This document summarizes a workshop presentation on the use of green infrastructure as an adaptation measure for climate change impacts on storm and urban flooding. It discusses the needs for adaptation in both new and existing developments. For existing developments, it notes challenges from historical development standards and potential risks from increased infiltration. It examines the cost effectiveness and feasibility of green infrastructure compared to traditional engineering measures. It also discusses potential risks of green infrastructure aggravating issues like increased infiltration stresses on wastewater systems or other constraints. Overall, the presentation questions the effectiveness of green infrastructure for flood risk reduction and argues it may not be suitable in areas with existing infrastructure limitations or infiltration issues.

1. Woodbine
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Workshop on adaptation to climate change impact on
Urban / rural storm flooding
February 27, 2018
Is green infrastructure an effective
adaptation measure to climate change in
old and new developments?
Robert J. Muir, M.A.Sc., P.Eng.
Manager, Stormwater, City of Markham

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Outline
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• What are new development adaptation needs (if any)?
– Riparian Flooding
– Storm System Flooding (sewer/foundation back-up & overland)
– Sanitary / Wastewater Flooding (sewer back-up)
• What are existing development adaptation needs?
– Modern vs Historical Development & Servicing Standards
• Does green infrastructure address or aggravate risk gaps (existing
infiltration stresses, other constraints (chlorides, F-6-1)) ?
• What is green infrastructure cost effectiveness & feasibility vs.
traditional engineering measures?

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Riparian
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Old (pre 1990) Development Resiliency & Risks
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• Regional Storm: Historical development / villages in floodplains (e.g., Unionville
Special Policy Area/Rouge, W. Thornhill/Don R. Tributary, Don Mills Channel)
• Today’s IDF: Some historical area risk (less than above), isolated flooding for
return period events (commercial areas property for 5 year event).
• Future IDF: Regulatory hyetographs do not follow IDF curve. Markham Class EA
Flood Remediation uses 3-Hr AES instead (separates regulation from risk mgmt)
• Conclusion: Risk reduction measures include planning (SPA policies & flood-
proofing); property acquisition/central municipal storage/ culvert replacement
synced with lifecycle replacement - Don Mills Class EA LID option had higher
lifecycle cost, less timely implementation, more business disruption, and no
lifecycle offsets (culverts replaced at end of service life). Conservation Ontario
Class EA for Remedial Flood and Erosion Control Projects lists only grey
infrastructure as alternative methods/designs to address riverine flooding.
Riparian

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New (post 1990) Development Resiliency & Risks
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• Regional Storm: No riparian flood risk post 1990
• Today’s IDF: No riparian flood risk post 1990
• Future IDF: Regulatory hyetographs do not follow IDF curve intensities,
no risk expected (regional storm typically governs).
• Conclusion: no CC adaptation required for new development post 1990
riparian systems. Upstream of Special Policy Risk areas requires regional
storm storage facilities; no credit given to LID / green infrastructure
measures for quantity control (e.g., North Markham upstream of Unionville
SPA, 2 to 10 mm LID per subwatershed study credited only for
erosion/water balance benefits, storage too small and not reliable for
controlling back-to-back real storms).
Riparian

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Wastewater
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New (post 1990) Development Resiliency & Risks
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• Markham has completed capacity assessments on:
– City-wide wastewater system (InfoWorks) with conservative Chicago
hyetograph
– Today’s IDF: No surcharge/back-up risk post 1990
– Future IDF (+30%, +100%): Virtually no surcharge & back-up risk post 1990,
only in isolated shallow sewer areas (but few property connections)
– Conclusion: no CC adaptation required for new development post 1990
wastewater systems. Existing design (i) conservative DWF rates and peaking
factors & (ii) partial-full flow design compensates for 100-yr WWF rates >
WWF ‘baseflow’ design allowances. Existing standards have safety factor for
future IDF + other O&M factors – insurance industry ratings show low risks in
new subdivisions.
Wastewater

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New (post 1990) Development Resiliency & Risks
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Wastewater
During 100-year
event, fully-separated
sanitary sewers
exceed design
baseflow allowance
by 2 - 6 times with
NO back-up risk.
= “design safety
factor”
real risks < model
Chicago storm risks
New Subdivision
100-yr I&I Peak Flow
Over 2x Design
Baseflow I&I
New
Subdivision
100-yrI&I
Peak Flow
Over 6x
Design
Baseflow I&I
Pre-1972
Pre-1972
Pre-1972

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Old (pre 1990) Development Resiliency & Risks
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• Markham has completed capacity assessments on:
– City-wide wastewater system (InfoWorks) with conservative
Chicago hyetograph
– Today’s IDF: Most surcharge/back-up risk pre 1980
– Future IDF (+30%, +100%): Higher surcharge & back-up risk
– Conclusion: existing risks in partially-separated areas vulnerable to
infiltration stresses. Cost-effective risk reduction measures include
downspout disconnection (only some areas) & MH cover pick-hole
plugs, isolated capacity upgrades (sewer replacement increasing
service life co-ord with water upgrades). LID not recommended due to
higher infiltration stresses (worse surcharge, basement back-up risk).
Wastewater

