Dr. Jakob, Senior Geoscientist with BCG Engineering, presented at Alberta’s Watershed Management Symposium: Flood and Drought Mitigation. Triggered by a series of damaging debris floods in the Bow River Valley in June 2013, Dr. Jakob explained how ongoing hazard and risk assessments for steep mountain creeks in Alberta will be used to mitigate the risk posed by debris floods in the future.

1. BGC ENGINEERING INC.
Mountain Creek Hazards
and Risks in the
Canmore Area
Dr. Matthias Jakob, PGeo. (BC), P.Geol. (AB)
April 28, 2014

2. Outline
• The Storm of June 19-21, 2013
• Notes on the hydroclimate
• Debris flows and debris floods
• Cougar Creek debris flood
• Hazard and Risk Assessment
• Outlook for Alberta standards
2

3. The evolution of an ugly storm
3
Low 1
(Cerberus)
Low 2
(Hades)
Low 3
(Poseidon)

4. Und then came the rain…
4
325 mm
200 mm
50 mm
Canmore

5. Pictures of a catastrophe
5

6. Kananaskis Station Rainfall
6

7. Changes in Heavy
Precipitation
YEARS
ReturnPeriod(years)
TotalPrecipitationperEvent(mm)
200 mm
100 mm
1990 2000 201019901970 198020101950
3 years
4 years
5 years
6 years
Source: Stull et al. 2014
Heavy precipitation has become more frequent
during the past 15 years
The return period of heavy precipitation has
decreased (now: 1 in 3 chance)
 = Banff
X = Bow Valley
= Kananaskis

8. Bow River Flows (1909-2011)
8

9. Bow River Flows (1879-2013)
9

10. transportation
zone
deposition zone
Elements at risk
The Debris Flow
System
Artwork: BGC Engineering

11. The Classic FanThe Classic Fan

12. DEBRIS FLOODS
Problems: debris aggradation, avulsion & bank erosion

13. Cougar Creek Fan
13

14. Cougar Creek Fan
probably one of Canada’s most densely developed fans
14
Floodplain
Canmore

15. Towards a systematic hazardTowards a systematic hazard
and risk assessmentand risk assessment
Hazard Recognition
Frequency-Magnitude Analysis
Hazard Intensity Mapping
Consequence Determination
Risk Calculations
Risk Evaluation
Development Decision
Risk Reduction
Numerical Runout Modeling

16. Historical Air Photographs
16

17. Evidence of Previous Events
17

18. Test Trenching Program
18

19. Test Trenching
19
Bridge River Tephra (~2500 yrs)
Paleosols (old soils)
Deciphering the “deep past”

20. Dendrochronolgy

21. Frequency-Volume Analysis
(How often, how big?)
21
Return Period (Years)
DebrisFloodVolume(m3
)

22. Debris Flood Modeling: Scenario
Analysis
14
ID
T
(Jahre)
Volumen
(m3
)
2 1:30 to 1:100 40,000
3a
3b
1:100 to 1:300 60,000
4 1:300 to 1:1000 160,000
5
1:1000 to
1:3000
260,000
6
1:400
(June 2013
Simulation)
90,000
2 3a 3b
4 5 6
2 3A 3B
4 5 6

23. Combined Hazard Map
• Hazard is expressed
as intensities (flow
depth times velocity square)
• The problem: neither
the exact probability
nor the risk is known
for specific lots.
• Risk maps are more
intuitive in that they
show the real risk
23
Note that this hazard map is from a study in the US and shows debris-flow hazards for a
500-year return period

24. Quantitative Risk Analysis (QRA)
)
24
“…estimation of the likelihood that a debris flood scenario will occur,
impact something, and lead to undesirable consequences.”

25. Risk Map (example)
25
• PDI >1:10,000 (Red)
• PDI of 1:10,000
to1:100,000 (Orange)
• Yellow means that the risk
is < 1:100,000.
PDI: Probability of Death of
an Individual
Note that this map is not an actual risk map but serves as an example of how risk maps could look like

26. Group Risk (example)
26
• Group risk is
unacceptable
• Needs to be
lowered to the
ALARP zone
• Goal of
mitigation is to
bring group risk
into the ALARP
zone
As low as
reasonably
possible
Unacceptable Risk
Acceptable
Risk
Potential Fatalities
AnnualProbabilityofCumulativeFatalities
Uncertainty Range

27. Building Damage, Safety Risk
27
Vulnerability
Criteria
(Buildings)
Assessed
Building Values
Model Results Building Damage Level
Building Damage Cost Probability of Life Loss
Elements at Risk
+
Vulnerability Criteria (Safety)

28. Building Loss Potential
28
5
• $600 k annualized direct building damage costs on fan
• Total costs likely more than a factor of 2 higher

29. Conclusions
29
• Cougar Creek and many other creeks in the Alberta Rocky
Mountains are very hazardous landforms with high risk potential
• Climate observations, theory and modeling all point towards a high
likelihood that extreme precipitation events will increase in
frequency and magnitude. This emerging trend should be reconciled
with landuse planning and structural mitigations
• Given that many fans are heavily developed, risk exists that must be
quantified systematically and transparently
• Risk should be expressed as in loss of life risk and economic risk
• The new Alberta Guidelines will aim to attain those goals
• Mitigation measures should strive to reduce risk to tolerable levels
and optimize costs and benefits.

30. 30
Thank you!