The mayor of Minot, N.D., says water from the Souris River is expected to start pouring over dikes protecting the North Dakota city within the hour.
Mayor Curt Zimbelman made the comments in a telephone interview with KXMC television.
Zimbelman said the city will sound its sirens when water is overtopping the levees at certain points.
Thousands of Minot residents have been facing a 6 p.m. deadline to evacuate their homes for a second time in a month as the rising Souris River moved closer to swamping the city with what is predicted to be its worst flood in four decades.
Earlier, about 11,000 Minot residents were ordered to leave their homes earlier than expected as the Souris River, which is creating havoc in southeastern Saskatchewan, gets closer to swamping the North Dakota city with the worst flooding in four decades.
"Public safety is paramount," Zimbelman said. "The water is rising fast, and people need to get evacuated as soon as possible."
The Souris River that loops down from Canada through north-central North Dakota is bloated by heavy spring snowmelt and rain on both sides of the border. Communities across southeastern Saskatchewan are dealing with flooded homes, businesses and crumbling roads following unprecedented rainfall.
'I've got three stories so I'm hoping the furniture will be OK upstairs, but I'm a single mom and I had to ship my kids off to their dad, so I don't have anyone to help me.' —Ann Hoggarth, Minot, N.D., resident
Water is expected to reach the top of Minot's levees within the next two days and the resulting flooding is expected to dwarf the historic flood of 1969, when the Souris River reached 474 metres above sea level.
Zimbelman said the river at the city's Broadway Bridge was just shy of that level Tuesday afternoon, and it's expected to hit about 476 metres this weekend.
The 1969 flood prompted the Army Corps of Engineers to build a dike system that has been beefed up several times this spring.
But those levees are unable to handle flows from Saskatchewan of approximately 793 cubic metres per second.
The corps will mitigate those high flows through its management of the Lake Darling reservoir, said Deputy Commander Lt.-Col. Kendall Bergmann.
The corps on Tuesday cut the outflow from Lake Darling to 226.5 cubic metres per second after nearly 51 milimetres of rain fell on Ward County's Des Lacs River.
Bergmann said the corps got approval from Congress to take Lake Darling 76.2 centimetres lower and to go 127 mm above management pool level.
"So by increasing the flows over the next few days, we're almost going to empty Lake Darling," he said.
Zimbelman said officials in Minot are focusing efforts on building dikes to protect critical infrastructure such as the sewer system, water plants, schools and City Hall. The city also is working on plans to put up secondary dikes outside fringe areas.
"Once we have the critical sites secured, we'll start on these other areas trying to protect as many homes and businesses as possible," he said. "We will continue until the water pushes us out of the area."
Officials at Minot International Airport, which sits on a hill on the north part of town, issued a statement Tuesday saying the airport will remain fully operational.
Similar efforts are being made to protect infrastructure in the nearby town of Burlington, where about 1,200 people live.
Gov. Jack Dalrymple said Tuesday afternoon that residents in Burlington evacuation zones need to be out by noon Wednesday. Ward County residents living along the river must evacuate by 6 p.m., he said.
About 10,000 Minot residents were evacuated earlier this month. They were later let back into their homes, but were cautioned to be ready to leave again quickly.
National Guard sent to area
North Dakota National Guard commander Dave Sprynczynatyk said the latest evacuation order affects about 11,000 people in 4,200 homes.
Nearly 500 National Guard soldiers were to be in Minot by the end of the day Tuesday, providing traffic control, making sure people had left their homes and securing neighbourhoods. The Guard also has increased monitoring of the city's levees to every 30 minutes.
Ann Hoggarth, who lives right next to the river, told The Associated Press that she feels numb and very emotional. She is struggling to move some of her belongings to higher ground.
"I've got three stories so I'm hoping the furniture will be OK upstairs, but I'm a single mom and I had to ship my kids off to their dad, so I don't have anyone to help me," she said.
The high water is expected to begin hitting Minot by about Thursday.
The historical record of about 475 metres set in 1881 is forecast to be topped on Friday or Saturday.