Natural Hazards Management for
local government
SFU November 2010
Landslide
Wildfire
Debris Flow
Severe
Storm
Earthquake
Flood
Delta Subsidence,
Sea Level Rise
Hazards
Tsunami
2
3
January 15 to 19, 2005 Rainstorm
January 15 – 19, 2005 Rainstorm
¾280 mm of rain;
¾intensities ~ 10mm/hr
Tropical Storm Kulap
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11
13
14
15
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Consequences
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Berkley Escarpment
Berkley Avenue
Riverside Drive
Seymour River
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Contributing Factors at Crest of Escarpment
•
•
•
•
•
Steep slopes
Presence of loose fill and colluvium
Old retaining walls
Soils promoting perched water table
Poor control of surface drainage
Fill / Retaining Walls
Marine Silt and Sand
Colluvium
Glacial Till
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landslide risk management
program
A systematic process to:
1. Identify potentially
hazardous areas
2. Assess and evaluate
landslide risk
3. Prioritize mitigation,
monitoring and
inspection
4. Guide future
development
20
DNV natural hazard risk management
framework (after CAN/CSA Q850-97)
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preliminary analysis
methodology
Initial Desk-Study Screening:
- Slopes >25o and >10 m high in close proximity to homes
Relative Ranking using Partial Risk Analysis
Probability of a specific landslide impacting
the identified elements at risk
Proximity of house to crest
or base of slope
Landslide Likelihood
Low
Moderate
High
Low
Very Low
Low
Moderate
Moderate
Low
Moderate
High
High
Moderate
High
Very High
Periodic Inspection
Recommended
Detailed Risk Assessment
Recommended
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Partial Risk Analysis
Factor
Rating
High
Hazard
Probability
(PH)
Moderate
Low
Criteria
Evidence of active or historical landslides or slope
deformation; such as
• landslide scarps containing exposed soil or revegetated with deciduous trees or young
conifers;
• visible settlement in fills, retaining walls; or
• abundant ‘pistol-butt’ or downslope leaning
trees.
Adverse slope conditions, but no evidence of
historical landslides or slope deformation; such as
• slopes steeper than 35°;
• the presence of random fills or yard waste;
• the presence of non-engineered retaining walls;
• abundant seepage or surface erosion; or,
• bedrock slopes containing adverse structure
(i.e. joints, faults).
Favourable slope conditions and no evidence of
historical landslides or slope deformation; such as
• slopes angles less than 35° and less than 10 m
high;
• engineered fills or retaining walls; or
• bedrock slopes lacking adverse structure.
Partial Risk Analysis
Factor
Spatial
Probability of
Impact to
Homes Above
Crest of Slope
(PS:H)
Factor
Spatial
Probability of
Impact to
Homes Below
Crest of Slope
(PS:H)
Rating
High
Criteria
Home or attached deck <3m from crest of slope
- high likelihood of initial landslide impacting the
element(s) at risk
Moderate
Home or attached deck 3 to 6m from crest of slope
- initial landslide or subsequent erosion or
landslide retrogression could impact the
element(s) at risk
Low
Home or attached deck >6m from crest of slope
- initial landslide or subsequent erosion or
landslide retrogression unlikely to impact the
element(s) at risk
Rating
High
Criteria
Angle between home and crest of slope or source
area >23o
- high likelihood of landslide debris impacting
the element(s) at risk
Moderate
Angle between home and crest of slope or source
area between 23 and 21o
- landslide debris impacting the element(s) at risk
is possible but unlikely
Low
Angle between home and crest of slope or source
area <21o
- highly unlikely that landslide debris would
impact the element(s) at risk
landslide risk estimation
risk = hazard likelihood x consequence
risk = PSLIDE x N (fatalities per year)
consequence = expected number of fatalities
N = PS:H x PT:S x V x E
based on position
of homes and
runout behaviour
of previous slides
on the Berkley
Escarpment
12 to 16 hrs
per day
based on
consequences
of previous
slides at the
Berkley
Escarpment
4 people
per home
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general recommendations
1. Manage storm water effectively
2. Remove lawn cuttings and garden waste
along escarpments; discourage further
placement
3. Ensure qualified professionals review
future construction along escarpments
4. Conduct visual monitoring every 3-5 years
by QPs.
