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WSRCD

West Souris River Conservation District
   Updated June 4, 2016

Souris River flood of 2011

The flood of 2011 in Southwestern Manitoba was record breaking in many ways. The Assiniboine River, the Souris River and almost every creek and river south of Riding Mountain flooded at least three times, each peak bigger than the one before.

The stage for these floods was being set  in the summer of 2010. Rainfall on the southern prairies was about 30% above normal in 2010 and just 1 mm short of the record. As the map shows soil moisture throughout the watershed at freeze up was 130 to 175% of normal. Also see the snow map showing the snow pack up to February 20. Chart 1 shows the monthly precipitation amounts and chart 2 shows percent of normal from August 2010 to August 2011. For the year, August 1, 2010 to August 1 2011, Weyburn received 167%, Minot 135% and Melita 112% of normal precipitation.

Chart 3 shows the daily precipitation for Melita, Minot and Weyburn averaged over the three sites to roughly show what fell on the watershed. The average of the three for the year adds up to just over 400 mm yet only 75 mm ran off indicating that more than 300 mm soaked into the ground, evaporated and went into reservoir storage. Also see the precipitation maps for May and June 2011.

As chart 4 shows there was first a peak in April primarily due to snowmelt. Then in June another higher peak due to rain. More rain in June caused Saskatchewan reservoirs to overflow and very high peaks all along the Souris flooding Minot and threatening many other communities. All three peaks were higher than every other flood since 1913 except 1976 see chart 5.

Until this year 1976 was considered the benchmark flood and nothing on record came even close. Although the peak flows in Manitoba weren't much different than in 1976 the volumes were spectacular see chart 5 and chart 6.

The flood peak at Wawanesa was 29,000 cubic feet per second on July 6, 2011. This was about a one in a 130 year event. The total volume of flow was about 4.59 million acre feet (that's equivalent to 4.59 million acres (7178 square miles) covered by a foot of water or the Souris River watershed covered with 3.6 inches of water and that is about a one in 500 year event. So the good news is that the odds of that happening again in your life time are pretty small.

The drainage area upstream of Wawanesa is 23590 square miles. The total runoff was about 3.7 million acre feet or about 3 inches over the entire watershed. The average annual runoff is equivalent to 0.1 inches off the entire watershed.

Here are some photos that show the progress of the flooding over Oak and Plum Lakes click here

 

2011 Peak Flows

River Return Period
Qu'Appelle 1 in 110 years
Assiniboine at Russell 1 in 70 years
Assiniboine at Brandon 1 in 400 years
Assiniboine at Portage 1 in 400 years
Souris at Westhope 1 in 450 years
Souris at Wawanesa 1 in 400 years
Pipestone near Pipestone 1 in 160 years
Elgin Creek 1 in 44 years
Pembina River at Neche 1 in 60 years
Red River at Winnipeg 1 in 30 years

There were more than 7200 evacuees, 835 road closures and 70 states of emergency. About 1500 army personnel were called in to help.

There were about 2.9 million unseeded acres due to the flooding in 2011.

The total volume of water that flowed through Wawanesa in 2011 was more than double the previous record set in 1976. The volume through Brandon was also double the previous record but set in 1955.

The cost to the province, from an article in the Free Press in November 2012, was well over $1 billion. "So far, the province has spent $359 million on agriculture assistance, $289 million on disaster financial assistance, $48 million on the Lake Manitoba Flood Assistance Program, $240 million in flood fighting, mitigation, restoration and flood-proofing and $89 million on an emergency channel and other infrastructure works."
This doesn't include all kinds of lost business and personal losses throughout Western Manitoba and costs and impacts continue into 2014.

Before 1999 rain flood events affecting large areas were rare. The worst events impacted small areas. Rainfall flood events causing serious damage to large areas of Western Manitoba occurred in 1999, 2005, 2011 and 2014. Rainfall events seem to have become more intense and cover much larger areas.