Update on Lake Superior Outflow & Expected Conditions

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The International Lake Superior Board of Control, under authority granted to it by the International Joint Commission (IJC), has set the Lake Superior outflow to 3090 cubic metres per second (m3/s) for the month of September, effective September 3rd. The September outflow will be released by discharging about 2189 m3/s through the three hydropower plants and passing most of the remaining flow through the control structure at the head of the St. Marys Rapids. The gate setting of the control structure will be reduced to the equivalent of approximately six gates open tomorrow, September 3rd, achieved by setting 14 gates to a partially open setting of 80 centimetres (cm) each.

As a result, the flow and water levels in the St Marys Rapids are expected to decrease from those experienced last month, but will still remain relatively high throughout September. Anglers are therefore advised to continue to be cautious of the unusually high flows and levels in the rapids during September. There will be no change to the setting of Gate #1 which supplies water to the channel north of the Fishery Remedial Dike, but with the equivalent of 6 gates fully open in the main rapids, water may overtop the dike along the north side of the rapids.

The September flow of 3090 m3/s is 10 m3/s less than that prescribed by Plan 1977-A. The outflow of Lake Superior continues to be adjusted to reduce the risk of unusually high flows expected in the St. Marys Rapids this summer. The Board requested and received approval from the IJC to temporarily deviate from Lake Superior Regulation Plan 1977-A to allow for these adjustments.

The monthly mean water level of Lake Superior in August was 183.67 m. This is 14 cm above the long-term (1918-2013) August average and the highest August level since 1997.

This past month the net water supplies to Lake Superior were above average. The level of Lake Superior rose 1 cm last month, which is the average amount the lake rises in August. The Lake Superior level at the beginning-of-September is 15 cm above average, and 20 cm above the level recorded a year ago at this time. It is 48 cm above its chart datum level. The level of Lake Superior is expected to begin its seasonal decline during September.

The monthly mean water level of Lake Michigan-Huron in August was 176.48 m. This is 7 cm below the long-term (1918-2013) August average, but the highest August level since 1998.

The net water supplies to Lake Michigan-Huron were well above average in August. The level of Lake Michigan-Huron rose 4 cm this past month, while on average the lake declines by 4 cm in August. The level of Lake Michigan-Huron is 2 cm below its long-term average beginning-of-September level, but 42 cm higher than it was a year ago. Lake Michigan-Huron is now 50 cm above its chart datum level. The level of Lake Michigan-Huron is also expected to begin its seasonal decline in September.

Mr. Jaymie Gadal is the Board Member for Canada. Ms. Deborah Lee is the Alternate U.S. Board Member. For further information, please contact Mr. Jacob Bruxer, Canadian Regulation Representative, International Lake Superior Board of Control, by phone at (613) 938-5862 or by e-mail at Jacob.Bruxer@ec.gc.ca

Additional information can also be found at the Board’s homepage: http://ijc.org/en_/ilsbc or on Facebook at: https://www.facebook.com/InternationalLakeSuperiorBoardOfControl