1. Water Environment Association of Ontario
WASTEWATER COLLECTION SYSTEM
PERFORMANCE UNDER CLIMATE CHANGE –
SAFETY FACTORS AND STRESS TESTS FOR
FLOOD RISK MITIGATION
Lijing Xu. M.A.Sc., P. Eng., LEED AP
Hydraulic Engineer, City of Markham
Robert J. Muir, M.A.Sc., P.Eng.
Manager, Stormwater, City of Markham
April 17, 2018
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2. OUTLINE
• New Policy and Legislation Requirements Regarding
Infrastructure Planning Under Climate Change
• Ontario Historical Extreme Rainfall and IDF Trends
• Future Climate Effects
• Design Safety Factors and Risk Gaps
• Design Storm Affects of Risk
• Case Study - Markham Sanitary System Climate
Change Resilience Assessment
• Conclusions
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3. Ontario Drivers for Assessing Climate Change Risks
3
• Provincial Policy Statement (Ontario 2014):
– Part IV: Vision for Ontario’s Land Use Planning System
• “Efficient development patterns optimize … public investment in
infrastructure and public service facilities. … Strong, liveable and healthy
communities … economically and environmentally sound, and are resilient
to climate change”.
– 1.6 Infrastructure and Public Service Facilities
• (1.6.1) “Infrastructure, electricity generation facilities and transmission and
distribution systems, and public service facilities shall be provided in a
coordinated, efficient and cost-effective manner that considers impacts from
climate change while accommodating projected needs.”
• Infrastructure for Jobs and Prosperity Act (2015):
– Infrastructure Planning Principles
• “11. Infrastructure planning and investment should minimize the impact of
infrastructure on the environment and respect and help maintain ecological
and biological diversity, and infrastructure should be designed to be resilient
to the effects of climate change.”
Provincial Policy Statement 2014 Infr. for Jobs and Prosperity

4. Ontario Drivers for Assessing Climate Change Risks (Cont.)
4
• (Class) Environmental Assessments (2017):
• Bill 139 (3rd reading Dec 6, 2017): “An official plan shall contain
policies that identify goals, objectives and actions to mitigate greenhouse gas
emissions and to provide for adaptation to a changing climate, including through
increasing resiliency.”
Bill 139EAs and Class EAs

5. 5

6. www.cityfloodmap.com
Decreasing Daily Max Rain Despite Recent Extremes
• Despite the
extreme event
on July 8, 2013,
the long term
trend in daily
maximum
rainfall totals
observed at the
Pearson Airport
climate station
is decreasing.
6http://www.cityfloodmap.com/2016/01/toronto-climate-change-extreme-rainfall.html
© CityFloodMap.Com, 2016

7. www.cityfloodmap.com
Less Extreme Rain - Ontario Long Records
• Stations
with 45+
years of
record and
recent data.
• More rain
decreases
than rain
increases.
7http://www.cityfloodmap.com/2016/01/climate-change-ontario-short-duration.html
© CityFloodMap.Com, 2016

8. Intensity Duration Frequency Trends – Lower TO
• As annual
maximum
values trend
lower, extreme
IDF intensities
decrease as
well.
• Toronto City
“Bloor Street”
trends are lower
for all durations
and for all
return periods.
http://www.cityfloodmap.com/2016/01/toronto-climate-change-extreme-rainfall.html
www.cityfloodmap.com
Source:
Environment Canada Engineering Climate Dataset
ftp://ftp.tor.ec.gc.ca/Pub/Engineering_Climate_Dataset/IDF/
Up to 2007 per Dataset v2.3, to 2003 per Dataset v1, to 1990 per hardcopy records
© CityFloodMap.Com, 2016
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9. Southern Ontario Extreme Rain Trends Decreasing -
Studies Related to IDF Trends and IDF Review
http://www.cityfloodmap.com/2017/11/less-extreme-short-duration-rainfall-in.html
http://www.cityfloodmap.com/2017/09/less-extreme-ontario-rainfall.html
http://guelph.ca/wp-content/uploads/SMMP-Appendix_E_Combined_IDF_Report.pdf
“new rainfall depths are lower
than current by 10 to 15 %”,
EarthTech
https://drive.google.com/open?id=1Gxmg8gtkzZuv-ZqiqYpc3tQ9r-Ie1v1p 9https://drive.google.com/open?id=1AngUYFFlm-RqQlmSC0gZqxy8nV61BW8J

10. Past Extreme Rain Trends Down = Safety Factor
200
210
220
230
240
250
260
270
280
290
300
1975 1995 2015 2035 2055 2075 2095 10
Buttonville
Airport
(Markham)
Pearson
Airport
(Mississauga)
Observed
Bloor Street
(Toronto)
Local IDF values to 2016 lower than standard
& declining like other S. Ontario stations
Markham IDF is
based on old
higher Toronto IDF
Markham Design Standard
GTA IDF
values now
dropped
below std.
RainIntensitymm/hr(5minute100-year)
Today’s
Safety Factor
up to 30 %

11. Infrastructure Resiliency To Consider Climate Effects
200
210
220
230
240
250
260
270
280
290
300
1975 1995 2015 2035 2055 2075 2095 11
Buttonville
Airport
(Markham)
Pearson
Airport
(Mississauga)
Observed
Bloor Street
(Toronto)
Predicted
Markham Design Standard
Future
Climate
Safety
Factor
Future
Climate
Stress
Test
RainIntensitymm/hr(5minute100-year)

