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Lake Ontario maximum outflows continue, as water levels remain high


Fri, Feb 2nd 2018 03:50 pm
The International Joint Commission announced this week that while several months of maximizing outflows has dropped Lake Ontario at an unprecedented rate and to well below the record peak set at the end of May 2017, water levels remain relatively high for this time of year following a cold and wet start to winter. As a result, IJC said that outflows will continue to be maximized in response while making intermittent and temporary reductions to manage challenging ice conditions in several areas of the St. Lawrence River.
Following last year's record-wet spring and despite several months of continuing wet weather thereafter, at the start of January, Lake Ontario's level had fallen 1.12 m (3.7 feet) below its 2017 peak, the largest drop ever recorded from June through the end of December. Extreme cold and snow near the start of 2018 followed by milder temperatures, heavy rain and snowmelt more recently has Lake Ontario's level rising once again, reaching a level of 74.91 m (245.77 feet) as of Jan. 30.
According to IJC's International Lake Ontario-St. Lawrence River Board of Control, this is 31 cm (12 inches) above average, although still 28 cm (11.0 inches) lower than the record-high for this time of year set in 1952. Lake levels have been higher at this time of the year 16 times since 1918 (when reliable records began), most recently in 2012.
In response to the high water levels, the board is still setting outflows from Lake Ontario at the highest rates while managing ice conditions. Recent reductions were required to promote the formation of a solid, stable ice cover in critical sections of the St. Lawrence River, thereafter allowing increased outflow under the ice.
Without stable ice cover, the risk of ice jams is high. These ice jams can clog the river, forcing sudden, significant flow reductions and an increased risk of localized flooding. Outflows are currently 1,730 cubic meters per second above average, 180 cubic meters per second above the previous record-high flow in 1986 and are expected to continue to increase gradually as ice and weather conditions allow.
While Lake Ontario remains well above average, historically, winter water levels have not provided an accurate indicator of the peak later in spring. Hydrologic conditions have a much greater influence and, while impossible to predict, it is unlikely last spring's combination of exceptional rainfall, snowmelt and rapidly rising inflows from Lake Erie will all repeat themselves and lead to extremely high water levels again this year.
Nonetheless, extreme conditions may occur in any given year, and when they do, the risk of extreme water levels cannot be substantially reduced through regulation of outflows. As a result, Lake Ontario shoreline property owners, businesses, and local government officials are advised to always be prepared for the full range of water levels that could occur on Lake Ontario, both highs and lows, now and in the future.
The board, in conjunction with its staff, continues to monitor and reassess conditions on an ongoing basis. Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the board's Facebook page at https://www.facebook.com/InternationalLakeOntarioStLawrenceRiverBoard.

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