Are LIDs Financially Sustainable in Ontario? Philadelphia Green Infrastructure Costs - 1100 Low Impact Development Projects Define Implementation Funding for Long Term CSO & Water Quality Improvement - Comparison with 24 Ontario Projects

Philadelphia Green Stormwater Infrastructure Projects Map - Over 1100
Low Impact Development Projects for CSO Control
See September 2019 Update at Bottom of This Post

Philadelphia has an extensive green infrastructure retrofit program with cost information - recent Ontario low impact development project costs show comparable unit cost for implementation.


The City of Philadelphia implements green infrastructure (GI), aka low impact development (LID) best practices (BMPs), to control combined sewer overflows (CSOs).  Having implemented 1100 features in a retrofit setting, Philadelphia has a clear understanding of retrofit implementation costs. The following is a summary of their green infrastructure design construction costs provided by the city program staff:

City of Philadelphia Green Infrastructure / Low Impact Development Best Management Practices - Construction, Design and Planning Budgets Per Total and Impervious Area

Construction Cost
- $175,000 per acre ($432,000 per hectare)
Philadelphia Green Infrastructure Map by SWP / LID Type 
- $270,000 per impervious acre ($667,000 per hectare)

Design Cost
- Design fees typically 20-25% of construction costs

Total Cost (Design & Construction)
Philadelphia Green Infrastructure Map - Spatial Location
of Low Impact Development Measure
- Total costs of $230,000 per acre ($568,000 per hectare)
- Total costs of $350,000 per impervious acre ($865,000 per hectare)

-  $350,000 per impervious acre ($865,000 per hectare) is the overall target/budget cost that is achieved for the program and that does not include contingencies that could be carried for individual projects within the program.
- If estimated costs exceed $400,000 per acre ($988,000 per hectare) based on design estimates and project cannot be re-scoped, it is deemed too expensive and does not go ahead.

In Ontario, green infrastructure has been promoted for stormwater management in new developments since the Ministry of Environment's 1991 Interim Guidelines. Green infrastructure measures were promoted as part of a 'source control' approach and features that promoted infiltration were called Best Management Practices (BMPs). Since then, Ontario cities have developed design targets for achieving specific water resources management goals and have implemented LID BMP measures in appropriate locations. In the City of Markham and York Region, his history was summarized in a National Water and Wastewater Benchmarking Initiative Stormwater Task Force presentation:

The presentation above summarized LID implementation costs for nine (9) recent Ontario projects including bioswales, bioretention, infiltration galleries and permeable pavement. Theses cost are receiving close attention as LID implementation targets in some regions have been increased, e.g., through the Lake Simcoe Protection Act to meet environmental protection / phosphorus reduction goals, and as generic province-wide targets are now being evaluated by the Ministry of Environment and Climate Change.

Additional Ontario LID project implementation costs have been compiled with information shared by Ontario municipalities and also the Lake Simcoe Regional Conservation Authorit. This expands/updates the project costs in slide 17 of the above presentation. These costs include construction, design, administration and in-kind staffing efforts related to implementation of LID projects in the City of Markham (2 projects), City of Brampton (1 project) Town of Whitchurch-Stouffville (1 project), City of Ottawa (2 projects), Town of Ajax (1 project), City of Mississauga (3 projects), Town of Newmarket (2 projects), City of London (7 projects), Town of East Gwillimbury (1 project), Town of Uxbridge (1 project), Town of Aurora (1 project), Town of Innisfil (1 project).

The project costs and unit costs per total catchment are are shown below:

green infrastructure construction cost Ontario low impact development implementation cost retrofit
Ontario Green Infrastructure / Low Impact Development Best Management Practice Implementation Costs (No Adjustment for Inflation to 2018 Dollars) - Normalized Unit Costs Per Catchment Area Managed
This is a link to the above compiled Ontario LID costs (let me know if you have projects to add or can suggest edits / updates): Excel - Ontario Low Impact Development BMP / Green Infrastructure Implementation Cost Summary - 24 Projects

The average cost per hectare of $575,000 for these 24 projects is very close to the City of Philadelphia budget cost of $568,000. Cost per impervious hectare treated by the LID BMP would typically be higher (i.e., catchment is less that 100% impervious). Some notes regarding the project costs:

