2019‐01‐26
1
A non-profit organization focused on bringing together
Contractors, Engineers, Geologists, Manufacturers and Public Agencies in the
pursuit of excellence
1
www.GeohazardAssociation.org – Est. 2013
Are human activities as close to other slope hazards?
Photo © Parks Canada / John Woods
Snow avalanche risk assessment and mitigation Bruce Jamieson and Chris Wilbur
1
2
2019‐01‐26
2
Characterizing, assessing
and mitigating snow avalanche risk
• Differences from other slope hazards• Methods not guidelines/thresholds• Qualitative and quantitative methods
Parks Canada & Dynamic Avalanche Consulting Ltd.
Some physical differences: re other slope hazards
Failures occur in bonds < 5 C from melting. Samples too fragile to be transported to lab.
UCalgary/ASARC photo
3
4
2019‐01‐26
3
Explosive triggering works. But timing critical!
B. Jamieson photo
The Frank Slide depositwon’t melt …but snow avalanche deposits do so no subsurface sampling of old deposits
5
6
2019‐01‐26
4
Snow avalanches vs other slope hazards:
Physical differences
• Many occurrences in same path / track• Vegetation damage useful up to ~100 y (in some paths)• Deposits melt, limiting estimation of return periods• Subsurface sampling ineffective• Failures occur in bonds < 5 C from melting• Explosive triggering works! But timing is critical.
Comments or questions?
Overview of methods
1. Characterization
2. Assessment
3. Mapping
4. Mitigation
7
8
2019‐01‐26
5
1. Characterization• Terrain identification
• Avalanche characteristics
• Occurrence records
• Vegetation damage
• Snow climate
• Dynamic models
• Statistical runout estimation
LiDAR data courtesy Parks Canada. Processing by C. Argue
Ucalgary/ASARC photo
Two strong factors for start zones: slope angle & forest cover
Characterization: Terrain
B. Jamieson photo
9
10
2019‐01‐26
6
W. Geary photo
powder (suspension) layer
saltation (fluidized) layer
dense core
snowpack
ground
Snow avalanche deposits
B. Jamieson photo
B. Jamieson photo
11
12
2019‐01‐26
7
Characterization: vegetation damage
A. Mears photo
B. Jamieson photo
2400
2300
2200
2100
2000
1900
1800
1700
0 200 400 600 800 1000 1200 1400
Ele
vatio
n (m
)
Horizontal distance from top of start zone (m)
35
30
0
15
5
10
25
20
Front speed
Mean particle speed
Deposit
Sp
eed
(m
s)
-1
Characterization: Avalanche dynamic models
13
14
2019‐01‐26
8
www.slf.ch/ramms
Statistical runout estimation
obs
point
Top of start zone
Observedendof
runout
Horizontal distance
Ele
vatio
n
cross section of path centerline
15
16
2019‐01‐26
9
Calculate parameters for distribution
30+ paths
= 0.92
r² = 0.90
20
25
30
35
20 25 30 35 40 (°)
(°)
Regress obs on obs(⁰)
Li
1. Characterization• Terrain identification
• Avalanche characteristics
• Occurrence records
• Vegetation damage
• Snow climate
• Avalanche dynamic models
• Statistical runout estimation
Comments or questions?
LiDAR data courtesy Parks Canada. Processing by C. Argue
17
18
2019‐01‐26
10
2. Assessment• Combining the runout estimates
• Qualitative and quantitative assessment: Avalanche hazard and risk
• Avalanche hazard to roads from clear cuts
• Risk for transportation corridors
Google Earth image© 2017 Digital Globe.
Assessment: a. Combining the runout estimates
Once the extreme runouts have been combined for, e.g. 300 y,a dynamic model can be fitted to this design runout so the velocity andimpact pressure can be back‐calculated for any point in the runout zone.
19
20
2019‐01‐26
11
An example of runout estimation using occurrence records and vegetation damage
50 m
40 m
30 m
transmissionline
forestry road
20 yveg.
