2011 Assiniboine River flood
Encyclopedia
The 2011 Assiniboine River flood was caused by above average precipitation in Western Manitoba and Saskatchewan. This was a 1 in 300 year flood that affected much of Western Manitoba. The flooding in Manitoba was expected to mostly involve the 2011 Red River Flood
but instead the more severe flooding was found on the Assiniboine in the west.
would be similar to the flood of 1995. During the winter of 2010–2011 the Shellmouth Reservoir
was emptied in preparation, to store water for the coming spring flood. As the year progressed, the estimates on the flood were revised upwards.
The first major settlement to experience the floodwater was St. Lazare, Manitoba
which was located near the confluence of the Assiniboine River and Qu'Appelle River
. Dikes were built up to protect against the rising floodwater, but unfortunately some residences were not spared as their protective dikes were overwhelmed. The flood continued downstream, spilling over its banks and flooding campgrounds and fields in the flood plain. Brandon
, Manitoba's second largest city, prepared well in advance of the anticipated flood building up both earthen dikes as well as sandbag/Hesco bastion
dikes. After a heavy snowfall on April 29 and 30 over much of the Assiniboine River watershed the crest forecast for Brandon was revised upward well above the flood of 1976. The river peaked at about 37100 cuft/s,60% higher than the previous highest recorded peak of 23000 cuft/s in 1923. The 2011 event is estimated to be a 1 in 300-year flood.
Shortly thereafter a state of emergency was declared in Brandon as well as other municipalities across Manitoba. Premier Greg Selinger requested from Prime Minister Stephen Harper
troops from the Canadian military to help with the flood fighting efforts; the previous time the military was called in to help fight a flood in Manitoba was the 1997 Red River Flood.
Downstream of Brandon, the Manitoba Government forecast that between 54000-56000 cu ft/s of water would enter into the Portage Diversion
reservoir near Portage la Prairie. The capacity for the Portage Diversion channel, which drains into Lake Manitoba
, is only approximately 25000 cuft/s, which would mean that between 29000-31000 cu ft/s of water would flow toward communities such as Poplar Point, St. Francois Xavier
, and Headingley
, before joining with the Red River
at The Forks
. This amount of water would overwhelm the dikes downstream, along the Assiniboine River, which were only built to allow for a channel capacity of about 19000-20000 cu ft/s before spilling over; otherwise breaching of dikes would occur.
On June 22, 2011 the city of Minot in North Dakota issued an evacuation of 12,000 residents due to the swollen Souris River that flows through the city. The Souris River starts in Saskatchewan and makes its way south across the border and then back north into Manitoba. Residents in Souris, Manitoba will be watching to see what happens. The Souris River then eventually joins up with the Assiniboine River past Brandon which could again raise water levels on the Assiniboine due to the swollen Souris and the possibility of Lake Manitoba raising up again. Preparations are under way for the communities along the Souris to raise dikes and evacuations have begun. The province has said it will push the limits of the flood protection again. 2011 Souris River flood
watershed, resulting in more manageable river levels along the Assiniboine River. The exact location decided on was at the Hoop and Holler Bend.
The controlled breach of the dike was estimated to flood approximately 225 square kilometres (86.9 sq mi). This option was chosen as opposed to risking an uncontrolled breach, which could release as much as 500 square kilometres (193.1 sq mi) with flows of up to 15000 cuft/s, while over 800 homes would be affected by the waters. Military personnel were assigned to build flood protection in Brandon, on the Assiniboine River west of Portage la Prairie, and for residences that were at risk of flooding due to the controlled breach.
The intentional breach and overland flooding began on Saturday May, 14. The resultant flooding was very slow moving and was expected to take several days to reach the La Salle River. The waters intentionally spilled from the Assiniboine were expected to cover 185 square kilometres (71.4 sq mi) and flood a possible 150 homes. The Expected crest at the Portage Reservoir was then downgraded to around 52000 cuft/s, leading some engineers to question the necessity of the breach at Hoop & Holler Bend as between the Portage Diversion (34000 cuft/s) and the Assiniboine River Channel (up to 20000 cuft/s) could have handled the floodwater. The controlled breach has carried no more than 400 cuft/s and flooding was modest.
resulted in an increase of 1.22 foot (0.371856 m) in the level of the lake http://www.gov.mb.ca/waterstewardship/reports/lake_manitoba/water_levels_summary2003-07.pdf. The Flood of 2011 would likely surpass these totals, causing flooding to Lake Manitoba, which has already surpassed 814 feet (248.1 m)above sea level (the flood stage on the lake), and is projected to reach as high as 817.81 feet (249.3 m) above sea level. This will likely lead to flood fighting efforts shifting from the Assiniboine River to Lake Manitoba as the flood progresses.
