Top ten weather stories for 2011: story one

Word came early that there would be some serious flooding in the eastern Prairies in 2011. Westerners are usually ready for a good flood flight because they face high waters every year, but nobody could have prepared for the flood of 2011 that was unprecedented on so many fronts. Epic melts occurred everywhere – from the Qu’Appelle Valley to eastern Manitoba and from The Pas south to the Canadian-American border – resulting in more acreage under water than ever recorded. Flood talk was continuous and exhausting, lasting from October 2010 when a weather bomb soaked the southern Prairies through to late July when the military on flood patrol finally went home. Known as the flood that would never end and the spring flood that became the summer flood, it featured the highest water levels and flows in modern history across parts of Manitoba and Saskatchewan. Statistically, the flooding on the Assiniboine River in 2011 was estimated to be at levels experienced once in 330 years. And on Lake Manitoba, engineers called the flood a one-in-2,000-year event. Governments at all levels spent close to $1 billion on flood fighting and victim compensation.

It was a recipe for disaster that started just before Halloween 2010, when a super-charged weather bomb dumped 50 to 100 mm of rain and big snows across the southern Prairies. Officials warned that conditions were ripe for one of the most destructive and disastrous spring floods in years, given that several Manitoba lakes and rivers were already near their highest levels ever. A normal or above-normal snowpack combined with a quick thaw would only worsen a bad situation.

Southern Manitobawas within a millimetre of having its wettest year on record in 2010. At freeze-up, soil moisture levels were the second highest since 1948; only 2009 had more. Cold temperatures throughout the winter resulted in deep soil-frost penetration, meaning spring meltwater was likely to spread out instead of soaking in. And at the season’s midpoint, the snowfall total was at a 15-year high. In January, hydrologists estimated an elevated spring runoff potential above 120 per cent across almost all of Manitoba south of the Nelson River. When spring did arrive, cold temperatures slowed the melt and the inevitable flooding. By mid-April, there was plenty of snow left to melt and nowhere for the water to go. Then came heavy spring precipitation, with rains and snow that added to an already bad flooding situation. Water levels climbed steadily, and not just on the perennial flooder, the Red River; the Assiniboine, Souris, Pembina, Qu’Appelle and several other rivers also swelled, as did a host of Manitoba lakes. In early April, Manitoba declared a high flood risk for six rivers, including two that pass through Winnipeg.

The Red River peaked in Winnipeg on the evening of April 7, when an ice jam drove up water levels. The high stage ranked the third largest in the last 150 years. Fortunately, the Assiniboine River only crested days later. Once again the Floodway saved the day, along with some help from Mother Nature, who brought no major rain or snow event to the area in April, May or June.

On May 9, the Manitoba government declared a province-wide state of emergency, issuing evacuation notices for several municipalities along the Assiniboine River. Brandon was at the epicentre of the months-long flood battle. There, the Assiniboine reached its highest level since 1923 and kept rising. The River was nearly seven metres higher than normal and 20 to 30 times wider in some places. Flooding on the Assiniboine near Brandon lasted 120 days and was the largest on record. The fight against the flood waters along the Assiniboine involved thousands of residents, 1,800 members of the Canadian Forces, emergency measures officials and volunteers, including inmates from a local jail.

In southern Saskatchewan, the historic flooding was the result of a number of events, including intense June rainfalls at the same time snowmelt waters were arriving from the Rockies and excessive precipitation during the previous summer, fall and winter. Five days of heavy rain between June 16 and 20 drenched already-soggy ground. Between 50 and 120 mm of added rain fell with heavier amounts occurring in thunderstorms.  Immediately, lakes and reservoirs filled to their maximum allowable flood level, necessitating increased water release through spillways and adding to the flood risk downstream. The deluge at Estevan led to flash flooding and swelled an already burgeoning Souris River, spilling its banks. In May and June, more than 323 mm of rain fell in the city – 14 per cent more than the previous record for that period. All Souris river channels, nearby sloughs and reservoirs were filled to the brim. Authorities were forced to release surplus waters from upstream dams to ease the pressure. The ensuing flood siege forced 800 people from their homes. The village of Roche Percee was almost swallowed by the overflowing Souris. Downstream, almost 4,000 residents along the river spent the Canada Day weekend displaced from their homes because of flooding, while 400 Canadian Forces reservists came to the rescue. The long duration of the flood season, more than 150 days, was evident when the Souris River crested during the second week of July at a worst-case level of 1,100 cubic metres per second – twice the rate experienced on April 26 when the Souris first peaked.