Update on Lake Superior Outflows and Expected Conditions - December 2022
Date

Anglers and other users of the St. Marys Rapids, please be advised that a higher than customary gate setting will be maintained this winter to minimize the impacts of ongoing maintenance at the Canadian hydropower facility. The gates of the Compensating Works at the head of the St. Marys Rapids have been set to an equivalent of two gates fully open (Gates #6 through #16 partially open 26 cm (10 in) each). 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.


The International Lake Superior Board of Control (Board) anticipates that the total St. Marys River flow will be 2,060 m3/s (72.7 tcfs) in December, which is 350 m3/s (12.4 tcfs) less than the flow prescribed by Regulation Plan 2012. When compared to plan flow, the expected December flow deficit will add approximately 1 cm (0.4 in) to the water level of Lake Superior and reduce the water level on Lake Michigan-Huron by less than 1 cm (0.4 in). Under most potential water supply scenarios, the  cumulative effect on the water levels of Lake Superior and Lake Michigan-Huron will be negligible by the Spring.


Water level changes over the month of November

  • Lake Superior rose by 5 cm (2.0 in) last month, while the seasonal long-term average decline in December is 5 cm (2.0 in).
  • Lake Michigan-Huron declined by 9 cm (1.6 in) last month, while the seasonal long-term average decline in November is 4 cm (3.5 in).

Water levels as of the beginning of December

  • At the beginning December, the lake-wide water level of Lake Superior is 17 cm (6.7 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 December, the lake-wide level of Lake Michigan-Huron is 11 cm (4.3 in) above average and 21 cm (8.4 in) below the level of a year ago.

Outlook

  • Lake-wide average water levels of both Lake Superior and Lake Michigan-Huron are expected to continue to decline through the winter months.
  • Depending on the weather and water supply conditions during the next month, Lake Superior may decline by as much as 14 cm (4.7 in) in December.
  • Depending on the weather and water supply conditions, Lake Michigan-Huron may decline by as much as 11 cm (4.3 in) next month, or it may rise by as  much as 3 cm (1.2 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.