The Manitoba Infrastructure and Transportation Hydrologic Forecast Centre’s preliminary 2014 spring flood outlook suggests, without additional significant precipitation between now and the spring thaw, the potential for a spring flood is below or near normal in most areas. This is due mainly to near-normal soil moisture content at freeze-up and near-normal water content in the snowpack.
Winter snow levels are near normal to above normal in many areas of the province, Saskatchewan and North Dakota, with the exception of the U.S. and Manitoba portions of the Red River Basin, which are below to near normal.
Parts of the Souris River basin and regions surrounding The Pas that have an above-average flood potential as the soil moisture content levels at freeze-up varied from above to well above normal and the snowpack water content is above to well-above normal, with levels up to 170 per cent of normal.
The magnitude of the spring flood potential is still dependent on weather conditions from now until the spring melt. Flood potential is significantly affected by the amount of additional snow, rain and frost depth during 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 the potential for spring rainstorms could result in rapid snowmelt aggravating overland flooding and increasing tributary flows.
Long-term weather forecasts are subject to change and late snowstorms or early heavy rain could change the current outlook, so three scenarios with different weather developments are described in the outlook. The scenarios are:
- 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.
The possible magnitude of flooding is designated as minor, moderate, major or severe:
- minor flooding results in minimal or no property damage, but there is the potential for flooding of roads below existing flood protection levels;
- moderate flooding has the potential for some flooding of buildings, structures and roads below the flood protection levels and could require the evacuation of people and relocation of property to higher ground or safer locations;
- major flooding presents the potential for flooding of buildings, structures and roads, and the need for evacuations; and
- severe flooding has the potential for extensive flooding, with water above flood protection levels, significant evacuations and movement of property to higher ground.
Rivers
On major rivers, including the Red and Souris rivers, flows are generally normal or near normal for this time of year.
Assiniboine River flows are slightly above normal for this time of year due to releases from the Shellmouth Reservoir, which increases its capacity to manage spring run-off.
Major Interlake rivers, including the Waterhen and Fairford rivers, are above normal due to the consistently high water level of Lake Winnipegosis.
The Red River has thicker-than-normal ice cover due to periods of well-below freezing temperatures this winter. Based on mid-February measurements this year, ice thickness ranged between 36 centimetres (14.2 inches) and 83 cm (32.7 in.). Normal ice thickness varies according to the size and the location of the river and typically ranges between 30 cm (one foot) and 61 cm (two feet).
Lakes
Lake Manitoba’s current level is 247.4 meters (811.8 feet), slightly above normal for this time of year but within the operating range of 247 m (810.5 ft.) to 247.7 m (812.5 ft.).
Lake St. Martin is currently at 244.5 m (802.1 ft.), 1.1 m (3.5 ft.) above normal for this time of year.
Lake Winnipeg’s current level is 217.6 m (713.8 ft.), slightly above normal for this time of year.
Lake Winnipegosis is currently at 253.8 m (832.7 ft.), 0.6 m (two feet) above normal for this time of year.
Dauphin Lake’s current level is 260.4 m (854.3 ft.), slightly above normal for this time of year but within the upper regulation range is 260.5 m (854.8 ft.).
The Shoal Lakes current level is 261.6 m (858.3 ft.), 1.3 m (4.2 feet) above normal for this time of year.
Flood Preparation
The Amphibex icebreakers and ice cutters will be focusing this year’s ice-jam-mitigation program on the north Red, Assiniboine, Icelandic, Brokenhead and Fisher rivers, as well as the Portage Diversion, to reduce the potential of ice jams. The Amphibex fleet has already broken a six-kilometre channel down the centre of the Red River and 12 km of ice has been cut.
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.
Additional 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 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-preparedness meetings in Morris, Brandon and Selkirk.
The next flood outlook is scheduled for the end of March.
