UPDATE ON LAKE SUPERIOR OUTFLOWS AND EXPECTED CONDITIONS - JUNE 2018
Lake Superior began its seasonal rise in May, but rose just 5 cm as dry conditions persisted in the basin for a third straight month. Conditions were wetter downstream, and Lake Michigan-Huron rose 11 cm last month. At the beginning of June, Lake Superior is 10 cm above average (1918 – 2017), but 12 cm below the level at this time last year. Lake Michigan-Huron is currently 44 cm above average, 10 cm above last year’s beginning-of-June level and the highest since 1997. The seasonal water level rise is expected to continue on both lakes in June.
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 spring and summer should active weather continue.
The Board recently 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 2,560 cubic metres per second (m3/s) for the month of June, which is 320 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 was adjusted to the equivalent of two gates fully open (Gates #2 through #15 open 26 cm each) on 7-8 May. There was 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 gate setting will be adjusted slightly in June, by raising Gates #7 through #10 to a setting of 33 cm open on Monday, 4 June. The average St. Marys Rapids flow is expected to be approximately 320 m3/s. 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 June.
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.