2011 Red River flood
The 2011 Red River flood took place along the Red River of the North in Manitoba in Canada and North Dakota and Minnesota in the United States beginning in April 2011. The flood was, in part, due to high moisture levels in the soil from the previous year which meant that further accumulation would...
but instead the more severe flooding was found on the Assiniboine in the west.
Early signs
Initially, it was predicted that the flood along the Assiniboine RiverAssiniboine River
The Assiniboine River is a river that runs through the prairies of Western Canada in Saskatchewan and Manitoba. It is a tributary of the Red River. The Assiniboine is a typical meandering river with a single main channel embanked within a flat, shallow valley in some places and a steep valley in...
would be similar to the flood of 1995. During the winter of 2010–2011 the Shellmouth Reservoir
Shellmouth Reservoir
The Shellmouth Reservoir is a man-made reservoir on the Assiniboine River in Manitoba and Saskatchewan, Canada.The Shellmouth Dam an embankment dam was built by the Prairie Farm Rehabilitation Administration . Construction started in 1964 and was completed in 1972 costing $10.8 million. The dam is ...
was emptied in preparation, to store water for the coming spring flood. As the year progressed, the estimates on the flood were revised upwards.
The first major settlement to experience the floodwater was St. Lazare, Manitoba
St. Lazare, Manitoba
St. Lazare is a small English and French-speaking village in western Manitoba, Canada. It is surrounded by the Rural Municipality of Ellice. The village showed a population of 265 inhabitants in both the 2006 census and the 2001 census.-Radio:...
which was located near the confluence of the Assiniboine River and Qu'Appelle River
Qu'Appelle River
The Qu'Appelle River is a Canadian river that flows 430 km east from Lake Diefenbaker in southwestern Saskatchewan to join the Assiniboine River in Manitoba, just south of Lake of the Prairies, near the village of St. Lazare....
. Dikes were built up to protect against the rising floodwater, but unfortunately some residences were not spared as their protective dikes were overwhelmed. The flood continued downstream, spilling over its banks and flooding campgrounds and fields in the flood plain. Brandon
Brandon
-Names and people:*Brandon , a male given name*Brandon , a surname with several different origins-Australia:*Brandon, a farm and 19th century homestead in Seaham, New South Wales*Brandon, Queensland, a small town just south of Townsville...
, Manitoba's second largest city, prepared well in advance of the anticipated flood building up both earthen dikes as well as sandbag/Hesco bastion
Hesco bastion
The HESCO bastion is both a modern gabion used for flood control and military fortification and the name of the British company that developed it in the late 1980s. It is made of a collapsible wire mesh container and heavy duty fabric liner, and used as a temporary to semi-permanent dike or barrier...
dikes. After a heavy snowfall on April 29 and 30 over much of the Assiniboine River watershed the crest forecast for Brandon was revised upward well above the flood of 1976. The river peaked at about 37100 cuft/s,60% higher than the previous highest recorded peak of 23000 cuft/s in 1923. The 2011 event is estimated to be a 1 in 300-year flood.
Shortly thereafter a state of emergency was declared in Brandon as well as other municipalities across Manitoba. Premier Greg Selinger requested from Prime Minister Stephen Harper
Stephen Harper
Stephen Joseph Harper is the 22nd and current Prime Minister of Canada and leader of the Conservative Party. Harper became prime minister when his party formed a minority government after the 2006 federal election...
troops from the Canadian military to help with the flood fighting efforts; the previous time the military was called in to help fight a flood in Manitoba was the 1997 Red River Flood.
Downstream of Brandon, the Manitoba Government forecast that between 54000-56000 cu ft/s of water would enter into the Portage Diversion
Portage Diversion
The Portage Diversion is a water control structure on the Assiniboine River in Portage la Prairie, Manitoba, Canada. The project was made as part of a larger attempt to prevent flooding in the Red River Valley...
reservoir near Portage la Prairie. The capacity for the Portage Diversion channel, which drains into Lake Manitoba
Lake Manitoba
Lake Manitoba is Canada's thirteenth largest lake and the world's 33rd largest freshwater lake. It is in central North America, in the Canadian province of Manitoba, which is named after the lake...
, is only approximately 25000 cuft/s, which would mean that between 29000-31000 cu ft/s of water would flow toward communities such as Poplar Point, St. Francois Xavier
St. François Xavier, Manitoba
St. François Xavier is a rural municipality lying west-northwest of Winnipeg, Manitoba, Canada. It is part of the Winnipeg Capital Region and had a 2001 census population of 1,024....
, and Headingley
Headingley
Headingley is a suburb of Leeds in West Yorkshire, England. It is approximately two miles out of the city centre, to the north west along the A660 road...
