The Province of Manitoba said Friday that flooding risks in Manitoba remain fairly low. Earlier this week, both the Winnipeg and Manitoba outlooks were given for potential spring flooding. Forecasters say the 2009 spring run-off is now expected to be above average over southwestern Manitoba, somewhat above average for most other portions of southern Manitoba and close to average for most of northern Manitoba.
River Forecasts
The spring flood outlook is based on three weather scenarios, favourable, average and adverse weather, in terms of precipitation and melt conditions.
Brief flooding can occur in locations where ice jams develop, even with below-average river flows.
Red River Watershed
The run-off, which started in most portions of the watershed this week, is expected to accelerate this weekend due to strong melting conditions.
Forecasters say a flood of 1979 proportions could occur in the Manitoba portion but the flood could be lesser or greater than this depending on weather conditions from now on.
A developing storm system threatens to bring substantial rainfall to the Red River watershed Monday and Tuesday.
Forecasters say it is possible the flood will be only of a 2006 magnitude at Manitoba points if the storm produces little precipitation.
Extensive flooding of agricultural lands and disruption to transportation is expected from Emerson to the Red River Floodway inlet.
They add operation of major flood control works such as the Red River Floodway will protect the City of Winnipeg from serious flooding.
Peak stages from Selkirk to Breezy Point will depend on whether ice jams develop.
Ice-cutting and breaking operations by North Red Community Water Maintenance Incorporated and Manitoba Water Stewardship have been underway around the clock this week. Officials say this action will reduce the chance of serious ice jams.
No significant flooding is expected on tributaries unless more than 0.9 inches (25 millimetres) of rain develops this weekend. Water is likely to pond in low-lying areas, especially east of the Red River, even without rain, due the high soil moisture.
Assiniboine River Watershed
Run-off has just begun and should slowly increase next week due to moderate melting conditions. There is a chance of significant amounts of rain or snow on Sunday, Mar. 22.
Spring river crests are expected to somewhat exceed the bank-full capacity, based on normal weather.
There would be little or no flooding with favourable weather from now on.
The unfavourable weather scenario would result in significant overbank flows, as occurred in 2007.
The Shellmouth Reservoir has been drawn down to provide storage space for the spring melt. The level of 426.7 metres (1,390 feet) (3.8 m (12.5 ft.) lower than the spillway) as of March 20 is lower than the average winter drawdown and is expected to provide adequate flood protection for valley agricultural lands from Shellmouth to St. Lazare.
The Portage Diversion will be operated to reduce the chance of ice jamming and associated flooding from Portage la Prairie to Winnipeg.
Flooding is not expected on tributaries unless adverse weather develops.
Souris River
Extensive flooding of agricultural lands is expected from the international boundary to Melita and moderate flooding is expected from Melita to Souris, based on normal weather conditions.
A flood similar to that of 1999 is expected, based on normal weather conditions.
The main cause of the flood is deep snow in North Dakota. An above-average snowpack in Saskatchewan may cause flooding to extend well into May, but much will depend on spring weather.
Some diking may be required in low areas on the south edge of Melita and for a few homes near Souris.
Flooding is not expected on most Manitoba tributaries.
Some flooding is possible on Waskada Creek if a rapid melt develops on Turtle Mountain.
Pembina River
Flooding of the Pembina River Valley similar to 2006 is expected from Rock Lake to La Rivière, based on normal weather conditions. Flooding downstream of La Rivière to Gretna should be significantly less than in 2006, unless adverse weather conditions develop.
Flows through the international boundary from North Dakota should be minor and insufficient to cause flooding along the Buffalo Channel or the Aux Marais River.
Sloughs upstream of Killarney are still empty from the 2008 drought and will help reduce run-off and flooding from heavy snow cover on Turtle Mountain.
Interlake
Minor flooding is expected even with favourable weather due to low areas being still nearly full of water from last summer’s heavy rains.
Flooding could rapidly escalate in case of adverse spring weather.
Some diking may be required at the Peguis town-site and ice jams may cause flooding and access difficulties at Fisher River if weather conditions are somewhat unfavourable.
Extensive overland flooding and seepage into basements could develop with an adverse weather scenario.
If required, equipment will be deployed to mitigate ice jams on the Fisher River.
Eastern Manitoba
Flooding is unlikely on the Brokenhead, Whitemouth and Whiteshell rivers. However, adverse weather could quickly increase the flood potential due to high soil-moisture conditions.
Flows on the Winnipeg River are likely to be above average. Above-average precipitation from now through the spring could result in flooding along the river.
Westman Region
Flooding is unlikely on the Whitemud and Turtle rivers, Big Grass Marsh and most streams flowing off the Riding and the Duck mountains with normal weather conditions.
Brief flooding could occur if a rapid melt were to develop on the high ground.
The flood potential is higher in a small area near Dauphin, including the Wilson River watershed, where heavy rain fell last autumn.
The spring flood potential is low from Swan River to Red Deer Lake due to below-average snow cover.
The Pas Region
Spring flooding is not anticipated on the Saskatchewan River at The Pas and on the Carrot River due to below-average snow cover and soil moisture in most of Saskatchewan and Alberta.
Northern Manitoba
Flooding should be minimal due to both snow cover and soil moisture being average in most areas.
Minor localized flooding may occur in the Thompson area which has seen snowstorms from mid-February onward.
Forecast Updates
Starting Sunday, Mar. 22, daily flood condition reports and flood sheets containing updated forecasts will be initiated and posted on the government website.
The latest outlooks and reports can be found at:
www.gov.mb.ca/waterstewardship/floodinfo/index.html
