Monday January 16, 2006, Centennial Theatre
Landslide Risk Management for Berkley-Riverside
EscarpmentPresentation to the Community
January 16, 2006
Michael Porter, M.Eng., P.Eng.Dr. Matthias Jakob, P.Geo.
Dr. K. Wayne Savigny, P.Eng., P.Geo.
BGC Engineering Inc.
Monday January 16, 2006, Centennial Theatre
What We Know
On January 19, 2005 a landslide killed Eliza Kuttner and seriously injured her husband
At least 5 other landslides since 1972
• all triggered by heavy rainfall
Many other locations in the GVRD are subject to landslide hazards
• not unique
Monday January 16, 2006, Centennial Theatre
Hong Kong (1972)
Po Shan Road Landslide
Monday January 16, 2006, Centennial Theatre
Hong Kong Slope Safety Program
Principles of risk management and quantitative risk assessment
Manage 58,000 registered slopes• Dr. Norbert Morgenstern (U of A) on Advisory Panel
Public education program
State-of-the-art monitoring
Hong Kong is now the world-leader in LRM
• Australia, California, Seattle, British Columbia
Thousands of lives have been saved!
Monday January 16, 2006, Centennial Theatre
Berkley Landslide Risk Management Program
Initiation Decision to use proactive risk management to guide landslide risk reduction program. DNV risk managementteam is identified.
Preliminary Review causes, triggers, behaviour and consequences ofAnalysis previous landslides.
Risk Estimation Apply a systematic and transparent methodology to rate landslide hazards on the basis of likelihood of occurrence,vulnerability of infrastructure, and consequences of failure.
Risk Evaluation Determine tolerable risk. Allocate investigation, monitoringand stabilization budet to top-rated sites exceeding tolerable risk threshold.
Risk Control Identify feasible risk control options (monitoring and inspection,improve surface water management, physical stabilization, orland sterilization).
Action/ Implement chosen risk control options. Re-rate landslide risksMonitoring to evaluate effectiveness of risk control options. Ongoing
monitoring.(In
cid
en
t R
ep
ort
s, R
atin
gs,
Sta
bili
zatio
n R
ep
ort
s, a
nd
Mo
nito
rin
g D
ata
Po
ste
d o
n W
eb
)
Ris
k C
om
mu
nic
atio
n
Monday January 16, 2006, Centennial Theatre
Work Completed to Date
Detailed investigations in the vicinity of the January 2005 landslide:
• escarpment geology
• assessment of landslide cause
• assessment of residual risk
Glacial Till
Fill / Retaining Walls
Marine Silt and Sand
Colluvium
Monday January 16, 2006, Centennial Theatre
Work Completed to Date
Along Rest of Escarpment (Current Contract):• inventory of past landslides
• evaluation of landslide-triggering storms
• rainfall and piezometer monitoring
• visual inspection and hand-auger drilling
• quantitative risk assessment
Monday January 16, 2006, Centennial Theatre
Landslide Likelihood Estimates
> 2 times Average
~ Average
< ½ Average
Subdivided crest into 75 Increments
Rank based on:• thickness of fill
• drainage conditions
• slope angle
• evidence of past movement
Monday January 16, 2006, Centennial Theatre
Landslide Runout
Consequence a function of the angle to the crest of the escarpment
Seymour River
Crest of Escarpment
Landslide Initiation Zone
Landslide Deposition Zone
19o 21o 23o 25o
Monday January 16, 2006, Centennial Theatre
Landslide Runout
Moderate to high likelihood of damage to homes
Low to moderate likelihood of damage to homes
Damage possible; mostly sedimentation and flooding
Minor flooding
>25o
>23o
>21o
>19o
Monday January 16, 2006, Centennial Theatre
Landslide Risk Estimates and Evaluation
Potential for fatality at crest and base of escarpment
To be safe, a property must pass two tests:• risk to individuals must be tolerable
• societal risks must be tolerable
Monday January 16, 2006, Centennial Theatre
Tolerable Risks
Within a range society can live with
Low, but not zero
Less than other risks in everyday life
Reduced further if practicable
Limits defined in collaboration with the affected Community
Monday January 16, 2006, Centennial Theatre
Individual Risk
Risk faced by a single individual exposed to one or more landslide hazards
Hong Kong:• Existing slopes: 10-4 per year (1:10,000)
• New development: 10-5 per year (1:100,000)
Monday January 16, 2006, Centennial Theatre
What Does 10-4 per year Mean?
10-4 per year = 0.0001 or a 1 in 10,000 chance of fatality per year of exposure
Equivalent to average Canadian’s risk from motor vehicle accidents
volvocanada.com
Monday January 16, 2006, Centennial Theatre
Individual Risk Estimates for Berkley-Riverside
Risk > 10-4 per year
• 51 properties at base
• 1 property at crest
Risk = 10-4 to 10-5 per year
• additional 56 properties
Risk < 10-5 per year
• rest of escarpment
Monday January 16, 2006, Centennial Theatre
Societal Risk
Risk imposed upon the community by a single landslide
Hong Kong:
• F-N Curves
Monday January 16, 2006, Centennial Theatre
Societal Risk
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1 10 100 1,000 10,000
Number (N) of Fatalities
Fre
qu
enc
y (F
) o
f F
ata
litie
s (p
er y
r)
UNACCEPTABLE
ALARP
BROADLY ACCEPTABLE
INTENSE SCRUTINY
REGION
Monday January 16, 2006, Centennial Theatre
Societal Risk Estimates for Berkley-Riverside
Unacceptable Risk
• 22 source areas
ALARP Zone
• 37 source areas
Broadly Acceptable
• 16 source areas
(Hong Kong Criteria)
Assigned to the 75 source areas along escarpment crest
Monday January 16, 2006, Centennial Theatre
Comments on Risk Estimates
They match the historical record• calibrated
They represent a snapshot in time• risk changes over time
They do not account for:• acquisition of 8 properties affected by the January 2005 landslide
• improvements to the storm sewer system
• increased public awareness of the hazards
• rainfall and piezometer monitoring program
Monday January 16, 2006, Centennial Theatre
Monitoring Program
Monday January 16, 2006, Centennial Theatre
Work Plan for Risk Reduction
More investigation of top rated sites
Evaluate viable risk control options:• ongoing monitoring and inspection
• drainage improvements
• removal of unstable retaining walls
• removal or recompaction of unstable fills
• slope reinforcement (new retaining walls; soil nails)
Quantify benefit and cost of each option
Implement preferred option(s)
Monday January 16, 2006, Centennial Theatre
Closing Remarks
A risk management program has been initiated• consistent with Canadian standards and international best practices
Baseline risks have been estimated• to prioritise sites for mitigation
• to facilitate evaluation of risk control options
Risks are currently managed through monitoring
We have an opportunity to apply best practices, exhibit leadership, and minimise the potential for future tragedy
Monday January 16, 2006, Centennial Theatre
Thank You