Update on Lake Superior Outflows and Expected Conditions - December 2023
Date

The gate setting of the Compensating Works at the head of the St. Marys Rapids will be lowered in December to a setting equivalent to approximately one-half gate fully open. After the gate adjustments on Wednesday, December 6, the St. Marys Rapids flow will be approximately 96 m3/s.

The Board expects the total St. Marys River flow in December to be 2,120 m3/s (74,900 ft3/s), as prescribed by Regulation Plan 2012. Actual hour-to-hour and day-to-day flows may vary depending on hydrologic conditions, as well as variations in flow from the hydropower plants.

Water level changes over the month of November

Water supply conditions were quite dry in Lakes Superior Michigan-Huron basins in November.

  • Lake Superior declined by 10 cm (3.9 in) last month, while the seasonal long-term average pattern is for Lake Superior to decline by 5 cm (2.0 in) in November.
  • Lake Michigan-Huron declined by 10 cm (3.9 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to decline by 4 cm (1.6 in) in November.

Water levels as of the beginning of December

  • At the beginning of December, the lake-wide average water level of Lake Superior was 5 cm (2.0 in) below the seasonal long-term average (1918-2022) and 22 cm (8.7 in) below the level of a year ago.
  • At the beginning of December, the lake-wide average water level of Lake Michigan-Huron was 8 cm (3.1 in) above the seasonal long-term average (1918-2022) and 4 cm (1.6 in) below the level of a year ago.
December 2023 infographic

Forecast outlook

Both Lakes Superior and Michigan-Huron are in their seasonal decline.

  • If weather and water supply conditions are near average, both Lake Superior and Lake Michigan-Huron are expected to decline in December by 8 cm (3.1 in) and 6 cm (2.4 in), respectively.
  • If conditions are wetter than average, Lake Superior may decline by 4 cm (1.6 in) and Lake Michigan-Huron may rise slightly by 1 cm (0.4 in).
  • If conditions are drier than average, the water level of Lake Superior is expected to decline by as much as 13 cm (5.1 in), and Lake Michigan-Huron is expected to decline by as much as 12 cm (4.7 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