Lost River Walks Toronto - Yesterday's Rivers Are Tomorrow's Flooded Basements

"The objective of Lost River Walks is to encourage understanding of the city as a part of nature rather than apart from it, and to appreciate and cherish our heritage. Lost River Walks aims to create an appreciation of the city’s intimate connection to its water systems by tracing the courses of forgotten streams, by learning about our natural and built heritage and by sharing this information with others."
Source http://www.lostrivers.ca/

www.lostrivers.ca

Today's Lost Rivers are tomorrow's flooded basements.

According to Lost Rivers, Walmsley Brook was named for John Walmsley, a settler in the Leaside area or Toronto. It started as small streams near Duplex Avenue and Alexandra Boulevard which joined west of Yonge Street and flowed east to Mount Pleasant Road, then past Bayview and Eglinton, before heading south east to Laird Drive, the CPR rail line and the Don River.

Downstream reaches around McRae Drive to the outlet were largely open in 1922. The reach was subsequently filled in as shown on the images below.

Walmsley Brook, tributary of the Don River was 'filled in' and piped near McRae Drive and Laird Drive and is a part of Lost River Walks, organized by Toronto Green Community.

The catchment draining to the low reach is over 400 hectares in area. That is significant as flood hazards were typically mapped when drainage areas reached 125 hectares, or approximately half a square mile. Today it is not uncommon to map river flood hazards for drainage areas as small as 50 hectares.

Given the large drainage area and the obstructions to flow along the overland flow path, it is no surprise that this are is subject to flood risks. But it does not manifest as river flooding - instead it is a combination of urban flooding overland, and basement flooding that is aggravated by extraneous inflows to the sanitary sewer system.

Over 250 flooded basements were reported after the May 12, 2000 storm in Toronto. The flooding was concentrated in the former Walmsley Brook watershed, and extended outside of it to the south west where the sanitary sewer system crossed into the watershed.

The former Walmsey Brook alignment through Leaside is shown to the left. The same alignment is shown on the right along with reported basement flooding locations in the former watershed. Residential development west of Laird Drive and commercial development east of Laird Drive has reduced the overland flow capacity needed during extreme rainfall events.

Perspective of Walmsley Brook from outlet to Don River.

Detailed analysis using Ontario topographic data, geographic information system hydrology tools, and geo-referenced Toronto flood locations for May 12, 2000, August 19, 2095, and July 8, 2013 storms shows quantitatively that the overland flow path along lost rivers affects basement flood risk. A summary of the analysis is in a previous post.

The lesson? "You can take the river out of the neighbourhood, but you can't take the neighbourhood's runoff out of the residual flow path". Lost rivers not forgotten.

Sag in the road - lost river near current Sunnybrook Plaza is along the original watercourse alignment. Eglinton Ave East, east of Bayview Ave, 1951. Source James Victor Salmon, Toronto Public Library:
http://www.torontopubliclibrary.ca/detail.jsp?Entt=RDMDC-PICTURES-R-3298&R=DC-PICTURES-R-3298 

Walmsley Brook in Leaside has been enclosed in sewers and the overland flow system has been filled in and blocked but the residual flow path remains in place. During extreme rainfall the storm sewer capacity will be exceeded and overland (urban) flooding will occur on the original brook flow path. Basement flooding is often concentrated along the flow path after impeded surface flow enters building flood drains and overwhelms the wastewater sewer system.

Bathurst Heights reach of Yellow Creek.
Map source Lost Rivers.

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Lost Rivers describes many other lost watercourse features in Toronto. We will highlight a few of them in the weeks to come, but first here is another smaller system that demonstrated flood clusters during extreme storm events, although not as extreme as Walmsley Brook in Leaside..

According to Lost Rivers, Yellow Creek originates in the Downsview area and entered the Don River just north of The Prince Edward. The Bathurst Heights reach experienced flood clusters on May 12, 2000, and also on July 8, 2013. Note that our mapping for all July 8, 2013 flood reports is incomplete and does not show all the reported flood locations as the individual site data is not available from the city. However our May 12, 2000 mapping does reflect all reported locations and this likely reflects the broader July 8, 2013 incidents as well - as most properties are built at grades and with service connection very close to their neighbours, back-ups at one property general reflect risks and incidents at adjacent ones. Sometimes property owners do not report flooding to the city and instead work through their insurance company. In the most chronically flooded locations where no back-up insurance is available, there may be no reports.