10. Partially-separated
sanitary stressed
with today’s and
future IDF (+30%).
Limited back-up/
surcharge risk in
1980-1990 service
areas (some due to
D/S constraints), no
risk beyond in post
1990 areas.
Shallow Sewer (limited freeboard for dry weather)
Existing 100-Year IDF - MH Freeboard < 2 m
Future 100-Year IDF – MH Freeboard <2 mToday’s IDF
Future IDF
Freeboard < 2 m = Back-up Risk
Risks in old
subdivisions
with existing
limitations
Pre 1980
80’s
90’s
Wastewater

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Stormwater
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New (post 1990) Development Resiliency & Risks
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• Markham has completed capacity assessments on:
– City-wide overland flow, sample subdivision dual-drainage with
PCSWMM, and dual-drainage storm systems (InfoWorks).
– Today’s IDF: No post 1990 overland risks. Inlet controls prevent
surcharge/back-up risk.
– Future IDF (+22% to 3-Hr AES): Insignificant overland depth impacts,
no post 1990 sewer risks (inlet controls).
– Conclusion: Cost-effective resiliency measures include inlet controls
and overland capacity. LID required only for water balance and erosion
control. LID cost of $360,000+ per hectare is unnecessary financial
burden where there are no flood risks & no regional IDF increases.
Stormwater

13. Unit Costs of LID and Traditional SWM
• ‘Normalized’ cost (annual cost per hectare served) needed for alternative evaluation
& system planning or budgeting.
• Past studies have not normalized costs in comparisons.
POND
LIDs
Non-normalized O&M Costs
0
2000
4000
6000
8000
10000
12000
14000
16000
Bioretention Permeable
Pavement
Infiltration
Trench /
Chamber
Enhanced Grass
Swale
Markham Wet
Pond Average
Annual Maintenance + Depreciation Cost
per Impervious Area ($ / ha / year)
Depreciation
Maintenance
POND
LIDs
Normalized O&M +
Depreciation Costs
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14. Transparency on Green Infr. (LID) Project Costs (high capital costs)
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City / Town LID Type
(Project Name)
Capital + Soft
Cost ($)
Service Area
(ha)
Cost / Hectare *
Markham Bioswale & Infiltration Trench (Green Rd) $ 783,602 1.90 $412,422 +
Markham Rain Garden (Glencrest Park) $216,000 1.6 ** $135,000
Brampton Bioswale (County Court SNAP) $130, 514 0.2 $652,570 +
Whitchurch-Stouffville Various Measures (Coultic Park & CC P. Lot) $103,026 0.11 $936,600
Ottawa Bioretention (Sunnyside / Road) $282,887 0.464 $609,670
Ottawa Bioswale (Stewart / Road) $363,452 2.010 $180,821
Ajax Rain Garden (Lake Driveway) $350,000 0.14 $2,500,000
Mississauga Bioswale & Pavers (Elm Drive) $226,000 0.633 $357,030
Mississauga Bioswale (Lakeview) $420,900 1.6 $363,063
Mississauga Bioswale/Permeable S.Walk (Alpha Mills Rd) $148,521 0.3 $495,070
Newmarket Bioswale/Biofilter/Rain Grd (Forest Glenn Rd) $440,000*** 1.16 $379,310
Area-Weighted Unit Cost > $360,000 / ha
* Range similar to TRIECA 2017 examples
** No impervious hectares
*** Assume 10% soft costs

15. Transparency on Pond O&M Costs (often overstated)
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Unit costs and soft
costs (design,
permitting and
contract. admin.)
increase with the
smaller and
decentralized SWM
works.
Lesson for LIDs? :
Many small features
are inefficient.

16. Transparency on Green vs. Grey Implementation Challenges
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US EPA survey of
municipalities shows
that compared to grey,
green infrastructure is
often more challenging
for:
- O&M costing
- Capital budgeting
- Design
- Overall costs
https://www.gao.gov/assets/690/687478.pdf

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Old (pre 1990) Development Resiliency & Risks
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• Comprehensive Class EA studies and Master Plans in Ontario have
completed storm system capacity assessments identifying:
– Today’s IDF: Core design standard limitations, uncontrolled overland
flow (century old grading / no dual drainage), limited sewer capacity.
– Future IDF: Accentuates limitations (where studied).
– Conclusion: highest risk pre 1980 areas for limited drainage
standards are also highest risk areas for wastewater infiltration. Core
risk reduction measures include storm capacity upgrades. LID not
recommended due to infiltration stresses (worse wastewater flooding,
treatment cost). Ontario Class EAs & LID Manual show most LIDs
ineffective for flood control (except large chambers).
Stormwater