- complete costs are not available for some projects (e.g., Markham Green Road bioswale vegetation)
- one service area has been adjusted based on different sources (e.g., East Gwillimbury area reflect municipality's project brief and not original TRIECA 2017 presentation value).
- one projects has only tender cost estimate available, not actual construction cost (e.g., Newmarket Forest Glenn Rd)
- one project from LSRCA was not included in the list as it did not proceed to construction, but nonetheless incurred design and administration costs (e.g., City of Barrie, Annadale Recreation Centre, design/administration/geotechnical/in-kind staff cost of over $78,000) - this may reflect go/no go decisions on implementation that the others also consider
- most projects are retrofits, however some are new builds (Markham Green Road, Innisfil Fire Station)
- bioswales/enhanced swales require review given the wide range in unit costs per hectare of $51,000 (Uxbridge) to nearly $1.9M (Newmarket), with obvious sensitivity to the drainage area served

Previous cost estimates cited on this blog considered unit costs of approximately $400,000 per hectare and significant concern regarding the financial viability of any widespread implementation across Ontario's 852,000 urbanized hectares. Considering the expanded project cost review and adjusting for inflation, today's Ontario green infrastructure implementation costs can be estimated to be in the order of $600,000 per hectare. This magnitude of cost is comparable to Philadelphia's budgeting cost, considering over 1100 projects. These costs support the concern related to emerging Ontario policies that have not considered implementation cost impacts or financial viability.

The Ontario Society of Professional Engineers (OSPE) has recently highlighted concerns with the implementation of green infrastructure in Ontario in comments on Ontario's Long-Term Infrastructure Plan (my bold emphasis on the recommendations)

"....OSPE recommends that the Government of Ontario:

i. Critically apply the proposed ‘risk lens’ to infrastructure investments related to extreme
weather adaptation, recognizing variations in observed and predicted trends across the

ii. Evaluate adaptation measures such as green infrastructure for stormwater management,
often cited as key mitigation measure, using the same ‘risk lens’ and consider the cost-
effectiveness of those infrastructure investments.

iii. Recognize that green infrastructure must be viewed through the same lens as
conventional infrastructure, adhering to established asset management principles and
full cost accounting—meaning it must be addressed up-front and directly, considering
system-wide costs."

OSPE has also commented on the limited role of green infrastructure for flood control and life cycle cost concerns in response to Ontario's draft Watershed Planning Guidance.


Green infrastructure LID implementation costs should be acknowledged to be potentially higher
than conventional grey infrastructure design, particularly for retrofits, and funding for additional
incremental retrofit costs should be considered in the comprehensive evaluation of alternative
management solutions beside green infrastructure and LIDs, including enhanced conventional
grey infrastructure designs with pollution prevention activities. Higher retrofit costs compared to
greenfield implementation should also be acknowledged.

Consideration for disproportionate costs should be acknowledged as a prohibitive constraint in
general and for linear development retrofits or widespread watershed implementation. A more
strategic approach to green infrastructure implementation, based on local needs and
considering local constraints (infiltration impacts and property flooding) is warranted."


The additional lifecycle cost associated with green infrastructure should be acknowledged to
support budgeting for long term operation, maintenance and depreciation.

The cost impacts of green infrastructure in existing communities should also be quantified
including costs in communities that are susceptible to infiltration stresses and sewer back-up
risks, additional treatment costs as infiltrated water is collected in foundation drains and
conveyed to treatment plants and cost of reduced service life of cast iron and ductile iron
watermains due to chloride infiltration in right-of-ways (i.e., accelerated corrosion). Such a
robust and holistic economic analysis can then support more strategic, financially sustainable
implementation policies for green infrastructure."

Let's work toward this sustainable implementation policies for all infrastructure - including green infrastructure - considering costs and strategic goals and specific performance outcomes. Low impact development implementation costs in the order of $600,000 per hectare, as shown through local and other jurisdictions, are simply not sustainable on a broad, system-wide basis.



September 2019 Update

Additional projects have been reviewed in Ontario and a couple have been added from Edmonton, Alberta.  The resulting average cost per hectare (area-weighted) is $581,000.  The following table presents a summary of cost per LID type (porous/permeable pavement, rain garden/bioletention, bioswale and infiltration/exfiltration).

