The history of flooding in Canada includes floods caused by snowmelt runoff or freshet flooding, storm-rainfall and "flash flooding", ice jams during ice formation and spring break-up, natural dams, coastal flooding on ocean or lake coasts from storm surges, hurricanes and tsunamis. Urban flooding can be caused by stormwater runoff, riverine flooding and structural failure when engineered flood management structures, including dams and levees, prove inadequate to manage the quantities and force of flood waters. Floods can also occur when groundwater levels rise entering buildings cracks in foundation, floors and basements. Flooding is part of the natural environmental process. Flooding along large river systems is more frequent in spring where peak flows are often governed by runoff volume due to rainfall and snowmelt, but can take place in summer with flash floods in urban systems that respond to short-duration, heavy rainfall. Flooding due to hurricanes, or downgraded severe storms, is a concern from August to October when tropical storms can affect Eastern North America. Flood events have had a significant effect on various regions of the country. Flooding is the costliest natural disaster for Canadians. Most home insurance claims in Canada deal with water damage due to sewer back-up, not fire.
Floods occur five times as often as wildfires, the second most frequent natural hazard in Canada. Between 1900 and 2005 there were 241 flood disasters in Canada.
The 1894 Fraser River flood had a return period of slightly more than 500 years and the 1948 flood was close to a 200-year event. The 1997 Red River flood was named the 'flood of the century'. The International Joint Commission (IJC)'s 1998 report warned that although the 1997 Red River flood had a "return interval ranging from 100 to 500 years, depending on the location", there was a "statistical probability of a similar flood each year." The 2011 Assiniboine River Flood was estimated to have a return interval of 300 years.
The Calgary flood had a return interval ranging from 70 to 100 years. A 100-year flood has a 1-percent annual exceedance probability (AEP) flood. with a flow of the Bow River in Calgary measured at c. when the flood reached its peak level on June 21, 2013.
List of floods.
1879 Fort Calgary flood.
The flood of 1879 had an estimated peak rate of based on high-water marks.
1894 Fraser River flood.
The largest flood of British Columbia's Fraser River on record occurred in May 1894, when rapid snow melt caused river levels to rise dramatically, triggering flooding from Agassiz to Richmond. The flood was significant in both height and breadth. In 2008, Northwest Hydraulic Consultants (NHC) recommended the adoption of the following flood frequency estimates at the Hope gauge on the Fraser River: 100 year daily maximum flow ; 200 year daily maximum flow ; 500 year daily maximum flow . The Fraser's highest recorded flow, in June 1894, is estimated to have been or within a range of about at Hope. Based on these flows, the 1894 flood had a return period of slightly more than 500 years and the 1948 flood was close to a 200-year event. Of the two catastrophic floods on the Lower Fraser River since European settlement in the Fraser Valley, the flood of 1894 is considered to be the "flood of record", but the flood of 1948 caused greater damage because of "intensive development" on the flood plain.
1897 Fort Calgary flood.
The flood of 1897 had an estimated peak rate of based on high-water marks. In comparison, 116 years later, in June 2013, the Bow River in Calgary peaked at c..
1902 Saint John River flood.
In March 1902, fifteen ice jams in the Saint John River basin resulted in some of the worst floods on that river in the 20th century with two deaths, and extensive damage to bridges, roads, railways, and lumber mills.
The Saint John River has a long history of flooding from 1696. Major reported flood events took place in 1887, 1902, 1923, 1936, 1970, 1973, 1976, 1979, and 1987, 2018.
1915 Calgary flood.
The 1915 Bow River flood in Calgary in June washed away the MacArthur Bridge, drowning city employee Edwin Tambling, and nearly drowning Calgary Commissioner for Public Works Jim Garden, and Aldermen Samuel Hunter Adams. Three people would die as a result of the flood. The Bow River rose above normal, a record height. The MacArthur Bridge was replaced by the Centre Street Bridge in 1916. The Sheep Creek floods in Okotoks cut gas mains left Calgarians without cooking fuel.
1929 Calgary and southern Alberta flood.
In June 1929, widespread flooding in southern Alberta caused major damage in Calgary and High River when the Bow River, Highwood River, and other rivers and creeks overflowed caused by extensive rainfall. Among some of the damage caused was extensive damage to the Calgary Zoo where several animals were killed, roads washed out at Banff, and homes flooded in Mission.
In June 1923, the Elbow River broke the 1915 record by when it rises to . The Bow River, though it rises above normal, is still about under the 1915 record height.
1929 Tsunami Burin Peninsula, Newfoundland flood.
On November 18, 1929, a tsunami stuck Burin Peninsula, Newfoundland, after a large-scale Grand Banks earthquake. Sometime after the quake, many people noticed the water draining out of the coves and harbours. In St. Lawrence, "the harbour bottom, which on average is deep, was visible in places." "As the water receded, it exposed portions of the ocean floor that were normally submerged and caused boats docked at various harbours to tumble over onto their sides. Minutes later, three successive waves hit the shore and water levels rose dramatically." Three waves hit the coast at about three hours after the earthquake occurred. "In most places, the sea level swelled three to seven metres above normal, but in some of the peninsula's long narrow bays, such as at Port au Bras, St. Lawrence, and Taylor's Bay, the water rose by between to ." The waves travelled at speeds up to at the epicentre; they were recorded as far away as Portugal. The tsunami destroyed many south coastal communities on the Burin Peninsula, killing 27 or 28 people, sweeping away homes, businesses, wharves, and fishing boats, and leaving 10,000 more homeless.
