The Manitoba Infrastructure and Transportation Hydrologic Forecast Centre’s second 2013 flood outlook calls for increased spring flooding potential. The increase pertains to the Red, Souris, Pembina, Assiniboine, Saskatchewan and Qu’Appelle rivers, and in the Interlake, due to additional March snowfall, above average snowpack with high water content in many parts of the province, and low temperatures that are keeping frost in the ground longer than normal.
Provincial forecasters say, while these conditions have increased the risk of flooding to moderate to major, up from minor to moderate as forecast earlier this year, the current outlook does not foresee prolonged river flooding and high lake levels as in 2011. The outlook has trended towards the 2009 flood in the Red River Valley and the Interlake.
In addition to heavier-than-average snowfall, which was 200 per cent of normal in much of Manitoba, Saskatchewan and North Dakota this month, provincial forecasters have concluded that cooler than normal temperatures have increased the depth to which soil remains frozen. Across southern Manitoba, soil is frozen to a depth of between 50 centimetres (1.5 feet) to more than 100 cm (three ft.), mainly due to prolonged periods of very cold temperatures. Frozen soil does not absorb meltwater as easily as thawed soils, and it can increase spring run-off and overland flooding.
The colder-than-normal temperatures will also cause a later spring melt, which increases the likelihood of a rapid melt. Cool temperatures later into the year also increase the likelihood that the melting snowpack and normal spring rains will occur at the same time.
While all these factors have increased the risk of flooding to moderate to major, conditions can change quickly and the outlook is still very dependent on weather conditions from now until the spring melt.
Lake Level and River Flow Conditions
Major rivers have thicker-than-normal ice cover with flows either below or close to normal for this time of year. Overall, river flows are below those of February 2011.
At the time of freeze-up, water levels for the Red, Assiniboine, Souris, Qu’Appelle and Winnipeg rivers were below normal. The Saskatchewan River at The Pas is above normal, but lower than it was going into the 2011 flood.
The Assiniboine River is high for this time of year due to controlled releases from the Shellmouth reservoir, which have brought the reservoir down to near-record low levels to accommodate potential high water flow from Saskatchewan’s above-average snowpack. In the Interlake, the Waterhen and Fairford river flows are above normal due to the consistently high water level of Lake Winnipegosis.
Water levels for lakes Winnipegosis, Manitoba and Winnipeg are all well below the levels going into the 2011 flood. Lake Manitoba is down to its current level of 811.8 ft. above sea level, which is within its operating range of 810.5 to 812.5 ft. and below its historical long-term average level of 812.12 ft. Lake St. Martin is presently at 801 ft. with flood protection levels at 806 ft.
FLOOD FIGHT PREPARATIONS
Enhanced Flood Forecasting
This year, 90 volunteers throughout Manitoba provided snow information, such as depth and density, on a regular basis to the forecasting centre, which has proved to be an invaluable data source in the development of this year’s forecasting.
The province also installed 22 new hydrometric stations for a total of 315 stations on Manitoba’s rivers and tributaries. These stations transmit real-time water levels and flows by satellite to Manitoba Infrastructure and Transportation’s Hydrologic Forecast Centre.
In addition, the province has purchased two portable acoustic velocity meters, which can be moved around the province to take real-time water data readings.
Flood Control Works
The Red River Floodway gates have been refurbished and are ready for operation once ice has cleared the inlet and control structure. The province has also installed three state-of-the-art acoustic velocity meters at the floodway to provide real-time flow data under ice conditions.
The Portage Diversion is fully operational following extensive damage in 2011. The drop structure has been repaired and critical areas of the dikes have been reinforced with rip-rap. It is probable that the Portage Diversion will be operated for all scenarios although the duration of its operation will be much shorter than 2011 unless heavy spring and summer rainfall develops. The Portage Diversion will be operated to prevent ice jamming on the Assiniboine River east of Portage la Prairie as it has been used in most years since its construction once the spring melt begins.
The Fairford Channel has been operating at full capacity since fall 2010 to draw down Lake Manitoba.
Community Flood Proofing
The Red River community ring dikes and drainage pump stations have been inspected and are operational. The current flood outlook indicates that dike closures and a PTH 75 detour could happen under the current outlook for flood protection, although no communities are expected to lose road access.
Provincial crews have inspected and made repairs at critical locations along the 160 km of Assiniboine River dikes which were heavily damaged in the 2011 flood.
Provincial officials continue to work closely with the City of Brandon as work continues on the $20 million flood-mitigation program. Under the current outlook, one row of super sandbags may need to be positioned at 18th and First streets. The recently completed eastern access roads will also provide alternatives when travelling in and around Brandon this spring in the event of significant flooding.
The permanent dikes for First Nations communities around lakes Manitoba and St. Martin that were built in 2011 remain in place. There are new dikes in Ralls Island (The Pas), the Shoal Lakes and East St. Paul’s Highland Park.
Since 2011, more than 180 homes around Lake Manitoba have been flood proofed under the province’s Building and Recovery Plan. Following the 2009 flood, the province bought out over 60 homes at Breezy Point to protect people and emergency rescue crews.
Emergency Response Equipment
Manitoba’s three Amphibexex broke 29 km of ice on the Red River this winter, more than four times the amount completed when an Amphibex was first used in the province in 2006.
Amphibexes have since been working along the Portage Diversion and the Icelandic River at Riverton. An Amphibex will be sent to Fisher River First Nation this week to break ice on the Fisher River. The Amphibex fleet can be deployed quickly to trouble spots throughout the province to break up ice jams as needed. The province is also stationing land-based heavy equipment at strategic locations and bridges along the Icelandic and Fisher rivers to combat ice jamming.
