The Manitoba Infrastructure and Transportation Hydrologic Forecast Centre’s spring flood information update shows the 2012 spring run-off occurred early and is complete on the Red, Souris, Assiniboine and Pembina rivers, and in the southern Interlake. Peak levels and flows in these areas were generally below normal.
In northern Manitoba, localized spring flooding could still occur in the The Pas region where there have been above-average soil moisture conditions and significant snowfall this season.
If a major storm develops this spring along the upper Assiniboine River and in the The Pas area, localized flooding could occur. On major lakes with open water, strong winds could still pose flooding problems along the beaches. Lakes Manitoba and Winnipeg still have ice cover. Forecast north winds of 40 km/h gusting to 60 km/h may cause moderate shoreline ice pileup. Lake ice conditions will continue to be monitored.
There is still a risk of spring storms producing significant amounts of precipitation leading to minor localized flooding, however, this is less likely to affect the main stems of the Red, Souris and Assiniboine rivers.
Flood reports will be issued in case of advisories, watches or warnings. Further information is available at www.gov.mb.ca/mit/floodinfo.
The province’s flood-protection infrastructure investment in 2011 served to minimize flood damage and will continue to protect Manitobans into the future. Recovery efforts are still underway to address the damage caused by last year’s flood. The full cost of flood-fighting and recovery efforts last year was approximately $936 million. About $445 million is expected to be recovered from the federal government.
Climatic Weather and River Conditions
Above-normal and record temperatures in February and March have melted most of the snow in Manitoba, North Dakota, Minnesota and Saskatchewan. Some remnants of snow still exist in northern parts of Manitoba including the Swan Valley and The Pas regions. Portions of the Assiniboine River Basin and the Interlake have measured snow-water equivalents of five to 10 millimetres (0.2 to 0.4 inches) and around 20 mm (0.8 in.) over mountains and the upper Interlake.
The major rivers and tributaries have open water conditions. There is little or no ice in small tributaries in southern Manitoba.
Some parts of the upper Assiniboine River have patches of thin ice but, with warmer weather in the forecast, most of the ice will likely be gone by next week.
Spring Run-off
The 2012 spring run-off was below normal in most parts of Manitoba and near normal in a few areas such as The Pas. Light showers on wet or partially frozen soils plus some expected extra precipitation this week will see some rivers and creeks either maintain levels close to peaks or experience slower recessions.
River Ice Conditions and Ice Jamming
Ice-jam flooding is unlikely to occur in the main stem of the Assiniboine River but moving ice could pose dangers within the river channels. It is impossible to predict the occurrence and extent of ice jamming.
Red River Basin
The Red River has crested at low peak levels from Emerson to Breezy Point, which are lower than 2008 peaks. As of March 26, river levels decreased from peak levels by four feet to two ft. from Emerson to the floodway inlet, and by one ft. to 0.28 ft. from James Avenue to Breezy Point. The current level at James Avenue is 7.54 ft.
Pembina River Basin
Due to below-average soil moisture and snow cover conditions, the peak flows and levels along Pembina River were dramatically low. The river peaked near Windygates at 700 cubic feet per second (cfs) and now flows are ranging between 60 and 100 cfs only from La Rivière to Windygates.
Assiniboine River Main Stem
Flows and levels along the Assiniboine River are still ice affected. The river is near crest level upstream of Brandon and levels are expected to decline during the next few days.
The Shellmouth Reservoir level is increasing. To achieve the summer target level of 1,402.5 ft., the Shellmouth Dam outflow was reset to 50 cfs on March 16, then to 30 cfs on March 19. The total inflow is decreasing; March 26 inflow was around 2,600 cfs after cresting at around 2,835 cfs on March 24. Outflows may be increased to maintain the average summer target level, balancing between drought and flood risks.
Souris River Basin
Below-average winter precipitation and below-normal soil moisture were recorded in the North Dakota, Saskatchewan and southern Manitoba portions of the watershed. Flows in the main stem are close to 400 cfs and should increase depending on the expected rainfall during the next few days as well as the possible release of water from the Westhope control structures by the U.S.
Interlake Region
With unfavourable weather, localized minor to moderate flooding could occur.
The emergency channel is helping bring down levels on Lake Manitoba and Lake St. Martin as predicted. In 2011, Lake Manitoba peaked at 817.15 ft. Lake St. Martin had a peak of 805.5 ft. With average conditions, Lake Manitoba is expected to drop from its current level of 813.49 ft. to about 812.8 ft. by the end of July. Lake St. Martin is also expected to continue dropping from its current level of 801.68 ft. to around 800.3 ft. by the end of July.
Fairford flows will remain high into spring time. No Portage Diversion flows are expected.
Eastern Region
Both the soil moisture and snow-water equivalent are below average at this time. An unfavourable weather scenario could produce minor flooding in the low areas along the Whitemouth and Brokenhead rivers.
Westman and The Pas Regions
Soil moisture and snow cover are below normal in most areas apart from areas around the The Pas region. An unfavourable weather scenario could produce localized flooding, especially if there is a rapid melt in the higher terrain. The projected river levels are expected to remain within river banks and are similar to those of 2005 in the The Pas region.
Northern Manitoba
Run-off in northern Manitoba north of 54 degrees is expected to be below average to near normal. Minor, localized flooding is expected if rapid snowmelt occurs.
