Manitoba Water Stewardship’s Hydrologic Forecast Centre has evaluated conditions for the Red River and an updated spring flood outlook indicates the potential for serious spring flooding in the Red River Valley has increased significantly due to a recent storm that brought heavy snow to areas south of Manitoba.
The March 10 blizzard in the U.S. portion of the Red River watershed was significant due to high soil moisture conditions and above-average snow cover which already existed in the U.S. prior to the storm.
The new outlook for the Red River in Manitoba is based on all available information including recent forecasts for locations south of the international boundary issued by the U.S. National Weather Service. It also looks at how three scenarios – favourable weather, average weather and adverse weather – will affect flooding.
• Even with favourable weather from now on, the updated forecast shows over-bank flows similar to 2006 are likely along the Red River. The probability of a flood of 2006 proportions or larger at Manitoba points is about 90 per cent.
• With average temperature and precipitation from now on, a 1979-magnitude flood on the Manitoba portion of the Red River is likely. 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 and St. Adolphe respectively.
• Even with adverse weather, the chance of a 1997-magnitude flood in the Manitoba portion is less than 10 per cent. Peak stages based on poor weather conditions would range from 0.15 m (0.5 ft.) below the 1997 peak at Emerson, to 0.24 m (0.8 ft.) below the 1997 peak at Morris, to 0.6 m (two feet) below the 1997 peak at St. Adolphe and 0.7 m (2.3 ft.) below 1997 in downtown Winnipeg.
• Major flood control works such as the Red River Floodway, Portage Diversion and Shellmouth Reservoir will be operated 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.
• A Manitoba air survey of snow conducted between March 12 to 14 over the Red River watershed showed the water content of snow ranged from 75 to 125 millimetres in the U.S. portion to between 50 to 75 mm over the Manitoba portion. This is well-above average over the U.S. portion and close to average for the Manitoba portion.
• Extensive flooding of agricultural lands is likely in the Red River Valley this spring. 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.
• 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.
• Flooding is not expected in the Selkirk area unless serious ice jams develop. The province has acquired a second, more capable Amphibex icebreaker, which will more effectively break ice due to a heavier hull and stronger hydraulics. The two Amphibex machines will be assisted by new ice-cutting technology that was piloted last year. The ice-cutting equipment will be used ahead of the Amphibex icebreakers to break up ice on the Red River from Selkirk to Lake Winnipeg.
• Weather conditions from now through the spring will be highly significant. 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.
• Manitoba Water Stewardship advises that due to the serious flood potential this spring, landowners in areas affected by major floods in the past should take precautionary actions to safeguard property.
• A second spring flood outlook for the rest of the province will be issued on Friday, March 20. This will be the last spring flood outlook unless unusual weather conditions develop during the next few weeks. Daily flood reports with specific updated forecasts will begin once spring run-off is well underway.
The latest information on flood forecasts for Manitoba is available online.
