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4 Olympic-sized swimming pools of water flying through this dam every second, and into the St. Lawrence River.
OUT OF THIS WORLD | Earth, Space and Everything In-Between - a daily journey through weather, space and science with meteorologist/science writer Scott Sutherland

Largest Lake Ontario water discharge ever is underway


Scott Sutherland
Meteorologist/Science Writer

Wednesday, June 14, 2017, 3:28 PM - With Lake Ontario water levels at their highest in a century, officials have now begun the largest outflow from the lake in history, to drain off the excess into the St. Lawrence seaway.

Some are saying it's about time. To others, it's too late, or even too much.

Lake Ontario is now into its second record-setting month, after a very wet spring caused water levels to slowly creep into the danger zone for lakeside communities.

Up until Wednesday, outflow from Cornwall's Moses-Saunders Power Dam - the drainage point at the eastern end of Lake Ontario - had already risen from roughly 7,000 cubic metres per second earlier this year to 10,200 cubic metres per second. For reference, that's over four Olympic-sized swimming pools worth of water passing through the dam, every second.

At just past noon on Wednesday, June 14, 2017, that outflow rate was increased to 10,400 cubic metres per second, apparently the highest outflow rate for the dam, ever.

The reason that so much water had been held back in the lake, in the first place, was due to what was occurring downstream. With communities along the St. Lawrence River, including Montreal, flooded or at risk of flooding due to these same rainfall events, allowing too much water to drain from the lake at once would simply turn a bad situation even worse.

Given the relative volumes of the waterways, lowering Lake Ontario by just 1 centimetre would cause Lac Saint-Louis, at the convergence of the St. Lawrence and Ottawa rivers, just west of Montreal, to rise by more than a metre. The discharge rate wouldn't happen all at once, but given the state of these waterways up until recently, the International Lake Ontario-St. Lawrence River Board - part of the International Joint Commission, a Canada-US cross border agency that manages water levels in the Great Lakes and St Lawrence Seaway - determined that the risk was too great.


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As of the end of May, the Great Lakes Environmental Research Laboratory (GLERL) logged water levels at 75.8 metres for the month, more than a metre above the long-term average for the lake, and roughly 15 centimetres higher than the previous record, set back in May of 1973. This was enough to close parts of Toronto Island to the public, and also enough for multiple flood watches and warnings to be issued, not only during times of further rainfall, but also simply due to wind-driven waves inundating shorelines.

Among those impacted are people living along the lake shore in New York State, which prompted local politicians, and even New York Governor Andrew Cuomo, to survey the damage sustained in these communities, and even witness the installation of a temporary dam to keep back flood waters.

According to Governor Cuomo and NY congressmen Chris Collins and John Katko, this increased discharge is coming far too late. Collins and Katko had already issued statements calling for relief, even going to far as to ask President Donald Trump to withdraw the United States from the International Joint Commission, over a new Plan 2014 that came into effect, earlier this year, to regulate discharge from the Cornwall dam.

"I think they pulled the trigger too late," Cuomo said, according to CityNews, referring to this decision to increase flows. "They got behind, and now we have a real problem."

In a statement back in May, however, the International Lake Ontario-St. Lawrence River Board said that even under the old plan, water levels would have still been at the same level, given the unexpected amount of rainfall that has fallen so far this year.


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While even the new record flow rate from the Moses-Saunders Power Dam will take some time to drain off all the excess water from Lake Ontario, ships travelling upstream into the lake have already been dealing with a stronger river current, and this promises to make things worse for them.

According to The Globe and Mail, Wallace James, captain of the 225-metre Algoma Strongfield, described the river conditions as "terrible," saying that the high water and strong currents around the locks near Montreal have made navigating the St. Lawrence Seaway more challenging.

"[The current] almost turned us around," Mr. James told The Globe and Mail.

Lake levels have already dropped by around 5 centimetres in the first half of June, according to GLERL, due to the relatively warmer, drier weather over the region, and the already increased flow rates. This was not been, however, enough to lower water levels back into the safety zone.

With water levels along the St. Lawrence and its tributaries having lowered to safer levels, the flow from Lake Ontario can now be increased. The new discharge rate is expected to last for 72 hours, as a trial period to see how the river system responds to the added volume and increased river current. Even at that increased rate, and the roughly 2.7 billion cubic metres of water it removes from Lake Ontario, due to continued inflow into the lake, this is only expected to lower the lake level by about 1 centimetre every week.

Sources: Globe and Mail | CityNews | GLERL | With files from The Weather Network

Watch Below: Record-high levels on Lake Ontario finally being relieved, watch for details

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