Lake Ontario Outflow Changes

The regulation plan (Plan 2014) specifies a weekly average Lake Ontario outflow from Saturday through the following Friday. Throughout the year, the Lake Ontario outflow, which is managed at the Moses-Saunders Dam, may be modified more frequently depending on the conditions in Lake Ontario and the St. Lawrence River. There are two different types of outflow modifications:

Operational Adjustments, which do not have to be offset at a later date, and
Deviations, which are classified as "minor" or "major" and generally do have to be offset at a later date.

Further details are available in the Directive on Operational Adjustments, Deviations and Extreme Conditions (https://ijc.org/en/loslrb/who/directives/deviations)

Summary of Outflow Changes in 2022

Summary of Outflow Changes for 2023

As of January 7, 2023, the water level of Lake Ontario was equivalent to the level it would have been if no outflow deviations from Plan 2014 had been conducted in 2022.

During the winter months, the outflow will be operationally adjusted in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of ice covers in the Beauharnois Canal and on Lake St. Lawrence. For more information,

This video demonstrates the importance of ice management in the St. Lawrence River: https://vimeo.com/168823489
FAQ 2.7 “What actions does the Board take to manage ice conditions in the St. Lawrence River during the winter?” : https://ijc.org/en/loslrb/watershed/faq/2#2-7
FAQ 4.8.4 “What is the I Limit?”: https://ijc.org/en/loslrb/watershed/faq/4#4-8-4
This video discusses winter operations under Plan 2014: https://vimeo.com/670845537

January 27, 2023:

The Lake Ontario outflow has been reduced to promote the formation of an ice cover in the Beauharnois Canal. This outflow reduction is considered an operational adjustment in accordance with the Plan 2014 I Limit. About 2 km of slush ice has accumulated in the Beauharnois Canal and there has been a significant rise in the tension on the ice booms.

February 2, 2023:

Ice began to form in the Beauharnois Canal on January 27. Since then, the outflow has been operationally adjusted several times (decreased on January 27, increased on January 29 and 30, decreased on January 31, and increased on February 1) in accordance with the Plan 2014 I Limit and in response to changing ice conditions.

The outflow target for the week of February 4 through 10 is the applicable Rule Curve flow of 7,720 m³/s. However, the outflow will continue to be operationally adjusted in accordance with the Plan 2014 I Limit, as needed, to promote the formation and stability of an ice cover in the Beauharnois Canal.

February 7, 2023:

As of February 4, an ice cover formed on Lake St. Lawrence, extending from the Moses-Saunders Dam to approximately Morrisburg, Ontario.

A partial ice cover also remains in the Beauharnois Canal.

Explore recent Sentinel-2 satellite imagery via the EO Browser: https://apps.sentinel-hub.com/eo-browser/

Further ice formation is not expected in the short term because of the mild temperatures, and the outflow will be gradually increased.

February 11, 2023:

The outflow target for the week of February 11 through 17 is the applicable J Limit flow of 7,660 m³/s. Based on the current level of Lake Ontario, and while ice remains in the St. Lawrence River, the J Limit prescribes a maximum change in weekly average flow of 700 m³/s from one week to the next. The design principle behind the J Limit is to prevent rapid velocity and water level changes in the St. Lawrence River to minimize potential impacts to interests along the river.

February 18, 2023:

The ice cover that had formed on Lake St. Lawrence has deteriorated. The ice cover in Beauharnois Canal has also receded. The outflow target for the week of February 18 through 24 is the applicable Rule Curve flow of 7,940 m³/s.

February 23, 2023:

As a result of the recent cold temperatures, ice has started to accumulate again in the Beauharnois Canal. The Lake Ontario outflow has been reduced in accordance with the Plan 2014 I Limit. The outflow target for the week of February 25 through March 3 is the applicable Rule Curve flow of 7,950 m³/s. However, the outflow will continue to be operationally adjusted in accordance with the Plan 2014 I Limit, as needed.

March 5, 2023:

The outflow target for the week of March 4 through 10 is the applicable Rule Curve flow of 7,940 m³/s. Further ice formation is not expected in the short term because of the mild temperatures.

However, the Board has authorized a minor deviation. The Lake Ontario outflow will be reduced through March 12 to facilitate a concrete inspection of Saint-Timothée Dam in preparation for planned upcoming rehabilitation work. This temporary period of reduced flows will be offset by increased flows from March 13 through 24, as conditions allow.

The Saint-Timothée Dam is part of the Beauharnois-Les Cèdres hydropower complex operated by Hydro-Québec. A modernization project is ongoing to ensure long-term operability of the facilities and extend the lifespan of the structures. For more information: https://www.hydroquebec.com/projects/beauharnois-les-cedres/installations.html

This type of maintenance is generally scheduled when periods of relatively low flows are anticipated, typically in the winter. However, because of the generally mild temperatures this winter, the periods of time when flows were reduced to promote ice formation and stability were not sufficient to allow all of the necessary maintenance activities to be completed.

March 9, 2023:

The concrete inspection of Saint-Timothée Dam is expected to be completed ahead of schedule. The outflow will be set to 8,080 m³/s on March 11, which is 90 m³/s above the applicable Rule Curve flow of 7,990 m³/s, to offset the temporary period of reduced flows beginning on March 6.

March 16, 2023:

On March 18, the outflow will be set to 7,970 m³/s, which is 30 m³/s above the applicable Rule Curve flow of 7,940 m³/s, to complete the offset of the temporarily reduced flows earlier in March.

March 24, 2023:

The outflow target for the week of March 25 through 31 is the applicable Rule Curve flow of 8,070 m³/s.

DATE	HOUR	OUTFLOW	OUTFLOW	NOTES
(YYYY-MM-DD)	(HHMM)	(m³/s)	(cfs)
2023-03-25	0001	8,070	285,000	Rule Curve
2023-03-18	0001	7,970	281,500	Offsetting Minor Deviation
2023-03-11	1401	8,080	285,300	Offsetting Minor Deviation
2023-03-06	0001	7,800	275,500	Minor Deviation
2023-03-04	0001	7,940	280,400	Rule Curve
2023-02-28	1201	7,950	280,800	Rule Curve
2023-02-27	1601	7,400	261,300	I Limit
2023-02-24	2101	6,600	233,100	I Limit
2023-02-24	1801	6,800	240,100	I Limit
2023-02-22	2001	7,300	257,800	I Limit
2023-02-18	0001	7,940	280,400	Rule Curve
2023-02-11	0001	7,660	270,500	J Limit
2023-02-08	1501	7,400	261,300	I Limit
2023-02-07	1201	7,000	247,200	I Limit
2023-02-04	1901	6,600	233,100	I Limit
2023-02-02	1701	6,800	240,100	I Limit
2023-02-01	1901	7,700	271,900	Rule Curve
2023-01-31	2001	7,000	247,200	I Limit
2023-01-30	1301	7,700	271,900	Rule Curve
2023-01-29	1201	7,500	264,900	I Limit
2023-01-27	1401	7,000	247,200	I Limit
2023-01-21	0001	7,620	269,100	Rule Curve
2023-01-14	0001	7,600	268,400	Rule Curve
2023-01-07	0001	7,490	264,500	Rule Curve