The image below shows where Yellow Creek fits into the broader lost rivers network and shows details of flooding along the Bathurst Heights reach.

Perspective of Bathurst Heights reach of Yellow Creek, southwest of Bathurst and Lawrence, looking northward. This ArcExplorer oblique image shows exaggerated topographic relief, clearly shows the ups and downs of the former creek catchment. Historical flooding has been concentrated along the flow path upstream and downstream of Dell Park where runoff is concentrated during extreme rainfall events.

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Link to More Toronto Lost Rivers

The Inconvenient Truth - Rainfall in Canada Not More Extreme with Global Warming

Unless you only look at meteorology, and forget
hydrology, and ignore hydraulics, in which case you
may prove that you are dumb too.

It's not just inconvenient its down-right annoying! Because Environment Canada data shows storms are not getting worse, we have to really think, think hard about why flood damages have been increasing in Canada. Scientists are muzzled from speaking about their research it seems.

"People are not accustomed to thinking hard, and are often content to trust a plausible judgment that comes to mind."
Daniel Kahneman, American Economic Review 93 (5) December 2003, p. 1450

Well we'll show you some hard thinking Mr. Kahneman, you and your fancy Nobel Prize! Here goes:

OK. First let's explain Alberta 2013 flooding. Easy peasey lemon squeezey: they built stuff in the river flood plain, right in the floodway, and they built more and more and then the expected design floods arrived, in line with expected statistical probabilities, and so Calgary flooded. And High River flooded too. No surprise there. Done. QED. Next?

Let's use the scientific method to explain Toronto 2013 urban flooding outside of river flood plains. Why outside the flood plain? Because that is where over 95% of the flood damages occurred in 2013, 2005 and 2000 floods.

Canadian Insurance Company Ad

Hypothesis #1 - Storms are becoming more severe or occurring more often. That would be so easy to explain all the flooding, right? And the insurance industry said it was true, just like the advertisement for flood insurance to the right.

Experiment #1 - The insurance industry statement that weather events (and thunderstorms and extreme rain) that occurred every 40 years are now happening every six years has been thoroughly discredited as an inaccurate mistake based on theoretical speculation and no data. Some insurance companies have recently updated their advertisements to remove the statement. Environment Canada has advised the CBC on reporting inaccurate insurance industry statements that claimed more storms are happening now - CBC corrected their report.

But don't take CBC's word for it - "Trust No One" as Mulder would say - do your own research. That's what CityFloodMap.Com did over the holiday break. We created a host of resources for you to explore extreme weather trends across Canada including interactive maps, summary tables, bar charts, pie charts ... whew!

This is a link to a post with all the resources. Spoiler alert. Only a few percentage of Canadian climate stations show any 'non-random' increase in recorded extreme rainfall intensity or frequency, despite the fact that temperatures have clearly increased.

You may want to believe that storms have become more severe because:

1. You have demonstrated heuristic biases in your reasoning around extreme rainfall and flooding, particularly Kahneman's defined anchoring bias, availability bias, and substitution bias.
2. You operate a commuter rail line in Toronto and inflating the severity of extreme rainfall events would divert attention from unsafe operational practices, like sending a GO Train into a high risk flood zone that flooded even worse weeks before.
3. It supports your ideological pursuit against greenhouse gas emissions if, like Milli Vanilli, you can Blame it on the Rain.

But back to Toronto flooding. We looked at the best rainfall records, screening out the less reliable short-duration monitoring periods and out-of-service climate stations. Here is what we have for rainfall trends in Ontario:

Ontario climate change trends in observed extreme storm intensity.

Southern Ontario has a lot of decreasing extreme rainfall trends, some are statistically significant, or strong, trends, including in Toronto and Windsor.  Ottawa Airport with 39 years of record had significant decreasing trends for short durations as well, but did not make the cut off.

Conclusion #1 - Are storms becoming more severe? Is that the cause of increased flooding? No. Environment Canada's official data does not support that hypothesis.

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Hypothesis #2 - Toronto flooding is not explained by meteorology, but rather hydrology and increased runoff, and hydraulics and constrained flow capacity.

