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WASTEWATER COLLECTION SYSTEM PERFORMANCE UNDER CLIMATE CHANGE – SAFETY FACTORS AND STRESS TESTS FOR FLOOD RISK MITIGATION

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Water Environment Association of Ontario
Annual Conference 2018
Lijing Xu, M.A.Sc., P.Eng., LEED AP, Robert J Muir, M.A.Sc., P.Eng.
City of Markham
April 17, 2018

This is the presentation of the paper findings: https://drive.google.com/open?id=15pc52qgbwOasSP5O1YU2GgEQLfqkjwbW

Published in: Engineering
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WASTEWATER COLLECTION SYSTEM PERFORMANCE UNDER CLIMATE CHANGE – SAFETY FACTORS AND STRESS TESTS FOR FLOOD RISK MITIGATION

  1. 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 1
  2. 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 2
  3. 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. 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. 5
  6. 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. 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. 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 8
  9. 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. 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. 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. 12. Design Standard Upgrades vs Climate Change Adaptation (Storm) 12 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. 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. 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) 14
  15. 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. 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. 17. Design Hyetograph Effects Surcharge (Flood Risk) 17 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. 18. Design Hyetograph Effects Surcharge (Flood Risk) 18
  19. 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. 19
  20. 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. 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. 21 Risk with conservative synthetic hyetograph and today’s climate is 50% higher than historical storm & future IDF increase
  22. 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. 23. Model Validation - July 16, 2017 Storm (50-100 year storm) Model Predicted Surcharge Monitored WWF Flood Reports
  24. 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. 25. July 16, 2017 Storm - Percentage of Properties Flooded Post-1980 Systems Have Design Safety Factor & Low Vulnerability To Extreme Rainfall 25 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. 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. 26
  27. 27. Thank You 27

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