Workshop on adaptation to climate change impact on Urban / rural storm flooding February 27, 2018 Changes in catchment characteristics and remediation priorities due to climate change and level of service upgrades Robert J. Muir, M.A.Sc., P.Eng. Manager, Stormwater, City of Markham

1. Woodbine
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Workshop on adaptation to climate change impact on
Urban / rural storm flooding
February 27, 2018
Changes in catchment characteristics
and remediation priorities due to CC and
level of service upgrades
Robert J. Muir, M.A.Sc., P.Eng.
Manager, Stormwater, City of Markham

2. Woodbine
Outline
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• Existing Urban Flood Remediation – Pre-1980’s Area Priority
• Catchment Hydrology
– Urbanization / Intensification Surpasses CC as Risk Factor
• Infrastructure Hydraulics
– Overland Lost Rivers and Sewer Surcharge Relief
• Level of Service Upgrades (vs CC) Adaptation

3. We have always had flooding
Engineers don’t let that stop them in
in their quests …
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4. Woodbine
Flood Plain to Floor Drain – Muir’s Unifying Theory of Urban Flooding
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Older 2-year storm sewers
stress major overland flow
systems ...
which impact buildings and floor
drains …
which impact sanitary systems
already stressed by infiltration.
Lost rivers impact major system
and sanitary in the same way.
Data: 2-3 more sewer back-up
claims in overland risk zones.
60 times less reported flooding
in post-1990’s subdivisions.
0
10
20
30
40
50
60
70
80
90
100
Storm Minor
Storm Major
Sanitary
WWF Floodplain
DesignRainIntensity(mm/hr)
Pre 1960 capacity
Post 1980 capacity
Uncontrolled
Overland FlowUndersized
Storm Sewers
Urban
"Lost Rivers"

5. 404
407
Steeles Ave. East
*
*
*
Storm Flooding
Sanitary Flooding
Unknown
August 19, 2005 Flood Characterization / Causes
*
**
****
*
*
* Riverine
5
West Thornhill

6. Fully
Separated
Low I&I
100 Year Dual
Drainage
Preserved
Partially
Separated
High I&I
Enclosed /
Encroached
Uncontrolled
Inflows
Steeles Ave. East
*
**
****
*
*
Post 1980
design
standards limit
flood risks
(storm, sanitary,
& riverine)
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Sanitary
Overland
Drainage
Flood
Plains

7. July 16, 2017 Storm - Percentage of
Properties Flooded
Modern Standards Effective – Risks Are Pre-1980 (Markham)
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Pre 1980
2.4 % Flooded
1980 - 1990
0.6 % Flooded
Newest areas are even
more resilient - 60 times
less flooding after 1990 as
before 1980.
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.

8. • Flood density varies according to design
standards / age of servicing, infiltration
and inflow stresses and “CSO relief”.
Upgrade Priority is Partially-Separated Areas (Toronto)
Combined Areas = Lower Risk
Toronto Basement Flood Reports
May 2000, August 2005, July 2013
& Age of Watermain Construction
(Estimated Era of Drainage Design Standards)
© CityFloodMap.com
8http://www.cityfloodmap.com/2016/04/design-standard-adaptation-vs-climate.html

9. • High Infiltration and Inflow in partially
separated sewer areas result in higher wet
weather stress and lower level of service.
• 100-Year Average Peak Flow:
– Partially-Separated = 4.87 L/s/ha
– Fully-Separated = 0.57 L/s/ha
• Fully-separated systems exceed 100-year
level of service.
• Partially-separated systems as low as 5-
year level of service (large areas).
Upgrade Priority is Partially-Separated Areas (Ottawa)
Fully Separated Areas = Lower Risk
9https://drive.google.com/open?id=0B9bXiDM6h5ViRl83Z1A1M19XM1E

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18. 10x Increase in Urban Land Use in Rouge, 7x in Duffins, 3x
in Etobicoke, etc. …
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19. Example intensification, just the 8 addresses north of Chez Robert (my house) since the late 1970's ... 19
45 yrs of adding hard surfaces = more runoff
and more flood stress for the same rain

20. Upper Decile of 𝐑𝐮𝐧𝐨𝐟𝐟 𝐂𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭𝐬
Moira River at Foxboro (02HL001): 1921-30, 1963-72, 2006-15
Don River at Todmorden (02HC024): 1963-72
Don River at Todmorden (02HC024): 2006-15
0.0
0.2
0.4
0.6
0.8
1.0
Mar Apr May Jun Jul Aug Sep Oct Nov
RunoffCoefficient
Month
Rural condition
0.0
0.2
0.4
0.6
0.8
1.0
Early urbanization
0.0
0.2
0.4
0.6
0.8
1.0
Significant…
https://www.slideshare.net/RobertMuir3/disentangling-impacts-of-climate-land-use-change-on-quantity-quality-of-river-flows-in-southern-ontario-trevor-dickinson-ramesh-rudra-university-of-guelph 21

