Flood plains to floor drains design standard adaptation for urban flood risk reduction
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Presented to Flood Master Class by Insurance Business Magazine this presentation examines quantitative risk assessment of riparian, overland and wastewater (sanitary) sewer system flooding. Analysis of City of Toronto and City of Markham historical flooding is shown to be highly correlated to design standard limitations related to the era of construction. Risks are shown to extend over a range of scales from floodplain (river) to flood drain (homes) based on detailed GIS spatial analysis. Flood risk mitigation measures are presented to achieve design standard adaptation in local areas with specific limitations.
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Flood plains to floor drains design standard adaptation for urban flood risk reduction
- 1. Flood Plains to Floor Drains Design Standard Adaptation for Urban Flood Risk Reduction Robert J. Muir. M.A.Sc., P.Eng. Manager, Stormwater, City of Markham Flood Risk and Insurance Master Class Toronto, Ontario June 16, 2016 1
- 2. The Truth is Out There 2 Fox Mulder Flood Muller … in the data
- 3. • Historical Flooding • Design Standard Evolution • Design Standard Adaptation for Flood Risk Reduction • Rain Frequency Facts • Correlation of Urban Flood Risks 3
- 4. Town Wide Implications August 2005 Extreme Rainfall & Flooding City of Markham West Thornhill (residential) Don Mills Channel (commercial)
- 5. Woodbine West Thornhill – August 19, 2005
- 9. Lot Grading Sanitary Major Drainage Flood Plains West Thornhill Don Mills Channel Steeles Ave. East YongeSt. ** * Storm Flooding Sanitary Flooding Unknown
- 10. Limited Lot Grading Drainage Easements & Flood Plains Overland Inflows Sanitary Wet Weather Input Enclosed Rivers Fully Separated Sanitary Major / Minor Drainage Controlled Lot Grading Adapted from www.CityFloodMap.com, with permission
- 11. Limited Lot Grading Overland Inflows Sanitary Wet Weather Input Enclosed Rivers Fully Separated Sanitary Major Drainage Controlled Lot Grading Inflow and Infiltration Reduction Activities •Extensive Monitoring •Downspout disconnection (roof to sanitary only) •Manhole Pick Hole Sealing (near road sags & high flow) •Manhole Chimney Sealing •Mainline & Lateral Lining •Storm System Upgrades Inflow and Infiltration Reduction Activities •Extensive Monitoring •Downspout disconnection (roof to sanitary only) •Manhole Pick Hole Sealing (near road sags & high flow) •Manhole Chimney Sealing •Mainline & Lateral Lining •Storm System Upgrades Design & Inflow and Infiltration Prevention Activities •Full separation design •‘Leak’ testing at assumption •Manholes/sewers beyond valley (Master Servicing) •Manholes beyond sags (commercial parking) Design & Inflow and Infiltration Prevention Activities •Full separation design •‘Leak’ testing at assumption •Manholes/sewers beyond valley (Master Servicing) •Manholes beyond sags (commercial parking) Reduced up to 50%Reduced up to 50% 100 Year I&I reduced 82 %100 Year I&I reduced 82 %
- 12. Limited Lot Grading Drainage Easements & Flood Plains Overland Inflows Sanitary Wet Weather Input Enclosed Rivers Fully Separated Sanitary Major / Minor Drainage Controlled Lot Grading Flood Risk Reduction Activities •Stormwater Funding Program (100% flood risk dedication) •Extensive Modelling & Planning •Sewer Capacity Upgrades (up to 400% above existing) •Inlet Capacity Upgrades •Channel Regrading •Building Flood Proofing •Special Policy Area •On-site Storage Flood Risk Reduction Activities •Stormwater Funding Program (100% flood risk dedication) •Extensive Modelling & Planning •Sewer Capacity Upgrades (up to 400% above existing) •Inlet Capacity Upgrades •Channel Regrading •Building Flood Proofing •Special Policy Area •On-site Storage Design & Flood Prevention Activities •Subwatershed Planning •Floodplain Mapping •Dual Drainage Design •Basements 0.5 m Above 100 Year Sewer Surcharge •Major Drainage Mapping (Infill Development) Design & Flood Prevention Activities •Subwatershed Planning •Floodplain Mapping •Dual Drainage Design •Basements 0.5 m Above 100 Year Sewer Surcharge •Major Drainage Mapping (Infill Development) Up to 100 Year Upgrades Up to 100 Year Upgrades 100 Year Major Drainage ‘Hazel’ Capacity Flood Plains 100 Year Major Drainage ‘Hazel’ Capacity Flood Plains
- 13. Lot Grading Sanitary Overland Drainage Flood Plains Controlled Fully Separated Low I&I 100 Year Dual Drainage Preserved Limited Partially Separate d High I&I Enclosed Uncontrolled Inflows Steeles Ave. East YongeSt.
