THUNBDER BAY, ON --- June 2, 2015 --- 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 2640 cubic metres per second (m3/s) for the month of June, effective June 3rd. The June outflow is expected to exceed the combined capacities of the hydropower plants on the St. Marys River, which will be approximately 1974 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 will be increased to an equivalent of approximately four gates fully open in June. The gate change will be conducted in two stages to help facilitate flow measurements at the rapids. Gates #9 to #13 and #15 will be further opened tomorrow, Wednesday, June 3rd, and Gates #3 to #8 will be opened next Wednesday, June 10th. These 13 gates will each be opened to a setting of 71 cm each. Gate #16 will also be opened 5 cm tomorrow to facilitate sea lamprey trapping. These gate movements will primarily affect water conditions in the main rapids. There will be no change to the setting of Gate #1, which supplies a flow of about 15 m3/s to the channel north of the Fishery Remedial Dike, and Gates #2 and #14 will be closed. Anglers need to be cautious of the changing flows and water levels in the rapids on June 3rd and June 10th and the unusually high flows and levels that will be experienced thereafter.
The June outflow of 2640 m3/s is 160 m3/s less than that prescribed by Regulation Plan 2012. The Board expects to continue to adjust the outflow of Lake Superior in accordance with the approved deviation strategy 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. The Board expects to release flows greater than Plan 2012 in July and August, and less than Plan 2012 in September through November.
The monthly mean water level of Lake Superior in May was 183.53 m. This is 18 cm above the long-term (1918-2014) May average and the highest May level since 1997. The net water supplies to Lake Superior were above average in May. The level of Lake Superior rose 11 cm last month, while on average the lake rises 10 cm in May. The Lake Superior level at the beginning-of-June is 19 cm above average, 5 cm above the level recorded a year ago at this time, and 39 cm above its chart datum level.
The monthly mean water level of Lake Michigan-Huron in May was 176.59 m. This is 12 cm above the long-term (1918-2014) May average, and the highest May level since 1998. The net water supplies to Lake Michigan-Huron were approximately average in May. The level of Lake Michigan-Huron rose 8 cm last month, which is the average rise in May. The level of Lake Michigan-Huron is 14 cm above its long-term average beginning-of-June level, 31 cm higher than it was a year ago, and 64 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.