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1 Civil Engineering Dept. University of Greenwich – UK
[email protected] 2 Civil and Environmental Eng.
University of Trento – Italy
Normalized Difference Vegetation Index
0.7
-0.6
Water + Gravel Sparse Vegetation Dense Vegetation
3 – Bands composite
Band 1 = Green Band 2 = Red
Band 3 = Near InfraRed
Characteristics of Rio Colonia
Average discharge = 110 m³/s
Length = 20 km
Maximum width ~1500 m
Discharge during GLOF ~ 4000 m³/s
A NEW CYCLE OF GLOFs
1
AIM: to investigate floods and sediment effects of extreme floods, using Colonia GLOFs as convenient case study (“field lab”) monitored by ground and remote sensing, and inform flood hazard analysis that includes flow and sediment impacts
2 STUDY SITE
3
• US$7 billion mega dam project: reservoir sedimentation
• GLOF frequency: op. to predict & study extreme flows that usually occur every 100’s of years several times a year!
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5 6
18
96
-1
96
3
7 A
pr
20
08
8 O
tt
20
08
2
1 D
ic
20
08
5
Mar
20
09
16
Sep
2
00
9
5 J
an
2
01
0
20
Jan
2
01
0
5 M
ar
20
11
27
Jan
2
01
2
2 A
pr
20
12
NO
G
LOFs
5 IMAGES
! 3° Feb 2002
! 22° Feb 2003
! 4° Feb 2008
! 5° Apr 2010
! 22° Feb 2012
Feb
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02
Feb
20
03
Feb
20
08
Ap
r 2
01
0
Feb
20
12
Veg
eta
ted
pro
po
rtio
n Upstream
Middle Downstream
Feb
20
02
Feb
20
03
Feb
20
08
Ap
r 2
01
0
Feb
20
12
Veg
eta
ted
pro
po
rtio
n
Dense Sparse
Feb 2012
Feb 2008
Vegetation has been eroded
1) along channels
2) where new branches have been activated
Braiding index & channel mobility
Pre 2008 2012
Aerial Photograph From SAF
• In the last 4 years we observed a decrease of vegetation cover (by 30%) and a simultaneous increase of the braiding index
• This sequence of GLOFs is an ideal case to study the effect of different (and extreme) discharges on braiding, flood risk and sediment flux
• River bed topo surveys, estimate bedload
• Suspended sediment, flood hazard, reservoir feasibility
• Vegetation studies, sensor network
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