(Repeats to widen distribution)
* Unplanned dike failure seen flooding bigger area
* CN main rail line not affected
* Prime minister to visit area Wednesday
By Rod Nickel
WINNIPEG, Manitoba, May 11 Manitoba prepared on Wednesday to open a dike along the swollen Assiniboine River in a desperate move that would flood a vast swath of farmland and at least 150 homes in the Canadian Prairie province but prevent an even worse disaster.
The Assiniboine flows from Saskatchewan eastward into Manitoba and has risen quickly due to rain and melting snow, resulting in a record-high level that would be expected only once in 300 years. The Canadian Army was called in earlier this week to help fortify dikes.
Prime Minister Stephen Harper was to tour the area on Wednesday morning, with the provincial government planning to open its dike as early as midday. The breach would flood 225 square kilometres, or about 55,600 acres, the province has said.
The alternative would be to risk unplanned flooding over an area twice as large if the dike fails, Manitoba officials said, but they admit they can't be sure where the water will go even with a planned release.
Chuck Fossay, whose family has farmed north of Starbuck, Manitoba, for more than 100 years, is out of the flood's path if it moves as the province expects.
But if it causes the smaller La Salle River to overflow, it's likely to swamp Fossay's grain and oilseed farm.
"Right now, we'll just wait and see how much damage is going to be done," he said. "Any time you're dealing with something new, you're wondering, can they control it?"
The province has said it expects 150 homes to be flooded by the controlled release, but some local politicians say the number could be much higher.
Nearly 3,000 people across the province have already been driven out of their homes due to widespread flooding, according to reports.
The farmland to be flooded isn't necessarily a writeoff for planned crop plantings this year, said Gerald Huebner, assistant deputy minister for Manitoba Agriculture. In 1997, the year Manitoba saw record flooding along the Red River, farmers still managed to plant crops, he said.
Wheat and canola are important crops in the flood zone, which represents less than 1 percent of Western Canada's farm area. The region also grows corn, soybeans, potatoes and other vegetables.
Manitoba is also concerned about its cattle herds. Rising water is affecting thousands of animals whose pastures are at risk of flooding.
Rail service has also been affected in the region, with Canadian National Railway (CNR.TO) closing its U.S. border-crossing and interchange point with BNSF Railway [BNISF.UL] at Emerson, Manitoba ,last month due to flooding on the Red River.
Canadian Pacific (CP.TO) has closed a branch line between Napinka and Killarney, Manitoba, due to high water.
Canadian National runs its main line not far from the Assiniboine River, but it has not been affected by flooding in either Manitoba or Saskatchewan, said spokesman Warren Chandler. (Additional reporting by Allan Dowd and Nicole Mordant; editing by Rob Wilson)