Environmental Fluid Mechanics

, Volume 17, Issue 5, pp 903–928 | Cite as

Compound channel flow with a longitudinal transition in hydraulic roughness over the floodplains

  • Victor DupuisEmail author
  • Sébastien Proust
  • Céline Berni
  • André Paquier
Original Article


Flows in a compound open-channel (two-stage geometry with a main channel and adjacent floodplains) with a longitudinal transition in roughness over the floodplains are experimentally investigated in an 18 m long and 3 m wide flume. Transitions from submerged dense vegetation (meadow) to emergent rigid vegetation (wood) and vice versa are modelled using plastic grass and vertical wooden cylinders. For a given roughness transition, the upstream discharge distribution between main channel and floodplain (called subsections) is also varied, keeping the total flow rate constant. The flows with a roughness transition are compared to flows with a uniformly distributed roughness over the whole length of the flume. Besides the influence of the downstream boundary condition, the longitudinal profiles of water depth are controlled by the upstream discharge distribution. The latter also strongly influences the magnitude of the lateral net mass exchanges between subsections, especially upstream from the roughness transition. Irrespective of flow conditions, the inflection point in the mean velocity profile across the mixing layer is always observed at the interface between subsections. The longitudinal velocity at the main channel/floodplain interface, denoted \(U_{int}\), appeared to be a key parameter for characterising the flows. First, the mean velocity profiles across the mixing layer, normalised using \(U_{int}\), are superimposed irrespective of downstream position, flow depth, floodplain roughness type and lateral mass transfers. However, the profiles of turbulence quantities do not coincide, indicating that the flows are not fully self-similar and that the eddy viscosity assumption is not valid in this case. Second, the depth-averaged turbulent intensities and Reynolds stresses, when scaled by the depth-averaged velocity \(U_{d,int}\) exhibit two plateau values, each related to a roughness type, meadow or wood. Lastly, the same results hold when scaling by \(U_{d,int}\) the depth-averaged lateral flux of momentum due to secondary currents. Turbulence production and magnitude of secondary currents are increased by the presence of emergent rigid elements over the floodplains. The autocorrelation functions show that the length of the coherent structures scales with the mixing layer width for all flow cases. It is suggested that coherent structures tend to a state where the magnitude of velocity fluctuations (of both horizontal vortices and secondary currents) and the spatial extension of the structures are in equilibrium.


Laboratory study Non-uniform flow Turbulent mixing layer Coherent structures Cylinder array Rigid vegetation 



The Ph.D. Grant of V. Dupuis was funded by Irstea and by the French National Research Agency (Flowres project, Grant No. ANR-14-CE03-0010, The authors greatly thank Fabien Thollet and Alexis Buffet for their technical support.


