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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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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

SéminaireGestrans, Grenoble, 21 Novembre 2012


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

BRAIDING & VEGETATION


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

TAGLIAMENTO RIVER, ITALY

~ 800 m WIDE

PINZANO GORGE

~ 120 m WIDE

~ 20 km LONG


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

0

250

500m

LiDAR ANALYSIS

Filtered and de-trended DEM

DEM + vegetation height

Canopy Surface Model


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

SUB-REACH COMPARISON

  • Sub-reach 3

  • Vegetation cover = 1.3%

    (~0% taller than 5m)

  • Sub-reach 13

  • Vegetation cover = 16%

    (~8% taller than 5m)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

BED STATISTICS

Area proportional to tall vegetation %

Positive Skew

SKEWNESS

Negative Skew

(Bertoldi et al., 2011- WRR)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

EFFECT ON SEDIMENT FLUX?

Sub-reach 3

Sub-reach 13

a ~ 5

a ~ 3

Euler Gamma pdf

(Paola, 1996; Nicholas, 2000)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

BANKEROSIONANDTREESINPUT

Where is vegetation coming from?

CORNINO

flow

direction


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

A

B

N

0.8 m

BED ELEVATION

DEPOSITED TREES

0

100

200m

- 0.8 m

TREESDISTRIBUTION

flow

direction

(Bertoldiet al., 2012 - Geomorphology)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

ELEVATIONDISTRIBUTION

(Bertoldiet al., 2012 - Geomorphology)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

ELEVATIONDISTRIBUTION

(Bertoldiet al., 2012 - Geomorphology)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

MODELLINGWOODDISPERSAL

Is it possible to model these processes in the lab?

 PhD work of MatildeWelber

3 m

25 m


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

MODELLINGWOODDISPERSAL

  • Wood scaling issues:

  • Diameter (2-6 mm)

  • Length (4-12 cm)

  • Density

  • Presence of roots, branches, ...


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

WOODDEPOSITIONPATTERNS

BAR APEX

ALONG BANKS


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

SPATIALVARIABILITY

5 RUNS WITH THE SAME PARAMETERS

COMPLEX SYSTEM +LONG TIME SCALE

INPUT


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

bar 1

bar 2

bar 3

bar 4

BAR- WOODINTERACTION

FLOW


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

ELEVATIONDISTRIBUTION

2D  high variability

3D  narrow range


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

WOOD/VEGETATIONINTERACTION

Tagliamento

flow


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

EXPERIMENTSSETUP

  • ’Aerial’ pictures to map

  • Planform configuration

  • Wood deposit

  • Vegetation growth


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

PRELIMINARYRESULTS

flow

Flume 3

flow

Flume 1

WEEK 1

WEEK 2

WEEK3

WEEK 4


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

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)


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

QUESTIONS ?


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

http://www.riverscience.eu/

9 positions (4 EU + 5 Non EU)

Application deadline: January 15, 2013


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

FLOW-VEGETATIONINTERACTION

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


The role of vegetation and large wood in braided rivers dynamics walter bertoldi

BRAIDING AT DWARF SCALE

~ 1 m

Courtesy of Jonathan Laronne


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