Update on Lake Superior Outflows and Expected Conditions - October 2023
The gate setting of the Compensating Works at the head of the St. Marys Rapids will be lowered in October to approximately four gates fully open. After the gate adjustments on Friday, October 6 (American gates), and Tuesday, October 10 (Canadian gates), the St. Marys Rapids flow will be approximately 650 m3/s. At this flow, some low-lying areas of Whitefish Island including recreational trails may still be flooded. Users are encouraged to use extreme caution.
The Board expects the total St. Marys River flow in October to be 2,640 m3/s (93,230 cfs) which is the same as the flow 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 September
Water supply conditions were drier than average in both Lake Superior and Lake Michigan-Huron basins in September.
Lake Superior declined by 5 cm (2.0 in.) last month, while the seasonal long-term average pattern is for Lake Superior to decline by 1 cm (0.4 in) in September.
Lake Michigan-Huron declined by 8 cm (3.1 in) last month, and the seasonal long-term average pattern for Lake Michigan-Huron is to decline by 6 cm (2.4 in) in September.
Water levels as of the beginning of October
At the beginning of October, the lake-wide average water level of Lake Superior is 6 cm (2.4 in) above the seasonal longterm average (1918-2022) and 4 cm (1.6 in) below the level of a year ago.
At the beginning of October, the lake-wide average water level of Lake Michigan-Huron is 11 cm (4.3 in) above the seasonal long-term average and 6 cm (2.4 in) below the level of a year ago.
Lakes Superior and Michigan-Huron are in their seasonal decline which will continue in October.
If weather and water supply conditions are near average, both Lake Superior and Lake Michigan-Huron are expected to decline in October (by 5 cm (2.0 in) and 8 cm (3.1 in), respectively).
If conditions are wetter than average, Lake Superior may rise by as much as 3 cm (1.2 in) and Lake Michigan-Huron may rise by as much as 1 cm (0.4 in).
If dry conditions continue, the water level of Lake Superior is expected to decline by as much as 11 cm (4.3 in.), and Lake Michigan-Huron is expected to decline 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