and large wood in braided rivers dynamics Walter Bertoldi Department of Civil Environmental and Mechanical Engineering University of Trento Séminaire Gestrans Grenoble 21 Novembre ID: 759837
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Slide1
The role of vegetation and large wood in braided rivers dynamicsWalter BertoldiDepartment of Civil, Environmental and Mechanical EngineeringUniversity of TrentoSéminaire Gestrans, Grenoble, 21 Novembre 2012
Slide2This 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
:
Matilde
Welber
, Sandra
Zanella
, Martino
Salvaro
, Marco
Redolfi
, Lorenzo
Forti
Hydralab
project Hull
:
Luca Mao, Michal Tal, Francesco
Comiti
, Diego
Ravazzolo
,
Matilde
Welber
, Sandra
Zanella
, Rob Thomas
+ discussions with
Peter
Ashmore
,
Hervé
Piégay
, Nicola
Surian
Slide33/30
BRAIDING & VEGETATION
Slide44/30
Gran and Paola, 2001
Tal and Paola, 2007, 2010Eaton et al. 2010
Murray and Paola, 2003Perona et al., 2009Crosato and Saleh, 2011
BRAIDING & VEGETATION
Slide55/30
TAGLIAMENTO
RIVER, ITALY
~ 20 km LONG
~ 800 m WIDE
PINZANO
GORGE
~ 120 m WIDE
Slide66/30
LiDAR ANALYSIS
0
250
500m
Canopy Surface Model
Filtered and de-trended DEM
DEM + vegetation height
Slide77/30
Sub-reach 3
Vegetation cover = 1.3%
(~0% taller than 5m)
Sub-reach 13Vegetation cover = 16% (~8% taller than 5m)
SUB-REACH COMPARISON
Slide88/30
FREQUENCY DISTRIBUTIONS
The vegetation induces fine sediment deposition and island aggrading
The flow is constrained in narrower and deeper channels
(
Bertoldi
et al., 2011-
WRR
)
Slide99/30
BED STATISTICS
Area proportional to tall vegetation %
SKEWNESS
Positive Skew
Negative Skew
(
Bertoldi
et al., 2011-
WRR
)
Slide1010/30
Sub-reach 3
Sub-reach 13
Euler Gamma
pdf
(Paola, 1996; Nicholas, 2000)
EFFECT ON SEDIMENT
FLUX?
a
~ 5
a
~ 3
Slide11flow
direction
CORNINO
BANK
EROSION AND TREES INPUT
11/30
Where is vegetation coming from?
Slide1226/10/2008 14.00
03/11/2008 14.0028/12/2009 14.00
A)
B)
C)
position of island edge
BANK
EROSION
AND
TREES
INPUT
flow
direction
12/30
Slide13A) 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
flow
direction
A)
B)
C)
BANK
EROSION AND TREES INPUT
13/34
Slide14(A)
(B)
(C)
(E)
(F)
(D)
0
100
200m
N
trunk diameter (cm)
35
25
15
5
# of trees
7
5
3
1
flow
direction
TREES
DISTRIBUTION
(
Bertoldi
et al., 2012 -
Geomorphology)
14
/30
Slide150
100
200m
N
- 0.8 m
0.8 m
BED ELEVATION
DEPOSITED TREES
A
B
flow
direction
TREES
DISTRIBUTION
15
/30
(
Bertoldi
et al., 2012 -
Geomorphology)
Slide16ELEVATION
DISTRIBUTION
16
/30
(
Bertoldi et al., 2012 - Geomorphology)
Slide17ELEVATION
DISTRIBUTION
17/30
(Bertoldi et al., 2012 - Geomorphology)
Slide183 m
25 m
18
/30
MODELLING
WOOD
DISPERSAL
Is it possible to model these processes in the lab? PhD work of Matilde Welber
Slide19Wood scaling issues:
Diameter (2-6 mm)Length (4-12 cm)DensityPresence of roots, branches, ...
19/30
MODELLING
WOOD
DISPERSAL
Slide20BAR APEX
ALONG BANKS
WOOD
DEPOSITION PATTERNS
20/30
Slide21SPATIAL
VARIABILITY
5 RUNS WITH THE SAME PARAMETERS
COMPLEX SYSTEM
+
LONG TIME SCALE
INPUT
21
/30
Slide22FLOW
bar 1
bar 4
bar 2
bar 3
BAR
-
WOOD
INTERACTION
22
/30
Slide23Q=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
ELEVATION
DISTRIBUTION
23
/30
Slide242D
high variability
3D narrow range
24/30
ELEVATION DISTRIBUTION
Slide25THE
MORPHODYNAMIC
IMPACTS
OF VEGETATION AND LARGE WOOD
IN FLUVIAL SYSTEMS
PI: Luca MaoParticipants: W. Bertoldi, N. Osei, D. Ravazzolo, M. Tal, M. Welber, S. ZanellaUoH staff: S. McLelland, B. Murphy, R. Thomas
Slide26flow
WOOD/VEGETATION
INTERACTION
Tagliamento
26
/30
Slide27’Aerial’
pictures
to
map
Planform
configurationWood depositVegetation growth
EXPERIMENTS SETUP
27/30
Slide28Flume 3
Flume 1
WEEK 1
WEEK 2
WEEK3
WEEK 4
flow
flow
28
/30
PRELIMINARY
RESULTS
Slide29Wood dynamics changed significantly even in the first hours with low vegetationDecrease in wood deposited as single logs from 40% to 25% <10% in long termDecrease 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
29/30
PRELIMINARY RESULTS
Slide30average
Low flood effect
Low vegetation growth
single runs
30
/30
average
High flood effect
Vegetation grows fast
single runs
Similar distributions
Different
distributions
Modelling vegetation after a sequence of floods
(
Gurnell
et al., 2012 - Earth-Science Reviews)
VEGETATION AND FLOODS
Slide31QUESTIONS ?
Slide32http://www.riverscience.eu/
9 positions (4 EU
+ 5 Non
EU)
Application deadline: January 15, 2013
Slide3333/34
FLOW-VEGETATION INTERACTION
(Gurnell et al., 2012 - Earth-Science Reviews)
Slide3434/22
~ 1 m
Courtesy of Jonathan
Laronne
BRAIDING AT DWARF SCALE