UPDATE ON LAKE SUPERIOR OUTFLOWS AND EXPECTED CONDITIONS - DECEMBER 2018
Following extremely wet conditions in October and relatively wet conditions in November, water levels of Lake Superior and Lake Michigan-Huron remain well above average. 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 fall and winter should active weather continue.
Lake Superior declined 6 cm overall last month and Lake Michigan-Huron declined 4 cm, which are both approximately average declines for November. At the beginning of December, Lake Superior is 28 cm above average (1918 – 2017) and equal to the level at this time last year. Lake Michigan-Huron is currently 49 cm above average, and 2 cm above last year’s beginning-of-December level. Both Lake Superior and Lake Michigan-Huron are expected to continue their seasonal declines in December.
In consideration of the continuing high water levels in the upper Great Lakes and to accommodate expected maintenance at the hydropower plants, the International Lake Superior Board of Control (Board) recently requested and received approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 this winter. All three hydropower plants will continue to be directed to flow at their maximum available capacity, but the total combined capacity is expected to be less than normal due to required maintenance activities in December and continuing into January. To offset the effects of these activities, over the winter months the Board will release more water through the control structure at the head of the St. Marys Rapids by maintaining a gate setting equivalent to two gates fully open instead of the typical winter setting equivalent to one-half gate open.
As a result, flows less than Plan 2012 are expected in December and January, while flows greater than Plan 2012 are expected later in winter as hydropower maintenance is completed and capacity returns to normal. The total amount of water released through the St. Marys River this winter will be approximately equal to releases called for by Plan 2012, and the net effects on the water levels of Lake Superior and Lake Michigan-Huron are expected to be minimal by spring.
The Board expects the total flow in December to be 2,280 m3/s, which is 130 m3/s less than that prescribed by Plan 2012. Actual outflows may vary depending on hydrologic and ice conditions, as well as maintenance activities at the hydropower plants on the St. Marys River. The equivalent two-gates open setting will be achieved by maintaining Gates #2 through #16 at a setting of 26 cm open. The gates were lowered to this setting in stages over 3-4 December to allow for a gradual reduction in the St. Marys Rapids flows and water levels prior to winter. 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 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 fall and winter.