Experiment #2 - Back to 'thinking hard', or as Kahneman said in his book, 'thinking slow'.

First let's recognize that between rain and flooding there are several processes, runoff and flow. Many factors affect runoff volume and rate and more affect flow (i.e., the complex hydraulic capacity of sewer infrastructure and the overland flow system (lost rivers). The only Toronto homes that flooded directed due to rain did not have a roof. Homes flood when flow rates, driven by runoff, exceed the hydraulic capacity of conveyance systems, causing them to "back-up" and cause flooding.

We have proposed several causes of flooding to the Minister of the Environment and Climate Change in a letter this summer based on these processes. These included observations about hydrology and increased runoff, and the hydraulics of wastewater collection systems including documented flood impacts in the Municipal Class Environmental Assessment study in my neighbourhood, and observations about overland flood hazard regulation, including correlation with observed basement flood density. Getting a response was slow - we just received a thank you email that did not address the questions on extreme rain trends, and instead doubled down on the emissions strategy as the means to address flooding.

Conclusion #2 - The Truth is "Out There". So is the Ontario government. It does not want to consider the inconvenient truth that extreme rainfall is not increasing in Ontario, and so it has misdirected policy solutions to flooding.  We've always said there are good reasons to be concerned about global warming. But mitigating flood risks is not one of them, despite predictions of more extreme rainfall - as Yogi Berra said "It's tough to make predictions, especially about the future."

Even if storms become worse in the future, the fact that flood damages have already increased in Canada but extreme weather has not, means there are some hard questions to answer on real causes. Some are technically hard, like simulating and calibrating hydrologic and hydraulic models to determine infrastructure constraints and upgrades. Cities are doing that. Some are politically hard, like regulating overland flow systems (lost rivers) in developed communities. Some are administratively hard, like expanding the Ministry of Natural Resources and Forestry and Conservation Authority mandates beyond valley natural hazards, and combining with Ministry of Municipal Affairs or Intrastructure ministry interests. These last two are in the hands of the Ontario government.  But unfortunately Kahneman is right, as people are not accustomed to thinking hard, increasing rainfall is a plausible judgment.

Long Term Climate Change - Short Term Extreme Rainfall Impacts - What Muzzled Scientists Can't Say

Previous posts have summarized trends in extreme rainfall for 565 climate stations across Canada. Its clear that while temperatures are up (global warming), climate change impacts are not affecting storm intensity.

Tables and maps have shown the trend direction (increasing or decreasing) and the strength of the trend (statistical significance). The complete list includes "out of service" stations and those with short periods of record, meaning their data are not as relevant to recent climate change trends. 

To focus on recent trends and more reliable long term records, the table below screens Environment Canada's stations to show only those with more than 45 years of record, and those whose last record is more recent than 2005. Only 26 stations meet this quality screening for long term, recent data sets.

Findings:

Short term extreme weather trends in western Canada show no statistically significant increase or decrease, meaning trends are minor / mild. Increases (shown as light red shading) are more prevalent than decreases (light green shading). Decreases have been observed over short durations (e.g., Calgary 5 and 10 minutes) and longer durations (e.g., Vancouver 6, 12 and 24 hour periods).

In Ontario, decreases in rainfall intensity are slightly more prevalent than increases. Statistically significant decreasing trends in rainfall extremes were observed in southern Ontario at two stations: Windsor Airport and Toronto City (aka 'Bloor Street'), shown with dark green shading. These decreases were for 7 statistics covering both short and long durations (10 minutes to 24 hours). Statistically significant increases were observed in eastern and northern Ontario for two statistics: Thunder Bay 30 minute duration, and Ottawa Airport 24 hour duration.

In the Maritimes and Newfoundland, increases are more prevalent than decreases. Statistically significant increases were observed in Moncton, New Brunswick, Shearwater Nova Scotia, and Gander, Newfoundland.

