• Internationally, overland flood is the most common natural peril
• Flooding – both riverine and urban - caused by extreme precipitation events –rain and snow – are worsening and will continue to worsen as a result of climate change
• Densification of cities is also a major contributing factor leading to an increase in both frequency and severity of riverine and urban flooding and will continue to be a key factor in the years ahead
• Lessons can be taken from virtually all flooding events, and applied to other high risk areas, regardless of where they are located
• As such, this session will consider the 2013 Calgary, Alberta, Canada floods – Canada’s most expensive natural catastrophe loss ever – as a case study and look at a number of lessons learned from the event.
In June 2013, southern Alberta in Canada experienced extensive damage from riverine flooding. More than 250 mm of rain fell over a 36 hour period just outside the City of Calgary (population 1 million) and rapidly flowed east. These storms also brought heavy rains in many urban centres, overwhelming sewer systems. Total insured losses exceeded CAD 1.7b with economic losses at around CAD 6b, making the event the costliest natural catastrophe in Canadian history. Actions to prevent or reduce the risk of flood damage must include actions to address both riverine and urban flooding. Many of these actions will be outlined in this presentation.
Basic Civil Engineering first year Notes- Chapter 4 Building.pptx
ICLR: Lessons learned from the 2013 Calgary floods (March 26, 2015)
1. Flood: Lessons learned
from North American
losses
Alberta, Canada flood (June 2013)
Glenn McGillivray
Managing Director
Institute for Catastrophic Loss Reduction
Toronto, Ontario, Canada
26 March 2015
2. ICLR
Mission - reduce loss of life and property caused
by severe weather and earthquakes
Created in 1997 by the Canadian non-life
insurance industry to confront rising disaster
losses
Multi-disciplinary research and education
provides an essential foundation for “science to
action”
Financed by member assessments (formula
based on premiums written), and flat-fee basis
for associate members
Historically, some funding through government
programs
Fee-based for specific research projects
3. Southern Alberta flood
June 19-24, 2013
50 to 150 mm of rain in 3 days
Small pockets of higher rainfall
‘Hybrid’ event (river and urban
flooding)
Evacuation of 100,000+
4 deaths
1000+ km of road damaged
In downtown Calgary alone 4000+
businesses and 3000+ structures
affected
CAD 1.7b insured (CHF 1.35b)
Approx CAD 6b economic damage
(CHF 4.75b)
Costliest insured natural catastrophe
in Canadian history
5. Lessons learned
Riverine (fluvial) flooding
Riverine or fluvial floods occur when a river bursts
its banks, whether due to extreme rainfall, snowmelt,
ice jamming or any combination thereof.
Source: iStockphoto
6. Lesson 1
Pay attention to most recent lessons learned
Flood in Alberta in 2005
2006 Groeneveld committee report outlined many actions
to prevent a repeat
Resources for mapping and communicating flood risk
Call to stop selling government land in floodplains
Report wasn’t made public until 2012
Essentially none of the report recommendations were
implemented
7. Lesson 2
Eliminate flood damage to homes in the floodway, the
zone of highest risk of flooding
Prohibit new development in the floodway
Commit resources for structural investments in flood
defence
Consider land buy-out offers to relocate those in high risk
zones
8. Lesson 3
Strongly discourage rebuilding in floodways
Provide compensation to landowners to convert land in
floodways to recreational or other use
Owners that rebuild in the designated floodway should not
qualify for future government disaster assistance
9. Lesson 4
Revisit design flood criteria and establish a high
standard
British Columbia has a 200-year standard
Saskatchewan has a 500-year standard
Parts of Manitoba have 700-year flood protection from
defence structures
Alberta has 100-year flood criteria
10. Lesson 5
Actively communicate the danger of flood to homes in
or near the flood fringe
Recognize that flood proofing reduces the cost of
recovery from flooding but does not prevent the risk of
flood damage
11. Lesson 6
Consider requiring additional flood proofing actions for
homes located in areas at risk of flooding
Raise the lowest-floor elevation of buildings above the
flood elevation with an acceptable safety factor (i.e.
freeboard).
Very important when factoring in climate change
Prohibit basements where there is risk of flooding
Prohibit the use of basements for living space
12. Lessons learned
Urban (pluvial) flooding
Urban or pluvial flooding is not directly associated with a
body of water and is largely caused by extreme rainfall
events.
Source: City of Ottawa
13. Lesson 7
Create a provincial urban flood damage reduction
strategy
The strategy should build on any existing guidance for
stormwater and sanitary sewage management
Should complement actions to reduce riverine flood
damage
14. Lesson 8
Develop a provincial strategy to upgrade sewer
infrastructure
Replace all combined sewer systems with independent
sanitary and storm sewers
Establish a timeframe for completion and clarify funding
options for local governments
15. Lesson 9
Consider increasing standards for sizing stormwater
pipes to focus on the 10-year-storm (not the 2 or 5 year
storm)
New standards should include a margin for uncertainty
about current and future precipitation for both the minor
system (i.e. underground pipes) and the major system
(i.e. overland flow routes)
This uncertainty is due, in part, to the impact of climate
change on frequency and severity of extreme rainfall
events
16. Lesson 10
Revise building codes to reduce the risk of urban flood
damage.
Codes should mandate the use of household mitigation
measures in new construction such as backflow
prevention devices
Ban use of reverse slope driveways etc
17. Lesson 11
Senior tiers of government should work with local
governments and other stakeholders - including the
(re)insurance industry - to promote actions that reduce
the risk of urban flooding for existing homes
May include bylaws, regulations and financial/insurance
incentives for homeowners to install risk mitigation
measures
18. Lesson 12
Major stakeholders, including local and senior levels of
government and (re)insurers do not always have
access to the information required to effectively manage
and reduce the risk of urban flooding
Senior tiers of government should require local
governments to create and disclose information about the
state and location of sewer/drainage systems and
overland flow routes
Senior government should work with local governments to
prepare and make available a property-by-property
database of actions implemented by homeowners that
affect or mitigate the risk of urban flooding
19. Alberta Auditor General report
(6 March 2015)
Update flood hazard maps and mapping guidelines
Assess risk to support mitigation policies and spending
Designate flood hazard areas and complete floodway
development regulation
Assess effects of flood mitigation actions
Develop plan to regulate dams
Improve dam regulatory activities
Full report at
http://www.oag.ab.ca/webfiles/reports/OAG%20March%202015
%20Report.pdf
20. Canadian catastrophes
10 killed/100 evacuated/community
assistance required/historically
significant/community unable to recover on
its own
Based on data from the Canadian Disaster Database, Public Safety Canada
23. Additional reading
Making flood insurable for
Canadian homeowners
(www.swissre.com or
www.iclr.org)
Best practices for
reducing the risk of future
damage to homes from
riverine and urban
flooding (www.iclr.org)
Flood Forecast
(www.amazon.com)
Cities adapt to
extreme
rainfall:
Celebrating
local
leadership
(www.iclr.org)
