The Ins and Outs of Lake Ontario

Note: This post was first published on June 1, 2019 with data available from May 30, 2019. It was updated on June 3, 2019 with the latest data available, and improved graphs. It was updated again on June 5 and July 2, 2019 to reflect new height records.

In June 2017, Lake Ontario rose to a height not seen in the last 100 years of recorded history. The pictures of how this impacted Toronto were dramatic; flooding parks, eroding shorelines, and boardwalks, beaches and the Islands underwater.

Two years later, we broke records again. Once again, it’s a shocking scene.

The height of water in a lake fluctuates naturally. The amount of rainfall flowing into it, and the rate at which it drains through an outlet (if it has one) is a major determinant. However, it can also be affected by temperature, sunlight, formation / melting of snow and ice, and wind.

But how have we hit crazy high levels within the last two years? Rain, and how much and how hard it falls, is definitely a huge factor. But you may be surprised to learn that its less about the rain that falls onto Lake Ontario’s surface and shores or how hard it fell, and more about what’s happening to the east and the west.

This is a look at where water in Lake Ontario comes from, and where it goes.

The Setup

Lake Ontario basin. From a Report for the International Joint Commission.

First, let’s set this up with some historical context on Lake Ontario’s water level (Note 1).

Prior to 2017, Lake Ontario had only gone above a height of 75.7 metres twice in the last century: 1952 and 1973. It has also only gone below 73.8 metres twice during the same period: 1934 and 1936. Otherwise, Lake Ontario has varied in height within this 1.9 metre range from year-to-year, and season-to-season.

Then in 2017, the previous record set in 1952 was broken by 5 centimetres, with the lake reaching a monthly average height of 75.81 metres above sea level. It was dramatic and visually striking, flooding the Toronto Islands and other shoreline areas on the mainland. The capital repair costs to the city were estimated to total $15.6 million.

This year, the high lake levels are repeating themselves. Most days in June 2019 broke Lake Ontario’s previous daily height record of 75.88 m set in 2017. June 2019 also saw a new record average lake height of 75.89 m, or 8 cm above the previous record set in June 2017.

Looking back makes you realize that in Lake Ontario’s history, a couple pairs of high level years occurring in close vicinity is not unprecedented. 1929 + 1930. ’43 +’ 47 + ’52. ’73 + ’74 +’76. Keep the last two sets in mind next time you’re looking at imprints on Toronto’s bridges and culverts. Same story goes for sets of years with record lows.

Graph of annual minimum, average and maximum levels in lake Ontario, 1918 to present.

What causes the changes in Lake Ontario to swing so much? Do I really need to bust out that graphic from your high school science class showing the water cycle? No? Good.

But as I alluded to, Lake Ontario’s water level isn’t affected as much by the rain that falls near the lake. Below is a chart showing the water balances for the Great Lakes.

As you can see, Lake Ontario’s levels are highly dependent on upstream inflow and downstream outflow (79% and 95% of total inflows and outflows, respectively). The remaining 21% of the total inflow is from water fed from rivers and streams, and 5% of the total water is evaporated (Note 2).

Upstream inflows come from the other Great Lakes, which are fed by rainfall and streamflow. So technically, it makes it an indirect impact. But it’s an important distinction to make. A closer look at where Lake Ontario’s water comes from and where it goes will make it clear why.

Ontario: Last Stop Before the St Lawrence

Lake Ontario is impacted by the fact that it is part of Great Lakes-St Lawrence River system. This means it is fed by water from (going upstream):

  • Lake Erie via the Niagara River;
  • Lake St Clair, via the Detroit River;
  • Lake Huron / Georgian Bay, via the St Clair River;
  • Lake Michigan, via the Straits of Mackinac; and,
  • Lake Superior, via the St Mary’s River.

Water from Lake Erie flows down the Niagara River, and its mostly unregulated, meaning it flows without anything really holding it back (i.e. a dam). Two exceptions are hydroelectric power plants on both the Canadian and American sides, as well as the Welland Canal. However, the power plants are restricted in how much water they take in; the International Join Commission (IJC) is a bi-national agency that has rules to ensure there is enough water flowing over Niagara Falls, so they look pretty and aren’t a pathetic dribble.

Courtesy Ontario Power Generation

Furthermore, they don’t have much capacity to hold what flows down the Niagara River, and they have to let it go eventually. It only manages to change the flow +/- 5%.

The Welland Canal is another pathway for water between Lakes Erie and Ontario. It isn’t a huge factor either; it’s 8.5% of what flows through the Niagara River (Note 3).

Continuing upstream, Lake Huron and Lake Michigan are technically one lake, as they are hydraulically connected through the Straits of Mackinac and generally sit at the same level. The water from them flows unregulated through the Lake St Clair and the St Clair and Detroit Rivers.