  1. 1.
    Bousmar D, Zech Y (1999) Momentum transfer for practical flow computation in compound channels. J Hydraul Eng 125(7):696–706CrossRefGoogle Scholar
  2. 2.
    Bousmar D, Wilkin N, Jacquemart JH, Zech Y (2004) Overbank flow in symmetrically narrowing floodplains. J Hydraul Eng 130(4):305–312CrossRefGoogle Scholar
  3. 3.
    Bousmar D, Riviere N, Proust S, Paquier A, Morel R, Zech Y (2005) Upstream discharge distribution in compound-channel flumes. J Hydraul Eng 131(5):408–412CrossRefGoogle Scholar
  4. 4.
    Brown GL, Roshko A (1974) On density effects and large structure in turbulent mixing layers. J Fluid Mech 64(04):775–816CrossRefGoogle Scholar
  5. 5.
    Chu VH, Babarutsi S (1988) Confinement and bed-friction effects in shallow turbulent mixing layers. J Hydraul Eng 114(10):1257–1274CrossRefGoogle Scholar
  6. 6.
    Dupuis V (2016) Experimental investigation of flows subjected to a longitudinal transition in hydraulic roughness in single and compound channels. PhD thesis, Université de LyonGoogle Scholar
  7. 7.
    Dupuis V, Proust S, Berni C, Paquier A (2016) Combined effects of bed friction and emergent cylinder drag in open channel flow. Environm Fluid Mech 16(6):1173–1193CrossRefGoogle Scholar
  8. 8.
    Dupuis V, Proust S, Berni C, Paquier A (2017) Mixing layer development in compound channel flows with submerged and emergent rigid vegetation over the floodplains. Exper Fluids 58(4):30CrossRefGoogle Scholar
  9. 9.
    Elliott S, Sellin R (1990) SERC flood channel facility: skewed flow experiments. J Hydraul Res 28(2):197–214CrossRefGoogle Scholar
  10. 10.
    Fjortoft R (1950) Application of integral theorems in deriving criteria of stability for laminar flows and for the baroclinic circular vortex. Geofys Publ 17(6):1–52Google Scholar
  11. 11.
    George WK (1989) The self-preservation of turbulent flows and its relation to initial conditions and coherent structures. In: George WK, Arndt R (eds) Advances in turbulence. Hemisphere, New York, pp 39–73Google Scholar
  12. 12.
    Goring DG, Nikora VI (2002) Despiking acoustic Doppler velocimeter data. J Hydraul Eng 128(1):117–126CrossRefGoogle Scholar
  13. 13.
    Jahra F, Kawahara Y, Hasegawa F, Yamamoto H (2011) Flow-vegetation interaction in a compound open channel with emergent vegetation. Int J River Basin Manag 9(3–4):247–256CrossRefGoogle Scholar
  14. 14.
    Knight DW, Demetriou JD (1983) Flood plain and main channel flow interaction. J Hydraul Eng 109(8):1073–1092CrossRefGoogle Scholar
  15. 15.
    Lukowicz JV (2002) Zu kohärenten Turbulenzstrukturen in der Strömung gegliederter Gerinne. PhD thesis, RWTH AachenGoogle Scholar
  16. 16.
    Moore D, Saffman P (1975) The density of organized vortices in a turbulent mixing layer. J Fluid Mech 69(03):465–473CrossRefGoogle Scholar
  17. 17.
    Nezu I, Nakayama T (1997) Space–time correlation structures of horizontal coherent vortices in compound open-channel flows by using particle-tracking velocimetry. J Hydraul Res 35(2):191–208CrossRefGoogle Scholar
  18. 18.
    Nikora V, McEwan I, McLean S, Coleman S, Pokrajac D, Walters R (2007) Double-averaging concept for rough-bed open-channel and overland flows: Theoretical background. J Hydraul Eng 133(8):873–883CrossRefGoogle Scholar
  19. 19.
    Peltier Y, Proust S, Riviere N, Paquier A, Shiono K (2013) Turbulent flows in straight compound open-channel with a transverse embankment on the floodplain. J Hydraul Res 51(4):446–458CrossRefGoogle Scholar
  20. 20.
    Proust S, Bousmar D, Riviere N, Paquier A, Zech Y (2009) Nonuniform flow in compound channel: A 1-d method for assessing water level and discharge distribution. Water Resour Res 45(12):1–16CrossRefGoogle Scholar
  21. 21.
    Proust S, Bousmar D, Rivière N, Paquier A, Zech Y (2010) Energy losses in compound open channels. Adv Water Resour 33(1):1–16CrossRefGoogle Scholar
  22. 22.
    Proust S, Fernandes JN, Peltier Y, Leal JB, Riviere N, Cardoso AH (2013) Turbulent non-uniform flows in straight compound open-channels. J Hydraul Res 51(6):656–667CrossRefGoogle Scholar
  23. 23.
    Rominger JT, Nepf HM (2011) Flow adjustment and interior flow associated with a rectangular porous obstruction. J Fluid Mech 680:636–659CrossRefGoogle Scholar
  24. 24.
    Tominaga A, Nezu I (1991) Turbulent structure in compound open-channel flows. J Hydraul Eng 117(1):21–41CrossRefGoogle Scholar
  25. 25.
    Townsend A (1961) Equilibrium layers and wall turbulence. J Fluid Mech 11(01):97–120CrossRefGoogle Scholar
  26. 26.
    Vermaas D, Uijttewaal W, Hoitink A (2011) Lateral transfer of streamwise momentum caused by a roughness transition across a shallow channel. Water Resour Res 47(2):1–12CrossRefGoogle Scholar
  27. 27.
    White BL, Nepf HM (2007) Shear instability and coherent structures in shallow flow adjacent to a porous layer. J Fluid Mech 593:1–32CrossRefGoogle Scholar
  28. 28.
    Winant C, Browand F (1974) Vortex pairing: the mechanism of turbulent mixing-layer growth at moderate reynolds number. J Fluid Mech 63(02):237–255CrossRefGoogle Scholar
  29. 29.
    Zong L, Nepf H (2010) Flow and deposition in and around a finite patch of vegetation. Geomorphology 116(3):363–372CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  • Victor Dupuis
    • 1
    Email author
  • Sébastien Proust
    • 1
  • Céline Berni
    • 1
  • André Paquier
    • 1
  1. 1.UR HHLY Hydrologie-HydrauliqueIrstea, Centre de Lyon-VilleurbanneVilleurbanne CedexFrance

Personalised recommendations