River Hydraulics > Research > Complex flows in rivers > Laterally confined flows through roughness elements and vegetated flows

Laterally confined flows through roughness elements and vegetated flows

Problematic issue

The aim is to study the influence of emerged or slightly submerged macro-roughness elements (modelling trees or houses in floodplains) on the structure of laterally confined flows (open-channel with a  single rectangular cross-section).

Scientific issues

  • Variation of the flow structure with the submergence parameter D/h of the macro-roughness elements (D = time-averaged water depth and h = macro-roughness height), for 1<D/h<1.5.
  • Influence of the Froude, Reynolds, and Strouhal numbers on the flow structure
  • Influence of the streamwise flow  non-uniformity on the flow structure (comparison  uniform flow / accelerated flow)
  • Influence of a longitudinal transition of hydraulic roughness on the flow structure.
  • Influence of the bed roughness (smooth bottom vs. rough bottom) on the flow structure.
  • Influence of unsteadiness on the flow structure.

Methodology

The experiments are conducted in an 18m x 3m  flume, but using only one third of the width (18m x 1m). The cross-section is rectangular, the side walls are made of glass. For the bottom, different hydraulic roughnesses are studied:

  • Tree models (wooden cylinders 1 cm in diameter) placed on a smooth bed (glass)
  • Tree models (wooden cylinders 1 cm in diameter) placed on a rough bed (dense artificial grass). Tree density: 81 trees/m², with a staggered distribution.
  • House models (6.4 cm side PVC cubes) placed on a rough bed (dense artificial grass). Density of houses: 49 houses/m².

The velocity field is measured using an ADV (side-looking probe) or  PIV 2D-2C (vertical-longitudinal plane). These flows are also  numerically modeled with 2D and 3D industrial or research codes.

Projects

  • ANR FlowRes  project (2015-2018). ‘Predicting flows in floodplains with evolving land use during extreme flood events’.

Partners

  • École Nationale Polytechnique d’Alger (ENPA)
  • Laboratoire d’Hydraulique Saint-Venant (LHSV)
  • National Institute of Technology (NIT) in Rourkela, India.

PhD theses and post-doctorates

  • January 2013 – June 2016: PhD of Victor Dupuis entitled : ‘Experimental investigation of flows subjected to a longitudinal transition in hydraulic roughness in single and compound channels’. PhD Université de Lyon, École Doctorale ED162. Co-supervised by S. Proust, C. Berni, and A. Paquier (director)
  • PhD of Meriem Chétibi (January 2016 – December 2019) entitled : ‘Turbulent flows in non-prismatic open-channels’ (co-directors : S. Benmamar, ENPA; S. Proust, Irstea)
  • PhD of  Marina Oukacine  (January 2016 – Juin 2019): ‘Experimental and numerical study of flows through emerged and slightly submerged macro-roughness elements’.  Co-directors:  N. Goutal (EDF), et S. Proust.
  •  Post-doctorate of  Marc Chatelain (March 2017 –  august 2018) entitled ‘3D LES (Large Eddy Simulation) of flooplain flows in the presence of emergent and slightly submerged macro-roughness elements’. Supervised by S. Proust.
  • PhD of Djnana Khuntia (2016-2020) entitled ‘Unsteady open-channel flows over a rough-bed with and without emergent rigid vegetation’, National Institute of Technology, Rourkela. Supervised by K. Khatua and S. Proust from March to September 2018.

Publications