Lake Superior is the one major upstream part of the basin that is regulated. Outflow is controlled via three power plants and a 16-gate dam on the St Mary’s River. However, the outflow of Superior pales in comparison to other inputs to Lakes Michigan, Huron and Erie, and even then, any water held back would be a percentage of that outflow.

All that to say Lake Ontario is fed by the other lakes and the rainfall that feeds into them, and there’s really nothing holding it back. So when all of the lakes are up, it can mean a significant cumulative height difference for Lake Ontario.

Outflow: A Balancing Act

Lake Ontario, and all of the water fed into it, flows into the St Lawrence River, and eventually the Atlantic Ocean. But it’s not as simple as draining a tub.

While the eastern end of Lake Ontario is defined as being at Kingston (where it passes both sides of Wolfe Island), there are locks and dams along the way, which widen the St Lawrence River behind them and form ‘lakes.’ These lakes are:

  • Lake St Lawrence, between Kingston and Cornwall
  • Lake St Francis, between Cornwall and Melocheville
  • Lake St Louis, along the west end of Montreal Island.

The key outlet is at Cornwall, between Lake St Lawrence and Lake St Francis, where the Moses-Saunders Dam controls the flow of water. How much water is released is once again determined by the IJC, but unlike the Niagara River, that goal is not making pretty waterfalls. Nor is it just contingent on what is happening to the west. The IJC has to play a balancing act between the height of Lake Ontario and how high the St Lawrence is downstream.

Courtesy ceedub13

Lake Ontario is 19,000 km² and an average depth of 86 m. Lake St Francis and Lake St Louis on the other hand are…not so big. I couldn’t find the figures I was looking for, but it’s in the ballpark of 400 km² and an average depth of 10-20 m (if you got better numbers give me a shout). But the magnitude speaks for itself; the same amount of water has a disproportionate impact on water levels.

Even if Lake Ontario is really high, increasing outflow to reduce its height by a couple centimetres could send downstream communities underwater. So even if the Toronto Islands are underwater and our shorelines are being eaten away by erosion, it’s a small cost relative to the damage that could occur down in Quebec.

Courtesy of the International Joint Commission

Another complicating factor is that the Ottawa River meets the St Lawrence at Lake St Louis. It is a very large river basin which is also relatively unregulated, and it can significantly alter the height of the St Lawrence at Lake St Louis. If there are already high flows coming down the Ottawa River, this put extra restrictions on the flow out of the Moses-Saunders Dam so that flooding in Montreal and other Quebec communities downstream doesn’t occur or isn’t worsened.

Seasonal Impacts

One mitigating factor in all of this is the evaporation off of the lakes. One would think that warm temperatures mean big thunderstorms, and that is a pathway for moisture to be carried out of the lake. Well, it actually it’s quite low.

Courtesy of the Great Lakes Commission

Just as snow melt starts entering the system and the rain begins to fall, evaporation rates nosedive, and whatever goes through a lake’s outflow is the only output of the system. When you put the plug in the tub while the water’s still pouring in, it’s gonna fill up.

The manner in which snow falls and melts can also have an impact on the system. I reached out to a friend who is more academically trained in earth and atmospheric sciences to expand on these effects of seasonal change on lake levels.

“A late start to spring and extended cold weather can delay local vegetation’s break from dormancy. This has the effect of reducing evapotranspiration rates early in the season. As plants take up water, they remove some moisture from the ground which would otherwise end up in local river systems, and eventually through to the St. Lawerence River. 

An extended winter may also delay snow melt timing, resulting in a greater surge of water into the Great Lakes, as opposed to the longer, drawn-out thaw that we are typically used to.

Downstream damming and excessive rainfall are much more significant contributors to lake level issues. Still, evapotranspiration and snow melt play an important part in our water cycle, and all of these factors together may have helped pushed things over the top this year.”

Alex Harris, B.Sc.(Env.), M.Sc. – Ecology candidate

The Perfect Storm

Putting it all together, you get an idea of why 2017 and this year saw crazy high water levels in Lake Ontario.

  • Extended winter and late spring
  • Significant spring rain
  • Significant unregulated flow into Lake Ontario from Lake Erie
  • Significant unregulated flow into the St Lawrence from the Ottawa River
  • Restricted outflow from Lake Ontario

And when you put this in chart form, with the lake level put against the rates of inflow and outflow, it becomes clear how restrictions at the Moses-Saunders Dam can play a large part in raising Lake Ontario’s height.

Between April 18 and May 21, 2019, there was an average of 114.85 million m³ more water flowing into Lake Ontario than flowing out each day. Over 34 days, that makes for a total of 3.9 billion m³ of water. If you didn’t account for elevation, that would be enough to cover the city of Toronto in 6.2 metres of water (Note 4). Accounting for elevation however, that’s enough water to flood downtown Toronto, East York and south Etobicoke (up to the old Iroquois shoreline) with as much as 50 metres of water (Note 5).

