Ottawa River hydro dams doing their job, says Quebec environment minister

Hydroelectric dams in the Ottawa River basin are dealing with historic water levels, but the structures are safe and up to the challenge, says Quebec Environment Minister David Heurtel.

"We're doing the utmost to try to slow the flow of water coming, and it's massive. We're talking about historic levels of water — we've never seen anything like this in over 55 years in Quebec," Heurtel said Monday.

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He said the nine dams in the Ottawa River watershed, upstream from the island of Montreal and Île Jésus, are holding back the equivalent flow 2,500 cubic metres a second. 

(Picture the amount of water in an Olympic-sized swimming pool: that's 2,500 cubic metres. Per second.)

"We'd be over 11,000 cubic metres per second," if the dams weren't holding back water, he said.

Without that effort, he said, the water level would be half a metre higher on the Lake of Two Mountains.

Communities on both sides of the lake at the confluence of the Ottawa and St. Lawrence rivers, such as Hudson and Oka, are experiencing some of the worst flooding in the province.

However, Heurtel said the water level in the Lake of Two Mountains has only gone up five centimetres since Sunday, thanks to water flow management on the dams. Prior to Sunday, the water level shot up by a metre.

Heurtel said there are early indications that the volume of the flow is slowing, after peaking at 9,000 cubic metres per second. He noted it had dropped to 8,900 cubic metres per second by early Monday.

Aim to minimize impact: Hydro

Hydro-Québec spokesperson Serge Abergel told CBC Monday that the process of regulating water volumes through the nine dams is managed with an eye on minimizing the impact on communities downstream.

"Nothing is taken lightly here. We make simulations months in advance, weeks in advance — and we determine our actions in accordance with what will have the lesser impact on residents along the river," Abergel said.

'Our dams are made to withstand flows of water that you see once every 10,000 years. Although this is big, this is not one of those. We have lots of capacity left.' - Hydro-Québec spokesperson Serge Abergel

One Ottawa River dam that many are watching is the Carillon Generating Station that spans the river between Carillon, Que., and Pointe-Fortune, Ont.

The 55-year-old dam is about 19 kilometres upstream from Rigaud, Que., which has been hard hit by flooding this spring.

Abergel explained that the Carillon dam is a run-of-the-river installation, meaning it has no reservoir and was never built to retain water. Instead, the dam was built to regulate water flow.

"We prevent peaks and lows and try to make it as even as possible, and that's what Carillon is doing," Abergel said.

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The volume of water passing through the dam reached 9,000 cubic metres per second recently — nearly twice the 5,000 cubic metres per second that's normal for this time of year.

That had many worried homeowners downstream fretting on social media about the dam's structural integrity.

However, Abergel said there is no reason for concern.

"Our dams are made to withstand flows of water that you see once every 10,000 years," he said. "This is not one of those. We have lots of capacity left."

"We're following it closely, our experts are doing regular inspections and everything is looking very good."​

Balancing act

Another dam that affects water levels in the Montreal area is the Moses-Saunders Power Dam located on the St. Lawrence River at Cornwall, Ont.

The body responsible for controlling the dam's outflow, the International Lake Ontario–St. Lawrence River Board, keeps a close eye on water levels in the Ottawa River as it calculates how much water it can let through from the Lake Ontario side. 

The dam was opened Monday to help reduce high water levels in Lake Ontario, which could mean a slight elevation in water levels downstream in the St. Lawrence River, notably in Lake Saint-Louis, west of Montreal.

Water levels are high in Lake Saint-Louis, but the board said the release from the Moses-Saunders dam won't cause significant flooding, if any.

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