Update on Lake Superior Outflows and Expected Conditions - October 2024

The Board expects the total St. Marys River flow in October to be 2,050 m³/s (72,400 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 October is expected to be approximately 272 m³/s, to meet the Plan 2012-prescribed flow in October in consideration of the capacity restrictions at the hydropower plants. 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.

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 October. The gate setting of the Compensating Works will be decreased from the current setting equivalent to approximately three gates fully open (Gates #7 through #15 open 76 cm each) to a setting equivalent to approximately one gate fully open. On Monday October 7, Gates #7 and #8 will both be lowered to 20 cm open, and the St. Marys Rapids flow is expected to be approximately 415 m³/s. Concrete core sampling at two Compensating Works piers requires Gates #9 through #15 to remain open 76 cm each on Tuesday, October 8 through Thursday, October 10. It is possible that a few of the gates on the US side may need to be temporarily adjusted to accommodate placement of the equipment that will be used for the concrete core sampling. Upon completion of the concrete core sampling, on Friday October 11, Gates #9 through #15 will each be lowered to 28 cm open, and the St. Marys Rapids flow is expected to be approximately 180 m³/s.

Water level changes over the month of September

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

• Lake Superior declined by 7 cm (2.8 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 12 cm (4.7 in) last month, and the seasonal long-term average pattern is for Lake Michigan-Huron 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 was 13 cm (5.1 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 October, the lake-wide average water level of Lake Michigan-Huron was 3 cm (1.2 in) above the seasonal long-term average (1918-2023) and 8 cm (3.1 in) below the level of a year ago.

Forecast outlook

• If weather and water supply conditions are near average, Lake Superior may decline by approximately 3 cm (1.2 in.) and Lake Michigan-Huron may decline by approximately 8 cm (3.1 in).
• If conditions are much wetter than average, Lake Superior may rise by as much as 5 cm (2.0 in) and Lake Michigan-Huron may rise by approximately 1 cm (0.4 in).
• If conditions are much drier than average, the water level of Lake Superior may drop by approximately 9 cm (3.5 in), and Lake Michigan-Huron may decrease by as much as 14 cm (5.5 in).