File
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:
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.
March 30, 2023:
The outflow target for the week of April 1 through 7 is the applicable Rule Curve flow of 8,220 m3/s.
April 6, 2023:
The outflow target for the week of April 8 through 14 is the applicable Rule Curve flow of 8,490 m3/s.
Depending on weather and water supply conditions during the next several weeks, the Lake Ontario outflow into the St. Lawrence River may need to be adjusted in accordance with the Plan 2014 F Limit (https://ijc.org/en/loslrb/watershed/faq/4#4-8-2). Since the level of Lake Ontario is below 75.3 m, the first F-limit tier applies and the outflow would be adjusted to maintain a maximum level of 22.10 m at Lake St. Louis (measured at Pointe Claire).
From Table B4 of the Plan 2014 Compendium:
|
Lake Ontario level (m, IGLD 1985) |
Lake St. Louis level at Pointe Claire (m, IGLD 1985) |
|
< 75.3 |
22.10 |
April 13, 2023:
Ottawa River flows into the St. Lawrence River have begun increasing due to snowmelt in the southern portion of the Ottawa River basin (https://ottawariver.ca/wp-content/uploads/2023/04/2023-04-07-Ottawa-River-Press-release.pdf). As a result, water levels in the lower St. Lawrence River have increased.
The Lake Ontario outflow into the St. Lawrence River will be adjusted in accordance with the Plan 2014 F Limit (https://ijc.org/en/loslrb/watershed/faq/4#4-8-2). Since the level of Lake Ontario is below 75.3 m, the first F-limit tier applies and the outflow will be adjusted to maintain a maximum level of 22.10 m at Lake St. Louis (measured at Pointe Claire).
April 20, 2023:
Ottawa River flows into the St. Lawrence River remain elevated in response to the rapid melt of the snowpack in the Ottawa River basin. Flows are expected to stabilize over the next week.
The Lake Ontario outflow into the St. Lawrence River will continue to be adjusted in accordance with the Plan 2014 F Limit. Since the level of Lake Ontario is below 75.3 m, the first F-limit tier applies and the outflow will be adjusted to maintain a maximum level of 22.10 m at Lake St. Louis (measured at Pointe Claire).
Lake Ontario outflow reductions over the past week, combined with strong southwesterly winds, caused water levels on Lake St. Lawrence (immediately upstream of the Moses-Saunders Dam) to rise. To mitigate the high water levels, Ontario Power Generation (OPG) adjusted the gates at Iroquois Dam on April 18 and 19. These gate adjustments, combined with subsiding and shifting winds, then caused water levels on Lake St. Lawrence to decline.
April 27, 2023:
Ottawa River flows into the St. Lawrence River have stabilized and are expected to slowly decline. However, Ottawa River flows could rise again depending on the path and size of future weather systems bringing additional precipitation to the basin.
The target outflow (from Lake Ontario into the St. Lawrence River) for the week of April 29 through May 5 is the applicable Rule Curve flow of 8,700 m3/s. However, the outflow will continue to be adjusted in accordance with the Plan 2014 F Limit. Since the level of Lake Ontario is below 75.3 m, the first F-limit tier applies and the outflow will be adjusted to maintain a maximum level of 22.10 m at Lake St. Louis (measured at Pointe Claire). If the level of Lake Ontario rises to 75.3 m, the second F-limit tier will apply, and the outflow will be adjusted to maintain a maximum level of 22.20 m at Lake St. Louis.
From Table B4 of the Plan 2014 Compendium:
|
Lake Ontario level (m, IGLD 1985) |
Lake St. Louis level at Pointe Claire (m, IGLD 1985) |
|
< 75.3 |
22.10 |
|
≥ 75.3 and < 75.37 |
22.20 |
May 2, 2023:
Ottawa River flows into the St. Lawrence River are rising in response to significant rainfall received over the last several days.
The water level of Lake Ontario has been rising at a rate of approximately 2 cm per day and has reached 75.30 m. The second F-limit tier now applies and the Lake Ontario outflow into the St. Lawrence River will be adjusted to maintain a maximum level of 22.20 m at Lake St. Louis (measured at Pointe Claire).
The level of Lake Ontario is expected to continue rising and is likely to reach 75.37 m as soon as this weekend, at which time, the third F-limit tier will apply, and the outflow will be adjusted to maintain a maximum level of 22.33 m at Lake St. Louis.
|
Lake Ontario level (m, IGLD 1985) |
Lake St. Louis level at Pointe Claire (m, IGLD 1985) |
Estimated Date of Occurrence |
|
< 75.30 |
22.10 |
Since early April, now surpassed |
|
≥ 75.30 and < 75.37 |
22.20 |
Reached May 2 |
|
≥ 75.37 and < 75.50 |
22.33 |
Between May 6 and May 12 |
Lake Ontario outflow reductions cause water levels of Lake St. Lawrence (immediately upstream of the Moses-Saunders Dam) to rise. To mitigate the high water levels, Ontario Power Generation (OPG) further adjusted the gates at Iroquois Dam on May 2.