21. Changes in Winter Hydrology in Ontario
Winter Rainfall
Winter Surface
Runoff
Springmelt
Infiltration
Springmelt Tile
Flow
Winter
Temperature
Frost-Free Days
Snowfall
Winter Infiltration
Winter Tile Flow
Winter
Streamflow
Winter Snowmelt
End of Winter
Snowpack
Spring Runoff
Springmelt
Streamflow
and/or
and/or
Variable has increased Variable has decreased Data Available

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23. © R.Muir - CityFloodMap.Com 2018
Urban Flood Risk - Flood Plain to Floor Drain

24. © R.Muir - CityFloodMap.Com 2018
Regulated Valleys / Flood Plain (Riverine / Fluvial Flood Risk)

25. © R.Muir - CityFloodMap.Com 2018
Overland Flow Path on Table Land (Beyond Valley)

26. © R.Muir - CityFloodMap.Com 2018
Overland Flow Spread (Multiples of 100-Year)

27. © R.Muir - CityFloodMap.Com 2018
Structures at Risk Of Overland Flooding (Pluvial)

28. © R.Muir - CityFloodMap.Com 2018
Up to 3x More Basement Flood Claims in Overland Zone
(insurance company analysis for July 8, 2013 storm)

29. © R.Muir - CityFloodMap.Com 2018
94% of Reported Flooding Beyond Regulated Zone
(May 12, 2000, August 19, 2005, July 8, 2013)

30. Sewer Design for
Minor Catchment
Extreme Rain Runoff
from Major Catchment
Stratford
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31. Sewer Design for
Minor Catchment
Extreme Rain Runoff
from Major Catchment
Markham
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32. Extreme Rain Runoff
from Major Catchment
Sewer Design for
Minor Catchment
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33. Woodbine
External Major Drainage Areas Accentuate Risks During Extreme Rain
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Adjacent Catchment
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10
20
30
40
50
60
70
80
90
100
Storm Minor
Storm Major
Sanitary
WWF Floodplain
DesignRainIntensity(mm/hr)
Pre 1960 capacity
Post 1980 capacity
Local
Uncontrolled
Overland
FlowUndersized
Storm Sewers
Urban
"Lost Rivers"
0
20
40
60
80
100
Storm
Minor
Storm
Major Sanitary
WWF Floodplain
DesignRainIntensity(mm/hr)
Pre 1960 capacity
Post 1980 capacity
External
Uncontrolled
Overland
Flow

34. Given known design limitations
and significant, quantifiable
hydrology stresses affecting
urban flooding ….
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35. .. should we “Blame it on the Rain”
like Milli Vanilli did ?
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36. Design Standard Upgrades vs Climate Change Adaptation
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Old 5-Yr
Design
Standard Upgrade (highest
expected damage deferral)
requires + 400% Capacity
Today’s 100-Yr
For New
Design
Future 100-Yr For New Design
Climate Adaptation
(lower incremental
benefits and ROI)
External Drainage Area Stresses Lowers
Existing Area Level of Service < 5-Yr
More Climate
Adaptation (even
lower incremental
benefits and ROI)

37. Conclusions
• Urbanization and intensification in existing catchments increase flood risk
and explain need for mitigation even where rainfall intensities have been
stationary (e.g., southern Ontario).
• Flood damages are limited in modern (post-1980’s) subdivisions where best
practices are followed (e.g., Intact Centre on Climate Adaptation BPs).
• Partially-separated sewer systems, prone to infiltration & inflows at highest
risk (confirmed with insurance industry risk rating at postal code level).
• Overland flow / building / sewer system interactions explain ‘lost river’ flood
risks in old areas (confirmed via insurance industry claims in Toronto 2013).
• Design standard upgrades to today’s IDF (e.g., sub-5-Year to 100-Year) can
be significant investment to improve level of service (LOS) / lower risks.
• Additional investments for higher LOS require further study to confirm ROI
and incremental benefits (e.g., cost effectiveness beyond 400% upgrades).
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38. Not long ago, in many cities
not far away ….

41. Woodbine
Evolution of Design Standards
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Luke Storm-whacker
CCTV-P0
Climate Change
R2-Vac-Poo