- 14. Steeles Ave. East YongeSt. Overland Catchment Building Risk Score • Overland flow model shows buildings within overland flow path & sags. • Non - dual drainage design areas have more at risk buildings & flood reports. Lot Grading SanitaryOverland Drainage Flood Plains
- 15. Lot Grading Sanitary Overland Drainage Flood Plains Steeles Ave. East YongeSt. • InfoWorks all- pipe hydraulic model analyzes flows & sewer surcharge for 100 year storm. • Partially separated areas have more surcharging and flood reports. Fraction Surcharged In Sewershed
- 16. Lot Grading Overland Drainage Steeles Ave. East • Flood Emergency Response Plan ranks road & building 10 year to Regional storms depths per CA models. • Maps critical infrastructure & vulnerable populations. Flood PlainsSanitary YongeSt.
- 17. Design Standard Risk Reduction 17 Pre 80’s : 1% Flooded Pre 80’s : 1% Flooded Post 80 : 0.1% FloodedPost 80 : 0.1% Flooded
- 18. • $40 M in 2009 dollars • Capacity upgrades up to 400% required to meet 100 year level or service. • Maximum size with physical constraints Existing 900 mm dia. (2 yr)Existing 900 mm dia. (2 yr) New 1800 mm dia. (100 yr) West Thornhill Storm Sewer Capacity Upgrades
- 19. • Super-inlets increase capture overland flow in roadway sags • Sanitary manhole sealing, lateral replacement .. plus cast iron watermain replacement, new road and curbs. West Thornhill Storm Sewer Capacity Upgrades Riser infiltration seal in new road base New ‘Super-inlet’ Old double CB
- 20. Don Mills Channel • Estimated $44M in 2009 dollars for 5 Year flood storage • Ongoing Class EA to evaluate flood risk reduction alternatives • River (700 hectares of drainage) or Municipal Infrastructure (50 hectares) ? 2005 HEC-GeoRAS Estimation Mapping
- 21. Don Mills Channel • On-site stormwater management since mid 1980’s flood to over-control runoff • Ongoing flood proofing by property owners • Need collective risk management (owner, government, insurer, regulator) Raised AC, Flood Gate Raised Openings Previous Wall
- 22. Inflow & Infiltration Reduction 22 • Overland flow model ranks high inflow risk manholes for pick hole sealing
- 23. Inflow & Infiltration Reduction 23 • Mandatory downspout disconnection from sanitary (subsidy program)
- 25. Negative trend is statistically significant Negative trend is statistically significant
- 26. www.cityfloodmap.com Rain Intensity Trends – Lower in S. Ontario • Stations with 45+ years of record and recent data. • More rain decreases than rain increases. • No Peason Airport significant trends despite 2013 event. 26http://www.cityfloodmap.com/2016/01/climate-change-ontario-short-duration.html © CityFloodMap.Com, 2016
- 27. 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. 27 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 http://www.cityfloodmap.com/2016/01/toronto-climate-change-extreme-rainfall.html www.cityfloodmap.com
- 28. Rain Intensity – Lack of National Trends • Environment Canada paper in Atmosphere-Ocean “Trends in Canadian Short Duration Extreme Rainfall: Including an Intensity–Duration–‐ Frequency Perspective”, by Mark W. Shephard, Eva Mekis, Robert J. Morris, Yang Feng, Xuebin Zhang, Karen Kilcup & Rick Fleetwood (November 2014). • Demonstrates: – “The single station analysis shows a general lack of a detectable trend signal, at the 5% significance level …” – “For the shortest durations of 5–15 minutes, the general overall regional trends in the extreme amounts are more variable, with increasing and decreasing trends occurring with similar frequency…” – “This indicates that at most locations across Canada the traditional single station IDF assumption that historical extreme rainfall observations are stationary (in terms of the mean) over the period of record for an individual station is not violated.” http://www.tandfonline.com/doi/abs/10.1080/07055900.2014.969677#.Vrc6d7I4HGI 28 NotIncreasingduetoclimatechange.
