Prime Minister Stephen Harper is to travel to Manitoba's flood zone Wednesday, a day after the federal government committed more troops to the stricken area.

Three hundred Alberta-based troops were ordered to Manitoba Tuesday and will join 700 from Saskatchewan, Manitoba and northwestern Ontario who are already battling floodwaters in the province.

After touring the area Tuesday, Defence Minister Peter MacKay said Manitoba had asked for the extra troops. "We have two major conflicts underway and now two major floods happening here in Canada," said MacKay. Troops have also been providing assistance in Quebec's Richelieu River region.

"I'm continually impressed by the ability of the Canadian Forces to adapt to circumstances. And they do the home and away game very, very well," said MacKay.

Manitoba Emergency Measures Minister Steve Ashton said troops from Edmonton will join regular soldiers from CFB Shilo in Manitoba and reservists from Saskatchewan and Thunder Bay. They will relieve flood-weary Manitobans and work to reinforce dikes along the surging Assiniboine River west of Winnipeg.

Ashton described the Assiniboine River flood of 2011 as a once-in-300-year event.

"This is something we don't have experience with," he said, noting the Assiniboine River is barreling through southern Manitoba carrying the equivalent of half the flow of Niagara Falls.

He said flood officials are still preparing to divert Assiniboine River water into the La Salle River watershed Wednesday — a move that could flood an area more than 200 kilometres wide.

The decision to undertake a controlled release of Assiniboine water into the La Salle basin depends on how much rain the area gets in the next 24 hours.

Farmers fear their livelihoods could be lost if the province deliberately breaches dikes meant to contain floodwaters in order to minimize damage to an even larger area should dikes fail.

The river will spill into a 225-square-kilometre area in the La Salle River watershed, putting 150 rural properties in the Rural Municipalities of Portage la Prairie, St. Francois Xavier, Headingley and Cartier at risk of flooding.

About 1,500 people in those areas, as well as in Elie, are on an evacuation notice in the event things get worse, or they are cut off from road access. As of Tuesday, more than 2,700 people, including 1,000 from Brandon, have been forced from their homes due to flooding in Manitoba.

Doug Connery, a vegetable and berry farmer in the Rural Municipality of Portage la Prairie, expects his crops and buildings to be flooded within a matter of hours once the dike is breached.

And he doesn't have a single sandbag at this point.

"I'm trying to convince the government this isn't the proper place to do it. Further downstream, where the water would be dumping into pastureland, where you don't have near the cost of agricultural production, would be the proper place to do it," he said.

Connery predicts flooding this year could put him and other producers in his area out of business once and for all.

Kam Blight, reeve of the RM of Portage la Prairie, said officials are moving as fast as they can to make sure everyone is prepared but so much is unknown.

"I think the biggest challenge is we don't know what we're faced with and we don't have all the information and we don't know how bad it can be and the other challenge is trying to get notification out to the people," he said, adding that he feels like his community has been thrown under the bus.

"Let's just say we feel we've been blindsided and that there's a little bit of … a lot of sacrificing taking place right here."

Blight said he is concerned for residents now in a mad scramble to protect their homes.

"My heart is hurting for a lot of people right now, but we know that we have to get down to business. And we have to do the best we can to stay calm and help people manage this potential situation."

Blight is urging people who want to shore up flood defences to meet at the RM of Portage la Prairie yards to help with the sandbagging machine.

Necessary damage

The release of water is necessary to prevent potentially more catastrophic uncontrolled flooding over a wider 500 square kilometre area and 850 properties should dikes fail, Emergency Measures Minister Steve Ashton said.

Crews work in the area of Hoop and Holler Bend on Tuesday to prepare for the roadway dike to be cut through as part of a controlled release of the swollen Assiniboine River. ((Trevor Brine/CBC))

The province may have no choice but to conduct a controlled release, he said, but will wait to gauge the effect of additional rainfall on Assinibone River flows following thunderstorms that passed through the area Tuesday evening. "We will use it if necessary, but we won't necessarily use it," Ashton said of the plan to cut the dike as early as Wednesday.

People whose property is damaged by any controlled release will be fully compensated, Ashton said.

Flows compared to Niagara Falls

The controlled spill would happen at the Hoop and Holler Bend, about midway between the hamlets of Southport and Newton, southeast of Portage la Prairie.

Floodwater gushes over the Shellmouth Reservoir, which normally restricts the flow of the Assiniboine River. ((Submitted))

The controlled release would occur if flows cannot be managed on the Portage Diversion and on the Assiniboine River, the province stated in a bulletin issued Monday.

The Portage Diversion is a water-control structure on the Assiniboine River just west of Portage la Prairie. The 29-kilometre diversion channel redirects some of the water into Lake Manitoba, helping minimize flooding downstream where the Assiniboine joins the Red River in Winnipeg.

Flood protection along the Assiniboine, using the Portage Diversion, is typically rated for a flow of 40,000 cubic feet per second but on Tuesday, Ashton said "we are looking at a minimum of 52,000 cfs."

Officials have been "working around the clock" to find ways to get the flood capacity up to that level, noted Ashton.

"We have the military, for example, building up the dikes on the Assiniboine and we've found ways of getting more water through the Portage Diversion, but it still doesn't give us enough flow to deal with peaks as high as 56,000 [cfs], so we have decided to move to a controlled release."

Some 400 Canadian Forces soldiers are on the ground building dikes in areas along the river in western Manitoba. Another 100 soldiers are expected to arrive Tuesday with 300 more on standby in Edmonton, waiting to join the effort if needed.

The right decision: professor

Jay Doering, a professor of civil engineering at the University of Manitoba, said the province is making the right decision about where to cut the dike.

"If you're to breach the Assiniboine at some location further to the east, it is going to flow on pasture land but the question is, where's it going to go when it hits the pasture land?" he said.

"There are lots of mile roads, there are lots of provincial roads, so there's lots of potential obstruction in the way of a breach further downstream."

The location chosen by the province is closest to the La Salle River, which will help move out the water quickly, Doering said, giving the province full credit for making the hard choice to go ahead with the spill.

"The last thing you want is an uncontrolled breach," he said.

Dry in Brandon

Notice posted in the window of a home in Brandon's evacuation zone. ((Wab Kinew/CBC))

For now, the city of Brandon remains dry.

The dikes are holding after a scare on Monday prompted officials to issue a precautionary evacuation for about 1,000 peoplein a low-lying area known as the Flats.

But a second stage of the evacuation was postponed as officials noticed water levels had not risen too much more.

Officials have described the situation behind dikes in that city of 40,000 as "guarded" because additional rain is expected in the area Tuesday.

About 40 military reservists are working in Brandon to monitor the dikes and help with any additional evacuations.

However, the city has lifted its evacuation order for households in the area around Kircaldy Drive north of the Assiniboine.