Lake Ontario sets new outflow record in 2019

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By Shawna O'Neill
Lake Ontario sets new outflow record in 2019
Cornwall's Moses-Saunders Dam during a summer month (Nick Seebruch/ Seaway News).

ONTARIO – Lake Ontario saw record breaking outflows this year with an average outflow from June through December of 9,560 m3/s (337,600 cfs), the highest flow ever released over this period of time since the start of records in 1900.

Beginning Tuesday, Dec. 31, outflows will be increased as much as possible until ice formation resumes on the St. Lawrence River, according to a press release from the International Lake Ontario – St. Lawrence River Board. Rates of flow are expected to increase in the New Year.

“A flow increase from 8,850 m3/s (312,500 cfs) to over 10,000 m3/s (353,000 cfs) may be possible in the coming days, with the exact amount depending on ice and water level conditions in the St. Lawrence River. Water levels downstream of the Moses-Saunders Dam, including around the Montreal area, are expected to rise, but will be monitored closely to ensure they are maintained below flood levels,” read a statement in the press release.

Lake Ontario outflows first set record rates in June as water levels of Lake Ontario reached a new daily record high following immense water levels and flows occurring across the Great Lakes and Ottawa River basins during the spring.

“High outflows from Lake Ontario continued through the summer, fall and early winter, resulting in more water released from Lake Ontario during the last seven months of 2019 than in any year since the start of records in 1900,” read a statement in the press release.

Inflows to Lake Ontario have also remained high, recorded at 75.00 m (246.06 ft.) on Sunday, Dec. 29, which is well above the seasonal average. High inflows are expected to continue into 2020.

Over the past several weeks, outflows were set at 200 m3/s (7,100 cfs) above the Plan 2014 maximum L-limit, which is the highest outflow that can be released from Lake Ontario. Safe navigation standards were maintained and the constraint outlined will no longer apply as of Tuesday, Dec. 31.

“The International Lake Ontario – St. Lawrence River Board, under authority granted to it by the International Joint Commission, will continue to deviate from Plan 2014 and will look for any and all opportunities to remove additional water from Lake Ontario prior to the spring,” read a statement in the press release, maintaining that staff monitor conditions on an ongoing basis.

Information on hydrologic conditions, water levels and outflows, including graphics and photos, are available on the Board’s website and posted to the Board’s Facebook page here. More detailed information on the process is available here.

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