Presentations by Rob Grech and Rob Muir, City of Markham on climate change and modelling uncertainty including past rainfall intensity trends, future climate projections, application of IDF data, and ROI and cost considerations for flood risk remediation.
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MNRF CWRA Technical Workshop March 6 2018 Rob Grech and Robert Muir City of Markham
1. Woodbine
Floodplain Mapping Knowledge Transfer Workshop
Climate Change and
Modelling Uncertainty
Rob Grech and Rob Muir
City of Markham
March 6-7, 2018
Vaughan, Ontario
3. data shows mostly an old extreme
http://www.cityfloodmap.com/2017/09/toronto-island-flooding-2017-were-lake.html
74
74.2
74.4
74.6
74.8
75
75.2
75.4
75.6
75.8
1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 2015
MonthlyLevel(m)
Year
Lake Ontario Historical May - August Levels
May Average
August Average
Source:
1918-2016 http://www.tides.gc.ca/C&A/network_means-eng.html
2017 http://tides-marees.gc.ca/C&A/pdf/Bulletin1708.pdf
May 5 cm above record
August not a record
3
14. What is Critical Data to Support Decision Making?
Intensity-Duration-
Frequency curves are
to water resources
engineering what flour is
to chocolate chip
cookies … i.e., just one
ingredient, but not the
most important part.
14
19. Design Standard Upgrades vs Climate Change Adaptation
19
Old
5-Yr
Design
Design Standard
Upgrade
(high loss reduction)
Today’s 100-Yr
For New
Design
Future 100-Yr For New Design
Climate Adaptation
(lower ROI)
Culvert Enclosures Reduce Level
of Service to Less Than 5-Yr
Further Climate
Adaptation
(lower incremental
return on investment)
ROI
Diminishing
Returns
$72M
Level of
Service
21. Project Delivery
Identify
Project
Goals &
Level of
Service
Hydrology
Hydraulics
Assess
Mitigation
Methods
Determine
Costs and
ROI
21
• IDF/Rainfall Volumes
• Storm Distribution
• Model Parameters
• Design Flows
• Model Approach
• Model Selection
• Model Parameters
• Water Levels
24. Flood Prediction Modelling
• A tool to be used to better understand where flooding will
occurs and how to mitigate flood damages
• Significantly improved technologically, but based on older
technical guidance
• Only as good as the quality of the information used for its
construction
• Based on several estimated parameters and founded on
managing uncertainties
• Heavily Dependant on Judgements Made by Individuals
• An exact science
• Heavily impacted by the estimate of any one parameter
(assuming correct modelling principles are applied)
• Ever going to account for every thing that can happen during
a flood
24
IS:
IS NOT:
30. Uncertainty in Project Cost Estimation
30
Pre-Project
Identifi-
cation
Project
Identifi-
cation
Environ-
mental
Assessment
Detailed
Design
Construc-
tion
• Specific Locations
• Causes
• Mitigations
Options
• Best Mitigation
Option
• What needs to be
Built and Where
• Mapped Site
Conditions
• Construction
Market Conditions
• Detailed Site
Conditions
• What needs to
be Built and
Where
• Mapped Site
Conditions
• Construction
Market
Conditions
• Detailed Site
Conditions
LOW
CONFIDENCE
LOW TO MEDIUM
CONFIDENCE
MEDIUM TO HIGH
CONFIDENCE
+ 60% + 30%-50%
• Construction
Market Conditions
• Detailed Site
Conditions
+ 10%-20%
HIGH TO VERY HIGH
CONFIDENCE
+ 0%-10%
PROJECT STAGE:
CONFIDENCE IN
ESTIMATE:
• Detailed site
conditions
• If Flooding is even
a problem
• Specific Locations
• Causes
• Mitigations
Options
• Best Mitigation
Option
• What needs to be
Built and Where
• Mapped Site
Conditions
• Construction
Market Conditions
• Detailed Site
Conditions
NO
CONFIDENCE
+ 80% OR MORE
UNKNOWNS :
31. Calculating Flood Damages
• MNRF Flood Damages Curves
(Ontario)
• HEC FIA (Army Corps of Engineers)
• HEC FDA (Army Corps of Engineers)
• Estimation based on Property Values
• Estimation based on Historical
Damages (Insurance Companies)
• DOS Based Programs!
31
Methods
Uncertainty
• Several Items very difficult to assess
• Information sharing on past data is
unavailable
• No standardized process
• Non-Tangible Benefits
32. Project Findings
• A 5 year level of service goal is preferred for the following reasons:
– The cost of mitigation was manageable (~$70M vs. $350M initial
investment for 100 year)
– The damages were reduced significantly (approximately $3.6M/yr ->
600k/yr)
– Policy and non-infrastructure methods are to be incorporated to
increase level of service in the longer term
• Despite project uncertainties, modelling tools are effective in characterizing
a system and developing mitigation options
• Dynamic modelling significantly improves the ability to understand the
system and to assess risk, but lacks policy direction
• Flood damage assessment and ROI calculations need better guidance,
data sharing and standardization
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33. Woodbine
Conclusions
33
• Higher urbanization & intensification increase flood risk despite
decreasing extreme rain trends in Southern Ontario
• Original design levels of service are a key indicator of where flooding will
occur
• Practitioners can embrace uncertainty in several engineering parameters
through the use of conservative methods in modelling – potential climate
change impacts should be incorporated into project uncertainty
• Modelling methods and approaches need more discussion beyond
IDF/Climate change uncertainties
• Cost and benefit considerations have to be looked at more critically and
be better incorporated into decision making
– Sometimes, choosing a lower level of service makes sense
34. We have always had flooding
Engineers don’t let that stop them in
in their quests …
34