Wet conditions continued across the upper Great Lakes basin in May.
Lake Superior has exceeded record high water levels for this time of year and water levels of Lake Michigan-Huron are also now approaching record high levels.
The Board advises all those that may be affected to prepare for coastal impacts similar or potentially worse than those that have occurred during the last few years, as the high levels coupled with potentially strong winds and waves are likely to continue to result in an increased risk of shoreline erosion and coastal damages across the upper Great Lakes system.
Lake Superior water levels increased by 13 cm (5 in) last month, while the average water level rise in May is 10 cm (4 in).
At the beginning of June, Lake Superior is 8 cm (3 in) above the record high beginning of month level set in 1986. The level is currently 41 cm (16 in) above average (1918 – 2018), and 28 cm (11 in) above its level of a year ago. Lake Michigan-Huron rose 18 cm (7 in) in May, which is much higher than the average water level climb of 8 cm (3 in) in May. Lake Michigan-Huron is currently 5 cm (2 in) below the record high beginning of month level set in 1986. The level is 75 cm (30 in) above average, and 29 cm (11 in) above last year’s beginning-of-June level. Lakes Superior and Michigan-Huron are expected to continue their seasonal rises in June.
The International Lake Superior Board of Control (Board) expects the total flow in June to be 2,860 cms (101.0 tcfs), which is the amount prescribed by Lake Superior 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. From 3-6 June, the gate setting at the Compensating Works will be temporarily adjusted to facilitate underwater inspections of the International Bridge piers.
Following these inspections, the gates will be set to the equivalent of six gates fully open. This will be achieved by raising Gate #10 to a setting of 71 cm (28 in) open, and Gates #11 through #14 to a setting of 254 cm (100 in) open. There will be no change to the setting of Gate #1, which supplies a flow of about 15 cms (530 cfs) to the channel north of the Fishery Remedial Dike. Gates #2 through #9 and #15 will return to their current setting of 26 cm (10 in) open. Gate #16 will be set to 5 cm (2 in) open to facilitate sea lamprey trapping.
The average St. Marys Rapids flow in June is expected to be approximately 953 cms (33.7 tcfs). 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 received approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 through November 2019. This deviation strategy is similar to those employed over the past four years, which were also marked by reduced hydropower capacity and high lake levels and outflows.
Over the next several months, the Board expects to adjust the gate settings at the Compensating Works in order to offset the effects of maintenance activities at the hydropower plants that are expected to continue through the summer and fall.
Over this time period, the total amount of water released through the St. Marys River will be approximately equal to the flow prescribed by Plan 2012 and the deviation strategy will have almost no impact on the water levels of Lake Superior and Lake Michigan-Huron, yet will provide benefits to the St. Marys Rapids directly downstream of the Compensating Works.