Flooding events in Canada: prairie provinces

In this Section:

• Introduction
• Alberta
• Saskatchewan
  • 1974
  • Qu'Appelle River
  • Rainstorm at Buffalo Gap
• Manitoba: Red River Floods
  • Earliest Red River floods on record
  • Flooding of the Red River in the 20th Century
    • The Winnipeg flood of 1950
    • Red River flooding, 1950-1996
    • Red River flooding, 1997
    • Red River flooding, since 2001

Introduction

Several of the larger river basins in the prairie region are located predominantly on the plains but derive a high proportion of their flows from the headwater regions located on the eastern slopes of the Rocky Mountains. These include the Oldman, Bow and Red Deer rivers, which are major tributaries of the South Saskatchewan River, and the North Saskatchewan River. There are also a number of rivers originating in the mountains of western Alberta or northern British Columbia that flow into the northern plains of Alberta. These include the Athabasca, the Smoky, and the Peace rivers.

The streams beginning in the eastern slopes of the Rockies traverse three major physiographic regions: the mountains, the Foothills, and the Great Plains. Rugged mountains capped by permanent snowfields and glaciers occupy a narrow belt bounded on the west by the continental divide and on the east by the most easterly range of the Rocky Mountains. The Foothills region is a transition zone between the mountains and the Great Plains, which is characterized by ridges and hills paralleling the mountain ranges.

The Great Plains region is generally one of low relief and poorly developed drainage patterns with many undrained lakes, sloughs and marshes.

In the mountains, most of the annual runoff volume and the annual flood peaks are due to spring and summer snowmelt. While snowmelt is a contributing factor to runoff in the Foothills, the major flood peaks are caused by rainfall and, often, in combination with snowmelt.

The storms that produce the major floods are associated with "cold lows," low pressure systems which originate off the west coast of North America or form in the lee of the Rockies. The "cold low" air mass has a counterclockwise circulation and travels generally from west to east across the continent. As the system crosses the continental divide it often intensifies and draws warm, moist maritime air from the Gulf of Mexico and mixes it with colder air from the polar regions at the ground surface. Circulation of the air mass is such that the moisture-laden air is then directed toward the Foothills and mountains where the orographic effect intensifies the rainfall.

Severe convective thunderstorms (precipitation resulting from upward movement and cooling of air that is warmer than its surroundings) also strike the prairies, producing high rainfall rates and extensive local flooding. One such storm, which occurred at Buffalo Gap, Saskatchewan, has been recorded as the most intensive rainfall in Canadian history.

For the larger basins of the agricultural areas of the plains, floods are generally due to spring snowmelt. The depth of the winter snowpack, its water content, and the occurrence of rain during snowmelt are significant in determining peak discharges. Other important factors include the preceding fall and early winter soil moisture conditions, and the extent of frozen ground. Also, ice jams may cause water levels to reach higher stages than open water flows.

Alberta

See: Anecdote: 1975 Spring flood - Waterton Lakes National Park

Saskatchewan

1974

Throughout Saskatchewan, the winter of 1973-1974 was characterized by near-record snowfall and few periods when the temperature exceeded the melting point. Consequently, by the end of winter, several areas reported extremely heavy snow cover.

Extensive flooding of farms and ranchland damaged roads and bridges along the Carrot and Red Deer rivers in eastern and central Saskatchewan. The communities of Pierceland and Green Lake on the Beaver River were also affected. Severe flooding occurred in the Ou'Appelle River basin as well.

Qu'Appelle River

In the spring of 1974, all signs pointed to a flood in the Ou'Appelle River basin. By mid-March, most snow courses operated by the Saskatchewan Department of the Environment indicated the water equivalent of the snowpack was between 127 and 152 millimetres. A cold spring in which the snowpack was not reduced by evaporation, sublimation or an earlier melt period was a positive indication that flooding might occur. A rapid warming trend in the basin beginning in late-April followed. The exceptional runoff from the extremely heavy snowpack resulted in widespread flooding in the Qu'Appelle River basin. The most serious conditions developed in Moose Jaw, Regina and Lumsden, where major damage occurred and flood fighting efforts were concentrated.

During April 18-19, the Moose Jaw River, Thunder Creek and Spring Creek, which join within the City of Moose Jaw, overflowed their banks, cutting the city in half and flooding commercial and residential properties. An estimated 60 city blocks were flooded, 480 homes inundated, and 1400 people evacuated. Several bridges and dams within the city limits were extensively damaged and essential services were disrupted.

