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City of Ottawa officials say they are preparing to call for voluntary evacuations of homes at risk of flooding, particularly in Constance Bay in the west end, as Ottawa River levels are now projected to rise about half a metre above their peak during the 2017 floods.

The update comes a day after Ottawa Mayor Jim Watson declared a state of emergency due to forecasts of heavy rainfall, melting snow and rapidly rising water levels, and hours after Canadian military troops arrived in the national capital to help affected residents.

“The situation is changing very quickly on the ground,” Ottawa city manager Steve Kanellakos said during a press conference at city hall on Friday afternoon.

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On Thursday, the city acted on forecasts that the river would peak at a level about 11 centimetres higher than the 2017 peak. The municipality and the Ottawa River Regulation Planning Board now expect the peak in Britannia on Monday to be 46 centimetres higher than 2017 levels; in Gatineau, they predict the peak on Tuesday to be 50 centimetres higher than in 2017.

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Between Friday and early next week, officials expect the waters in Britannia to rise by 63 centimetres, and by 84 centimetres in Gatineau.

WATCH: Ottawa’s deputy mayor said Friday that they expect water levels higher than what was seen in 2017 and they are preparing for voluntary evacuations in parts of the Ottawa area. 3:44 Ottawa deputy mayor says expecting to see water levels higher than 2017 Ottawa deputy mayor says expecting to see water levels higher than 2017

The Ottawa River Regulation Planning Board’s forecasted water levels of the Ottawa river as of April 26 at 5 p.m. Ottawa River Regulation Planning Board / http://www.ottawariver.ca/forecast.php

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Many residents in Constance Bay, Britannia and Cumberland are racing against time to fortify their homes with sandbags before the river levels peak early next week. Deputy Mayor George Darouze described the West Carleton-March area in Ottawa, where Constance Bay is located, as “the community most immediately under threat.”

Darouze said the city expects evacuations may also be necessary in Britannia and Cumberland but will know more “in the days to come.”

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The city can’t force residents to leave their homes, Kanellakos said, but he warned that staying put will make it harder for city and emergency crews to help residents as they brace for flooded streets and washed-out roads.

“We can’t help people in emergency situations if we can’t get to them,” he said.

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“I don’t want to mince words. If we call for a voluntary evacuation there could be real repercussions if residents choose to ignore that advice and stay in place.”

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If there is more than 30 centimetres of water on the roads, emergency vehicles can’t drive on them, Kanellakos said, and utilities such as gas and power will be shut off if water levels get too high.

Officials encouraged residents in flood zones to begin preparing their families and belongings now for possible evacuation.

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The city said about 500 homes were at risk of evacuation in 2017; based on the data and projections available to the city now, Kanellakos said the number of homes in this instance “could be larger than that.”

Darouze, standing in for Watson this weekend, thanked the provincial and federal governments, volunteers and the Canadian military troops that arrived in Ottawa on Friday for their support.

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On Thursday, the city requested military help with protecting properties. About 400 troops arrived in Ottawa on Friday, a spokesperson for the Department of National Defence confirmed.

Ontario Premier Doug Ford also met with city officials on Friday morning and toured the flood zone in Constance Bay.

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“I told the mayor (of Ottawa) last night that anything he needs, we’re going to be there for him,” Ford told reporters.

The city said local volunteers are still needed for flood operations.

According to the city, shelter will be offered to those who do decide to evacuate their homes. Emergency centres are will be turned into lodging centres but the city said fewer than a dozen residents actually took the city up on the same offer in 2017.

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With files from Christopher Whan