St. Mary's Rapids users need to be cautious of changing water levels

NEWS RELEASE
LAKE SUPERIOR BOARD OF CONTROL
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The Board expects the total St. Marys River flow in November to be 1,850 m³/s (65,300 cfs), 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. The average St. Marys Rapids flow in November is expected to be approximately 108 m³/s, to meet the Plan 2012-prescribed flow in November.

Anglers and other users of the St. Marys Rapids need to be cautious of the flows and water levels that will be experienced in the rapids in November. The gate setting of the Compensating Works will be decreased from the current setting equivalent to approximately one gate fully open (Gates #7 and Gate #8 open 20 cm each, and Gate#9 through #13 open 38 cm each) to the typical winter gate setting (Gates #7 through #10 open 20 cm each) equivalent to approximately one-half gate fully open. Gate #1 will remain at its typical setting which supplies a flow of about 15 m³/s to the channel north of the Fishery Remedial Dike. On Friday November 8, Gates #9 and #10 will both be lowered to 20 cm open, Gates #11 through #13 will be closed, and the St. Marys Rapids flow is expected to be reduced from approximately 180 m³/s to approximately 86 m³/s.

Water level changes over the month of October

Water supply conditions were drier than average in both the Lake Superior and Lake Michigan-Huron basins in October.

• 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 4 cm (1.6 in) in October.
• Lake Michigan-Huron declined by 17 cm (6.7 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to decline by 7 cm (2.8 in) in October.

Water levels as of the beginning of November

• At the beginning of November, the lake-wide average water level of Lake Superior was 19 cm (7.5 in) below the seasonal long-term average (1918-2023) and 19 cm (7.5 in) below the level of a year ago.
• At the beginning of November, the lake-wide average water level of Lake Michigan-Huron was 7 cm (2.8 in) below the seasonal long-term average (1918-2023) and 21 cm (8.3 in) below the level of a year ago.

Forecast outlook

Water level changes based on water supplies over the month of November.

• If weather and water supply conditions are near average, Lake Superior may decline by approximately 5 cm (2.0 in.) and Lake Michigan-Huron may decline by approximately 6 cm (2.4 in).
• If conditions are much wetter than average, Lake Superior may rise by as much as 2 cm (0.8 in) and Lake Michigan-Huron may rise by approximately 2 cm (0.8 in).
• If conditions are much drier than average, the water level of Lake Superior may drop by approximately 10 cm (3.9 in), and Lake Michigan-Huron may decrease 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.

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