How does the Board’s new tool help inform deviation decisions?
The Board is responsible for setting outflows to respond to extreme high or low water, however, due to the complexity and limitations of the system, the Board generally is unable to bring about large changes in water levels on Lake Ontario in a short period of time.
As Lake Ontario water levels rise, Plan 2014 automatically increases the outflow from the lake, sometimes greatly. While no regulation plan can eliminate all impacts, the plan aims to the degree possible to balance the impacts of high water levels on various locations and users of the Lake Ontario-St. Lawrence River system.
Board members often are concerned that with high water levels everywhere, any decision they make to deviate from the plan rules to help one use or interest may unfairly harm another. For example, increasing outflows to decrease water levels on Lake Ontario by just an inch (or cm) in a week can cause water levels of the St. Lawrence River near Montreal to rise tenfold that week, and cause levels on the river immediately upstream of the dam (known as Lake St. Lawrence) to fall by a similar amount that week.
The new Decision Support Tool will help the Board better understand the impacts associated with these sorts of tradeoffs. The tool presents the Board with a collection of information on the impacts of high water, much of it gathered after the 2017 and 2019 high-water events. This information will show the Board how impacts may change throughout the system if a particular outflow strategy were used and depending on a range of forecast weather-driven inflow conditions.
The lack of reliable long-term forecasts of the weather and of the water supply to Lake Ontario and the St. Lawrence River remains a challenge for the Board. While the tool cannot eliminate this uncertainty, it does allow the Board to explore and better understand this uncertainty with the ability to test and assess outcomes under different possible weather conditions.