The area below the “Iroquois shoreline” (Note 5).

So, a lot of water. Spread out over the entirety of Lake Ontario however, it rose 70 cm, which is enough to impact the entirety of Toronto’s 111 km of shoreline, and thousands more kilometres of shoreline across the rest of the lake (Note 6).

So what are the odds of this happening again? I can’t tell you exactly. I have delivered simplified numbers here, and don’t have a good enough understanding of inter-year and inter-seasonal effects on basin supply and drain.

But based on my knowledge of climate change phenomena, I think the chances are good. Climate change is forecasted to increased precipitation for the Great Lakes Basin, and this may have an impact, particularly if increasingly severe storms means more rainfall runs off into local watercourses instead of being absorbed by the ground and transpired by plants. Furthermore, there is increasing evidence to suggest climate change may increase the frequency and severity of polar vortexes, which could extend winters and delay spring vegetation growth.

So perhaps it’s time to talk about how we manage the inflows and outflows of the Great Lakes. Should we be taking steps to regulate flows out of Lakes Michigan, Huron and Erie? Should we begin to deregulate flows out of Lake Ontario and find another way to mitigate flooding in the St Lawrence?

That discussion would be a geographical (upstream and downstream) and impact-based (net natural, social and economic) balancing act. And that’s way beyond a single blog post or a single year of records.

Notes

1. Lake height measurements are from the National Oceanic and Atmospheric Administration’s master gauges (Superior – Marquette C.G., Michigan – 9099018 | Michigan-Huron – Harbor Beach, MI – 9075014 | Erie – Fairport, OH – 9063053 | Ontario – Oswego, NY – 9052030) and are based on the International Great Lakes Datum, 1985. Monthly/annual maximums, averages and minimums available here.

2. Neff and Nicholas (2005). Uncertainty in the Great Lakes Water Balance: U.S. Geological Survey Scientific Investigations Report 2004-5100, Table 6. Data is from 2003, and a contact at the University of Michigan indicated that it is out of date. A more up-to-date water balance model is available, but I did not have enough time to crunch the data. That said, these figures should provide a good sense of magnitude of importance.

3. Flow rates on the Niagara River and Welland Canal are obtained from Hydrometric Data provided by Environment Canada’s Water Office.

4. Not accounting for elevation, Toronto has an area of 630.2 km² (per StatsCan); taking the volume (of water in lake Ontario) and dividing it by area (of Toronto) equals height (3.9 million km³ / 630.2 km² = 6.2 m).

5. I obtained a simplified line drawing of the shore from BlogTO, eliminated the segment east of Scarborough Heights Park, and converted into a polygon (area is 152 km²). I then employed simplified math to illustrate how much water there is; assuming that this area was a triangular prism, with a height equal to point where the slope starts a significant elevation increases (~130 m above sea level, near Yonge Street and Woodlawn Ave; difference from the lowest point in Toronto of 76.5 metres of 53.5 metres from the shore). The volume of this perfect triangular prism is therefore area * height divided by 2 (152 km² * 53.5 m = 4,066 km³). To reverse-calculate how high the water would be for a different volume of water (e.g. the net flow into Lake Ontario; 3.9 million km³), you can multiply the volume by 2, and divide by the area ([3.9 million km³ * 2] / 152 km² = 51.4 m).

6. Toronto’s shoreline length is calculated based on my previous #shorelineTO work. Lake Ontario’s shoreline length is quoted as 1,020 km, however, this measurement may be subject to the coastline paradox to a greater degree than my measurements in Toronto.

Pan Am Path: An Update on our Legacy

Toronto hosted the Pan Am and Parapan Am Games in 2015. Along with hosting such a large sporting event, Toronto invested in several facilities to host the games, to be reused for community benefit afterwards.

There was also one “legacy project” to pay tribute to the games. The Pan Am Path was a proposed 84-kilometre continuous off-road multi-use trail to connect the city, from the northwest Etobicoke, through downtown, to southeast Scarborough. Much of it was along existing trails, but there were a few gaps that needed to be completed:

  1. East Highland – Orton Park Road to Morningside Park
  2. Don Valley – Forks of the Don to Eglinton Avenue
  3. Waterfront – Stadium Road Park to Sherbourne Common
  4. Humber Marshes – Riverwood Parkway to South Humber Park
  5. Weston – Crawford Jones Memorial to Cruickshank Park
Courtesy City of Toronto
Courtesy Friends of the Pan Am Path

So as a legacy to a significant event that happened in the summer of 2015, these projects should be done almost 4 years later…right?

