Toronto Island Community Association

FLOOD 2020

 

Dodging the Bullet

 

Lake Ontario riparians may have dodged a bullet as the 2020 lake levels appear to have peaked without reaching the forecast levels. How did this happen? 

 

Since 2017, riparians have been crying foul over the newly implemented Regulation Plan 2014, which places an unfair burden on the Lake Ontario shoreline residents during the spring flood season. The Plan has regulations in effect to limit Lake Ontario outflows to protect Montreal when the total flow in the St. Lawrence River increases the river levels beyond certain limits.

 

During the spring freshet, the Ottawa River flow, which joins the St. Lawrence River above Montreal, increases the total flow of the St. Lawrence River and results in an increase in the river level. In order to protect Montreal, the IJC cuts back on the Lake Ontario outflow at the Moses-Saunders dam, located upstream at Cornwall. During this period of reduced outflow, the level of Lake Ontario will rise. The amount of the rise is dependent on a few factors, including the amount of inflow from the upper Great Lakes, the amount of net basin supply (run-off+precipitation-evaporation) and the amount of the outflow. 

 

The Lake Ontario outflow reductions and duration are linked to the freshet flows and overall levels of the St. Lawrence River. In normal lake level years, the rise and fall of Lake Ontario is noticeable, but not of great concern. However, since 2013, the upper Great Lakes have had year-over-year increases in level and have reached record levels. As a result, their unregulated inflow into Lake Ontario has been extraordinarily high.  This inflow accounts for about 85% of Lake Ontario’s total supply, so when the outflows are cut back, the rise in Lake Ontario becomes very significant. When climate effects are factored in, such as in 2017 and 2019, it pushed the lake into flood condition.

 

Plan 2014 does not work well in high water conditions. It does not permit enough flow out of the lake in the fall to drop the lake level to a safe level to have a buffer during the spring freshet, so as 2019 started into the fall, there was great concern that the Lake Ontario level was too high. Lake Ontario riparians were organizing and raising awareness of the potential problem coming in 2020 unless immediate action was taken.

 

Forecasts were presented to the IJC and government officials to present the possibilities of never before seen lake levels unless the IJC deviated from the Plan 2014. Naturally the IJC pushed back and discounted the forecasts, but in the fall of 2019, they started to increase the outflows above the navigation L-Limits by 200 m3/s. They continued this until the end of the navigation season, but the lake levels were at record level by January 1.

 

The IJC then proceeded to let out record amounts of water from Lake Ontario from Jan1-Apr1. They increased outflows between 35%-50% over the 100 year average outflows in order to lower the lake level. Interestingly, this did not lower the lake, but it did “flatten the curve”.  This was the most critical factor in the lake not reaching flood levels. It held the lake level to a reasonable starting point for the spring freshet.

 

Since the shipping season has restarted on April 1, the outflows have been cutback, but they are still higher than Plan 2014 would normally allow. The IJC is pushing the limits and trying to balance upstream and downstream concerns, which is what we have been asking for! Mother Nature has given us a break this year too with only moderate net basin supplies.

 

    

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

Going forward, it is crucial that the IJC continue monitoring conditions and making good decisions to lower Lake Ontario, while the inflows from the upper Great Lakes remain high, and to maintain a balanced approach in governing the St. Lawrence River. Until the upper Great Lakes levels drop to a normal level, we will continue to be at risk of flooding each spring.

​

Political pressure must remain high otherwise the IJC might revert back to the Plan 2014. This plan does need modification to account for abnormal conditionals, such as the last few years.

But for 2020, it looks like we may have dodged that bullet!

 

Regards,

Mike French, P.Eng.