5. Continue to educate and update the
public on reducing landslide risk
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Capilano
Mosquito Creek
Mount Fromme
Debris Flows:
1.
2.
3.
4.
Preliminary Analysis
Risk Assessment
Mitigation: warning system
Monitoring
Berkley Escarpment:
5 Areas:
1.
2.
3.
4.
Preliminary Analysis
Risk Assessment
Mitigation
Monitoring
1.
2.
3.
Risk Assessment
Mitigation: drainage
improvement & removal
of fill/retaining walls
Monitoring
Deep Cove/
Cove Cliff
Pemberton / Westlynn:
1.
2.
3.
4.
Preliminary Analysis
Risk Assessment
Mitigation: drainage improvement
Monitoring
Riverside West
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debris flow warning system
• accessed by the public via website and
phone line October – April
• must be combined with knowledge
about risks at specific sites and
personal risk tolerance
• based on:
• statistical analysis of historical
events
• antecedent rainfall
• current rainfall intensities
• forecasted rainfall
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Warning Level
Message
No watch
Due to current and forecasted weather conditions, it is very
unlikely that debris flows will occur in the North Shore
Mountains.
Watch 1
(conditions improving)
Due to current and forecasted weather conditions, it is
unlikely that debris flows will occur in the North Shore
Mountains, and it is unlikely that the Warning level will be
reached.
Due to current and forecasted weather conditions, it is
unlikely that debris flows will occur in the North Shore
Watch 2
Mountains, but it is possible that the Warning level will be
(conditions deteriorating) reached.
Warning
Due to current and forecasted weather conditions, it is
likely that debris flows will occur in the North Shore
Mountains.
Severe Warning
Due to current and forecasted weather conditions, it is very
likely that debris flows will occur in the North Shore
Mountains.
Winter ’08 - ’09
www.geoweb.dnv.org
www.dnv.org/hazards
Implementation Considerations
•
Not 100% accurate and cannot predict the exact
location of debris flows nor their total number.
•
On average, 5 warnings per year and only one
to two debris flow-triggering storms will occur
(warning ≠ debris flows)
At any given site, the probability of it having a
debris flow may be very low, but increases by
an order of magnitude for severe warnings
versus warnings
•
•
The only way to increase personal safety is to
evacuate
risk tolerance
krisholm.com
volvocanada.com
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Risk in Decision Making
Risk is a measure of the probability and
consequence of an adverse affect to health,
property, environment, or other things of value
(CSA 1997)
Risks are usually associated with a perceived
benefit
Level of control influences behaviour
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Community natural hazards
task force - 2007
1. reviewed risk tolerance
criteria established by
others
2. developed an
understanding of the risks
faced in everyday life
3. hosted community
consultations
4. prepared and presented
recommendations for
establishing risk tolerance
criteria in the DNV
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Survey Summary - Hazards
•
Severe storms, landslide and forest fire
hazards were of greatest concern to District
residents
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Survey Summary – Tolerable Risk
14 %
7%
7%
1:600
1:3,700
10 %
1:10,000
1:20,000
1:100,000
14 %
1:200,000
48%
•
72% of survey respondents placed tolerable
risk between 10-4 and 10-5 risk of death per
year.
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Survey Summary - Responsibility
•
Majority of respondents felt DNV should:
• be responsible for managing risks from
natural hazards on public lands
• regulate and/or be responsible for risk
mitigation on private lands
• not spend more than $1million per year on
natural hazards.
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Survey Summary - Preparedness
Majority felt that
personal emergency
preparedness was
the responsibility of
the resident
To learn more - take a free workshop offered by the North
Shore Emergency Management Office www.nsemo.org
or visit www.pep.bc.ca for educational information
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Task force recommendations
April 2008
1. Risk tolerance criteria be adopted by the DNV:
ƒ 1:10,000 risk of death per year for existing developments
ƒ 1:100,000 risk of death per year for new developments
2. Staff develop a plan to implement risk tolerance criteria within a
clearly understood public policy framework and Natural Hazard
Management Plan
3. Risk tolerance criteria be reviewed from time to time to reflect
changes or advancements in engineering standards, awareness
and best practices.