May 5, 2023:
Much of the region received 40-90 mm of rain – about a month’s worth – over the past several days. The persistent rain and continued runoff, combined with recent and ongoing outflow adjustments in response to the wet conditions, continues to cause water levels in Lake Ontario and the St. Lawrence River to rise.
With the return of sunny and drier weather forecast for the coming week, Ottawa River flows into the St. Lawrence River are expected to gradually decline. This will allow Lake Ontario outflows into the St. Lawrence River to be gradually increased, in accordance with the Plan 2014 F Limit.
The gates of Iroquois Dam remain lowered to prevent high water levels on Lake St. Lawrence. The Iroquois Dam gates will be raised again as Lake Ontario outflows are gradually increased in the coming days and weeks. Note that the seasonal forecast of Lake St. Lawrence water levels is now available on the forecast page (click the tab on the right).
May 7, 2023:
The water level of Lake Ontario has reached 75.37 m. The third tier of the F Limit now applies, and the Lake Ontario outflow into the St. Lawrence River will be adjusted to maintain a maximum level of 22.33 m at Lake St. Louis (measured at Pointe Claire).
It is possible under wetter-than-average water supply scenarios that Lake Ontario could reach 75.50 m, at which time the fourth tier of the F Limit would apply and the Lake Ontario outflow into the St. Lawrence River would be adjusted to maintain a maximum level of 22.40 m at Lake St. Louis.
May 9, 2023:
The water level of Lake Ontario appears to be approaching its seasonal peak. Under most potential water supply scenarios, the level is likely to remain near its current level (~75.40 m) for a few weeks, and then begin a gradual seasonal decline.
The Lake Ontario outflow into the St. Lawrence River is being gradually increased, in accordance with the Plan 2014 F Limit, as Ottawa River flows decline. Based on the current level of Lake Ontario (~75.40 m), the third F-Limit tier continues to apply and the Lake Ontario outflow into the St. Lawrence River continues to be increased to maintain a maximum level of 22.33 m at Lake St. Louis. This is the minor inundation threshold at Lake St. Louis identified by Sécurité Publique Québec. Moderate flooding occurred further downstream around Lake St. Pierre. Water levels of Lake St. Pierre are now declining, but remain above the minor inundation threshold.
The gates at Iroquois Dam have been lowered since mid April to help suppress the high water levels of Lake St. Lawrence (immediately upstream of the Moses-Saunders Dam) while the Lake Ontario outflows were reduced. Now that Lake Ontario outflows are being increased, Ontario Power Generation (OPG) began raising the gates of Iroquois Dam today (May 9).
May 11, 2023:
The Lake Ontario outflow into the St. Lawrence River continues to be gradually increased, in accordance with the Plan 2014 F Limit, as Ottawa River flows continue to gradually decrease.
The outflow target for the week of May 13 through 19 is the applicable Rule Curve flow of 9,070 m3/s. As the outflow continues to be gradually increased, it is expected that 9,070 m3/s will be reached by ~May 18.
May 15, 2023:
Based on the current level of Lake Ontario, the Plan 2014 J Limit prescribes a maximum change in weekly average flow of 1,420 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. The weekly average flow for the week of May 6 through 12 was 7,300 m3/s. Based on the J limit, the maximum weekly average flow for the week of May 13 through 19 cannot exceed 8,720 m3/s (7,300 m3/s + 1,420 m3/s). The outflow will therefore remain at 8,800 m3/s through May 19 and will be increased to the applicable Rule Curve flow on May 20.
Water levels of Lake St. Lawrence have declined in recent days as Lake Ontario outflows have increased. Lake St. Lawrence water levels are expected to rebound tomorrow (May 16) when Ontario Power Generation (OPG) raises the gates of Iroquois Dam.
Water levels in the lower St. Lawrence River are expected to decline as Ottawa River flows continue to decrease, and as Lake Ontario outflows into the St. Lawrence River remain relatively stable.
May 19, 2023:
As reported by Ontario Power Generation, all of the gates of Iroquois Dam are now raised fully out of the water. Two marked gates are raised higher than the rest to allow recreational boats to pass underneath.
On the evening of May 19, the outflow will be increased to next week’s (May 20-26) applicable Rule Curve flow of 8,960 m3/s. The outflow will then remain at 8,960 m3/s through May 26. The goal of this flow increase is to return to Rule Curve as soon as possible, while ensuring the weekly average flow for May 13-19 respects the J Limit of 8,720 m3/s.