12. Design Standard Upgrades vs Climate Change Adaptation (Storm)
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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)
Operational Constraints Can
Reduce Level of Service to Less
Than 5-Yr (rare instances)
Further Climate
Adaptation
(lower incremental
return on investment)
ROI
Diminishing
Returns
???
Level of
Service

13. 13
Steeles Ave
Major Mackenzie
Hwy404
YongeSt
YorkDurhamLine
City was founded in 1790’s,
covers 212 sq. Km, 330K
residents
920 Km of municipal
sanitary sewers
 30% of sewers constructed
before 1980 with potential
downspout/foundation drain
connecting to sanitary
system
City of Markham Sanitary System Resilience Testing
Subdivisions
built pre-1980’s

14. City of Markham Sanitary System Design and Existing
System Capacity Analysis
New Sanitary System Design
 Design Population with Unit Flow Rate 365 L/Cap/day
 Harmon Peaking Factor
 0.26 L/s/ha of “infiltration allowance” (inflow?)
 85% full (q/Q) under design conditions
Existing System Capacity Evaluation
 Calibrated hydrological/hydraulic model – InfoWorks ICM
 Design Storm – 24-hour Chicago synthetic hyetograph
 Under DWF condition – less than 85% full in terms of HGL (d/D)
 Under 25 year design storm – less than 100% pipe full
 Under 100 year design storm – no basement flooding risk (HGL 2 m
below MH rim elevation)
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15. Existing System Resiliency & Risks – New Developments vs. Older Areas
Old pre-1980 subdivisions
Surcharged MHs Under
Today’s IDF 100- Year Storm
 Basement flooding risks concentrated
in older areas, i.e. built before 1980’s
 New subdivisions have high resiliency
(even for peaky Chicago storm)

16. Existing System Resiliency & Risks – New Developments vs. Older Areas
 Under the 100-year design event,
fully-separated sanitary sewers
exceed design I/I allowance by 2 -
6 times with NO back-up risk.
 Safety factors are built into new
system design criteria:
 Conservative DWF
 Partially full flow
100- Year Storm
Inflow & Infiltration Rate
< 0.57 L/s/ha
0.57 – 1.61 L/s/ha
> 1.61 L/s/ha

17. Design Hyetograph Effects Surcharge (Flood Risk)
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Markham 100yr Chicago Storm
York Region 25 yr storm
(historical storm distribution
@ 25yr volume)
Ottawa 100 yr
storm (historical
storm distribution)
Toronto May 2000
Design storm (25-
50 yr storm)

18. Design Hyetograph Effects Surcharge (Flood Risk)
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19. Design Hyetograph Affects Surcharge (Flood Risk)
• Storms were simulated in Markham’s all-pipe Infoworks model to assess
basement flooding risk (surcharged MHs)
• “Chicago” storm has highest surcharge/flood potential (conservative):
– 20 times more flood risk compared to historically-based design storms.
– 4.3 times more flood risks compared to Region operational / trunk storm.
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20. WastewaterClimate Change Affects Surcharge (Flood Risk)
Flooded Manholes under Existing 100 year Design Storm
 Risks increase in old areas with future IDF
 New subdivisions not impacted - today’s
design safety factors provide future
resiliency too
Old pre-1980 subdivisions
Surcharged MHs Under
Today’s IDF 100- Year Storm
Additional MHs Surcharged
With Future IDF (+ 30%)

21. Design Hyetographs Can Account for Many
Uncertainties, Even Future Climate “Safety Factors”
• Robust Markham
‘Chicago’ 100 Year
with Today’s IDF
more conservative
that other
historically based
‘real’ storms with
Future Climate
IDF increases.
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Risk with conservative synthetic hyetograph and today’s
climate is 50% higher than historical storm & future IDF
increase

22. Model Validation - July 16, 2017 Storm (50-100 year storm)
407
Major Mackenzie
9thLine
Post 90’sPre 80’s
Model Predicted
Surcharge
Monitored WWF
Flood Reports

23. Model Validation - July 16, 2017 Storm (50-100 year storm)
Model Predicted
Surcharge
Monitored WWF
Flood Reports

24. Model Validation - July 16, 2017 Storm (50-100 year storm)
407
Major Mackenzie
9thLine
Post 90’sPre 80’s
Model Predicted
Surcharge
Monitored WWF
Flood Reports
Post 90’s
Pre 80’s

25. July 16, 2017 Storm - Percentage of
Properties Flooded
Post-1980 Systems Have Design Safety Factor
& Low Vulnerability To Extreme Rainfall
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Pre 1980
2.4 % Flooded
1980 - 1990
0.6% Flooded
Post 1990
0.04% Flooded
• Considers north-east quadrant of the City where the
storm intensities were highest (25,527 properties). Post-
1990 servicing flooded 7 of 15,889; 1980-1900 servicing
flooded 21 of 3366; pre-1980 servicing flooded 151 of 6272.

26. Conclusions
• Long term local historical rain data trends indicated that local IDF data
remain stationary.
– The current IDF data can be used to assess existing system
performance and risk.
• Markham’s wastewater system surcharge and back-up risk is
concentrated in partially-separated pre-1980 service areas under both
existing and future climate conditions.
• Markham’s fully separated, modern subdivisions are resilient to existing
and future (30% increase) extreme rainfall conditions.
– Safety factors are built into the current design criteria.
• Markham’s synthetic Chicago hyetograph with today’s climate and IDF
data is more conservative than historically-based design storms + future
climate IDF increases
– Conservative design hyetographs can address many uncertainty
risks including future climate change effects.
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27. Thank You
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