The Ontario/Alberta costs now represent almost 8 hectares of catchment area, close to the EPA BMP database catchment area for projects with costs data (middle column).  Note that the Ontario/Alberta project costs may include several types of LID types in the treatment train.

Is Climate Change Making Flooding Worse? - Stormy Data Trumps Fake News on Extreme Weather Trends and Flooding

From the Toronto Star: "Once, when he [Environment Canada's Dave Phillips] offhandedly uttered the words “storm porn” in a pre-interview, a TV reporter built a whole segment around the phrase, because there is only one thing editors and the public crave more than a weather story or a sex story, and that is a sexy weather story." link


"Stormy Data" is in the news almost daily - the media is obsessed with stories about big rain events and flooding - but sometimes the media is full of "weather porn", i.e., sensational stories and video clips that skew the reality behind severe flooding events. Certainly flooding is a critically important issue across Canada that needs careful and sustained attention to make improvements. But the focus on changing weather as the cause is often incorrect, and the tendency to point to climate change as the cause is equally wrong... Fake News. Fake News! Confused Media!

This post talks about storm porn (sometimes used in insurance marketing), flood loss trends in Canada and the causes, and a history of flooding in the Toronto area that suggests flood events and road/bridge washouts were more frequent in the past before modern floodplain management and design practices. That is good news that Best Practices can reduce flood risk over time!

On Weather - More Extreme? No. Its Storm Porn

Almost 30 years ago we has a cable weather channel that was had simple weather forecasts on the 'tube' (The Weather Network History). Today The Weather Network gives us:

"Force of Nature - (Featured every 20 minutes on the 3's, a show-reel of significant weather making headlines around the world), and Force of Nature Extended segment where a news reporter gives an in-depth description of the footage shown."

and "Storm-Hunters - weekends at 7 and 10pm." and "Angry Planet".... - I call this "storm porn", or "weather porn".

And no fallen limb or large puddle escapes weather reporting. Reporters know to go to the underpasses because they flood in extreme weather ... just like they are designed to - but there is no capacity in weather reporting or mainstream media to even remotely consider these design facts. It is better for business to sensationalize the events. What is better for science and public policy however?

But storms are not bigger or more frequent, or more sever today than they used to be - Environment and Climate Change Canada's Engineering Climate Datasets (Version 2.3) show this, despite what the insurance industry has stated (unfortunately by mixing up predictions with observations, theory with facts, annual precipitation totals with short-duration rain bursts):

Intact Financial Weather Frequency Shift
Intact Financial video promotes disproved 40 year to 6
year weather shift (Telling the Weather Story).
The insurance industry does not properly consider storm/weather data that engineers rely on to assess flood risks and continues to state that "In Canada, weather events that used to occur every forty years are now happening every six years in some regions"  as in this video on their web site/blog. That statement about more frequent weather has been shown to be a 'made-up', theoretical bell-curve shift and not actually real data.

On Flood Causes - Many Factors

Flood incidents are caused by many factors. For example, high risk, historical land use planning:
  1. Gatineau 2017 flooding was due primarily to having 75% of buildings in the 1-in-20 year flood plain, a high risk zone that has a 5% chance of flooding every year.
  2. Toronto Island 2017 flooding was due primarily to not completing the buy-outs of the remaining high risk properties.
Or sometimes operational decisions (mistakes) result in flood incidents. The 2013 GO Train flood is a clear example of known floods risks and inadequate operational care - deeper flooding happened regularly at the stranded train site (even just 6 weeks before), and happened over the span of the line's operation, dating back to the early 1980's. But no operational procedures were in place to check water levels or stop trains from entering the floodplain. When the last train was stranded on July 8, 2013, the Don River Watershed did not receive record rain at all and the river flow was a less than a frequent 1-in-5 year flow rate, something with a 20% chance to occur every year. 

Or sometimes stuff was just built kinda small back in the day. That's right. Infrastructure is just like cars or anything else and used to be built to a lower standard of performance - cars did not have seatbelts or anti-lock brakes and guzzled gas in the 1950's. Similarly, sewer and drainage systems in the 1950's were prone to excess wet weather flow inflow and infiltration (I&I) stresses, inadequate overland flow planning/design, and no river flood hazard mapping or land use regulation.

