UPDATE ON LAKE SUPERIOR OUTFLOWS AND EXPECTED CONDITIONS - September 2018
At the beginning of September, Lake Superior is 14 cm above average (1918 – 2017), but 11 cm below the level at this time last year. Lake Michigan-Huron is currently 43 cm above average, and at the same level as last year’s beginning-of-September level. Lake Superior rose 2 cm last month, while on average Lake Superior rises 1 cm in August. Lake Michigan-Huron remained stable in August, while on average it declines 4 cm. The level of Lake Superior is expected to remain relatively stable in September, 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 International Lake Superior Board of Control (Board), under authority granted to it by the International Joint Commission (IJC), has set the Lake Superior outflow to 2,600 cubic metres per second (m3/s) for the month of September, which is as 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.
Adjustments to the gate setting at the Compensating Works are expected to continue in early-September as the construction project to automate four of the gates comes to completion. On 4 and 5 September 2018, each of Gates #2 through #16 will be lowered from the current setting (91 cm open) to a setting of 81 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.
The average St. Marys Rapids flow is expected to be approximately 901 m3/s in September, 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 September. Furthermore, some flooding of low-lying areas of Whitefish Island is expected to continue this month and 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 continue this summer and fall.