International Lake Ontario-St. Lawrence River Board Approves Minor Deviation Request by Hydro-Quebec to Accommodate Inspections at Dam Facilities

Ottawa – The International Lake Ontario-St. Lawrence River Board has approved a request from Hydro-Quebec to allow 12 hours of reduced flows on September 24, 2024, to accommodate inspections at dam facilities. Plan 2014 is a set of rules that govern Lake Ontario outflows through the Moses-Saunders Dam and Long Sault Dam located between Massena, New York and Cornwall, Ontario. Board Directives from the International Joint Commission determine what approvals can or cannot be granted and may specify limitations to deviations.

Hydro-Quebec has requested a Minor Deviation to occur on Tuesday, September 24 to reduce the outflow by 410 m3/s (14,500 cfs) for a 12-hour duration. Outflows will return to Plan 2014 prescribed flows at 1701 hrs on September 24.

This temporary flow reduction will have a +0.09 cm impact on Lake Ontario. This deviation will be offset beginning on October 19, in accordance with the Board’s strategy to maintain a minimum weekly mean Lake St. Lawrence level of 73.10 m (239.8 ft) through October 18.

During the 12 hours of reduced flows, water levels upstream of the Moses-Saunders Dam are expected to increase and water levels downstream are expected to decrease – similar to water level fluctuations observed during the minor deviation conducted on June 19 which were as follows:

• Kingston: <1 cm
• Ogdensburg: <1 cm
• Cardinal: +7 cm
• Iroquois Headwater: +9 cm
• Iroquois Tailwater: +8 cm
• Waddington: +11 cm
• Morrisburg: +11 cm
• Long Sault: +13 cm
• Cornwall: -9 cm
• Summerstown: – 7 cm
• Pointe Claire: -7 cm
• Montreal Jetty #1: -5 cm
• Sorel: -5 cm

The flow adjustments will be documented on the Lake Ontario Outflow Changes webpage in the tabular summary located at the bottom of the page.

Water levels upstream of the Moses-Saunders Dam are expected to decrease at an accelerated rate beginning on October 19. As water levels throughout the system continue their gradual seasonal decline, the Board encourages recreational boaters to monitor the water level forecasts to determine the optimal time to remove their vessels and equipment for the season.

For questions related to the work to be conducted by Hydro-Quebec, please contact their office at ramrichelieu@hydro.qc.ca.

For more information on:

Lake Ontario Outflow Changes: https://ijc.org/en/loslrb/watershed/outflow-changes
Water Levels: https://ijc.org/en/loslrb/watershed/water-levels
Water Supplies: https://ijc.org/en/loslrb/watershed/flows
Water Level Forecast: https://ijc.org/en/loslrb/watershed/forecasts

To contact the International Lake Ontario-St. Lawrence River Board:

United States: ILOSLRB-USSection@usace.army.mil

Canada: ec.cilofsl-iloslrb.ec@canada.ca

Facebook: https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard

The International Lake Ontario-St. Lawrence River Board ensures that outflows from Lake Ontario meet the requirements of the International Joint Commission’s Orders of Approval. Under any regulation plan, the ability to regulate the outflow from Lake Ontario does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes – precipitation, evaporation, and runoff – cannot be controlled, and are difficult to accurately predict.