More rain pushing Ottawa River levels back up

Heavy rains could give flood-weary homeowners along the Ottawa River an unfortunate sense of déjà vu this weekend, as waters climb again to levels near or above last week's peaks.

The Ottawa River Regulation Planning Board issued new numbers on Wednesday afternoon that show flood waters are set to climb again this weekend.

Starting Thursday, the region could see between 20 and 40 millimetres of rain and that is driving water levels back up. That rain is expected to fall across the basin and flow into a river that is already nearing record highs.

Michael Sarich, a senior water resources engineer with the board, said the river forecast they issued assumes the rain will be on the high side of forecasts, because they have to be cautious.

"We've got to be realistic on the potential of what can be happening in the system, particularly because we're right at the peak of snowmelt runoff with our northern reservoirs," he said.

Those reservoirs held water back during earlier flooding, but Sarich said they can't hold back the water anymore and so water from up north will come along with the increased rains.

"There's just a finite amount of storage available and most of that storage was used to try and reduce, to the utmost, the amount of the peak that occurred last week," he said.

He said if rain keeps falling it could push levels to a second peak, which the board had previously predicted wouldn't happen this year.

He said levels in Pembroke, Ont., and other northern sections of the river would be particularly high in the next few days, possibly reaching heights not seen in decades.

By the numbers

The board said at 5 p.m. Wednesday the water level in Pembroke was at 113.53 metres above sea level, up six centimetres from Tuesday. The board believes the river will peak there on Friday at a height of 113.75 metres, breaching a historic record set in 1960.

Lac Coulonge is at 108.90 metres on Wednesday, up ten centimetres from Tuesday and is now predicted to rise to 109.30 metres on Saturday, a second peak for that section of the river.

Arnprior, Ont., is at 76 metres, but it's forecasted to climb another 20 centimetres, bringing it within 11 centimetres of the peak it hit last week.

Britannia in west Ottawa is at 60.43 metres, but is also set to rise to hit 60.70 metres by Sunday, which will be the same height it hit during last week's record highs and well above 2017 levels.

The Hull Marina in Gatineau is at 44.63 metres, but could climb 27 centimetres due to the rain by Monday.

Thurso, Que., is at 43.16 metres, but is now predicted to climb to 43.50 metres by Monday.

And Hawkesbury, Ont., is at 42.36 metres, but is set to climb to 42.60 by Monday.

The next update is expected at 5 p.m. Thursday, May 9.

All forecasts are approximate and subject to change based on the weather and other factors.

All records are based on data from the planning board, which goes back as far as the 1930s in some areas.