Ottawa River peaks, but could take weeks to return to normal

The historically high water levels along the Ottawa River appear to have peaked Monday — but it may be weeks before those levels return to seasonal norms.

No significant rain, warmer weather forecast in next week

Water levels at many points on the Ottawa River reached their peak on May 8, 2017, according to the authority that manages the river's flow. (Andrew Lee/CBC)

The historically high water levels along the Ottawa River peaked Monday and are now expected to slowly recede, according to the group managing the river basin — but it may be weeks before those levels return to seasonal norms.

The Ottawa River Regulation Secretariat forecast on Monday afternoon said that peak water levels occurred Monday at the Hull Marina in Gatineau, as well as in Thurso, Que. and Hawkesbury, Ont.

The South Nation Conservation Authority confirmed Tuesday that peak levels were reached along the Ottawa River from Mattawa to Hawkesbury.

The flood warning for the Mississippi Valley watershed, however, will remain in place until Friday, according to the Mississippi Valley Conservation Authority.

Levels on Dalhousie Lake appear to have stabilized and should start to decline Thursday, but there is some rain in the forecast for the weekend which could lead cause it them to rise again.

"Simply put, we have nowhere left to put any additional water," water management supervisor Gord Mountenay said in a news release Tuesday.

Flows on the upper Clyde River peaked and have been dropping since yesterday. The lower part of the river peaked Monday night but had not started to decline as of Tuesday. Water levels on the Fall River have also stabilized, the authority confirmed.

The one exception is Mississippi Lake, where water levels are expected to climb another 10 to 20 centimetres before levelling off Friday, the authority said. 

Levels at Britannia in Ottawa reached their high point Sunday, the Ottawa River Regulation Secretariat said.

In Quebec, Public Security Minister Martin Coiteux said Tuesday water levels in the province have peaked and should begin to recede slowly. It will likely be the end of May before water levels are back to normal, he said. 

The updates are welcome news for areas hit hard by flooding, like Gatineau's Pointe-Gatineau neighbourhood and Ottawa's Constance Bay.

Warmer weather and a break from significant rain are helping to provide the timely relief, said Michael Sarich, the senior water resources engineer with the secretariat.

But water levels will continue to be high over the next couple of days before starting to drop, he added.

"We're going to be literally weeks with levels that are above normal. Probably it's going to be a week to 10 days until we get down to even to what would be considered a high spring level," Sarich said.

Gatineau water levels 3 metres above normal

The May mean water level for the Ottawa River at Britannia is about 58.78 metres above sea level. On Monday the water level was forecast to be about 60.45 metres, or 1.67 metres higher than normal.

Similarly, the mean water level in May at the Hull Marina in Gatineau is 42.18 metres; on Monday it was expected to peak at 45.18 metres, or about three metres higher than normal.

Sarich doesn't know exactly when water levels will recede enough for flooded neighbourhoods to return to normalcy, but said it won't take much of a drop in recently-hit areas before they notice a significant retreat from their homes.

"A lot of the questioning people have is how long is it going to take to go down. So our focus is going to change from forecasting when the peak is to the rate of recession," he said.

Rain showers possible, but not significant

The wild card, of course, is the rain.

After an April that had twice the normal rainfall and more rain in the first week of May than the normal average for the month, all eyes are on the weather forecast.

As of Monday evening, Environment Canada's forecast called for some flurries on Tuesday and then mostly sunny skies on Wednesday through Friday, followed by cloudy skies on the weekend and a chance of showers.

It's a similar story in many surrounding regions that feed water into the Ottawa River basin.

Ian Black, CBC Ottawa's climatologist, said the rain that's expected is nothing significant.

"This is good news," he said.

David Phillips, the senior climatologist for Environment and Climate Change Canada, agrees.

"At first blush, if you look at the forecast, it looks more depressing," said Phillips. "But if you dig down deeper you are not dealing with major weather systems, so [there won't be] a lot of accumulation."

Rainfall forecast murky after this week

Beyond that, the forecast becomes more difficult to predict, says Phillips.

Black and Phillips both say the temperature for the rest of the month is expected to be warmer, which will also help, but rainfall predictions are harder to pin down.

"Precipitation is a real crap shoot," said Phillips. "It's hard to get tomorrow and next day right, let alone next week."

Sarich said any length of time without significant rain in the region will help water levels drop — and that's something the region hasn't had in the past few weeks.

"[It was] one event after another, just one kind of building on another, not allowing the river system time to decrease," he said.