The International Lake Ontario-St. Lawrence River Board has granted approval for a temporary reduction in water flows requested by Hydro-Quebec to accommodate inspections at dam facilities on September 24, 2024. The adjustment will involve a 12-hour period during which outflows through the Moses-Saunders and Long Sault Dams, located between Massena, New York, and Cornwall, Ontario, will be reduced by 410 cubic meters per second (14,500 cubic feet per second).
This request constitutes a minor deviation from Plan 2014, the regulatory framework that governs Lake Ontario outflows. Plan 2014 is overseen by the International Joint Commission, which sets directives that outline permissible deviations and any associated limitations. According to the board, the outflows will return to Plan 2014’s prescribed levels by 5:01 PM on September 24.
The temporary reduction in outflows is expected to result in a modest rise in water levels on Lake Ontario by 0.09 centimeters. From October 19, measures will be taken to offset this deviation as part of a strategy to maintain a minimum weekly average water level of 73.10 meters (239.8 feet) on Lake St. Lawrence through October 18.
During the 12-hour reduction, water levels upstream of the Moses-Saunders Dam are anticipated to rise, while downstream levels are expected to decrease. These fluctuations are expected to be similar to those observed during a similar adjustment on June 19, 2024. The recorded water level changes in June were minor, with locations such as Kingston and Ogdensburg experiencing less than 1 cm of change, while other areas like Waddington and Morrisburg saw increases of up to 11 cm. Downstream, locations including Cornwall and Montreal recorded decreases between 5 and 9 cm.
Following the temporary flow reduction, the water levels upstream of the Moses-Saunders Dam are projected to decrease at an accelerated rate beginning on October 19. The board advises recreational boaters to closely monitor water level forecasts to determine the best time to remove their vessels and equipment for the season, as water levels throughout the system continue their gradual seasonal decline.
Hydro-Quebec has provided a point of contact for any inquiries related to the dam inspection work at ramrichelieu@hydro.qc.ca. Information regarding the flow adjustments will also be available on the Lake Ontario Outflow Changes webpage, where a detailed summary will be posted.
Photo: Wikimedia Commons (pd)
