“Extensive flooding” of farmland in southern Manitoba’s Red River Valley is seen as likely this spring at levels near those seen in 1979, the province predicts.
A March 10 blizzard in the U.S. portion of the Red River watershed played a “significant” role in the revised forecast, Manitoba Water Stewardship’s Hydrologic Forecast Centre said Monday. The U.S. watershed already has high soil moisture conditions and above-average snow cover.
“Even with favourable weather from now on, the updated forecast shows over-bank flows similar to 2006 are likely along the Red River,” the centre said in its updated outlook. “The probability of a flood of 2006 proportions or larger at Manitoba points is about 90 per cent.”
And with average temperature and precipitation from now on this spring, a 1979-magnitude flood on the Manitoba portion of the Red River is likely, the centre said.
The 1979 flood was “very similar in magnitude” to 1950, ranging from 0.3 metres (one foot) below to 1.22 m (four feet) below 1997 peaks at Emerson (about 130 km north of Grand Forks, N.D.) and St. Adolphe (about 15 km south of Winnipeg) respectively.
The 1950 flood, which predated construction of the protective Red River Floodway around Winnipeg, flooded over 10,000 city homes and forced the evacuation of about 100,000 people.
“A 1979-type event would flood additional land and cause overtopping of more municipal and provincial roads than a 2006-type flood and this would increase further if the flood should approach that of 1997.”
A 1979-level flood “is more than a flood of inconvenience,” the Reuters news service quoted provincial flood forecaster Alf Warkentin as saying Monday. “It is a serious flood. It would affect a lot of people, a lot of transportation.”
Even with “adverse” weather, the chance of a 1997-magnitude flood in the Manitoba portion is less than 10 per cent, the centre said.
All towns and individual homes in the Red River floodplain are protected to 1997 levels plus 0.6 m (two feet), so structural damage to buildings should be “minimal,” the province said.
That said, weather conditions from now through the spring will be “highly significant,” the centre said. “A gradual thaw with little additional precipitation would reduce the flood potential. However, a late breakup with additional snowstorms and an untimely spring rainstorm could still produce a record-high Red River flood in 2009.”
With that in mind, the provincial water stewardship department advised that landowners in areas affected by major floods in the past should take “precautionary actions to safeguard property.”
North of Winnipeg, flooding is not expected in the Selkirk area unless serious ice jams develop. The province said it has acquired a second and “more capable” Amphibex icebreaker, which along with another Amphibex and ice-cutting equipment will be used to break up ice on the Red from Selkirk to Lake Winnipeg.
The region’s major flood control works, such as the Red River Floodway, Portage Diversion and Shellmouth Reservoir, will be used to reduce river flows and levels in the Winnipeg area and on the Assiniboine River.
“Closures will be made on ring dikes at valley towns at an appropriate time so as to cause the least disruption to traffic,” the province said.
The Canadian Wheat Board announced last week it would co-ordinate additional rail cars into the valley to clear space in elevators at or near valley towns such as Morris and Letellier, for affected farmers to deliver accepted Series A and B grain.