- 29. Design Storm “Hyetograph” Review • 100 year storms not created equal, with same IDF. • ‘Watershed’ regulatory storms in flashy urban catchments can underestimate design flows. • Urban-scale storms can govern the ‘regulatory’ 29http://www.cityfloodmap.com/2016/01/idf-curve-update-for-climate-change.html Watershed stormsWatershed storms `Urban’ storm`Urban’ storm Up to 100% Flow Increase `Urban’ storm`Urban’ storm
- 30. Media, Agency & Government Data Gaps • Operational issues mis-characterized as a climate change-induced event. • Reported “unprecedented” conditions contradict observed data (facts). 30http://www.cityfloodmap.com/2015/12/stranded-metrolinx-go-train-avoidable.html July 8, 2013 GO Train Flood Don River
- 31. May 28-29, 2013 River Levels July 8, 2013 River Levels Media, Agency & Government Data Gaps 31http://www.cityfloodmap.com/2015/12/stranded-metrolinx-go-train-avoidable.html track level No Trains Deeper Flood Union Departures Data from TRCA’s website http://www.trcagauging.ca/ using Custom Graphs with site DON AT TODMORDEN Metrolinx: “unprecedented” ON Gov. says : supports GHG policy Data says : less than 5-year flood Data says : train frequency more critical than rain frequency Ignored known risks www.cityfloodmap.com
- 32. www.cityfloodmap.com ?? Telling the Weather Story - Gordon McBean - Empire Club presentation - YouTube Media, Agency & Government Data Gaps 32http://www.slideshare.net/RobertMuir3/storm-intensity-not-increasing-factual-review-of-engineering-datasets Confused prediction with real data
- 33. Data Affecting Drainage Standards • Rain intensities are down. Impervious percentage and runoff are up. • Markham maintains old, higher rain design intensities, had increased design runoff coefficients by 75% to reflect higher impervious cover. 33 1952 32 % 1971 45 % 1981 56 % 2002 70 % Or meteorology ?Or meteorology ? Is it hydrology ?Is it hydrology ?
- 34. Data Affecting Storm System Upgrades • Intensification in older development areas • Conservative hydrological design 1953 Additional Runoff Considered in Storm System Upgrades Additional Runoff Considered in Storm System Upgrades
- 35. Design Standard Adaptation Before CC Adaptation 35 Toronto Basement Flood Reports May 2000, August 2005, July 2013 & Age of Watermain Construction (Estimated Era of Drainage Design Standards) © CityFloodMap.com • Toronto flood density varies according to design standards / age of servicing, “CSO relief”. • Overland risks increase basement back-up risks. CSO’sCSO’s
- 36. Flood Plain to Floor Drain – Continuum of Risk © CityFloodMap.com Flood Plain Flood Plain Sanitary Floor Drain Sanitary Floor Drain
- 37. Overland Risk Drives Neighbourhood Back-Up Risk Overland Drainage Flood Plain Flood Plain Overland Drainage © CityFloodMap.com Sanitary Floor Drain Sanitary Floor Drain
- 38. Many Urban Ontario Priorities Beyond Flood Plains Flood Plains © CityFloodMap.com Overland Drainage Sanitary Floor Drain Less than 3% Toronto 2000, 2005 and 2013 Floods Reported in ‘Flood Vulnerable’ Areas Over 95% of Floods Reported Beyond Regulated Area
- 39. Conclusions • Post 1980 design standards have significantly: – reduced sanitary I&I stress, limiting floor drain back-up risks – designed major overland flow paths, limiting surface flooding risks – avoided river flood plain risks • Design standard adaptation is pursued in pre-1980 developments to increase level of service & reduce urban flood risks • Rainfall intensities have decreased in Markham and southern Ontario like national data that show ‘no detectable trend’ … beware media data gaps … predictions vs. observations • Conservative rainfall hyetographs required for urban flood risk management (different than watershed-critical events) • Runoff coefficients have been updated to reflect more compact new development and infill expansion (high runoff potential) • The Truth is Out There …. 39
Editor's Notes
- I’d like to share with you how Markham is adapting design standards – that is increasing level of service to reduce urban flood risks over range of scales from large river flood plains to down to building floor drains.
