The Manitoba Infrastructure and Transportation Hydrologic Forecast Centre’s second 2014 spring flood outlook suggests the potential for spring flooding is near normal in most areas of Manitoba.
The The Pas region is an exception where above-normal soil moisture and above-normal winter precipitation have resulted in the potential for greater-than-normal run-off and the potential for localized flooding. The existing flood protection is expected to be adequate for projected levels.
Run-off in most areas of the province is expected to be near normal, as soil moisture and winter precipitation are near normal. Some areas have high soil moisture but low winter precipitation, or low soil moisture and high winter precipitation.
At this time it appears the Red River Floodway will not be operated under favourable or unfavourable conditions. However, there is a 10 per cent chance the flows on the Red River will exceed the forecast unfavourable condition, which may result in floodway operations.
The Portage Diversion will likely only be operated under unfavourable weather conditions but could operate under lower-flow conditions if required to help prevent and manage ice jams on the lower Assiniboine River between Portage la Prairie and Headingley.
The Shellmouth Dam and Reservoir have been operated to allow for storage capacity for the upcoming spring run-off. They will continue to operate throughout the flood period in consultation with the Shellmouth Operations Liaison committee to balance flood control and water supply objectives.
Additional snowfall and predicted blizzard conditions for southeast Manitoba and the northern North Dakota region will be monitored by the Hydrologic Forecast Centre.
Flood Outlook
In general, potential for overland flooding is near normal as the majority of areas that have above- or well-above-normal soil moisture have received below or near normal precipitation.
The exception is the The Pas region that has above-normal flood potential due to above to well-above-normal soil moisture levels at the time of freeze-up and normal to above-normal snowpack water content.
Long-term weather forecasts are subject to change and late snowstorms or early heavy rain could change the current outlook. Three scenarios with different weather developments are described in the outlook:
- favourable, without much more precipitation and a gradual snowmelt;
- normal, based on 30 to 40 years of climate trends; and
- unfavourable, which includes significant additional snow and rain, and a rapid snowmelt.
Flood potential for the unfavourable weather scenario is noted for the following watersheds:
- Red River: decreased from moderate to minor to moderate;
- Pembina River: remains the same with minor to moderate flooding;
- Roseau River: remains the same with minor to moderate flooding;
- Assiniboine River: remains the same at minor to moderate flooding;
- Southwest region: decreased from moderate to major to moderate flooding;
- Interlake region: remains the same at minor to moderate flooding;
- Eastern region, the Winnipeg River: remains the same at moderate flooding;
- Fisher River: remains the same at moderate flooding; and
- Northern Manitoba and The Pas regions including the Saskatchewan, Carrot and Swan rivers: remains the same at moderate flooding.
Delayed thaw and the potential for spring rainstorms could result in rapid snowmelt, aggravating overland flooding and increasing tributary flows.
Environment Canada’s long-term March to May climate outlook indicates a chance that temperatures will be near normal in most of the province, except for the southeast portion which is expected to experience below-normal temperatures. Precipitation is expected to be near normal across the province.
Soil Moisture Conditions
Fall 2013 soil moisture:
- The Pas region and Souris River watershed: above normal to well-above normal with soil moisture levels up to 200 per cent of normal in portions of the Souris River watershed;
- Southern Manitoba including the Red River valley: below normal to near normal;
- Western Manitoba: near normal to above normal;
- Central Interlake: below normal; and
- Eastern Manitoba: below normal.
Snowpack Conditions and Snow Water Content
Winter precipitation is generally below normal in a band stretching from the upper Assiniboine, Souris, Pembina and the upper Red rivers watersheds, with the exception of near-normal precipitation on the upstream Saskatchewan side of the Souris River.
Winter precipitation in The Pas region, the east and north side of Lake Winnipeg, and the Whiteshell area is above normal to well-above normal. Precipitation is normal to above normal in the Interlake region.
Within the city of Winnipeg, the snowpack is above normal. Local run-off potential within the city could be above normal if a faster rate of melt occurs.
Ice Jams
At the onset of run-off, there is a chance of localized flooding due to ice jams or snow blockages in drains, ditches and small streams. Major ice jams are difficult to predict as to location and magnitude, and the possibility of ice jams cannot be ruled out.
Flood Preparation
Though ice jams cannot be predicted, ice-cutting and Amphibex icebreaking activities should limit ice jam related flooding on the lower Red River and a number of other streams.
The Amphibex fleet has broken a 28-kilometre, 100 metre-wide channel down the centre of the Red River from downstream of Netley Lake through the community of Selkirk. As well, two km of river ice was broken by the Amphibexes on the Brokenhead River through the Brokenhead Ojibway Nation, two km was broken on the Icelandic River at the community of Riverton, three km was broken on the Fisher River through the community of Fisher River and Lake Manitoba ice was broken at the outlet of the Portage Diversion channel. Additionally, three km of ice was cut on the Whitemud River at the outlet of the river into Lake Manitoba.
The chances of minor localized flooding due to snow blockages in drains, ditches and small streams during the early part of the run-off period will be dependent on the nature of the spring breakup and rate of melt.
Manitoba’s flood-fighting equipment includes:
- two million regular sandbags;
- six sandbag-making machines;
- 17,000 super sandbags;
- 43 km of Hesco cage barriers, into which sand or other heavy material is placed;
- 50 km of water-filled barriers, of which 22 km are in rapid-response trailers;
- 34 mobile pumps; and
- 61 heavy-duty steamers.
The detailed forecast with text and charts is available at www.gov.mb.ca/flooding.
