While hour-to-hour and day-to-day flows will vary some, the St. Marys Rapids will see a flow increase beginning today.
The increase in flow through the rapids comes as gate settings at the head of the St. Marys Rapids will be increased from a setting equivalent to approximately one-half gate fully open (Gates No. 7 through No. 10 open 20 cm (7.9 in)) to a setting equivalent to approximately three gates fully open.
The gate adjustments will mean a flow increase from ~85 m3/s to ~575 m3/s.
Following is a full release from the Board detailing the flow changes along with water level information for Lake Superior:
The Board expects the total St. Marys River flow in May to be 2,000 m3/s (70,600 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 gate setting of the Compensating Works at the head of the St. Marys Rapids will be increased on May 6 from a setting equivalent to approximately one-half gate fully open (Gates No. 7 through No. 10 open 20 cm (7.9 in)) to a setting equivalent to approximately three gates fully open, to meet the Plan 2012-prescribed flow in May in consideration of capacity restrictions at the hydropower plants. Gate No. 1 will remain at its typical setting of 20 cm (7.9 in) open which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike. The St. Marys Rapids flow will increase from ~85 m3/s to ~575 m3/s after the gate adjustments on Monday, May 6.
The MacArthur Lock reopened on April 25.
Water level changes over the month of April
Water supply conditions were near average in the Lake Superior basin and above average in the Lake Michigan-Huron basin in April.
- Lake Superior rose by 8 cm (3.1 in) last month which matches the seasonal long-term average pattern in April.
- Lake Michigan-Huron rose by 14 cm (5.5 in) last month, while the seasonal long-term average pattern is for Lake Michigan-Huron to rise by 11 cm (4.3 in) in April.
Water levels as of the beginning of May
- At the beginning of May, the lake-wide average water level of Lake Superior was 2 cm (0.8 in) below the seasonal long-term average (1918-2023) and 30 cm (11.8 in) below the level of a year ago.
- At the beginning of May, the lake-wide average water level of Lake Michigan-Huron was 6 cm (2.4 in) above the seasonal long-term average (1918-2023) and 11 cm (4.3 in) below the level of a year ago.