- The truth is out there on urban flood risk – and it’s in the data that guide our programs. Today think of me as Agent Flood Muller and I will share with you secrets in the F Files on Markham flooding.
- I’ll cover historical flooding in Markham, how our design standards have evolved, activities to adapt old services, look at rain intensity trends and design storms – what truth about rain is keeping me up at night, and look at the continuum of flow in urban areas and how overland and sewer back up risks are correlated – maybe different endorsements for insurance companies but they are different side of the same drop of water.
- Markham was hit hard by the August 19, 2005 storm and it caused flooding in residential and commercial areas at the south end of the City where over 100 mm of rain was recorded – orange and red areas had 100 year storm volumes.
- What happened? Roads became rivers. Catchbasins worked overtime. Cars floated away. Major roadways impassable. Contents damaged. Parking lots become lakes.
- Here is the Don mills channel along Woodbine below .. Some low parking lots too
- No pictures like this in new post 1980 areas
- Low lying buildings
- Various types of flooding were reported. This shows the hardest hit West Thornhill and the Don Mills Channel areas. Storm flooding, sanitary back-up flooding and sometimes ‘unknown’. All south Markham had high rain – why are the reports concentrated where they are? It’s the design standards. How major drainage, sanitary infrastructure and floodplain and other grading were designed and built.
- How have those standards changed over time? In the 1960’s lot grading was limited around buildings, smaller rivers were enclosed and major drainage would leave the road and affect buildings. And the sanitary system was ‘leaky’ – high wet weather flows from rooftops and foundations drains. Standards improved by the 1980’s. Fully separated sanitary sewers with no foundation drain inflow, controlled lot grading keeping water out of window wells, major minor drainage design keeping large storm runoff in the right of way, or conveyed safely through easements and ponds and to river flood plains – a lot more resilient.
- What are we doing to address those risk and stresses? For the sanitary wastewater system its Inflow and Infiltration reduction (I&I) through downspout disconnection, manhole sealing, pipe lining and storm system upgrades to keep the rivers inflows out of the buildings. In new areas, design standards prevent I&I problems through full sewer separation, leak testing after construction – we will not assume a developer’s leaky sanitary sewer. And we keep manholes away from rivers and sags now. The result is a 50% reduction in wet weather flows in old areas, and over 80% reduction in new areas on average.
- On the stormwater side. This is where the big costs are for Markham. We could not do large scale capital upgrades until we had a funding source - so it took over 5 years to develop a funding model and stormwater fee structure to fund a $288 M long term flood control program. Now Markham is the only municipality with a stormwater fee dedicated 100% to flood control. The fee funds studies and capital upgrades : bigger sewers, inlets, channels and where it is not practical, floodproofing and special planning policies in high risk areas, like Unionville. We also require onsite storage overcontrol on redevelopment and infill sites if there is an existing downstream flood risk. In new development areas its about flood prevention through design. Subwatershed scale master planning and risk mapping, and robust subdivision design standards with dual drainage design and basements set high above sewer surcharge levels. And for infill development, we map and manage the overland flow routes to make sure infill designers accommodate the broader neighbourhood scale risks (are you quantifying property risk or the critical broader scale risk?). With this we can get 100 year level of service in old and new areas and contain hurricane hazel in our floodplains.
