applications 29(5): 735-747.
  • Dudill A, Frey P, Church M. 2017. Infiltration of fine sediment into a coarse mobile bed: A phenomenological study. Earth Surface Processes and Landforms 42(8): 1171-1185.
  • Maurin R, Chauchat J, Chareyre B, Frey P. 2015. A minimal coupled fluid-discrete element model for bedload transport. Physics of Fluids 27(11): 113302.
  • Frey P. 2014. Particle velocity and concentration profiles in bedload experiments on a steep slope. Earth Surface Processes and Landforms 39 (5): 646-655.
  • Frey P, Church M. 2011. Bedload: a granular phenomenon. Earth Surface Processes and Landforms 36: 58-69.
  • Hergault V, Frey P, Métivier F, Barat C, Ducottet C, Böhm T, Ancey C. 2010. Image processing for the study of bedload transport of two-size spherical particles in a supercritical flow. Experiments in Fluids 49: 1095-1107.
  • Frey P, Church M. 2009. How River Beds Move. Science 325: 1509-1510.
  • Ancey C, Davison AC, Böhm T, Jodeau M, Frey P. 2008. Entrainment and motion of coarse particles in a shallow water stream down a steep slope. Journal of Fluid Mechanics 595: 83-114.
  • Böhm, T., P. Frey, C. Ducottet, C. Ancey, M. Jodeau, and J.-L. Reboud, 2006: Two-dimensional motion of a set of particles in a free surface flow with image processing. Experiments in Fluids, 41, 1-11.
  • Böhm, T., C. Ancey, P. Frey, J. L. Reboud, and C. Ducottet, 2004: Fluctuations of the solid discharge of gravity-driven particle flows in a turbulent stream. Physical Review E, 69, 061307, 1-13
  • Ancey, C., F. Bigillon, P. Frey, J. Lanier, and R. Ducret, 2002: Saltating motion of a bead in a rapid water stream. Physical Review E, 66, 036306, 1-16.

PhDs , HdR

  • Lafaye de Micheaux Hugo (2017) Traitement d’images pour la ségrégation en transport de sédiments par charriage :Morphologie et suivi d’objets. Université de St Etienne. 112p.
  • Dudill Ashley (2016) Experimental study of segregation mechanisms in bedload sediment transport. Co-tutelle University of British Columbia / Université Grenoble Alpes. 152 p.
  • Hergault V., 2011. Étude microstructurelle du transport par charriage de mélanges bidisperses à forte pente, Université de Grenoble, 180 pp.
  • Frey, P., 2008.Transport solide par charriage à différentes échelles. Application aux cours d'eau de montagne, Habilitation à Diriger les recherches de l’Institut polytechnique de Grenoble, 120 p.
  • Böhm T., 2005. Motion and interaction of a set of particles in a supercritical flow, Thèse de l’Université Joseph Fourier, 172 p.
  • Bigillon F., 2001. Étude du mouvement bidimensionnel d’une particule dans un courant d’eau sur forte pente, Thèse de l'Université Joseph Fourier, 217 p.

 

Contact

Dr Philippe Frey (HDR)
Tel: +33 (0)4 76 76 27 71 – Fax: +33 (0)4 76 51 38 03
2 rue de la papeterie BP 76 38402 Saint Martin d'Hères Cedex
philippe.frey@irstea.fr
Specialties: Fluid mechanics, hydraulics, sediment transport, morphodynamics, mountain stream hazards