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The role of vegetation and large wood in braided rivers dynamics Walter Bertoldi

The role of vegetation and large wood in braided rivers dynamics Walter Bertoldi Department of Civil, Environmental and Mechanical Engineering University of Trento Séminaire Gestrans , Grenoble, 21 Novembre 2012. This work has been possible thanks to the help of many collaborators:

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The role of vegetation and large wood in braided rivers dynamics Walter Bertoldi

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  1. The role of vegetation and large wood in braided rivers dynamics Walter Bertoldi Department of Civil, Environmental and Mechanical Engineering University of Trento SéminaireGestrans, Grenoble, 21 Novembre 2012

  2. This work has been possible thanks to the help of many collaborators: Leverhulme Project: Angela Gurnell, Nick Drake, Alex Henshaw Trento Lab work + Tagliamento field work: MatildeWelber, Sandra Zanella, Martino Salvaro, Marco Redolfi, Lorenzo Forti Hydralab project Hull: Luca Mao, Michal Tal, Francesco Comiti, Diego Ravazzolo, MatildeWelber, Sandra Zanella, Rob Thomas + discussions with Peter Ashmore, HervéPiégay, Nicola Surian

  3. BRAIDING & VEGETATION

  4. BRAIDING & VEGETATION Murray and Paola, 2003 Perona et al., 2009 Crosato and Saleh, 2011 Gran and Paola, 2001 Tal and Paola, 2007, 2010 Eaton et al. 2010

  5. TAGLIAMENTO RIVER, ITALY ~ 800 m WIDE PINZANO GORGE ~ 120 m WIDE ~ 20 km LONG

  6. 0 250 500m LiDAR ANALYSIS Filtered and de-trended DEM DEM + vegetation height Canopy Surface Model

  7. SUB-REACH COMPARISON • Sub-reach 3 • Vegetation cover = 1.3% (~0% taller than 5m) • Sub-reach 13 • Vegetation cover = 16% (~8% taller than 5m)

  8. FREQUENCY DISTRIBUTIONS The flow is constrained in narrower and deeper channels The vegetation induces fine sediment deposition and island aggrading (Bertoldi et al., 2011- WRR)

  9. BED STATISTICS Area proportional to tall vegetation % Positive Skew SKEWNESS Negative Skew (Bertoldi et al., 2011- WRR)

  10. EFFECT ON SEDIMENT FLUX? Sub-reach 3 Sub-reach 13 a ~ 5 a ~ 3 Euler Gamma pdf (Paola, 1996; Nicholas, 2000)

  11. BANKEROSIONANDTREESINPUT Where is vegetation coming from? CORNINO flow direction

  12. BANKEROSIONANDTREESINPUT A) B) flow direction C) • 26/10/2008 14.00 • 03/11/2008 14.00 • 28/12/2009 14.00 position of island edge

  13. BANKEROSIONANDTREESINPUT A) B) flow direction C) • A) 18/12/2009 16.00 • B) 26/12/2009 16.00 • C) 15/01/2010 16.00 position of island edge on 18/12/2009

  14. 0 100 200m TREESDISTRIBUTION (A) (B) (C) flow direction trunk diameter (cm) # of trees 35 7 25 5 N 15 3 5 1 (E) (F) (D) (Bertoldiet al., 2012 - Geomorphology)

  15. A B N 0.8 m BED ELEVATION DEPOSITED TREES 0 100 200m - 0.8 m TREESDISTRIBUTION flow direction (Bertoldiet al., 2012 - Geomorphology)

  16. ELEVATIONDISTRIBUTION (Bertoldiet al., 2012 - Geomorphology)

  17. ELEVATIONDISTRIBUTION (Bertoldiet al., 2012 - Geomorphology)

  18. MODELLINGWOODDISPERSAL Is it possible to model these processes in the lab?  PhD work of MatildeWelber 3 m 25 m

  19. MODELLINGWOODDISPERSAL • Wood scaling issues: • Diameter (2-6 mm) • Length (4-12 cm) • Density • Presence of roots, branches, ...

  20. WOODDEPOSITIONPATTERNS BAR APEX ALONG BANKS

  21. SPATIALVARIABILITY 5 RUNS WITH THE SAME PARAMETERS COMPLEX SYSTEM +LONG TIME SCALE INPUT

  22. bar 1 bar 2 bar 3 bar 4 BAR- WOODINTERACTION FLOW

  23. ELEVATIONDISTRIBUTION Q=0.9 l/s Q=1.2 l/s Q=1.5 l/s Q=1.8 l/s Braiding formed with Q = 1.8 l/s

  24. ELEVATIONDISTRIBUTION 2D  high variability 3D  narrow range

  25. THE MORPHODYNAMIC IMPACTS OF VEGETATION AND LARGE WOOD IN FLUVIAL SYSTEMS PI: Luca Mao Participants: W. Bertoldi, N. Osei, D. Ravazzolo, M. Tal, M. Welber, S. Zanella UoH staff: S. McLelland, B. Murphy, R. Thomas

  26. WOOD/VEGETATIONINTERACTION Tagliamento flow

  27. EXPERIMENTSSETUP • ’Aerial’ pictures to map • Planform configuration • Wood deposit • Vegetation growth

  28. PRELIMINARYRESULTS flow Flume 3 flow Flume 1 WEEK 1 WEEK 2 WEEK3 WEEK 4

  29. PRELIMINARYRESULTS • Wood dynamics changed significantly even in the first hours with low vegetation • Decrease in wood deposited as single logs from 40% to 25%  <10% in long term • Decrease in wood moved after one hour from 40% to <20% • Increase in wood deposited in already existing groups from <10% to ~20 %  > 80% in long term

  30. VEGETATIONANDFLOODS Modelling vegetation after a sequence of floods High flood effect Vegetation grows fast average single runs  Different distributions  Similar distributions Low flood effect Low vegetation growth average single runs (Gurnell et al., 2012 - Earth-Science Reviews)

  31. QUESTIONS ?

  32. http://www.riverscience.eu/ 9 positions (4 EU + 5 Non EU) Application deadline: January 15, 2013

  33. FLOW-VEGETATIONINTERACTION (Gurnell et al., 2012 - Earth-Science Reviews)

  34. BRAIDING AT DWARF SCALE ~ 1 m Courtesy of Jonathan Laronne

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