The International Lake Superior Board of Control.
Conditions in the Lake Superior and Lake Michigan-Huron basins were near average last month and the seasonal water level rise continued on both lakes. At the beginning of July, Lake Superior is 11 cm above average (1918 – 2017), but 14 cm below the level at this time last year.
Lake Michigan-Huron is currently 45 cm above average, 4 cm above last year’s beginning-of-July level, and the highest since 1997. The seasonal water level rise is expected to continue on both lakes in July.
The above-average levels coupled with strong winds and waves continue to result in shoreline erosion and coastal damages across the upper Great Lakes system. Additional shoreline erosion and coastal damages may occur this summer should active weather continue.
The Board obtained approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 from May through November 2018 in a manner similar to that employed in the past three years, which were also marked by high lake levels and outflows.
Over the next several months, the Board expects to adjust the gate settings at the Compensating Works and release flows greater than those prescribed by Regulation Plan 2012 in order to offset the effects of reductions in hydropower flows due to maintenance activities that occurred this past winter and that are expected to continue through the summer and fall.
Accordingly, the Board, under authority granted to it by the IJC, has set the Lake Superior outflow to 2,800 cubic metres per second (m3/s) for the month of July, which is 390 m3/s more than that prescribed by Regulation Plan 2012. Actual outflows may vary depending on hydrologic conditions, as well as maintenance activities at the hydropower plants on the St. Marys River.
The gate setting at the Compensating Works will be increased on 9 July 2018, from the current setting equivalent to approximately two gates fully open to a setting equivalent to approximately three gates fully open. This will be achieved by partially opening each of Gates #2 through #15 to a setting of 53 cm open.
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. Gate #16 was set to 5 cm open to facilitate sea lamprey trapping. The average St. Marys Rapids flow is expected to be approximately 463 m3/s in July.
Note that beginning in late July, the gate setting of the control structure will be adjusted to facilitate a construction project to automate Gates #11-14. Adjustments to the gate setting are expected to continue in August as the gate automation project proceeds. Anglers and other users of the St. Marys Rapids need to be cautious of the changing flows and water levels that will be experienced in the rapids in July and August.
The Board stresses that hydrologic conditions are the primary driver of water level fluctuations. Water levels of the Great Lakes cannot be fully controlled through regulation of outflows, nor can regulation completely eliminate the risk of extreme water levels from occurring during periods of severe weather and water supply conditions.
It is not possible to accurately predict such conditions weeks in advance, but given the current levels of the lakes and the possibility that wet conditions may continue, the Board advises all those that may be impacted to prepare for the possibility of high water levels, should they occur this summer and fall.