Or the cumulative effect of urbanization and intensification over a century in urban areas aggravates the issues associated with the factors above. Same old rain results in more flooding.

How many times do we have to say it? "There has been No Collusion between storm frequency and flood frequency". OK, we meant "No Causation", but you get the message.

On Flood Damages / Losses

Damages need to be mitigated. I charted out a Best Practices approach for identifying and mitigating flood risks holistically from 'flood plain to floor drain', looking at riverine, storm and sanitary/wastewater systems in this blog post.

Insured and uninsured losses from catastrophic and relevant events in Canada are charted by Munich RE. These flood losses include categories of hydrologic events and meteorologic events (hurricanes) that are normalized by inflation and growth in GDP to provide an indication of trends over time. The chart below shows flood losses between 1980 and 2017 in Canada:
Canadian Flood Damage Trends Insurance Losses
Canadian Catastrophic and Relevant Event "Flood" Losses, Inflation and Growth Adjusted for Hydrological and Meteorological Events in USD - Prepared by Munich RE NatCatSERVICE.
Losses are creeping up. We do have to address flood risks.

On Flood Frequency - New Normal? Or Old Extremes?

We have a tendency to forget the past. Its not well documented or easy to find.  So this should help.

The Toronto and Region Conservation Authority has documented past flooding in its jurisdiction showing flooding back to 1804 in this undated document called "A History of Flooding in the Metropolitan Toronto and Region Watersheds":

Link to full report.

The report acknowledges that prior to 1850, records of flooding are limited and suggests that many have been lost -  those that survived are in letters and diaries, and do not give a complete picture of past flooding risks.

This is noted in the excerpt below:

Some nice take-aways:

We build better today: "Over the years, road bridges became higher and stronger in response to the changing type and volume of traffic that they were required to carry. Consequently, reports of bridges descruction became rarer over time."

We keep better records today: "... newspapers and other sources tended to record only the most severe events, particularly in areas which flooded almost every spring."

Seems we used to flood A LOT in the past: The number of flood events documented by watershed and tributary/site are listed below. Often small bridges were destroyed but are not listed below. Where major road bridge's were damage and had to be replaced, or where roads washed-out, those events are noted below as "Notable Events". Mill destruction was frequent but is not noted:

Etobicoke Creek Watershed
- Long Branch - 1930 to 1954 - 9 flood events (7 in the spring)
- Brampton - 1854 to 1974 - 22 flood events (13 in the spring)
- Highway 7 at East Branch - 1968 - 1 flood event
- Tributary near Dixie Road and Dundas Street - 1974 - 1 flood event

Total Number of Documented Flood Events = 33
Notable Road and Bridge Destruction Events: 1
- Brampton April 7, 2012 "severe damage to roads, bridges, buildings"

Mimico Creek
- "No flood records have been kept..."
- 2 floods are listed, in 1850 and 1954

Total Number of Documented Flood Events 2

Humber River
- Bloor Street Bridge - 1850 to 1954 - 7 flood events
- Lambton Mills - 10 flood events (5 in the spring)
- Eglinton Flats - 1804 to 1954 - 10 flood events (5 in the spring)
- Weston - 1842 to 1954 - 10 flood events (7 in the spring)
- Albion Road Bridge - 1850 to 1954 - 6 flood events (4 in the spring, Feb-May)
- Thistletown -1878 to 1954 - 4 flood events (2 in the spring)
- Gristmill, Holm, Cord - 1850 to 1893 - 4 flood events (2 in the spring)
- Humber Summit, Rowntree's Mill - 1850 to 1893 - 5 flood events (4 for mill and 1 for subsequent cottages)
- Sawmill J. Brown - 1850 to 1893 - 4 flood events
- Woodbridge - 1878 to 1961 - 19 flood events (13 in the spring)
- Mills on Main Branch - 1850 to 1925 - 6 flood events (5 in the spring)
- Bolton - 1850 to 1972 - 22 flood events (18 in the spring)
- Mills on the Upper Humber River - 1850 to 1909 - 4 flood events (3 in the spring)