On April 20, Wascana Creek, a tributary of the Ou'Appelle River flowing through the centre of Regina, overflowed its banks, endangering residential properties in low-lying areas adjacent to the creek. Some 85 families were evacuated, but early action taken by the city in raising dyke levels prevented major damage.

Both the Moose Jaw River and Wascana Creek enter the mainstem of the Qu'Appelle River above Lumsden. The combination of record flows on these two tributaries with already high flows in the Ou'Appelle resulted in record flows in the Lumsden portion of the river. A flow of 436 cubic metres per second was recorded at Lumsden on April 25, topping the previous record flow of 187 cubic metres per second in 1969. To hold back the rampaging waters, 5.6 kilometres of massive, roof-level dykes were added to the existing dykes in Lumsden. Although at times in danger of being washed out, the dykes succeeded in preventing serious damage to the town.

Rainstorm at Buffalo Gap

On May 30, 1961, a severe rainstorm dropped up to 10 inches (254 mm) of precipitation in less than one hour over a small area near Buffalo Gap, Saskatchewan. In terms of high-intensity short-duration rainfall, it is the greatest flash flood on record in Canadian history.

Hopscotching across the south for the second successive night, a series of violent thunder storms Tuesday... washed away rail and highway grades... flooding hundreds of acres of farmlands.

Source: The Leader-Post, May 31, 1961

Several residents described unusual colours associated with the black storm cloud as "greenish," "pinkish" and "brownish." There was a huge dust cloud ahead of the main storm cloud, and in almost every case this was described as appearing south of the observer, no matter where the point of observation was located in relation to the approaching storm. In some parts of the storm area, heavy hail occurred which remained in drifts several days later. A detailed account of the storm at Buffalo Gap was filed by an agent for the Saskatchewan Wheat Pool.

See also: Anecdote: Wind, hail and rainstorm at Buffalo Gap, Saskatchewan

Manitoba : Red River Floods

The watershed of the Red and Assiniboine rivers is situated almost exactly in the geographic centre of North America and forms part of the larger Nelson River drainage system.

The Red River originates in South Dakota and flows north, forming the boundary between North Dakota and Minnesota, to enter Canada at Emerson, Manitoba. From the border the river continues northward for 250 kilometres to Lake Winnipeg.

The streamflows of the Red River basin are highly variable. Discharge rates at Emerson have ranged from a low of 0.03 cubic metres per second in February 1937, to 3750 cubic metres per second in April 1997. Most of the runoff occurs in the spring as the result of snowmelt and spring rains.

Floods in the lower reaches of the Red River have always been associated with the spring snowmelt. Although snow only makes up about 17% of the total yearly precipitation, its accumulation in combination with other factors has been the main cause of general river overflows. The major factors affecting snowmelt runoff in the basin are:

• extent and moisture content of snowcover;
• rate of melting of the snow;
• rain coincident with snowmelt;
• soil moisture and temperature; and
• low absorptive capacity of the clay soils.

Ice jams occur occasionally, particularly on the tributaries, and these may cause increased flood stages locally.

Courtesy of Manitoba Department of Natural Resources, Water Resources Branch; data provided by A.A. Warkentin.

Earliest Red River floods on record

Little information is known about flood events in the area prior to organized settlement of the region in 1812. Subsequently, the greatest known Red River flood occurred in the spring of 1826. The flood resulted from wet weather the previous autumn, a winter of heavy snow, followed by a late spring with a sudden thaw in early May coinciding with heavy rainfalls. The chance of a flood of this magnitude occurring is about once in 667 years.

At Fort Garry, the Red River rose 2.7 metres in 24 hours; this quick rise in water level may have been due to an ice jam. The estimated maximum discharge of the river through the town was 6371 cubic metres per second.

Floodwaters forced the abandonment of Fort Garry and virtually destroyed every building in the town. Much of the destruction was caused by floating ice that split trees and demolished houses. Eight settlers in Fort Garry and several Indians along the Assiniboine River were reported to have drowned. Boats from the Hudson's Bay Company rescued many people stranded on rooftops. An eyewitness account describes the destruction:

Hunger and famine followed the flood. The long, hard winter had depleted food stores, the floodwaters had swept away livestock and seed, and the soil was too wet to plant until well past the usual planting time. As a consequence, the townsite was abandoned for several years and moved to Lower Fort Garry.

The second and third largest floods occurred in 1852 and 1861, respectively. Again, the floods were due to a wet autumn, heavy snows during the winter, a late and sudden thaw, and rainfall during the snowmelt runoff period.

