The International Lake Ontario–St. Lawrence River Board agreed on March 11 to amend its Plan 2014 temporary deviation strategies to allow for additional increases to the rate of water removed from Lake Ontario through the spring.
The first adjustment to the deviation strategy involves the Plan 2014 rule that attempts to balance high water impacts upstream and downstream of the Moses-Saunders Power Dam known as the Flood Limit (F Limit). When applicable, outflows are adjusted to maintain corresponding levels upstream and downstream. For example, when Lake Ontario is below 247.05 feet, outflows can be adjusted to bring Lake St. Louis up to its flood alert level of 75.51 feet.
While Lake Ontario remains below 247.05 feet currently, the Board expects Lake Ontario to rise through spring. The Board is proactively increasing outflows to target downstream levels to 72.80 feet or more, in anticipation of Lake Ontario eventually reaching 247.05 feet. Please note, water levels may at times rise above this level by several centimeters, particularly during periods of rapid snowmelt and heavy rains in southern parts of the Ottawa River basin and around the Montreal area. The Board is also considering further increases at Lake St. Louis, which may be necessary should Lake Ontario continue rising.
The second deviation strategy amendment will begin April 1, following the opening of the St. Lawrence Seaway. Working closely with commercial navigation experts, outflows will be increased as quickly and as much as possible above the Plan 2014 usual safe navigation limit (L Limit). This strategy will be implemented to ensure that the maximum possible outflows are maintained while allowing for safe navigation to continue. The Board notes that other considerations may take precedence and limit outflows, including Ottawa River flows and water levels in the lower St. Lawrence River.
The Board continues monitoring conditions throughout the system, including the effects of high outflows on lower St. Lawrence River water levels in order to continue maximizing outflows from Lake Ontario as much as possible.
Lake Ontario’s seasonal rise has begun, and will generally continue in the coming weeks. Residents and communities along Lake Ontario should remain vigilant and continue to make preparations for potential impacts of high water this spring, as the risk remains elevated, particularly during periods of strong winds and waves.
There remains considerable long-term uncertainty for peak levels that will be reached this season, both upstream on Lake Ontario and downstream in the lower St. Lawrence River. Water levels will largely be determined by precipitation, inflows from Lake Erie, and from the Ottawa River system over the next several weeks. Updated information on current conditions on the Ottawa River can be found on the Ottawa River Regulation Planning Board’s website here: http://ottawariver.ca/conditions/.
These deviation strategies are being implemented in a very specific window of opportunity and will help remove an additional amount of water from Lake Ontario in the coming weeks before the Ottawa river freshet begins; at which time the Lake Ontario outflows will need to be reduced significantly until the Ottawa river flows from melted snow has receded.
The Board has recently created a new website page focused on the recent high-water events: https://ijc.org/en/loslrb/watershed/2017-and-2019-high-water-events. All high-water related materials are now in one place.
Please consult your local officials for flood preparedness and response measures.
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