In the declaration, the mayors office says the water levels pose "an ongoing threat" to property, health and safety of nearby residents.
“There’s always a safety factor in any design. The law on dam safety makes us define a certain level where we guarantee the dam and we have reached that level right now,” he said. “We’re entering an unknown zone, so we have to wait and see over the next few days.”
Environment Canada has issued a special weather statement forecasting up to 35 millimetres of rain in the capital region by Saturday.
“Police are using all the means at their disposal to ensure people’s safety,” said the Sûreté du Québec on Twitter. “We ask residents of the areas affected by forced evacuations to co-operate with the authorities.”
The mayors office says the combination of already high water levels and further rainfall give rise to a situation that "constitutes a danger of major proportions that could result in serious harm."
Watson says about 400 soldiers with the Canadian Armed Forces are expected to assist with flooding efforts in the city.
At a press conference Thursday evening, Public Security Minister Geneviève Guilbault confirmed the evacuation of 23 principal residences and 38 cottages in Grenville-sur-la-Rouge.
He says the declaration will help city crews, volunteers and residents in affected areas, which are mainly in outlying suburbs.
“We’re confident today, because we’ve done frequent security analysis and this specific dam was designed for a flood once every thousand years,” he said.
Ce matin, Environement Canada a lancé une alerte météorologique spéciale, annoncant beaucoup de pluie. Afin de venir en aide au personnel de la ville, aux bénévoles et aux résidents dans les régions affectées, jai déclaré une situation durgence dans la ville dOttawa. pic.twitter.com/qDtCktCmxc
The City of Ottawa has declared a state of emergency as river levels continue to rise, threatening to surpass those reached when flooding devastated some neighbourhoods two years ago.
We can no longer do it alone.- Ottawa Mayor Jim WatsonEnvironment Canada has issued a special weather statement predicting up to 35 millimetres of rain by Saturday morning, and river authorities are now forecasting that in some areas, the water could rise up to 11 centimetres above peak levels reached in May 2017.
Watson said he's also asked for help from the Canadian Armed Forces, and has been told 400 troops will be deployed to key areas.
"We can no longer do it alone," Watson said. "We are now beyond our city's capacity, and that is why we have called in the Armed Forces."
City manager Steve Kanellakos said the city felt prepared until the latest forecast from Environment Canada.
"I can say with certainty that the flooding situation has changed almost in the blink of an eye," he said.
"I cannot tell you how long we will be in this state of emergency. If the flooding is severe there could be weeks of recovery operations."
Premier Doug Ford has also pledged the provincial government's support, and will visit the region on Friday.
The dam failure alert will be maintained until 11:45 p.m. Thursday, according to the Quebec public security website.
While levels on the Rideau River have stabilized, the Ottawa River is expected to rise about half a metre from Constance Bay to east of Cumberland by the weekend, according to South Nation Conservation.
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