UPDATE ON LAKE SUPERIOR OUTFLOWS AND EXPECTED CONDITIONS - AUGUST 2018
At the beginning of August, Lake Superior is 13 cm above average (1918 – 2017), but 9 cm below the level at this time last year. Lake Michigan-Huron is currently 39 cm above average, but 4 cm below last year’s beginning-of-August level. The level of Lake Superior is expected to remain relatively stable in August, and Lake Michigan-Huron is expected to continue its seasonal decline.
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 and fall 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. The Board continues 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 continuing through the summer and fall.
Accordingly, the Board, under authority granted to it by the IJC, has set the Lake Superior outflow to 2,760 cubic metres per second (m3/s) for the month of August, which is 150 m3/s more than that prescribed by Regulation Plan 2012. The additional flow offsets the reductions that occurred this past winter, and August will be the final month requiring increased outflow above plan flow to account for the winter hydropower outage. Actual outflows may vary depending on hydrologic conditions, as well as maintenance activities at the hydropower plants on the St. Marys River.
Adjustments to the gate setting at the Compensating Works are expected to continue in August as the construction project to automate four of the gates continues. On 7 August 2018, each of Gates #2 through #11 will be raised to a setting of 140 cm open. As the second phase of the construction project is scheduled to begin next week, Gates #12 through #15 will be closed on 7 August. 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 will remain set to 5 cm open to facilitate sea lamprey trapping.
The average St. Marys Rapids flow is expected to be approximately 870 m3/s in August, which is equivalent to approximately six gates fully open. 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 August. Furthermore, some flooding of low-lying areas of Whitefish Island is expected as the gates are opened further and flows increase. As a result, some recreational trails and features in these areas will likely be inundated and may sustain damage. Users are encouraged to use extreme caution.
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, the Board advises all those that may be impacted to prepare for the above-average water levels, should they occur this summer and fall.