- Let’s look at the standards where we had flooding. West Thornhill built before the 1960’s in most areas has design limitations and a high concentration of flooding. Beside it, along Leslie, post 1980’s standards and very little flooding. Why? What does the data show?
- Take the major drainage. We built an overland flow model to show us where buildings are at risk near high overland flow paths and in sags – this is beyond the valleys on ‘table land’. We have aggregated the risk by catchment and show the pre 1960’s non-dual drainage design areas have issues that help explain the reported flood clusters. This high level screening sets priorities for detailed studies and design. This inset shows the approach up close – elevation model – flow path – ponding areas – building risks.
- Take the sanitary system data. Our calibrated all-pipe hydraulic model shows us where wastewater levels surcharge the pipes putting basements at risk of back-up. The 100 year storm surcharge values have been aggregated by sewershed and show the partially separated, high I&I areas have wastewater levels rising closer to basements levels, explaining some more flood clusters. This modelling and flow monitoring help set priorities for downspout disconnection investigations. Note that Unionville and Old Markham Village have high predicted surcharging in the model but limited flooding in 2005 – why? – because the storm did not hit that part of the City as hard.
- On flood plains. We have mapped flood depth at buildings and over roads for small to large floods using the conservation authority models. Don Mills channel had many buildings in the floodplain in 2005. So floodplain mapping explains what happened in that area.
- This graph shows flooding by construction era – blue bars are flood count and the dashed line is percentage of homes flooded. Pre 1980’s have about 1% flooded, while post 80’s have an order of magnitude lower flooding. So that shows us post 1980’s design standards have reduced risk – we don’t even need 90’s quality ponds or Green Infrastructure to keep neighbourhoods safe.
- What are some specific risk reduction activities in the old areas then? In West Thornhill its sewer capacity upgrades. $40 million dollars worth in 2009 dollars to bring it to a 100 year storm level of service – up to 400% increase in sewer size at this new outlet. So residents ask me “Agent Flood Muller? You just made these big upgrades – but my insurance wet up - can you call the insurance companies and get some credit”.
- Along with the sewer upgrades we increase inlet capacity significantly, seal manholes and replace sanitary laterals to reduce I&I. As a bonus – new road and watermain while we have it all dug up (adding 30% to costs). On the right are photos of the original double catchbasin replaced by a 20 foot super inlet.
- The Don Mills channel is our next priority area and a bit different – its like a river floodplain through an area developed 40 years ago. The cost to store just a 5 year storm was estimated at 44 million. We are now have an ongoing Class Environmental Assessment to evaluate flood risk alternatives in detail. The interesting governance questions here are “Is this a river or municipal infrastructure?” Who is responsible for flooding? Well that question will soon be before the courts – ask me at the break what I think. 10 years ago when I was a consultant we analyzed it as a river with cross sections, and now we are developing a very detailed 2D model to assess remediation.
- In the Don Mills Channel area, to reduce the flows going into a constrained system, we have been requiring on-site stormwater over-control up upstream properties since a moderate flood in the mid 1980’s. And building owners have been taking on flood proofing – like this wall, raising openings, raising mechanical equipment and intakes, and this flood gate. Great demonstration site. Interesting story – we recommended many such measures to one owner 4 years ago, but they had insurance so didn’t act – they flooded again, lost insurance and are suing us – we gather a subrogated claim. Moral hazard? The big question is what is the role and scope of municipality-private owner-insurance industry-regulatory agency so best risk and economic decisions are made.
- On the sanitary I&I side. Our overland flow model ranks manhole lids for sealing based on flow risk and ponding potential. Red symbols are high risk inflow points we’ve plugged.
- And mandatory downspout disconnection if a roof is found connected to the sanitary sewer. First we confirm the connection with smoke and dye test and there is a subsidy for the property owner to disconnect
- All these improvements and no talk of rainfall? We look at rain trend data when we update our engineering standards. This shows maximum recorded rainfall each year at the Buttonville Airport rain gauge – good news – trends are down – less severe rain over durations for 5 minutes to 25 hours. Less flood risk.
