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


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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

Department of Civil, Environmental and Mechanical Engineering

University of Trento

SéminaireGestrans, Grenoble, 21 Novembre 2012


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


BRAIDING & VEGETATION


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


TAGLIAMENTO RIVER, ITALY

~ 800 m WIDE

PINZANO GORGE

~ 120 m WIDE

~ 20 km LONG


0

250

500m

LiDAR ANALYSIS

Filtered and de-trended DEM

DEM + vegetation height

Canopy Surface Model


SUB-REACH COMPARISON

  • Sub-reach 3

  • Vegetation cover = 1.3%

    (~0% taller than 5m)

  • Sub-reach 13

  • Vegetation cover = 16%

    (~8% taller than 5m)


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)


BED STATISTICS

Area proportional to tall vegetation %

Positive Skew

SKEWNESS

Negative Skew

(Bertoldi et al., 2011- WRR)


EFFECT ON SEDIMENT FLUX?

Sub-reach 3

Sub-reach 13

a ~ 5

a ~ 3

Euler Gamma pdf

(Paola, 1996; Nicholas, 2000)


BANKEROSIONANDTREESINPUT

Where is vegetation coming from?

CORNINO

flow

direction


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


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


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)


A

B

N

0.8 m

BED ELEVATION

DEPOSITED TREES

0

100

200m

- 0.8 m

TREESDISTRIBUTION

flow

direction

(Bertoldiet al., 2012 - Geomorphology)


ELEVATIONDISTRIBUTION

(Bertoldiet al., 2012 - Geomorphology)


ELEVATIONDISTRIBUTION

(Bertoldiet al., 2012 - Geomorphology)


MODELLINGWOODDISPERSAL

Is it possible to model these processes in the lab?

 PhD work of MatildeWelber

3 m

25 m


MODELLINGWOODDISPERSAL

  • Wood scaling issues:

  • Diameter (2-6 mm)

  • Length (4-12 cm)

  • Density

  • Presence of roots, branches, ...


WOODDEPOSITIONPATTERNS

BAR APEX

ALONG BANKS


SPATIALVARIABILITY

5 RUNS WITH THE SAME PARAMETERS

COMPLEX SYSTEM +LONG TIME SCALE

INPUT


bar 1

bar 2

bar 3

bar 4

BAR- WOODINTERACTION

FLOW


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


ELEVATIONDISTRIBUTION

2D  high variability

3D  narrow range


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


WOOD/VEGETATIONINTERACTION

Tagliamento

flow


EXPERIMENTSSETUP

  • ’Aerial’ pictures to map

  • Planform configuration

  • Wood deposit

  • Vegetation growth


PRELIMINARYRESULTS

flow

Flume 3

flow

Flume 1

WEEK 1

WEEK 2

WEEK3

WEEK 4


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


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)


QUESTIONS ?


http://www.riverscience.eu/

9 positions (4 EU + 5 Non EU)

Application deadline: January 15, 2013


FLOW-VEGETATIONINTERACTION

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


BRAIDING AT DWARF SCALE

~ 1 m

Courtesy of Jonathan Laronne


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