The expected flows reported in the updates provided on May 11 and May 15 were based on provisional data. Near the end of the week, there is more certainty since the daily average flows for most of the week (i.e. May 13 through 18) are known.
|
Date |
Average Outflow |
|
May 13 |
8,350 |
|
May 14 |
8,640 |
|
May 15 |
8,800 |
|
May 16 |
8,800 |
|
May 17 |
8,810 |
|
May 18 |
8,800 |
|
May 19 |
8,840 (provisional*) |
|
Weekly Average |
8,720 (provisional*) |
*At the time of posting (morning of May 19), the daily average flow for May 19, as well as the weekly average flow for May 13-19 are provisional estimates. Actual flows may differ slightly from these targets.
May 25, 2023:
The outflow target for the week of May 27 through June 2 is the applicable Rule Curve flow of 8,880 m³/s.
June 1, 2023:
The outflow target for the week of June 3 through 9 is the applicable Rule Curve flow of 8,700 m³/s.
| DATE | HOUR | OUTFLOW | OUTFLOW | NOTES |
| (YYYY-MM-DD) | (HHMM) | (m3/s) | (cfs) | |
| 2023-06-03 | 0001 | 8,700 | 307,200 | Rule Curve |
| 2023-05-27 | 0001 | 8,880 | 313,600 | Rule Curve |
| 2023-05-19 | 1801 | 8,960 | 316,400 | J Limit / Rule Curve |
| 2023-05-14 | 1401 | 8,800 | 310,800 | F Limit |
| 2023-05-13 | 1301 | 8,500 | 300,200 | F Limit |
| 2023-05-12 | 1501 | 8,200 | 289,600 | F Limit |
| 2023-05-11 | 1901 | 8,000 | 282,500 | F Limit |
| 2023-05-10 | 1801 | 7,800 | 275,500 | F Limit |
| 2023-05-09 | 1301 | 7,600 | 268,400 | F Limit |
| 2023-05-08 | 2101 | 7,400 | 261,300 | F Limit |
| 2023-05-08 | 1201 | 7,200 | 254,300 | F Limit |
| 2023-05-08 | 0001 | 6,900 | 243,700 | F Limit |
| 2023-05-07 | 1201 | 6,800 | 240,100 | F Limit |
| 2023-05-07 | 0801 | 6,700 | 236,600 | F Limit |
| 2023-05-07 | 0001 | 6,500 | 229,500 | F Limit |
| 2023-05-06 | 1101 | 6,300 | 222,500 | F Limit |
| 2023-05-05 | 2001 | 6,050 | 213,700 | F Limit |
| 2023-05-05 | 1301 | 5,900 | 208,400 | F Limit |
| 2023-05-04 | 1801 | 5,750 | 203,100 | F Limit |
| 2023-05-04 | 1101 | 5,900 | 208,400 | F Limit |
| 2023-05-04 | 0001 | 6,000 | 211,900 | F Limit |
| 2023-05-03 | 1301 | 6,250 | 220,700 | F Limit |
| 2023-05-02 | 1901 | 6,400 | 226,000 | F Limit |
| 2023-05-01 | 1801 | 6,600 | 233,100 | F Limit |
| 2023-05-01 | 1101 | 7,000 | 247,200 | F Limit |
| 2023-04-29 | 1301 | 7,400 | 261,300 | F Limit |
| 2023-04-28 | 1501 | 7,300 | 257,800 | F Limit |
| 2023-04-27 | 1201 | 7,100 | 250,700 | F Limit |
| 2023-04-26 | 1201 | 7,250 | 256,000 | F Limit |
| 2023-04-25 | 2001 | 7,150 | 252,500 | F Limit |
| 2023-04-23 | 1301 | 7,000 | 247,200 | F Limit |
| 2023-04-20 | 1101 | 7,400 | 261,300 | F Limit |
| 2023-04-20 | 0001 | 7,600 | 268,400 | F Limit |
| 2023-04-17 | 0001 | 7,800 | 275,500 | F Limit |
| 2023-04-15 | 1501 | 8,000 | 282,500 | F Limit |
| 2023-04-14 | 1101 | 8,200 | 289,600 | F Limit |
| 2023-04-08 | 1601 | 8,490 | 299,800 | Rule Curve |
| 2023-04-08 | 0001 | 8,300 | 293,100 | F Limit |
| 2023-04-07 | 0001 | 8,100 | 286,000 | F Limit |
| 2023-04-01 | 0001 | 8,220 | 290,300 | Rule Curve |
| 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 |
To view outflow change records from previous years, please use the links below: