Update on Lake Superior Outflows and Expected Conditions - February 2020
Lake Superior and Lake Michigan-Huron water levels are above record-highs for this time of year as wet conditions persisted across the upper Great Lakes basin in January.
With all of the Great Lakes near or above record-highs for this time of year, there is an exceptional volume of water in the system. Water levels are expected to remain high over at least the next several months and further record-highs are possible if wet conditions continue in 2020. As a result, there will continue to be a significantly increased risk of shoreline erosion, lakeshore flooding and coastal damages over the next several weeks and into the spring. The International Lake Superior Board of Control (Board) advises all those that may be affected to prepare for potentially severe coastal impacts, especially during periods of strong winds and high waves.
January is typically a month when water levels continue their seasonal decline. Lake Superior declined 6 cm over the course of the month, while on average the water level declines 7 cm in January. At the beginning of February, Lake Superior is 1 cm above the record-high beginning-of-month level set in 1986. The level is currently 38 cm above average (1918 – 2019) and 10 cm above its level of a year ago.
Lake Michigan-Huron rose 2 cm over the course of the month, while on average the water level declines 2 cm in January. Lake Michigan-Huron is currently 15 cm above the record-high beginning-of-month level set in 1987. The level is 99 cm above average, and 48 cm above last year’s beginning-of-February level.
In early December, the Board received approval from the International Joint Commission to continue to deviate from Lake Superior Regulation Plan 2012 through this winter. A small amount of additional flow will be released through the St. Marys Rapids this winter to offset expected and potential unscheduled reductions in flows at the hydropower plants that often occur in challenging winter conditions. This will be achieved by maintaining a gate setting equivalent to one gate fully open over the winter months instead of the typical winter setting equivalent to one-half gate open. Gates are typically maintained at a constant setting in winter to avoid issues with ice, including the potential for ice jams in the St. Marys River. Additionally, the higher rapids flows from December through April provide an increase in wetted habitat for fish that have already spawned in the rapids or that may over-winter in this area. It is anticipated that this deviation will have a minimal impact on Lake Superior and Lake Michigan-Huron water levels.
In consideration of the above, the Board expects the total outflow to be 2410 m3/s in February, which is 20 m3/s more than that prescribed by Lake Superior Regulation Plan 2012. Actual outflows may vary depending on hydrologic and ice conditions, as well as maintenance activities or other unexpected outages at the hydropower plants on the St. Marys River. Gates #5 through #12 will be maintained at a setting of 26 cm open (equivalent to one gate fully open) through the winter months. 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.