There is a variable risk of potential flooding across the province according to the Hydrologic Forecast Centre of Manitoba Infrastructure and Transportation’s first 2015 spring flood outlook.
This first outlook estimates the potential for overland flooding is normal to above normal in the western areas of the province and normal to below normal in the rest of the province. This could change depending on weather conditions between now and the spring melt. The second outlook at the end of March will further define the flood potential.
Most of the major lakes are well-above normal levels for this time of the year and the risk for potential flooding is above normal even under normal weather conditions. Flows and levels in most rivers are well-above normal for this time of the year.
Run-off
The potential for spring run-off is normal to above normal in the Assiniboine River basin, the Qu’Appelle River basin and the upstream watersheds of the Souris River basin. The potential for a spring run-off is below normal in the Red and Pembina river basins, the Roseau River and the Interlake region. The run-off potential is near normal in the Saskatchewan River basin and is normal to below normal throughout the rest of the province including the Winnipeg River basin.
The potential for increased run-off in the Assiniboine, upper Souris and Qu’Appelle river basins is a result of above-normal soil moisture content at freeze-up and normal to above-normal snowpack water content. The Red River Valley has experienced normal to below-normal soil moisture conditions and well-below-normal precipitation, resulting in a low risk of flooding.
Frost in Soil
Due to the extreme cold weather and lack of sufficient snow cover on the ground, frost depth is above normal in the Red River Valley. Frost depth is near normal throughout the remainder of the province. Above-normal frost depth means that frozen soil cannot absorb melting water and could result in overland flooding.
Soil Moisture Conditions at Freeze-up
- southern Manitoba including the Red River Valley – below normal;
- western Manitoba and eastern Saskatchewan – above normal;
- Interlake and northern Manitoba regions including The Pas region – near normal; and
- eastern Manitoba – near normal.
Winter Precipitation
Winter precipitation is below normal to well below normal throughout the central and southern portions of the province including the Red and Winnipeg river basins, the Interlake region and the downstream watersheds of the Souris and Assiniboine rivers.
It is near normal to above normal in eastern and southern portions of Saskatchewan including the headwaters of the Souris, Assiniboine and Qu’Appelle rivers. Winter precipitation is above normal to well-above normal in central and western Saskatchewan including the Saskatchewan River watershed.
Ice Jams
When warmer temperatures arrive and run-off starts, 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 cannot be ruled out. On most major rivers, ice thickness is above normal for this time of the year due to lack of sufficient snow cover to provide insulation and inhibit freezing.
Ice Jam Mitigation Program with Ice Cutters and Amphibex Fleet
The North Red Community Water Maintenance Corporation will be focusing this year’s ice jam mitigation program with ice cutters and the Amphibex icebreakers on the north Red, Assiniboine, Icelandic, Brokenhead and Fisher rivers as well as the Portage Diversion to reduce the potential of ice jams.
On the Red River, the Amphibex fleet has already broken a seven-kilometre channel down the centre and 15.5 km of ice have been cut, slightly more than this time last year.
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 depend on the nature of the spring breakup and rate of melt.
Flood Outlook
The potential for overland flooding is normal to above normal on the Assiniboine, Qu’Appelle and Saskatchewan rivers and the headwaters of the Souris River due to normal to above-normal water content in snow and above-normal soil moisture levels at freeze-up. The potential for overland flooding is below normal in the Red and Pembina river basins, the Roseau River and the Interlake region. The potential for overland flooding is normal to below normal for the Winnipeg River basin and near normal for the rest of the province.
The magnitude of spring flood potential is still very dependent on weather until the spring melt. Flood potential is significantly affected by:
- the amount of additional snow and rain;
- frost depth at the time of run-off;
- the timing and rate of the spring thaw; and
- the timing of peak flows in Manitoba, the U.S. and other provinces.
Delayed thaw and spring rainstorms could result in rapid snow melt, aggravating overland flooding and increasing tributary flows. A single precipitation event similar to the rainstorm that occurred in the summer of 2014 could change the flood outlook significantly.
The province’s practice is to plan and prepare for unfavourable weather conditions, the highest levels of the three scenarios. The outlook shows the risk of overland flooding for the unfavourable weather scenario in the following watersheds:
- Red River – minor risk;
- Pembina River – minor risk;
- Roseau River – minor risk;
- Assiniboine River – moderate to major risk;
- southwest region – moderate to major risk;
- Interlake region and the Fisher River – minor to moderate risk;
- eastern region and the Winnipeg River – minor to moderate risk; and
- northern Manitoba/The Pas regions and the Saskatchewan, Carrot and Swan rivers – moderate risk.
Preparations
The Manitoba government and municipalities are continuing to prepare for spring flooding. This includes working with municipal emergency management teams to review existing emergency response plans and sharing information through conference calls and flood information seminars in Morris, Brandon and Selkirk.
Provincial flood-fighting equipment includes:
- 2.5 million regular sandbags;
- six sandbag-making machines;
- 19,900 super sandbags;
- 32.5 km of Hesco cage barriers, into which sand or other heavy material is placed;
- nearly 67 km of water-filled barriers, of which 35.3 km are in rapid-response trailers;
- a total of 34 pumps 17 of which are heavy-duty pumps used to move large volumes of flood water – the remainder are part of mobile trailers kits used to fill water barriers, and
- 61 heavy-duty steamers.
The Manitoba government continues to work with stakeholders across the Assiniboine River basin through the newly formed Assiniboine River Basin Initiative. Representatives from the Manitoba government, Keystone Agricultural Producers, the Association of Manitoba Municipalities and Manitoba Conservation Districts Association will join other stakeholders for a meeting next week in Moosomin, Sask. The goal is to discuss options and solutions to common concerns such as drainage, flooding, water quality and drought.
