Calgary and other devastated communities are starting a painstaking recovery after the worst flood in Alberta's history, even as the southeast of the province braces for the arrival of the peak of surging waters early Monday.

Alberta Premier Alison Redford said that while Calgary, Canmore and High River are shifting into recovery mode, other communities such as Drumheller and Medicine Hat are bracing for their own ordeal. The government has examined river flows, rainfall and the flooding impact, and Ms. Redford says they have confirmed the floods of the last several days are the largest in Alberta's history.

"It's been shocking to see the unbelievable destruction and the powerful impact of these floods," Ms. Redford told reporters Sunday night. "We will live with this forever."

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Tens of thousands of Calgarians were allowed to return to their homes Sunday as river waters receded, and the province's largest city and business centre shifted to the daunting task of cleaning up – and paying for – the unprecedented flood damage.

Still, thousands of residents remain under evacuation orders and unable to survey the damage to their homes. And Calgary's iconic Saddledome remains wet and muddied, less than two weeks before the Calgary Stampede, while parts of the downtown – the hub of Canada's oil and gas sector – remain under water and without power.

In High River, the hardest-hit community, 80 per cent of the town is without power or basic services, and the RCMP expects search and rescue efforts to take days.

The financial impact on the province's and country's economy has yet to be tabulated, and Ms. Redford would not speculate on an amount. But it's starting to become clear how long a road lies ahead. She announced the appointment of three junior cabinet ministers to oversee "reconstruction" and said the province will help people with uninsurable losses.

"This is like nothing that we've ever seen in Alberta and it is going to require monumental marshalling of resources, skills and people," she said.

Three flood-related deaths in the High River area were confirmed on the weekend.

Although Calgary municipal officials had originally predicted it could take weeks or months for the downtown to be powered and open for business, late Sunday Mayor Naheed Nenshi said the buildings occupied by 90 to 95 per cent of the city's downtown workers could be functioning again by Tuesday. Still, he advised companies to keep non-essential employees home for at least Monday and Tuesday.

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But Mr. Nenshi is determined that the Stampede, the 101-year-old rodeo and festival that brings hundreds of thousands to the city each year, will go ahead, despite the Saddledome and Stampede grounds still being partly flooded Sunday. The mayor said the fairgrounds are draining "remarkably fast" and noted the Stampede has its own electrical generators.

"So Stampede 101 may look very, very different than the 100th Stampede, but it will happen 12 days from today."

On Sunday, Isha Sharif was able to enter her Calgary home, for the first time since a frantic evacuation Thursday evening, to find her basement nearly full of water, and her living room and garage covered with water and mud. Her six-year-old son cried for his lost toys, but one of the family's greatest losses is Ms. Sharif's extensive library, which included a collection of 100-year-old medical textbooks.

"We have small children and we don't want to be back in the house because of mould concerns," Ms. Sharif said, acknowledging she's still in shock over the damage, and the realization that her home may still have to be demolished. "We'll have to do a full or partial tear-down. It's pretty bad."

The focus of concern has now shifted to the southeastern corner of the province. In preparation for flooding in Medicine Hat, more than 10,000 residents have been evacuated in the city of 61,000. Mayor Norm Boucher said that although peak water flows won't be as high as the province originally predicted, the city was already seeing some homes and downtown parking garages flooded by midday Sunday. "The sandbagging didn't help very much," Mr. Boucher said. "But we think everyone is safe now."

Siksika Nation chief Fred Rabbit Carrier said the community east of Calgary was heavily damaged from the floods, with nearly a quarter of the reserve's population forced to flee. The chief said it was too soon to tell how many of the water-damaged houses can be salvaged or how much the cleanup will cost. "This is the worst flooding I have ever seen in my life," he said over the phone from Siksika's Deerfoot Sportsplex, which is serving as a shelter.

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Across Alberta, there are now more than 2,200 Canadian Forces troops on the ground, plus seven Griffon and two Cormorant helicopters either on standby or being used.

Although city officials insist the Stampede will go on, a number of events have already been cancelled. The Conservative Party of Canada had planned to hold a convention in Calgary this summer but cancelled the event this weekend. On Sunday, Immigration Minister Jason Kenney said while the party remains committed to holding the policy convention in Calgary, it would postpone the event until at least the fall.

With files from Carrie Tait, Renata D'Aliesio, Kim Mackrael and Tu Thanh Ha