Manitoba Infrastructure and Transportation’s Hydrologic Forecast Centre has issued its third 2013 spring flood outlook for the province.
Additional snowfall in Saskatchewan and continued cool temperatures have delayed snow melt and kept frost in the ground much longer than normal across Manitoba, increasing the likelihood of moderate to major flooding for the Assiniboine and Souris rivers.
Based on additional information from American forecasters, the outlook also indicates the flood risk has increased from minor to moderate to moderate to major for the Roseau and Pembina rivers.
The risk remains moderate to major for the Red River, as indicated in the March outlook, and is also unchanged for the northwest and Interlake regions of the province.
The delayed melt has left major rivers and tributaries with a thick ice cover and below-normal flows for the month of April. Future weather conditions will affect the magnitude of the spring flood potential. The amount of additional snow and rain, the timing and rate of the spring thaw and the timing of peak flows in Manitoba, the U.S. and other provinces will have a significant effect on flood potential. Delayed melt and the potential for spring rainstorms could result in rapid snow melt, aggravating overland flooding and increasing tributary flows. Based on today’s Environment Canada long-range weather forecast, melt and subsequent run-off may start as early as April 17.
Flood-fighting equipment has been placed around the province to bolster emergency response. This includes two million sandbags, six sandbagging machines, 17,000 super sandbags, 43 kilometres of Hesco cage barriers, 50 km of water-filled barriers, and 34 mobile pumps ready to deploy on an emergency basis provincewide.
Souris River
The U.S. and Saskatchewan portions of the Souris River have snow packs ranging between 150 and 200 per cent of normal, higher than they initially reported in March. As a result, Manitoba’s forecast has been revised upwards.
For all weather scenarios, flooding of the Souris River and its tributaries will be moderate to major. Over-bank flows are likely from the U.S. border to downstream of Hartney. An unfavourable weather scenario would result in major over-bank flooding, with peak stages one to 1.5 feet below 2011, from the U.S. border to the town of Souris.
With unfavourable conditions, the towns of Melita and Souris will need additional flood protection.
The town of Souris has dikes that remain in place following preparation for the 2011 flood and will be supplemented with additional protection as needed.
The community of Melita has a permanent dike that was completed in 2009 and the community of Wawanesa is protected by a dike built in 2011 and should not expect over-bank flooding. Aquadams and other temporary flood protection equipment have been deployed to the area should they be required.
The Manitoba government’s regional flood team will continue regular contact with municipal officials from the three towns and the RM of Arthur as the melt unfolds.
Assiniboine River
The forecast for the Assiniboine River has been revised upward to moderate to major flooding due to additional snow in Saskatchewan, above-normal snow moisture content in most of the basin, and above-normal soil moisture in the upper portions of the watershed.
Higher water levels from Saskatchewan are expected on the Qu’Appelle and Souris rivers, which flow into the Assiniboine River. A controlled release from the Shellmouth Dam has brought the reservoir down to a record low level to make room for potential high-water flow from Saskatchewan’s above-average snowpack. Over-bank flooding of agricultural land could occur along the Assiniboine River from Shellmouth to St. Lazare with favourable weather conditions and to Griswold with average weather conditions.
There could be major flooding through the valley to Brandon with unfavourable weather conditions, though it would be expected at levels much lower than those of 2011.
The Manitoba government will station a sandbag machine along with super sandbags and sand in Brandon. Brandon flood protection levels are adequate for the unfavourable weather scenario. There are already plans to add a single row of super-sandbag dikes and/or aquadam protection to First Street and 18th Street if needed.
Brandon’s recently completed eastern access roads will provide alternatives when travelling in and around Brandon this spring in the event of significant flooding.
Provincial officials and City of Brandon staff are working closely together as progress is made on the $20 million flood-mitigation program.
East of Portage la Prairie, provincial crews have inspected and reinforced critical sections of the 80-km lower Assiniboine River dikes built in anticipation of the 2011 flood. Heavy earth-moving machinery for dike support will be ready on mobile trailers to be positioned in strategic locations.
The Portage Diversion is fully operational following extensive damage in 2011. The drop structures have been repaired and critical areas have been reinforced with rip-rap.
Under all weather scenarios, the diversion will be required to manage ice jamming on the Assiniboine River east of Portage and to provide flood protection to the city of Winnipeg. The flow range is expected to be between 9,400 cubic feet per second (cfs) and 18,500 cfs depending on weather conditions. This is considerably less than the 35,000 cfs seen in the 2011 flood.
Duration of diversion flows will be much shorter than 2011, unless heavy spring and summer rainfall develops, and is not expected to have a significant impact on Lake Manitoba levels. Lake Manitoba is currently at 811.8 ft. above sea level (asl). With average weather, the lake is expected to peak at 812.4 ft. asl, close to its top operating range of 812.5 ft. asl and below the historical long-term average. With unfavourable conditions, the lake could peak at 813.3 ft. asl and the province has prepared for all weather scenarios. Geo-tube wave breakers are in place at locations at Delta Beach, Twin Lakes Beach and in the RM of St. Laurent at Sandpiper Beach.
Roseau River
Based on additional information from American forecasters, the potential for spring flooding has increased to moderate to major on the Roseau River.
The average weather scenario would produce moderate flooding similar to 2006 and an unfavourable weather scenario could produce major flooding with over-bank levels slightly above those of 2009.
Dominion City and the Roseau River First Nation are protected by a ring dike that will provide protection above forecast river levels for unfavourable conditions.
Pembina River
The risk for flooding on the Pembina River has been revised upwards to the range of minor to major. Average weather would produce minor to moderate flooding in low-lying areas. However, due to high snow moisture content, an unfavourable weather scenario would produce major flooding. The town of Gretna has a permanent community dike in place that would protect against levels in unfavorable weather conditions.
Red River
The potential for spring flooding on the Red River remains the same as the March flood outlook. Favourable weather would result in minor localized flooding, median conditions could produce minor to moderate flooding similar to 2011 and unfavourable weather conditions could result in major flooding higher than in 2011 but slightly less than 2009 from Emerson to Winnipeg. The Red River valley community ring dikes would protect against these levels in unfavourable weather scenarios. Today’s flood outlook confirms the March outlook, which indicated that dike closures and a PTH 75 detour could be required although no communities are expected to lose road access. A PTH 75 detour was in place for 36 days in 2009 and 44 day in 1997.
Operation of the Red River Floodway will be required for all weather scenarios. 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 metres at the floodway to provide real-time flow data, even under ice conditions, for precise and timely floodway operations.
Levels at James Avenue are forecast to be 17.7 ft. Jamesunder favourable conditions, 18.8 ft. Jamesfor average conditions and 20.5 ft. Jamesfor unfavourable weather conditions. (James refers to the long-term mean winter ice level at James Avenue in Winnipeg)
Water levels on the Red River north of the city of Winnipeg are likely to be close to those of 2009. Manitoba’s Amphibex fleet broke 29 km of ice on the Red River north of Winnipeg this winter as an ice-jam prevention measure. Since then, the Amphibex fleet has also worked on the Portage Diversion, Assiniboine, Whitemud, Fisher, Icelandic and Brokenhead rivers and can be deployed quickly to trouble spots throughout the province to break up ice jams as needed.
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.
