Update on Lake Superior Outflows and 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 2600 cubic metres per second (m3/s) for the month of June, effective June 2nd. The June outflow is 190 m3/s more than that prescribed by Regulation Plan 2012.

The Board recently requested and received approval from the IJC to temporarily deviate from Plan 2012. The outflow of Lake Superior will be adjusted over the next several months to accommodate expected maintenance at the hydropower plants, and reduce the potential for adverse consequences of high and fluctuating flows and water levels in the St. Marys Rapids. To maintain more consistent flow conditions in the rapids and minimize the effects on both Lake Superior and Lake Michigan-Huron water levels, the Board expects that flows greater than those prescribed by Plan 2012 will be released in June through August, and that these flow increases will be offset by releasing flows less than Plan 2012 in September through November.

Outside of the rapids area, the effects of these flow adjustments will be small. Differences in lake levels are expected to be less than 1 cm on both Lake Superior and Lake Michigan-Huron in any given month, and cumulative differences are expected to be negligible by the end of November.

The June outflow of 2600 m3/s is expected to exceed the combined capacities of the hydropower plants on the St. Marys River, which will be approximately 2040 m3/s in June, and the excess flow will be released through the control structure at the head of the St. Marys Rapids. The gate setting of the control structure for the month of June will be maintained at the current setting equivalent to three gates open.

The net water supplies to Lake Superior were below average in May. The level of Lake Superior rose 3 cm last month, while on average the lake rises 10 cm in May. The Lake Superior level at the beginning-of-June is 13 cm above average, 6 cm below the level recorded a year ago at this time, and 33 cm above its chart datum level.

The net water supplies to Lake Michigan-Huron were also below average in May. The level of Lake Michigan-Huron rose 3 cm last month, while on average the lake rises 8 cm in May. The level of Lake Michigan-Huron is 33 cm above its long-term average beginning-of-June level, 19 cm higher than it was a year ago, and 83 cm above its chart datum level.

The levels of Lake Superior and Lake Michigan-Huron are both expected to continue their seasonal rise in June.

Mr. Jaymie Gadal is the Board Member for Canada. Mr. Stephen Durrett is the 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 [email protected]

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

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