- But we don’t use the Buttonville data – our standards are built on the long term Toronto Bloor Street gauge. Again, decreasing rain intensities again - some statistically significant. The result is Markham’s rain standards are 17% above todays less severe values.
- Same trends in Ontario. This table shows long term station trends – green means rain intensities down – red mean up. There are more southern Ontario significant downward trends. Even Toronto Pearson on the bottom row with the 2013 storm has no significant trends and 5 minute, and 6-12 hour trends all down.
- As observed rainfall decreases so do extreme value statistics – IDF curve intensities. This is the Toronto Bloor Street trend – look at the bottom row, the 100 year rain intensity, its down over 5% since I graduated.
- Same across the country – “general lack of detectable trend signal”. I think the Environment Canada scientists are muzzled because this message is not getting out. My Agent Flood Muller theory is we just assume rain has gone up like temperatures.
- But rain is still important in other ways. In Markham we are critical of design storms, as not all are created equal – even with the same IDF input. We found that regulatory watershed storms in urban catchments – the area we have problems in – can significantly underestimate design flow. I read JFlow runs 3 storms – great idea – some conservation authorities should do this to be conservative too.
- We spend a lot of time responding to media data gaps … sometimes the truth is not out there. Sensational events mischaracterized in the media like the 2013 GO Train flood – it was called an unprecedented event – and government infographics ring alarm bells - but the data in the F File tell a different story.
- On July 8 flood levels rose rapidly – train stuck in flood plain - Metrolinx called it unprecedented and the Ontario government says its evidence of climate change (last years policy paper that got us cap and trade). Here’s a secret from the Flood Files. 6 weeks before, under cover of night. A larger flood – deeper. Also over the tracks. But no trains and no flood. Both events less than 5 year flood. Rain frequency or train frequency? The flood inquiry for Premier Davis in the early 1980’s defined the flood risks here – they were just ignored. Is Calgary 2013 much different?
- Insurance advertising has had data issues too. Weather events that used to happen every 40 year now happen every 6. This would be true if we shifted theoretical probability curves 1 standard deviation. Many organizations promote this statement – even TD chief economists. This statement has even been referenced as real Environment Canada research and data – but the truth it is only a theoretical future shift misreported as historical data. Thanks you sponsors and Advertising Standards Canada for helping to correct this.
- So why are flood damages increasing if data say its definitely not the rain? In Markham we have measured that impervious high runoff surfaces have increased over decades from 30% in the 50’s to over 70% now – that is what a sustainable non-sprawl neighbourhood look like. We can account for that in updated design standards, higher runoff coefficients and conservative hyetographs. Agent Flood Muller asks : “What’s increasing flood risks? Hydrology or meteorology?”
- Another factor is intensification. It causes higher runoff in older developments bit by bit. This shows today’s monster homes and circular drives. When the area was built there we smaller driveways and homes with less runoff potential in the 1950’s. When we rebuild the storm sewer in this area, we are conservative and account for the intensification and the added runoff in our simulation and design models.
- To pull this all together, we need design standard adaptation before climate change adaptation. Analysis in Markham and independent research I’ve done for Toronto show flood risk varies by infrastructure design standard. Areas with overland flow limitations flood more. Areas with CSO relief flood less. But let me drill down to neighbourhood scale risk and show the continuum of flow and risk and explain why.
- Flood plain to floor drain risks. We have mapped and regulated flood plains – the red areas around permanent creeks. And we have sanitary flood drain flooding up on the table land. How is this related? By the overland flow – it does not know the regulation limit, raindrops don’t read.
- The transient overland flow connects the dots – floor drain flood clusters to river flood plain. This is quantifiable. Should you only offer overland insurance to those with back-up endorsements? Perhaps not – offer it outside the overland flow path and mandate it within the flow path.
- Based on where urban risks and damages are – mostly outside flood plain – we should all be putting efforts into mapping modelling and regulating the most important parts of the system to get the most benefit. In the GTA its not in flood plains, its more about overland flow and floor drains.
- So that is Markham’s data-driven, evidence-based approach to flood risk reduction. The truth is out there. For more F Files check out my blog cityfloodmap.com . Thank you for your attention.