Total Number of Documented Flood Events = 111
Notable Road and Bridge Destruction Events5
- Weston, October 15-16, 1954, "Lawrence Avenue Bridge destroyed"
- Eglinton Flats, June 3, 1947. "roads washed out, buildings flooded"
- Humber River, Bloor Street Bridge, Spring 1916 "completely washed out"
- Woodbridge, August 5, 1882 "approaches to bridge on main road washed out"
- Woodbridge, January 13, 1937 "roads flooded and some washed out"

Black Creek
- Floodplain near Mt. Dennis - 1878 to 1954 - 5 flood events (3 in the spring)
- Maple Leaf Drive Area - April 5, 1951 - 1 flood event (in spring)
- Tributary - March 12, 1959 - 1 flood event (in spring)

Total Number of Documented Flood Events7
Notable Road and Bridge Destruction Events2
- Near Mt. Dennis, September 13, 1878, "railroad bridge and bridge on Weston Road destroyed"
- Near Mt. Dennis, May 14, 1893, "bridges destroyed"

Don River
- Lower Don - 1804 to 1954 - 19 flood events (15 in the spring)
- Riverdale Flats - 1804 to 1970 - 19 flood events (15 in the spring)
- Mills Taylor Family - 1850 to 1902 - 5 flood events (4 in spring)
- Mills on Lower East Branch - 1850 to 1902 - 5 flood events (4 in spring)
- Sheppard Avenue Bridge - October 15-16, 1954 - 1 flood event
- Cummer Avenue Bridge - February 11, 1965 - 1 flood event (in spring)
- Gristmills - 1850 to 1881 - 4 flood events (3 in the spring)
- Thornhill - 1850 to 1975 - 11 flood events (9 in the spring) - 11 listed, report cites 12
- Mills and Small Dams, 1850 to 1881, 4 flood events (3 in the spring)
- Yonge Street at Highway 7, 1943 to 1975, 5 flood events (4 in the spring)
- Highway 7 Bridge, 1943 and 1950, 2 flood events (in the spring)
- Gristmill, Hosiel, 1835 to 1881, 5 flood events (4 in the spring)
- Bayview Avenue Bridge, 1850 to 1954, 4 flood events (2 in the spring)
- Hogg's Hollow, 1850 to 1954, 6 flood events (4 in the spring)
- Gristmill, Boyle, 1850 to 1881, 4 flood events (3 in the spring)
- Bathurst Street Bridge, October 15-16, 1954 - 1 flood event
- Mills on West Branch, 1850 to 1881, 4 flood events (3 in the spring)
- Highway 7 Bridge, 1943 to 1975, 4 flood events (3 in the spring)
- CNR Bridge Near Concord, 1878 to 1954, 3 flood events (1 in the spring)
- Small Dam, Lamer, 1850 to 1881, 4 flood events (3 in the spring)

Total Number of Documented Flood Events 111
Notable Road and Bridge Destruction Events13
- Lower Don, April 5, 1850, "Queen Street bridge destroyed, as well as Kingston Road bridge"
- Lower Don, September 13, 1878, "bridges destroyed at Gerrard Street, Queen Street, Kingston Road, as well as many smaller ones"
- Lower Don, February 28, 1902, "roads washed out"
- Sheppard Avenue Bridge (Sheppard Avenue and Leslie) , October 15-16, 1954, "Destroyed during Hurricane Hazel"
- Thornhill, April 5, 1850, "100 feet of Yonge Street washed out"
- Thornhill, spring 1943, "Yonge street washed out in several places"
- Bayview Avenue Bridge, April 5, 1850, "destroyed"
- Bayview Avenue Bridge, September 13, 1878, "destroyed"
- Bayview Avenue Bridge, October 15-16, 1954, "destroyed"
- Hogg's Hollow, April 5, 1850, "approaches to Yonge Street bridge washed out, bridge isolated"
- Hogg's Hollow, October 15-16, 1954, "Yonge Street bridge washed out"
- Bathurst Street Bridge, October 15-16, 1954, "Destroyed"
- CNR Bridge Near Concord, September 13, 1878, March 10-11, 1936, and  October 15-16, 1954, "The railroad was washed out"

Highland Creek
- Cottages and Highland Creek Drive, 1936 to 1977, 24 flood events (20 in the spring)
- Gristmill, Helliwell, 1869 to 1878, 2 flood events (1 in the spring)
- Highway 2 or Kingston Road Bridge, 14 flood events (12 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)
- Cottages at "The Willows", 16 flood events (14 in the spring)
- Scarborough Golf and Country Club, 1950 to 1977, 19 flood events (16 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)
- Military Trail Bridge, 1948 to 1977, 19 flood events (15 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)