80 yforest
mature forest 15 m
center-flowof path
trim line 1
trimline 2
proposed pedestrian walkway
‐60
‐40
‐20
0
20
40
60
80
100
0 50 100 150
Run
out
(m)
x
Return period (years)T
x T = -78.2 + 33.2 ln ( )
17 in 40 y
3 in 30 y
2 in 80 y
1 in 80 y
Pedestrian walkway
21
22
2019‐01‐26
12
Assessment: Hazard then sometimes riskAvalanche risk assessment is consistent with international landslide guidelines
Example of qualitative hazard assessment
Hazard ratings for expected avalanche size and frequency for forest harvest when downslope transportation corridors, facilities or essential resources may be affected. After CAA (2002a).
Frequency range (avalanchesper year)
Average frequency
(avalanchesper year)
Avalanche destructive size
D2 D3 > D3
1:10 to > 1 1:3 Mod. High High
1:10 to 1:100 1:30 Low Mod. High
< 1:100 1:300 Low Low High
Chris Stethem photo
23
24
2019‐01‐26
13
Quantitative assessment: Risk to transportation corridors:Moving and waiting traffic
Google Earth
2. Assessment• Combining the runout estimates (prior to back‐calculating velocity & impact pressure)
• Qualitative and quantitative assessment: Avalanche hazard and risk
• Avalanche hazard from clear cuts. Risk for transportation corridors
Hazard ratings for expected avalanche size and frequency for forest harvest when downslope transportation corridors, facilities or essential resources may be affected. After CAA (2002a).
Frequency range (avalanchesper year)
Average frequency
(avalanchesper year)
Avalanche destructive size
D2 D3 > D3
1:10 to > 1 1:3 Mod. High High
1:10 to 1:100 1:30 Low Mod. High
< 1:100 1:300 Low Low High
25
26
2019‐01‐26
14
Model‐based Large Scale Mapping
3. Mapping: Examples of avalanche maps
Exposure of workers
SLF Swiss Federal Institute for Snow and Avalanches
Occupied Structures
Avalanche Zones
Red (high) Hazard
Blue (moderate)
Yellow (low)
White (negligible)
Wilbur Engineering, Inc.Rico, Colorado
27
28
2019‐01‐26
15
• Hazard mapping for occupied structures
• Exposure mapping for backcountry workers
Comments or questions?
3. Mapping
4. Mitigation• Avalanche impact
• Defense structures (start zone, runout zone)
• Structural design for avalanche impact
• Temporary measures: ‐ Detection systemsforecasting, closures, evacuations
‐ explosive triggering includingRemote Avalanche Control Systems
B. Jamieson photo
29
30
2019‐01‐26
16
Mitigation: Avalanche impact
HSprevious deposits
dense flow
fluidized
hdf
himp
powderHw
M
IN,df
IN,p
Sudavik, Iceland, 1995, 14 deaths(also 1995: Flateryi, Iceland, 20 deaths)
Stationary snowB. Jamieson photo
BC Ministry of Transportation and Infrastructure and S. Brushey.
Mitigation: Defense structures
B. Jamieson photo
31
32
2019‐01‐26
17
B. Jamieson photo
Stopping DamTaconnaz, France
Splitting WedgeGirdwood, Alaska
B. Jamieson photo
33
34
2019‐01‐26
18
C. Wilbur photo
Photo courtesy B. Glude andAlaska Light & Power
Chris Wilbur photoRyan Buhler photo
35
36
2019‐01‐26
19
Towers designed for impact
If consequences of an outage are high(e.g. aluminum smelter),the transmission lines can be twinned.
Arni Jonsson photo
Chris Wilbur photo
Temporary measures
Photo: BC Ministry of Transportation and Infrastructure
Photo: Wyssen Avalanche Control AG
Photo: AvaTek Mountain Systems Inc.
37
38
2019‐01‐26
20
Detection
Infrasound
Radar
Seismic
Mechanical
Time lapse Geopraevent image
4. Mitigation• Avalanche impact
• Defense structures (start zone, runout zone)
• Structural design for avalanche impact
• Temporary measures: ‐ Detection systems‐ forecasting, closures, evacuations‐ Remote Avalanche Control Systems
Comments or questions?
B. Jamieson photo
39
40
2019‐01‐26
21
Case study:Kangiqsualujjuaq
B. Jamieson photos
Snow avalanche risk assessment and mitigation
Questions and comments?
B. Jamieson photos
41
42
