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Robert Muir Level of Service Upgrades and Climate Change 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
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

Published in: Engineering
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Robert Muir Level of Service Upgrades and Climate Change 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 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. 2. Woodbine Outline 2 • 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. 3. We have always had flooding Engineers don’t let that stop them in in their quests … 3
  4. 4. Woodbine Flood Plain to Floor Drain – Muir’s Unifying Theory of Urban Flooding 4 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. 5. 404 407 Steeles Ave. East * * * Storm Flooding Sanitary Flooding Unknown August 19, 2005 Flood Characterization / Causes * ** **** * * * Riverine 5 West Thornhill
  6. 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) 6 Sanitary Overland Drainage Flood Plains
  7. 7. July 16, 2017 Storm - Percentage of Properties Flooded Modern Standards Effective – Risks Are Pre-1980 (Markham) 7 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. 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. 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. 18. 10x Increase in Urban Land Use in Rouge, 7x in Duffins, 3x in Etobicoke, etc. … 18
  19. 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. 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. 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. 23. © R.Muir - CityFloodMap.Com 2018 Urban Flood Risk - Flood Plain to Floor Drain
  24. 24. © R.Muir - CityFloodMap.Com 2018 Regulated Valleys / Flood Plain (Riverine / Fluvial Flood Risk)
  25. 25. © R.Muir - CityFloodMap.Com 2018 Overland Flow Path on Table Land (Beyond Valley)
  26. 26. © R.Muir - CityFloodMap.Com 2018 Overland Flow Spread (Multiples of 100-Year)
  27. 27. © R.Muir - CityFloodMap.Com 2018 Structures at Risk Of Overland Flooding (Pluvial)
  28. 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. 29. © R.Muir - CityFloodMap.Com 2018 94% of Reported Flooding Beyond Regulated Zone (May 12, 2000, August 19, 2005, July 8, 2013)
  30. 30. Sewer Design for Minor Catchment Extreme Rain Runoff from Major Catchment Stratford 31
  31. 31. Sewer Design for Minor Catchment Extreme Rain Runoff from Major Catchment Markham 32
  32. 32. Extreme Rain Runoff from Major Catchment Sewer Design for Minor Catchment 33
  33. 33. Woodbine External Major Drainage Areas Accentuate Risks During Extreme Rain 34 Adjacent Catchment 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 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. 34. Given known design limitations and significant, quantifiable hydrology stresses affecting urban flooding …. 35
  35. 35. .. should we “Blame it on the Rain” like Milli Vanilli did ? 36
  36. 36. Design Standard Upgrades vs Climate Change Adaptation 37 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. 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). 38
  38. 38. Not long ago, in many cities not far away ….
  39. 39. Woodbine Evolution of Design Standards 42 Luke Storm-whacker CCTV-P0 Climate Change R2-Vac-Poo

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