, before joining with the Red River
Red River of the North
The Red River is a North American river. Originating at the confluence of the Bois de Sioux and Otter Tail rivers in the United States, it flows northward through the Red River Valley and forms the border between the U.S. states of Minnesota and North Dakota before continuing into Manitoba, Canada...
at The Forks
The Forks
- Canada :*The Forks, Winnipeg, Manitoba, a district around the confluence of the Red River of the North and Assiniboine River*Saskatchewan River Forks, where the North Saskatchewan and South Saskatchewan rivers combine to form the Saskatchewan River...
. This amount of water would overwhelm the dikes downstream, along the Assiniboine River, which were only built to allow for a channel capacity of about 19000-20000 cu ft/s before spilling over; otherwise breaching of dikes would occur.
On June 22, 2011 the city of Minot in North Dakota issued an evacuation of 12,000 residents due to the swollen Souris River that flows through the city. The Souris River starts in Saskatchewan and makes its way south across the border and then back north into Manitoba. Residents in Souris, Manitoba will be watching to see what happens. The Souris River then eventually joins up with the Assiniboine River past Brandon which could again raise water levels on the Assiniboine due to the swollen Souris and the possibility of Lake Manitoba raising up again. Preparations are under way for the communities along the Souris to raise dikes and evacuations have begun. The province has said it will push the limits of the flood protection again. 2011 Souris River flood
2011 Souris River flood
The 2011 Souris River flood is a record hundred-year flooding event on the Souris, a tributary of the Assiniboine River, which it meets near Treesbank, Manitoba. The Assiniboine meets the Red River of the North south of Winnipeg, Manitoba. The flooding has affected Saskatchewan and North Dakota,...
Intentional breach and flooding
It was determined by the Manitoba government that that the capacity could be increased to 32000-34000 cu ft/s by building up the banks of the Portage Diversion, depending on hydraulic resistance on bridges along the channel. This would reduce the flows on the Assiniboine River somewhat, but still not enough for the dikes to hold. It was also determined that a controlled release of water from the Assiniboine in the range of 2000–6000 cu ft/s should be created downstream of the Portage Diversion in order to reduce flows on the river, and divert the water into the La Salle RiverLa Salle River
The La Salle is a river in Manitoba, with its source near Portage La Prairie and terminating in the Red River in Saint Norbert . The La Salle River flows mainly through agricultural land. It is a slow-moving, meandering prairie river with variable depth...
watershed, resulting in more manageable river levels along the Assiniboine River. The exact location decided on was at the Hoop and Holler Bend.
The controlled breach of the dike was estimated to flood approximately 225 square kilometres (86.9 sq mi). This option was chosen as opposed to risking an uncontrolled breach, which could release as much as 500 square kilometres (193.1 sq mi) with flows of up to 15000 cuft/s, while over 800 homes would be affected by the waters. Military personnel were assigned to build flood protection in Brandon, on the Assiniboine River west of Portage la Prairie, and for residences that were at risk of flooding due to the controlled breach.
The intentional breach and overland flooding began on Saturday May, 14. The resultant flooding was very slow moving and was expected to take several days to reach the La Salle River. The waters intentionally spilled from the Assiniboine were expected to cover 185 square kilometres (71.4 sq mi) and flood a possible 150 homes. The Expected crest at the Portage Reservoir was then downgraded to around 52000 cuft/s, leading some engineers to question the necessity of the breach at Hoop & Holler Bend as between the Portage Diversion (34000 cuft/s) and the Assiniboine River Channel (up to 20000 cuft/s) could have handled the floodwater. The controlled breach has carried no more than 400 cuft/s and flooding was modest.
Effects on Lake Manitoba
With the diversion of water from the Assiniboine using the Portage Diversion into Lake Manitoba, the water level on the lake increased. Increasing the capacity of the Diversion put surrounding residences in danger of being flooded, also prompting an evacuation of Delta Beach on Lake Manitoba. Due to the increased capacity of the diversion and the duration of its use, it was likely to increase water levels on Lake Manitoba significantly, likely more than the 1976 Assiniboine River Flood, which resulted in approximately 1420000 acre.ft of water being diverted. The Manitoba Government's own projections indicated that excluding the outflows of Lake Manitoba through the Fairford RiverFairford River
The Fairford River is a river of Manitoba, Canada. It flows into Lake Pineimuta and Lake St. Martin. The river is used to control the water level of Lake Manitoba. Regulation of Lake Manitoba dates back to the late 1890s and in 1961 the current form of the dam on the river, the Fairford River...
resulted in an increase of 1.22 foot (0.371856 m) in the level of the lake http://www.gov.mb.ca/waterstewardship/reports/lake_manitoba/water_levels_summary2003-07.pdf. The Flood of 2011 would likely surpass these totals, causing flooding to Lake Manitoba, which has already surpassed 814 feet (248.1 m)above sea level (the flood stage on the lake), and is projected to reach as high as 817.81 feet (249.3 m) above sea level. This will likely lead to flood fighting efforts shifting from the Assiniboine River to Lake Manitoba as the flood progresses.