Manitoba spring flood outlook released
By Top Crop Manager
Feb. 29, 2016 - Risk of overland flooding in Manitoba is generally minor to moderate as the run-off potential is normal to below normal across the province, according to the Hydrologic Forecast Centre of Manitoba Infrastructure and Transportation's first 2016 spring flood outlook.
The outlook notes the overall flood risk could change depending on weather conditions between now and the spring melt.
The flood potential is estimated to be moderate in the northwestern areas and minor to moderate in the rest of the province. The second outlook at the end of March will further define the overall flood potential.
Most of the major lakes are near normal levels for this time of the year and the risk for potential flooding is minor under normal weather conditions. Flows and levels in most rivers are near normal for this time of the year.
Frost in Soil
Mild weather and below-average snow cover has resulted in frost depth near-normal to slightly less than normal throughout most of Manitoba. Generally below normal frost depth means that the soil can absorb more melting water and potentially decrease the amount of overland flooding. Above normal frost depth can contribute to increased run-off.
Soil Moisture Conditions at Freeze-up
• Southern Manitoba including the Red River Valley – near-normal to below normal;
• Western Manitoba – near normal;
• Saskatchewan – above normal;
• Northern Manitoba including The Pas region – above normal;
• Interlake – near normal to above normal; and
• Eastern Manitoba - above normal.
Winter precipitation is below to well below normal throughout the central and southern portions of Manitoba and Saskatchewan including the Interlake, Souris River, Qu'Appelle River, Pembina River and Assiniboine River basins. Winter precipitation is normal to below normal for the Red and Roseau River basins.
Winter precipitation has been near-normal for eastern Manitoba including the Whiteshell area, the Saskatchewan River watershed in Saskatchewan and the northern part of the Lake Winnipegosis basin. Localized above normal precipitation has occurred near The Pas.
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 normal to below normal for this time of the year due to above normal temperatures and lower than normal snow cover to provide insulation and prevent freezing.
Ice Jam Mitigation Program with the Ice Cutters and Amphibex Fleet
At this time the ice jam mitigation program, using the ice cutters and Amphibex fleet, has already broken a channel approximately 13 km long down the center of the north Red River and work is ongoing. Ice conditions on the Icelandic, Brokenhead and Fisher rivers will be assessed this week to determine if icebreaking would benefit those communities.
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.
Future Weather Outlook
The extent of the overall spring flood potential is still very dependent on future weather conditions. Most weather prediction centers predict normal to below normal precipitation and above normal temperatures for most of Manitoba and Saskatchewan for the coming three months. Above normal temperature forecast indicates the potential for an early melt.
The potential for spring run-off is below normal in the lower Assiniboine, Pembina, Qu'Appelle and Souris river basins. The potential is normal to below normal in the Red River as w ell as the Interlake region.
The potential for spring run-off is near normal in the upper Assiniboine and Roseau river basins and throughout the rest of the province, including the Winnipeg River basin.
The potential is normal to above normal in the Saskatchewan River basin. The potential for normal to above normal run-off in the Saskatchewan River basin, including Carrot River, is a result of above normal soil moisture content at freeze-up and normal to above normal snowpack water content.
The extent 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 scenario of highest flood risk. 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 – moderate risk;
• Assiniboine River – moderate risk;
• southwest region – minor risk;
• Interlake region and the Fisher River – moderate risk;
• eastern region and the Winnipeg River – moderate; and
• northern Manitoba/The Pas Regions and Saskatchewan, Carrot and Swan rivers – moderate risk.
The Manito ba 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:
• six sandbag-making machines;
• 19,900 super sandbags;
• 2.2 million regular sandbags;
• 32.5 km of Hesco cage barriers, into which sand or other heavy material is placed;
• 69 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 and the remainder are part of mobile trailers kits used to fill water barriers; and
• 61 heavy-duty steamers.
Manitoba continues to work with stakeholders across the Assiniboine River basin through the 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 month in Minot, North Dakota. The goal is to discuss options and solutions to common concerns such as drainage, flooding, water quality and drought.