1948 Fraser River flood.
In 1948, the second largest Fraser River flood of record occurred. By this time, the Lower Fraser Valley was a highly developed agricultural area, with commercial and industrial development and the beginnings of residential development. As well, two transcontinental rail lines and the Trans-Canada Highway had been built through the valley, and the province's major airport had been established in Richmond. Personal and financial impact was much greater than in 1894. Thousands of people were displaced and infrastructure, including bridges and roads, was significantly damaged. Based on the 2008 NHC estimates of a 200-year daily maximum flow of , the 1948 flood was close to a 200-year event. The flood of 1948 caused greater damage than the 1894 flood because of "intensive development" on the flood plain. At the height of the 1948 flood, stood under water. Dykes broke at Agassiz, Chiliwack, Nicomen Island, Glen Valley, and Matsqui. By the time the flood waters receded a month later, 16,000 people had been evacuated, and damages totalled $20,000,000.
1950 Red River flood.
During the 1950 Red River flood the Red River reached its highest level since 1861
 resulting in a major flood from April to June turning of Manitoba farmland into a vast inland sea. On May 18, the Red River reached 30.3 feet above normal. Approximately 107,000 people were evacuated from the area. Prime Minister Louis St. Laurent called it the "most catastrophic flood ever seen in Canada". Only one person, Lawson Ogg, lost his life to the flood. Estimated costs were from $600,000,000 CAD to over $1,000,000,000 CAD.
The province of Manitoba completed the Red River Floodway in 1968 after six years of excavation, put up permanent dikes in eight towns south of Winnipeg, and built clay dikes and diversion dams in the Winnipeg area. Other flood control structures completed later were the Portage Diversion and the Shellmouth Dam on the Assiniboine.
1954 Toronto region flood: Hurricane Hazel.
The most famous hurricane in Canadian history struck on October 15, 1954, causing catastrophic flooding. Hurricane Hazel submerged low-lying land from Etobicoke to the Holland Marsh and left 81 people dead. No natural disaster since has led to such a high death toll in Canada. Over 4,000 families were left homeless.
Sandink argued that there are major discrepancies in cost estimates for flood damage in general and for Hurricane Hazel in particular. Neither insurance companies nor governments cover the full damage. The Department of Public Safety and Emergency Preparedness Canada estimates the total cost of Hurricane Hazel for Canada, taking into account long-term effects such as economic disruption, the cost of lost property, and recovery costs, as being $137,552,400 CAD. University of Western Ontario Geography professor Dan Shrubsole estimated the costs at about $2,000,000,000 CAD (2008). Environment Canada estimated the flood damages at $25,000,000 (1954) or $205 million (in 2008 dollars)
In the Toronto area, winds reached per hour and there was of rain in 48 hours. The Humber River, located in the west end of the city, caused the most destruction, as a result of an intense flash flood. Toronto's infrastructure took a heavy hit. Not built to withstand serious flooding, as it is in a climate area that does not see exceptionally prolonged or heavy rainfall, over 50 bridges, many part of important highways, were heavily damaged or put out of commission, when high water itself washed them out or debris in the water smashed them. Numerous roads and railways were also washed out. At the peak of the flooding, the Don River's flow rate was . Normally the Don River flow is rising to during the spring.
By 1959, as a result of Hurricane Hazel, a regional approach to flood control and water management was adopted in Ontario and by 1959 the Metropolitan Toronto and Region Conservation Authority (MTRCA) finalized a comprehensive Plan for Flood Control and Water Conservation, which included the proposed development of large dams and major flood control channels, with future plans for an erosion control program and the acquisition of 7,300 acres of land.
1973 Saint John River flood.
Known as the Great Flood of 1973, this flood in late April 1973 was driven by a combination of snow melt and heavy rain. Flooding occurred almost the entire length of the river, with the worst damage in the Fredericton area. At the time it was the most serious flood on the Saint John River in historic times.
1974 Grand River flood.
In May 1974, several communities along the Grand River were flooded as a result of 50 mm of rain falling in the upper part of the watershed, quickly overflowing reservoirs which had been filled to capacity in anticipation of the dry summers months. The flooding caused almost $7 million (unadjusted) in damage, with more the $5 million of that coming from Galt, Ontario. Significant improvements were made to the dike system along the river which could withstand a flow rate of 2,352 m3/s in Cambridge and 3,400 m3/s in Brantford, significantly above the 1,800 m3/s peak during the flood.
1979 Tropical Storm David hit Moncton.
In September 1979, Tropical Storm David caused an estimated $881,600 CAD (1998) in flood damages in the area around Moncton, New Brunswick.
1984 Pemberton Valley flooding.
In October 1984, a large rain system held its ground over Howe Sound and the Fraser Valley regions, leading to unprecedented rains on alpine snowpacks in the area of the Pemberton Valley. Waters backed up from Lillooet Lake to the Village of Pemberton overnight. North of that, the valley was flooded for upstream past Pemberton Meadows, caused by the dual "dams" created by the causeways used to cross the valley between Pemberton and Mount Currie, with the deepest waters reaching 10 feet above normal. 100 families were evacuated.
1986 Winisk flood.
On May 16, 1986, the Northern Ontario community of Winisk was completely washed away. A spring ice jam on the Winisk River caused flood waters to reach as far as inland, sending every structure but two into the Hudson Bay.
1987 Montreal flood.
The Montreal Flood of 1987 happened on July 14 of that year when a series of strong thunderstorms crossed the island of Montreal, Canada, between the noon hour and 2:30 p.m. Over of rain fell during this very short