Total Number of Documented Flood Events100
Notable Road and Bridge Destruction Events4
- Cottages at "The Willows", February 15, 1949, "roads washed out"
- Cottages at "The Willows", July 4, 1951, "roads washed out"
- Cottages at "The Willows", October 15-16, 1954, "roads, bridge near present Lawrence Avenue washed out"
- Military Trail Bridge,  August 27-28, 1956, "bridge destroyed"

Rouge River
- CNR Bridge, April 10, 1973, 1 flood event in spring
- Highway 2 of Kingston Road Bridge, 1878 to 1956, 5 flood events (3 in the spring)
- Caper Valley Ski Hill, February 2-3, 1978 , 1 flood event in spring
- Meadowvale Avenue Bridge, October 15-16, 1954, 1 flood event
- Mills, 1878 to 1929, 3 flood events (2 in the spring)
- CPR Bridge, October 15-16, 1954, 1 flood event
- Mills below Markham, 1878 to 1929, 3 flood events (2 in the spring)
- Markham, 1837 to 1973, 7 flood events (4 in the spring)
- Unionville, 1878 to 1973, 6 flood events (3 in the spring)
- Mills and Dams, 1878 to 1929, 3 flood events (2 in the spring)
- CNR Tracks, July 19, 1944, 1 flood event
- Mills, 1878 to 1929, 3 flood events (2 in the spring)
- Rouge Valley Inn, October 15-16, 1954, 1 flood event
- Mills on the Little Rouge, 1878 to 1929, 3 flood events (2 in the spring)
- Con.9 Markham Township, 2 flood events (2 in the spring)
- CNR Bridge, 1947 to 1954, 2 flood events
- Mills and Small Dams, 1878 to 1927, 3 flood events (1 in the spring)

Total Number of Documented Flood Events46
Notable Road and Bridge Destruction Events6
- Markham, May 16, 1937, "bridge washed-out (on present Hwy. 7)"
- Markham, October 15-16, 1954, 'town "marooned" by Hwy. 7 washouts on both east and west sides'
- Unionville, October 15-16, 1954, "Main Street washed out north of Hwy. 7"
- CNR Tracks, July 19, 1944, "The tracks were washed out"
- CNR Bridge, August 18, 1947, "Washed out"
- CNR Bridge, October 15-16, 1954, "Washed out" "passenger train partially derailed"

Duffin Creek
- Gristmill, 1878 to 1919, 3 flood events (1 in the spring)
- Pickering Village and Cottages on Riverside Drive, 27 floods (24 in the spring)
- Mills on West Branch, 1878 to 1890, 2 flood events
- Whitevale, 1878 to 1950, 5 events (3 in the spring)
- Green River, 1878 to 1954, 6 events (3 in the spring)
- Mills between Stouffville and Green River, 1878 to 1919, 3 flood events (1 in the spring)
- Stouffville, 1878 to 1972, 10 flood events, (7 in the spring)
- Mills and Small Dams, 1878 to 1919, 3 flood events (1 in the spring)
- Greenwood, 1878 to 1956, 7 flood events (4 in the spring)
- Mills on East Branch, 1878 to 1919, 3 flood events (1 in the spring)

Total Number of Documented Flood Events = 69

Grand Totals:
Total Number of Documented Flood Events = 479
Notable Road and Bridge Destruction Events31

So yes, we have always had many floods in the past and many road, bridge and rail washouts too. And urban areas have expanded considerably since 1804, meaning more places to experience high rainfall and more runoff (before we started to practice better stormwater management quantity control). While the loss of Finch Avenue during the August 19, 2005 storm was significant, we have not had any major road or bridge washouts since, only Military Trail Bridge, August 27-28, 1956 which it is noted "has not been redesigned and remains low and vulnerable to flooding". So despite high runoff stresses and more and more crossings, the loss of roads and railways has not been an issue. This suggests that today's floodplain management and hydraulic structure (i.e., bridge and culvert) practices are largely effective as well, resulting in overall resilient infrastructure.

