mountain creek hazards and risks in the canmore area - dr. matthias jakob

BGC ENGINEERING INC.

Mountain Creek Hazards and Risks in the Canmore AreaDr. Matthias Jakob, PGeo. (BC), P.Geol. (AB)

April 28, 2014

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

The evolution of an ugly storm

3

Low 1(Cerberus)

Low 2(Hades)

Low 3(Poseidon)

Und then came the rain…

4

325 mm

200 mm

50 mm

Canmore

Pictures of a catastrophe

5

Kananaskis Station Rainfall

6

Changes in Heavy Precipitation

YEARS

Ret

urn

Per

iod

(yea

rs)

Tot

al P

reci

pita

tion

per

Eve

nt (

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)

= BanffX = Bow Valley= Kananaskis

Bow River Flows (1909-2011)

8

Bow River Flows (1879-2013)

9

transportation zone

deposition zone

Elements at risk

The Debris Flow System

Artwork: BGC Engineering

The Classic FanThe Classic Fan

DEBRIS FLOODSProblems: debris aggradation, avulsion & bank erosion

Cougar Creek Fan

13

Cougar Creek Fanprobably one of Canada’s most densely developed fans

14

Floodplain

Canmore

Towards a systematic Towards a systematic hazard and risk assessmenthazard and risk assessment

Hazard Recognition

Frequency-Magnitude Analysis

Hazard Intensity Mapping

Consequence Determination

Risk Calculations

Risk Evaluation

Development Decision

Risk Reduction

Numerical Runout Modeling

Historical Air Photographs

16

Evidence of Previous Events

17

Test Trenching Program

18

Test Trenching

19

Bridge River Tephra (~2500 yrs)

Paleosols (old soils)

Deciphering the “deep past”

Dendrochronolgy

Frequency-Volume Analysis(How often, how big?)

21

Return Period (Years)

Deb

ris F

lood

Vol

ume

(m3 )

Debris Flood Modeling: Scenario Analysis

14

IDT

(Jahre)

Volumen

(m3)

2 1:30 to 1:100 40,000

3a3b

1:100 to 1:300 60,000

4 1:300 to 1:1000 160,000

51:1000 to

1:3000260,000

6

1:400(June 2013 Simulation)

90,000

2 3a 3b

4 5 6

2 3A 3B

4 5 6

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

Quantitative Risk Analysis (QRA))

24

“…estimation of the likelihood that a debris flood scenario will occur, impact something, and lead to undesirable consequences.”

Risk Map (example)

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• 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

Group Risk (example)

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• 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

An

nu

al

Pro

ba

bil

ity

of

Cu

mu

lati

ve

Fa

tali

tie

s

Uncertainty Range

Building Damage, Safety Risk

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Vulnerability Criteria(Buildings)

Assessed Building Values

Model Results Building Damage Level

Building Damage Cost Probability of Life Loss

Elements at Risk

+

Vulnerability Criteria (Safety)

Building Loss Potential

28

5

• $600 k annualized direct building damage costs on fan• Total costs likely more than a factor of 2 higher

Conclusions

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• 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.

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Thank you!