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Limited role of LID for flood risk management
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• City of Barrie, Comprehensive Stormwater Management Master Plan Final
Report (Aquafor Beech, November 8, 2016)
“LID does not typically provide flood protection for major storm events”
• City of Waterloo, East Side Lands Master Drainage Plan (Aquafor Beech,
November, 2013)
“Source Controls Only/Conveyance Controls Only…ineffective for flood control..
increase in flood risk is anticipated ..construction-related difficulties are anticipated”.
• City of Ottawa, Basement Flooding – Summary of Investigations and Action
Plan (Report to Council, October 25, 2005)
35 neighbourhoods assessed, solutions included protective plumbing, internal plumbing
corrections, pump station modifications, sanitary sewer improvements and flow removal,
sewer capacity improvements, improved outlets, diversions, sewer alarms. No LID.

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Limited role of LID for flood risk management
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• Preventing Disaster Before It Strikes: Developing a Canadian Standard for New
Flood-Resilient Residential Communities, 20 Best Practices. Prepared for
Standards Council of Canada (Intact Centre on Climate Adaptation, 2017)
“…(LID) measures, such as rain gardens and bioswales, can be effective to treat
rainwater “at the source” during small, frequent rainfall events … traditional stormwater
design features.. continue to be required to accommodate large, infrequent rainfall”
• Town of Markham, West Thornhill Stormwater Flood Remediation Class EA
Study (Clarifica, November, 2010)
“the main disadvantage is that in most cases implementing source controls does not
provide a complete solution of eliminating basement flooding to the required level of
protection .. success is subject to implementation and maintenance by the homeowners.
For these reasons, they were not considered in the analysis and not carried forward..”

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Limited role of LID for flood risk management
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• City of Toronto, "What the City is doing: Basement Flooding Protection
Program“ (April 2014)
"The EA studies examine the ability of the sewer system and overland flow paths to
safely carry stormwater runoff during severe storms and recommend infrastructure
improvements to increase the capacity of the sewer system that will reduce the risk of
future flooding.
Improvements may include:
• Storm sewer tunnels
• Underground and above ground storage facilities
• Additional or larger storm or sanitary sewers
• Inlet control devices
• Additional catch basins in low lying areas
• Sealing sanitary manhole covers“ …. No LID / green infrastructure
“Bio-retention medians and swales
are recommended mainly for water
quality improvements, not basement
flooding protection nor flood risk
reduction.” P. Cheung, Toronto Water,
Feb.20, 2018

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Limited role of LID for flood risk management
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• Tommy Kokas, "EFFECT OF LAND USE AND LOW IMPACT DEVELOPMENT
MEASURES ON URBAN FLOOD HAZARD: A CASE STUDY IN THE BLACK
CREEK WATERSHED “ (2016), M.A.Sc. Thesis, University of Western Ontario
Evaluates allocating entire Toronto stormwater budget or increasesd budget (Scenario
2) to single watershed to implement LIDs – also assessed scenarios with budget
applied to small single catchments. Assessed peak flow reductions.
" a reduction of 2.5% and 6.3% for a 2-year event are not enough to validate the large
investment of LID measures for Scenarios 1 and 2, respectively. Reductions for 5-year
to 100-year events are even lower as a result of extreme amounts of rainfall and
runoff…”
NB – did not account for infiltration impacts on wastewater systems. Uses TRCA unit
costs (lower than Ontario tender costs + soft costs)

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Adverse Impact of LIDs on Existing Infrastructure
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• Water Environment Association of Ontario (July 17, 2017 memo)
Identifies concerns interference with wastewater systems (flood impacts), water distribution
systems (chlorides/corrosion), human health impacts to drinking water distribution (compliance
with Procedure F-6-1), excessive costs:
https://drive.google.com/open?id=1T3vXEJ_nBi8e30KpcawVTfFPKx7A6y_v
• City of Ottawa (February 23, 2017 letter)
"While the intent appears to be not to "make things worse or better" (specifically with respect to
current condition runoff volumes), there should be recognition of situations in older
neighbourhoods (with partially separated sewers, for example) where increased infiltration should
be avoided given the cumulative impacts over time that could raise groundwater levels leading to
increased risk of basement flooding, increased I & I to sanitary sewers, etc.”:
https://drive.google.com/open?id=12IQjlaKvbCakqx7Brw9DJ97Oi5a0OHx-

