Update on Lake Superior Outflows and Expected Conditions - March 2023
Anglers and other users of the St. Marys Rapids, please be advised that a higher than customary gate setting continues to be maintained to minimize the impacts of ongoing maintenance at Evolugen’s Clergue hydropower facility in Canada. The gates of the Compensating Works at the head of the St. Marys Rapids will be maintained at an equivalent of two gates fully open (Gates #6 through #16 partially open 26 cm (10 in) each) in March. A setting equivalent to one-half gate open (Gates #7 through #10 open 20 cm (8 in) each) is typically used during the winter months from December through April. A setting of two gates fully open is the maximum allowable winter gate setting under Regulation Plan 2012 to prevent premature ice cover breakup which could result in increased ice jams and flood risk.
The International Lake Superior Board of Control (Board) expects that the total St. Marys River flow will be 2,020 m3/s (71.3 tcfs) in March, which is 390 m3/s (13.8 tcfs) less than the flow prescribed by Regulation Plan 2012. When compared to plan flow, the expected March flow deficit is equivalent to approximately 1 cm (0.4 in) added to the water level of Lake Superior and approximately 1 cm (0.4 in) removed from Lake Michigan-Huron cumulatively over the course of the month.
Water level changes over the month of February
- Lake Superior declined by 3 cm (1.2 in) last month, while the seasonal long-term average decline is 5 cm (2.0 in) in February.
- Lake Michigan-Huron declined by 2 cm (0.8 in) last month, while on average the lake remains stable in February.
Water levels as of the beginning of March
- At the beginning of March, the lake-wide water level of Lake Superior is 21 cm (8.3 in) above the seasonal long-term average (1918-2021) and 30 cm (11.8 in) above the level of a year ago.
- At the beginning of March, the lake-wide level of Lake Michigan-Huron is 11 cm (4.3 in) above average and 12 cm (4.7 in) below the level of a year ago.
- Depending on the weather and water supply conditions during the next month, Lake Superior may decline by as much as 8 cm (3.1 in) in March, or it may rise by as much as 4 cm (1.6 cm).
- Depending on the weather and water supply conditions, Lake Michigan-Huron may decline by as much as 2 cm (0.8 in) next month, or it may rise by as much as 14 cm (5.5 in).
The International Lake Superior Board of Control is responsible for managing the control works on the St. Marys River and regulating the outflow from Lake Superior into Lake Michigan-Huron. Under any outflow regulation plan, the ability to regulate the flow through the St. Marys River does not mean that full control of the water levels of Lake Superior and Lake Michigan-Huron is possible. This is because the major factors affecting water supply to the Great Lakes (i.e. precipitation, evaporation, and runoff) cannot be controlled, and are difficult to accurately predict. Outflow management cannot eliminate the risk of extreme water levels from occurring during periods of severe weather and water supply conditions. Additional information can be found at the Board’s homepage: https://ijc.org/en/lsbc or on Facebook at: https://www.facebook.com/InternationalLakeSuperiorBoardOfControl