Update on Lake Superior Outflows and Expected Conditions - December 2021

Date

As a result of the drier than average weather and water supply conditions, the water levels of Lake Superior and Lake Michigan-Huron declined by more than the average amounts in November. Lake Superior outflows continue to be set in consideration of water levels upstream and downstream.

The Board expects the total outflow to be 1,700 m3/s (60.0 tcfs) in December, which is as prescribed by Lake Superior Regulation Plan 2012. The gate setting at the Compensating Works will be maintained at the setting equivalent to one half gate open (Gates #7 through #10 partially open 20 cm (7.9 in)). There will be no change to the setting of Gate #1, which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike.

Weather and water supply conditions were a record low in the Lake Superior basin in November. As a result, Lake Superior declined 12 cm (4.7 in), while on average the lake declines 5 cm (2.0 in) in November. Weather and water supply conditions on Lake Michigan-Huron basin in November were well below-average, and as a result, Lake Michigan-Huron declined 13 cm (5.1 in) last month, while the average historical decline is 5 cm (2.0 in) in November. At the beginning of December, Lake Superior is 13 cm (5.1 in) below the long-term average water level (1918 – 2020) and 38 cm (15.0 in) below the level of a year ago. Lake Michigan-Huron is 34 cm (13.4 in) above average, 45 cm (17.7 in) below the level from last year, and 60 cm (23.6 in) below the record level set in 1986.

Lake Superior and Lake Michigan-Huron water levels typically decline in December. Depending on the weather and water supply conditions during the next month, Lake Superior may decline by as much as 12 cm (4.7 in) in December. Lake Michigan-Huron water levels could decline by as much as 13 cm (5.1 in).

The International Lake Superior Board of Control is responsible for regulating the outflow of Lake Superior and managing the control works on the St. Marys River. Under any regulation plan, the ability to regulate the outflow from Lake Superior does not mean that full control of lake levels is possible. This is because the major factors affecting water supply to the Great Lakes, 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