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Robert Muir Green Infrastructure for Climate Adaptation NRC Workshop on Urban Rural Storm Flooding February 27 2018 Ottawa


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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

Published in: Engineering
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Robert Muir Green Infrastructure for Climate Adaptation NRC Workshop on Urban Rural Storm Flooding February 27 2018 Ottawa

  1. 1. Woodbine 1 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
  2. 2. Woodbine Outline 2 • 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?
  3. 3. Woodbine Riparian 3
  4. 4. Woodbine Old (pre 1990) Development Resiliency & Risks 4 • 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
  5. 5. Woodbine New (post 1990) Development Resiliency & Risks 5 • 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
  6. 6. Woodbine Wastewater 6
  7. 7. Woodbine New (post 1990) Development Resiliency & Risks 7 • 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
  8. 8. Woodbine New (post 1990) Development Resiliency & Risks 8 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
  9. 9. Woodbine Old (pre 1990) Development Resiliency & Risks 9 • 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. 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
  11. 11. Woodbine Stormwater 11
  12. 12. Woodbine New (post 1990) Development Resiliency & Risks 12 • 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 $360,000+ per hectare is unnecessary financial burden where there are no flood risks & no regional IDF increases. Stormwater
  13. 13. Unit Costs of LID and Traditional SWM • ‘Normalized’ cost (annual cost per hectare served) needed for alternative evaluation & system planning or budgeting. • Past studies have not normalized costs in comparisons. POND LIDs Non-normalized O&M Costs 0 2000 4000 6000 8000 10000 12000 14000 16000 Bioretention Permeable Pavement Infiltration Trench / Chamber Enhanced Grass Swale Markham Wet Pond Average Annual Maintenance + Depreciation Cost per Impervious Area ($ / ha / year) Depreciation Maintenance POND LIDs Normalized O&M + Depreciation Costs 13
  14. 14. Transparency on Green Infr. (LID) Project Costs (high capital costs) 14 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. 15. Transparency on Pond O&M Costs (often overstated) 15 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. 16. Transparency on Green vs. Grey Implementation Challenges 16 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
  17. 17. Woodbine Old (pre 1990) Development Resiliency & Risks 17 • 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
  18. 18. Woodbine Limited role of LID for flood risk management 18 • 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 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.
  19. 19. Woodbine Limited role of LID for flood risk management 19 • 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..”
  20. 20. Woodbine Limited role of LID for flood risk management 20 • 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
  21. 21. Woodbine Limited role of LID for flood risk management 21 • 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)
  22. 22. Woodbine Adverse Impact of LIDs on Existing Infrastructure 22 • 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: • 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.”:
  23. 23. Woodbine Adverse Impact of LIDs on Existing Infrastructure 23 • 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” : • 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.”
  24. 24. Woodbine Adverse Impact of LIDs on Existing Infrastructure 24 • 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: • 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”
  25. 25. Woodbine Adverse Impact of LIDs on Existing Infrastructure 25 • 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” • 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.” :
  26. 26. Woodbine Adverse Impact of LIDs on Existing Infrastructure 26 • 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. • 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”
  27. 27. Woodbine Feasibility of LIDs on Existing Infrastructure 27 • 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)
  28. 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). 28
  29. 29. The Laff – 9 PM Songs of Love, Storms .. …. and Cats 29