The province also has two million sandbags and sand, six sandbagging machines, 17,000 super sandbags, 43 km of Hesco cage barriers, 50 km of water-filled barriers, 61 heavy-duty steamers and 34 mobile pumps ready to deploy on an emergency basis.
The Manitoba government has hosted more than a dozen training sessions with municipal emergency management staff as well as regional pre-flood information sessions with officials in Brandon, Morris and Selkirk. The province will begin regular regional forecast reviews with municipalities as the spring melt begins.
The province will have staff dedicated to work directly with First Nations on the flood forecast. The province will continue to work with Aboriginal Affairs and Northern Development Canada to ensure that First Nation communities are prepared for potential flooding.
The potential for spring flooding is minor to major on the Red River main stem. There is normal to above-normal and widespread snowpack in most of the basin. With favourable weather from now on, minor localized flooding is expected. Median conditions could produce minor to moderate flooding but levels would be lower than those of 2010.
Unfavourable weather conditions would result in moderate to major flooding. Flooding is expected to occur in small tributaries such as the LaSalle, Rat and Morris rivers.
Levels in the main stem would be higher than 2011 but slightly less or the same as 2009 from Emerson to Winnipeg. Water levels north of the city of Winnipeg are likely to be close to those of 2009. There is sufficient community protection along the river to prevent flooding as community dike elevations are higher than the predicted flows, although ice-jam related flooded can be sudden and unpredictable.
The risk for flooding is expected to range from minor to major in the Pembina River. The favourable weather scenario could produce minor localized flooding. Due to above-average snow-water equivalent in the snow, an unfavourable weather scenario is expected to produce major flooding with levels close to those of 2005.
The spring flood risk is minor to moderate on the Roseau River for favourable and median weather conditions. However an unfavourable weather scenario could produce major flooding with levels close to those of 2011.
There is a risk of moderate to major flooding on the Assiniboine River due to normal to above-normal average soil moisture in the upper portions of the watershed and above-normal snow-water equivalent in most of the basin. An unfavourable weather scenario would result in major flooding of the Assiniboine Valley from Shellmouth to Brandon similar to those levels of 1974 but lower than those of major floods in 2011, 1995 and 1976. Brandon flood protection works are higher than the predicted flows.
With unfavourable weather, the Fisher River could experience major flooding with levels slightly higher than 2009 levels.
Lake Manitoba is expected to be close to or higher than the top of the operation range at the conclusion of spring run-off. With median conditions the lake is expected to peak at 812.7 ft., close to the top operating range of 812.5 ft. The lake level would rise to 813.5 ft. with unfavourable conditions. The current level is 811.8 ft., which is within its operating range of 810.5 to 812.5 ft. and below its historical long-term average level of 812.12 ft.
Lake St. Martin
Lake St. Martin is currently at 801 ft. above sea level. Lake levels for the normal weather scenario are forecast to be 801.4 ft. and 802.7 ft. for the unfavourable weather scenario. Both Lake St. Martin and Little Saskatchewan First Nations are protected with dikes of 806 ft., much higher than the forecasted levels.
Lake Winnipegosis is likely to stay near the same as the current level of 811.7 ft. under favourable weather conditions. Expected levels are more than 1.5 ft. lower than the 2011 peak level.
Shoal Lakes levels will experience a half-foot rise with favourable conditions and a one-foot rise with median conditions. With unfavourable weather conditions, the level is likely to rise close to two ft., which is one-half a foot lower than the record level in 2011. The Shoal Lakes current level is 859.1 ft.
Red Deer Lake
Record flooding is expected near Red Deer Lake with all weather conditions.
For all weather scenarios, due to above-average winter precipitation in the North Dakota, Saskatchewan and southern Manitoba portions of the watershed, flooding of the Souris River and its tributaries will be minor to moderate. There is potential for minor to moderate flooding for the normal weather scenario for the Souris River.
Over-bank flows are likely to occur from the U.S. border to Hartney. The unfavourable weather scenario would result in moderate to major over-bank flooding with peak stages similar to those of 2009 from the U.S.-Manitoba border downstream up to the town of Souris. The towns of Souris and Wawanessa should not expect over-bank flooding. The town of Melita has sufficient dike elevation to protect against these levels.
Both soil moisture and winter precipitation are normal to above-normal in the Interlake region. With favourable weather conditions from now on, there is a chance of minor flooding. Average weather conditions are expected to cause moderate flooding. Moderate to major flooding is expected with unfavourable weather conditions. Environment Canada’s long-term April to June climatic outlook calls for above-normal precipitation in the northern Interlake region.
The soil moisture is below normal but the snow-water content is normal to above normal for this region with minor localized flooding under the unfavourable weather scenario producing moderate flooding due to over-bank flows in areas around the Poplar, Bloodvein, Bisset and Berens rivers.
Northern Manitoba and The Pas Regions
Soil moisture and snow cover are both near normal to above normal in the Saskatchewan and Manitoba portions of the Saskatchewan River Basin. Minor flooding is likely with favourable weather conditions from now on. The average weather scenario would produce minor to moderate flooding. The unfavourable weather scenario calls for localized moderate to major flooding, especially if there is a rapid melt in areas with heavier snowpack like the Pasquia region. The Saskatchewan River is predicted to see levels similar to those of 2006. The river would be expected to remain within its banks. With median weather conditions, the Carrot River is expected to be close to bank-full level. With the unfavourable weather scenario, the Carrot River is expected to overflow its banks with levels higher than those experienced in 2011.
Swan River may see minor flooding with a favourable weather scenario, moderate (similar to 1979) with median weather conditions and moderate to major flooding (less than 2006 and higher than 2011) under an unfavourable weather scenario.
This is the final outlook with daily flood reports to be issued beginning in April during the time of active melt and river flow. The detailed outlook with text and charts is available at www.gov.mb.ca/mit/floodinfo.
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