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tolerable vs. acceptable
Tolerable risks can be tolerated in order to
realize some benefit, are not negligible, and
should be kept under review and reduced further
if possible (ALARP).
Acceptable risks are considered broadly
acceptable to the public and further efforts to
reduce risks are not warranted.
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ALARP
“as low as reasonably practicable”
Under the common-law system, risks should be
reduced if reasonable opportunities exist.
The cost involved in reducing the risk further
would be grossly disproportionate to the benefit
gained.
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Application of criteria
Implementation
planning:
• literature review
• staff consultation
• interview
leading experts
• further discussion
with task force
members
• legal advice
Official
Community
Plan
Subdivision
• DPAs
• Hazard
mapping
Building
Permits
• APEGBC
guidelines
• MRLs
Bylaws
• Sewer
bylaw
• Building
bylaw
• Criteria for
approval
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application of criteria (cont.)
Type of Application
1:10,000
+ ALARP
Building Permit (<= 25%
increase to gross floor
area)
X
1:100,000
FOS>1.3
(static)
FOS>1.5
(static)
X
Building Permit (> 25%
increase to gross floor
area and/or retaining
walls >1.2m)
X
X
Re-zoning
X
X
Sub-division
X
X
New Development
X
X
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good terrain hazard management
includes…
9 effective storage of all hazard-related information
9 proactive identification and analysis by
registered qualified professionals of suspect areas
9 development of risk-rather than just hazard- based
assessment and management procedures
9 incorporation of risk acceptability into risk
management process - ensuring that risk
acceptability thresholds are quantitatively
established through legislated standards.
F. Baumann, P. Eng. (Coroner’s subject-matter expert)
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Managing Wildfire Risk
in the District of North
Vancouver
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11/8/2010
CWPP Implementation plan
presentation
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Wildfire Risk Management System 11/8/2010
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Pre-treatment stand characteristics
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•
•
•
•
•
Dense unhealthy
stand.
No understory
vegetation.
Lack of biodiversity.
Forest health issues.
Tinder box in the
summer.
Challenging
Topography.
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Proposed treatment
Treatment goals
•
Thin / re space understory ladder
fuels.
•
Prune large trees.
•
Chip and remove fine surface fuels.
Stewardship goals
•
Protect riparian forests and aquatic
habitat.
•
Re distribute course woody debris.
•
Create scattered habitat piles for
ground nesting birds.
•
Deal with forest health issues.
•
Replant to restore natural
biodiversity.
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Community Workshops
•
Mail out letters /
Park signage
•
Website / media
announcements
•
Maintain open
dialogue
•
Science-based
information
packages
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Information packages
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Successful messaging
•
•
•
•
•
•
•
Mail outs / web notification / media
Maintain an open dialogue
Public respect honesty
Embrace environmental stewardship BMPs
Emphasise ecosystem restoration
opportunities
Use science-based data to support
decisions, don’t “dumb down” for the public
Get the community involved (replanting,
invasive removal, yard waste cleanup)
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Exercise Objectives
• Enhance interagency cooperation
• Test communication systems – ICP to
EOC; agency to agency; air to ground
• Plan and practice evacuation
strategies
• Media coordination
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natural hazards management
Hazard
Database &
Mapping
www.geoweb.dnv.org
Structural
Mitigation
Situation
monitoring &
warning
systems
Risk
Assessments
Public
Safety
Public
Education
Policy
Development
Emergency
Plans &
Exercises
Land Use
Planning
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What we have learned (so far)...
1.
2.
3.
4.
5.
6.
7.
Proactively investigate hazards & risks
Partner with science-based organizations
Involve the community throughout the process
Make information visual & accessible to all
Educate & inform – aware vs. alarm
Encourage shared responsibility
Political support is crucial
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dnv.org/hazards