1. East Highland

This segment would connect from the Forks of Highland Creek to an existing trail where Ellesmere Avenue crosses the East Highland Creek. The current detour is following the existing multi-use trail along West Highland Creek south, and Orton Park Road back north to the Gatineau Hydro Corridor.

The City of Toronto’s project site for this connection says that planning did start with the Toronto and Region Conservation Authority back in 2014, with construction starting last year, and completion in 2020. However, I walked the East Highland Creek back in July, and the only construction I saw was old construction accesses from previous creek remediation work. That said, I was able to reach out to the city and confirm that construction will start this year, and it is still anticipated to be done by next year.

2. Don Valley

This segment would connect an existing trail along the Gatineau Hydro Corridor, down the East Don River to the Forks of the Don. The current detour is along various streets to Taylor Massey Creek, and along that ravine.

The East Don Trail and connection to the Gatineau Hydro Corridor was another project planned through a city-conservation authority partnership back in 2016. Construction started in September last year, and is ongoing for Phases 1. This completes this connection for the Pan Am Path, despite leaving an unfunded gap along the East Don Trail north to Wigmore Park.

3. Waterfront

This connection was missing when the Pan Am Path was first announced, but was well under construction, and was completed in June 2015, one month prior to the opening of the games.

The path was created out of Waterfront Toronto’s revitalization of Queens Quay. The former 4-lane industrial boulevard with a streetcar saw itself cut down to 2 lanes, 1 in each direction north of the streetcar right-of-way, and the former eastbound lanes reclaimed as a dedicated cycling trail and wide pedestrian promenade. For a progressive dense community that was forced into amalgamation and dominated by suburban conservative politics, it was a breath of fresh air. It also made a track record for Waterfront Toronto, the tri-governmental agency that made it happen.

4. Humber Marshes

This is a connection I am not very clear on; the gap exists between King’s Mill Park and South Humber Park, requiring users to travel via Riverwood Parkway and Stephen Drive.

However, where exactly you would place a dedicated trail connection is a mystery to me, as welcome as it would be. This is akin to the TRCA’s proposal to extend a trail through the bottom reach of the Rouge River; it’s entirely a wide river channel with wetlands, and the adjacent tableland is taken up by private residential housing. Creating a path would be tricky and expensive, so this might be one acceptable on-street connection.

5. Weston

This segment would make the Humber River Trail continuous by making a connection between Memorial Park and Cruickshank Park, going under the GO Transit Kitchener line. The current detour up the St Phillips Steps, and along Weston Road.

I have seen no indication of this moving forward, and it’s extremely disappointing. Metrolinx recently completed work here to widen the rail bridge over the Humber River, and while other trail projects have taken advantage of old constructions accesses, nothing seems to have been left behind in this case. For extra irony, it is in the old Ward 11, where local councillor Frances Nunziata hosted a ribbon-cutting ceremony for the path back in 2014.

Other Gaps

Besides the 5 main connections identified, there are still some other gaps that should be addressed to ensure the Pan Am Path is a legacy to be proud of.

Military Trail

This gap requiring use of a sidewalk on Military Trail to cross Highland Creek, and a looparound back under the road could simply use a dedicated bridge to create a more direct route.

Missing Meadoway Segments

While these could be considered in the pipeline, there are segments of trail along the future Gatineau Meadoway that will need to be finished. I have previously written at length about the work that should be done in the corridor.

Old Mill

While dedicated space along the driveway into King’s Mill Park may be a bit of nitpicking, it has always driven me crazy that trail users must face off with vehicles on the skinny Old Mill Road bridge. A dedicated connection should be made, as I suggested in my analysis of TRCA’s Trail Strategy.

Eglinton

It may be of lower priority, but an opportunity exists to improve the trail in the vicinity of Eglinton Avenue. Two additional river crossings grade-separate the trail from Eglinton, and avoid the steep climb around Humber Creek.

Final Notes

As with any trails in Toronto, I place a lot of emphasis on ensuring that off street connections are minimized, and grade separations are created where required. Completing the identified connections and filling the other gaps will mostly address both these elements.

One aspect of the Pan Am Path that I cannot knock on is the branding and wayfinding. The city, in partnership with Friends of the Pan Am Path, have made an excellent website with helpful and informative resources, great navigational signs and maps, and a distinct logo.

At the same time, the branding, wayfinding, and general fanfare for the Pan Am Path feels like a bot of a slap in the face when not all of the larger capital improvements have been completed. Almost four years after the games, I feel the legacy should almost be complete.

Perhaps I am impatient; at least 1/5 of the identified connections is complete, and another 2 will be on the way. But the lack of plans for the remaining 2 really fits with a theme of what feels like a second-class treatment of active transportation in this city; lack of maintenance, lack of building, and lack of progress. Perhaps Toronto’s legacy is talking big, and not following through.