The flood of 1852 was 0.6 metres lower than the 1826 flood level. The water rose rapidly due to an ice jam. Although flooding was not as extensive as in 1826, more damage was caused due to the interim increase in settlement. About 3500 people, representing 75% of the population, abandoned their homes, and at least one person drowned. Property damage was estimated at 25 000 pounds sterling.

The 1861 flood was 1.2 metres lower than the 1826 flood. Damage was significantly less, with fewer homes evacuated.

Flooding of the Red River in the 20^thCentury

Red River flooding still occurs and, regardless of the magnitude of the floods, damages have steadily increased as development proceeds along the river. In rural areas, floods damage residential and farm buildings and equipment; drown livestock; and delay spring planting.

In urban areas, there is a continuing trend to build on low-lying land and much of this development is residential. The business district of Winnipeg, however, is located on somewhat higher ground.

A characteristic of the Red River is that water levels rise slowly during flood events unless an ice jam develops. With proper warning, loss of household goods, personal property and equipment can be reduced by evacuation. Time may also be available to construct dykes. During the floods of 1948, 1966 and 1997, major damage was avoided in several residential areas of Winnipeg by the construction of emergency dykes.

The Winnipeg Flood of 1950

Another major flood occurred during April, May and June of 1950. The river's peak discharge of 3058 cubic metres per second was less than half the peak discharge of the 1826 flood. A heavy snowcover caused the Red River to reach flood levels by April 22. In early May, a heavy rainfall, twice the normal for the month, occurred. In Winnipeg, the river was above flood stage for 51 days.

At the peak of the flood, the water was 4.6 metres deep in some of the low-lying districts. All that could be seen were rooftops of houses. Water covered one tenth of the city, and an estimated 60 000 people fled their homes. Military cargo planes delivered millions of sandbags, which were piled by thousands of volunteers. Some 3000 soldiers were called in to operate the dykes and pumps. During the flooding two dykes were breached and one volunteer pump operator drowned. Through considerable effort the dykes were able to keep 4700 houses dry.

In rural areas, many towns were inundated and buildings swept away. "I remember seeing a small cottage floating down the river," one resident recalled. "It struck a bridge pillar and the furniture popped out at the one end as it opened like a cardboard cereal box."

Livestock huddled on patches of high ground. Some animals were lucky and food was dropped to them from helicopters. Others were shot so they wouldn't starve.

Source: The Ottawa Citizen, retrospective article, June 9, 1990

One life was lost. Flood damages in 1957 dollars were estimated to be $125.5 million ($610 million in 1998 dollars). Disaster assistance payments amounted to $25 million ($169.5 million in 1998 dollars); over 11 000 claims were paid out for structural damages. The dyking operations were responsible for reducing the overall damages significantly.

Floods above bankfull stage between Emerson and Winnipeg may be expected to occur on average every ten years. Due to the flat topography, flooding can be extensive; the 1950 flood covered 1373 square kilometres.

See also: Anecdote: Reflections on the Winnipeg Flood of 1950

Red River Flooding, 1950-1996

Despite the flood of 1950, development has continued on the floodplain. A flood in 1966 resulted in $12.2 million ($54.2 million in 1998 dollars) in flood disaster assistance.

Between 1962 and 1972, a major flood control program was undertaken to protect Winnipeg. The program, involved the construction of the Red River Floodway, the Portage Diversion, and the Shellmouth Dam.

Two major floods, in 1974 and 1979, have occurred since the completion of the flood control program. The 1974 natural discharge at Winnipeg exceeded that of the 1966 flood event.

The 1979 natural discharge was close to that of the 1950 flood. As in 1974, most of the damage occurred in the valley. Many of the ring dykes protecting the communities were temporarily raised and no communities were flooded. In the town of Morris, 1450 residents were evacuated and 400 from the Roseau Reserve also left for safety reasons. In total, 10 000 people were ordered to evacuate. More than 600 soldiers were brought in to help them leave and to patrol the area. Livestock (12 000) and poultry (145 000) were also evacuated.

Since 1979 under the Canada-Manitoba Flood Protection Projects Agreement, all of the ring dykes in the Red River valley have been upgraded, internal drainage improved, emergency pumps purchased and a communications network installed. These projects now provide 1:100 protection to the communities.

Red River Flooding, 1997

See:

• Flood of the Century 1997. City of Winnipeg: Remembering the Flood of the Century. 

Red River Flooding, Since 2001

See:

• 2009 Flood Forecast (City of Winnipeg)

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