The TRCA flood history report notes wet cellars or basements for only a couple of the nearly 400 events. That is in contrast with today when it is basement flood damages that are driving flood losses in southern Ontario, not riverine flooding.


Interesting comment on land use planning practices:
- in Hogg's Hollow, "All of the houses flooded during Hurricane Hazel remain in the floodplain, and several more have been built" ... obviously this just adds to old risk
- in The Willows, "The cottages at The Willows which survived Hurricane Hazel were removed shortly afterwards, and the valley is now parkland" ... and this is the best way to remove risk in the highest risk zones

Climate Change Impacts on Ontario Highway Infrastructure Design Shows High Resiliency - Wastewater Systems Too - Media Reports Ignore Engineering Design Practices and Intrinsic Resiliency / Design Safely Factors

There is a tendency to jump to conclusions when considering climate change impacts on drainage infrastructure. For example, if storms 80 years from now are predicted to be 30% bigger (more rain depth), do sewer pipes, culverts and bridges under our our highway's need to be 30% bigger to handle the additional runoff?

No. Effects of rain are attenuated through the system due to hydrology and hydraulics. Plus there are intrinsic design safety factors to account for uncertainty in design already.

Hydrology mitigates the impact on rainfall on runoff, so 30% more rain depth results in less than 30% higher peak runoff flowing into drainage systems. This is due to things like storage on the surface, in ditches, etc. before the rain can become runoff.

Hydraulics mitigates increases in peak flows as well due to non-linearities in how flow rates show up as flow depths in channels - there is not a 1-to-1 relationship between peak flow and depth. And sometimes hydraulics throttle how much flow can enter into systems, for example sewer grates at the surface can control how much flow gets into underground sewers.

The Ontario Ministry of Transportation completed a review of their drainage system vulnerability to climate change, showing quantitatively that the overwhelming majority of storm sewers, roadway gutters, culverts and bridges meet design standards under projected future climate conditions:

Projected rain intensity increases are 10-30%. Assuming a 20% increase, with no change in today's designs:

- 96% of storm sewers already meet design standard of flowing less than 100% full
- the average flow spread in roadway gutters increases 5-7%
- 93% of culverts meet headwater depth requirements that relate to upstream flood depths
- 96% of culverts meet exit flow velocity criteria related to erosion potential
- all bridges are assessed for regulatory (historical) storms that exceed return period events, and "These storms are generally in excess of the design storm used in determining the size of the structure
opening and erosion protection measures."

So future climate change rainfall intensities do not cause today's highway drainage systems to fail - the majority of features still meet design requirements / standards / criteria. This is in direct contrast with media reports that incorrectly assume that rainfall changes translate into infrastructure changes - in fact, recently Gord Miller stated that all culverts and sewer pipes are too small:

Specifically: “I don’t think here in Canada we understand what’s coming,” said Miller during the talk. “We have no predictability any more. One has to look from the perspective that all culverts are undersized. All sewers are undersized.”

All culverts undersized? All sewers undersized? Obviously that is incorrect based on the Ministry of Transportation's careful and comprehensive resiliency analysis.

What about wastewater systems? Are all sanitary sewers undersized too? I co-wrote a paper for the Water Environment Association of Ontario annual conference on this topic, looking at sanitary sewer system resiliency under higher potential climate change rainfall intensities. It shows that most new post-1980's subdivisions are resilient with no sewer back-up risk with potential higher future rainfall. Here is the paper with the details:

And here is the presentation:

Analysis of all sewer pipes in the City of Markham shows that very few locations are at a risk of flooding for today's or for future climate as shown in the following table from the paper:

So less than 2% of old sewers are flood prone. Just more than 1% of new sewers are flood prone. This is shown on the following map:

Blue dots show where maintenance hole surcharge to basement levels with today's climate, concentrated largely in older, partially-separated sewer service areas. With higher potential future rainfall intensities, there are more at-risk maintenance holes / locations, concentrated again in the older areas. So over 98% of sanitary sewers are not undersized with the future predicted climate.

Media reports (like the TVO article with the Gord Miller quote above generally do not rely on engineering data or comprehensive analysis to make broad statements about climate change impacts. Too bad. We deserve better or else public policy geared to climate adaptation and mitigation will be uninformed and resources to address risk will be misdirected.