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Adverse Impact of LIDs on Existing Infrastructure
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• City of Barrie (July 10, 2017 letter)
Identifies financial impacts, capital cost increase of 200%, lifecycle cost increase of 550%,
concerns for “damage to private properties and excessive sewer infiltration”, LIDs “highly
susceptible to failure due to sand accumulation” :
https://drive.google.com/open?id=1HDd24FpFmLsFTAA7kEdC5mk8N8Oau8Ox
• City of Guelph (June 28, 2017 memo)
"Guelph downtown stone rubble masonry heritage buildings are prone to flooding with raised
groundwater elevation; any additional infiltration measures using LIDs may aggravate basement
flooding due to leaky masonry walls and severe impacts on the buildings structural stability; in
addition, impacts on aged infrastructures such as, watermain corrosion, potable water quality
interference (F-6-1) and enhanced sanitary infiltration can be anticipated.”
https://drive.google.com/open?id=1OAnqraDz9NuBD1ZCsY4dzeDXeyZzf66-

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Adverse Impact of LIDs on Existing Infrastructure
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• City of Markham (July 14, 2017 memo)
Identifies sanitary infiltration impacts, adjacent property impacts, excessive capital cost based on
completed tenders, high soft cost, high lifecycle costs, chlorides/watermain corrosion:
https://drive.google.com/open?id=1RGwiyeaqihdmjI2owDY0R-Cw9CcGbEKu
• Ministry of the Environment / Workshop on Stormwater Quality Best
Management Practices (1992)
Identifies impacts of on-site infiltration source controls called Best Management Practice:
" - basement leakage problems related to infiltration near housing
- surcharging of sanitary sewers by short circuiting of infiltrated water”

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Adverse Impact of LIDs on Existing Infrastructure
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• US Transportation Research Board / Evaluation of Best Management
Practices for Highway Runoff Control, Issue 565 (2006)
Identified inflow and infiltration (I/I) risks with infiltration BMPs in urban areas:
“In urban areas, unrestricted infiltration may exacerbate infiltration and inflow (I/I)
problems in both separate and combined systems”
https://books.google.ca/books?id=jKR-CF7PG6AC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
• City of Seattle / Street Edge Alternatives Project (city web site)
Identified bioretention groundwater impacts to adjacent properties through engineering analysis:
"Our original hope for retaining flows and allowing infiltration into the native soils throughout the
length of the block was not possible because some homes had an existing groundwater intrusion
problem. To limit the potential for stormwater to adversely impact the residences of concern, our
geotechnical engineers identified some swales that needed an impermeable liner.” :
http://www.seattle.gov/UTIL/EnvironmentConservation/Projects/GreenStormwaterInfrastructure/CompletedGSIProjects/StreetEdgeAlternatives/DrainageImprovements/index.htm

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Adverse Impact of LIDs on Existing Infrastructure
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• Ontario Society of Professional Engineers (January 27, 2018 letter on Long
Term Infrastructure Plan, EBR posting (EBR 013-1907))
MOECC LID Manual is ‘fundamentally flawed’ and that “Ontario should be encouraged
to critically apply the proposed ‘risk lens’ to infrastructure investments related to
extreme weather adaptation ..”, notes IBC reports with “no engineering input, devoid of
hydrology and hydraulics considerations”. Must consider system-wide costs.
https://drive.google.com/open?id=1_ehoK0opvzeBFLv1Vrc6QFIbS9B5qFA8
• Ontario Society of Professional Engineers (October 18, 2017 letter on Bill 139,
Building Better Communities and Conserving Watersheds Act, 2017 )
Identified green infrastructure implementation cost concern, hundreds of billions, “These
additional costs have an inverse relationship with other provincial priorities, like improving
housing supply and affordability, or the delivery of new transportation and transit
infrastructure” https://drive.google.com/open?id=1az42-2TZrcmRm2uHVcxG6mc3LBtb8vv-

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Feasibility of LIDs on Existing Infrastructure
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• City of Toronto (April 27, 2017 - 2017 WWFMP Implementation Update)
“Design and implementation issues concerning the installation of green infrastructure
in an urban municipality can impact the construction of green infrastructure projects.”
(i.e., practical constraints)
https://www.toronto.ca/legdocs/mmis/2017/pw/bgrd/backgroundfile-103216.pdf

28. Conclusions
• New (post 1990) developments that incorporate Best Practices (e.g., ICCA
BPs) exhibit safety factors that can accommodate future IDF shifts:
– no storm or riparian system adaptation requirements
– no wastewater system surcharge (double 100-yr), possibly check HGL
• Old (pre 1990) developments first have design standard adaptation needs:
– capacity upgrades required for many systems (storm and wastewater)
– Class EAs in Ontario have not identified LIDs for flood control
• LID adverse impacts to existing infrastructure and property (per OSPE,
WEAO, Ottawa, Markham, Barrie, Guelph, MOE, US Transportation
Board, etc.), and excessive capital/soft costs based on tenders and
lifecycle analysis (Barrie, Markham).
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29. The Laff – 9 PM
Songs of Love, Storms .. ….
and Cats
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