Climate Station Province / Region		Station ID	Engineering Climate Datasets Annual Maximum Rainfall Trend and Significance									Length of Record (Years)	Most Recent Year
			5 min	10 min	15 min	30 min	1 hr	2 hr	6 hr	12 hr	24 hr
British Columbia
Victoria Intl A	BC	1018621	4	4	4	4	4	4	4	4	4	46	2013
Mission West Abbey	BC	1105192	4	4	4	2	2	2	4	4	4	48	2010
Vancouver Intl A	BC	1108395	4	4	4	4	4	4	2	2	2	59	2013
Alberta
Edmonton Int'L A	AB	3012205	4	2	2	2	4	4	2	2	4	46	2011
Red Deer A	AB	3025480	4	4	4	4	4	4	4	4	4	47	2012
Calgary Int'L A	AB	3031093	2	2	4	4	4	4	4	4	4	56	2009
Saskatchewan
Estevan A	SK	4012400	4	4	4	4	4	2	4	2	4	48	2011
Kindersley A	SK	4043900	4	4	4	4	4	4	4	4	4	47	2013
Ontario
Ear Falls (Aut)	ON	6012199	4	4	4	4	2	2	4	4	4	49	2006
Geraldton A	ON	6042716	4	4	4	4	4	4	4	4	4	48	2006
Thunder Bay Cs	ON	6048268	4	4	4	5	4	4	4	4	4	47	2006
Timmins Victor Power A	ON	6078285	4	4	4	4	4	4	2	2	2	47	2006
Kingston Pumping Station	ON	6104175	4	4	2	2	2	2	2	2	2	63	2007
Ottawa Cda Rcs	ON	6105978	2	2	2	2	2	2	4	4	5	50	2007
St Thomas Wpcp	ON	6137362	4	2	2	2	4	2	4	4	4	75	2007
Windsor A	ON	6139525	2	1	2	2	2	1	1	1	2	60	2007
London Cs	ON	6144478	4	4	4	4	2	2	2	2	2	57	2007
Toronto City	ON	6158355	2	2	2	2	2	2	1	1	1	59	2007
Toronto Intl A	ON	6158731	2	4	4	4	4	4	2	2	2	60	2013
Maritimes / Newfoundland
Charlo Auto	NB	8100885	4	4	4	4	4	4	4	4	4	51	2013
Moncton Intl A	NB	8103201	4	4	4	4	4	4	4	5	5	64	2013
Sable Island	NS	8204700	4	4	4	4	4	4	4	4	2	50	2012
Shearwater Auto	NS	8205091	4	4	4	5	4	4	4	4	4	53	2009
Sydney Cs	NS	8205702	4	4	4	4	4	4	4	2	4	50	2013
Gander Airport Cs	NL	8401705	4	2	2	4	4	4	5	5	5	65	2009
Goose A	NL	8501900	4	4	4	4	4	4	4	2	2	50	2013

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Sensitivity analysis on the screening criteria do not change the overall trends. We looked at period of record greater than 38 years, instead of 45 years, and this doubled the number of stations. Highlights:

• The Ottawa International Airport station was added and had a statistically significant decrease in short term rainfall intensity (10 minutes, 15 minutes, 1 hour) - this is consistent with Ottawa CDA which had decreasing non-significant trends for 5 minute to 2 hour durations.
• In the northern Ontario, Sault St. Marie Airport was added with a statistically significant increase over a one hour duration, just like Thunder Bay.
• Statistically significant increases in rainfall over long durations (12-24 hours) were added in British Columbia (Tofino Airport, Blue River Airport).
• A statistically significant increase was added at Fredericton CDA (5 minute duration).

Environment Canada's recent article on extreme rain trends published in Atmosphere-Ocean confirms there are no overall trends in rain intensity, and there are some regional minor increases and decreases - click for abstract.

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Extreme rainfall trends in Canada (Environment Canada Engineering Climate Datasets):

Static Maps: http://www.cityfloodmap.com/2015/12/severe-storm-trends-canada-rainfall.html

Interactive Map: http://www.cityfloodmap.com/2015/12/canadian-extreme-rainfall-map-climate.html

Table Summaries: http://www.cityfloodmap.com/2015/12/canadian-extreme-rainfall-summary-by.html

Chart and Table: http://www.cityfloodmap.com/2015/12/top-weather-story-in-canada-2015-less.html

Environment Canada Denies Changes: http://www.cityfloodmap.com/2015/10/bogus-statements-on-storms-in-cbcnewsca.html

Contradicting Insurance Industry Claims: http://www.cityfloodmap.com/2015/12/trends-in-canadian-shortduration.html