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."Events in the Canadian Disaster Database meet at least one of the following criteria: 10 or more people killed; 100 or more people affected/injured/evacuated or homeless; An appeal for national or international assistance was made; It was an event of historical significance; There was a level of damage/disruption such that the community affected could not recover on its own (PSC, 2007) Canadian Disaster Database.
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)'sThe Boundary Waters Treaty of 1909 "established the International Joint Commission (IJC) as an organization designed to resolve disputes and to avoid conflicts between Canada and the United States from coast to coast ." 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."In the 1960s, the United States government decided to use the 1-percent annual exceedance probability (AEP) flood as the basis for the National Flood Insurance Program. The 1-percent AEP flood was thought to be a fair balance between protecting the public and overly stringent regulation. Because the 1-percent AEP flood has a 1 in 100 chance of being equalled or exceeded in any 1 year, and it has an average recurrence interval of 100 years, it often is referred to as the "100-year flood" USGS 2010."Holmes, R.R., Jr., and Dinicola, K. (2010) 100-Year flood–it's all about chance U.S. Geological Survey General Information Product 106The 100-year flood is generally expressed as a flowrate. Based on the expected 100-year flood flow rate in a given creek, river or surface water system, the flood water level can be mapped as an area of inundation. The resulting floodplain map is referred to as the 100-year floodplain, which may figure very importantly in building permits, environmental regulations, and flood insurance. with a flow of the Bow River in Calgary measured at c. when the flood reached its peak level on June 21, 2013.
Large flood disasters in Canada and estimated total costs + Table from Data sources. Year Province City/Location Total Costs in millions (trended to 2008) 1954 ON Southern ON (Hurricane Hazel)5,392 1948BCFraser River5,172 1950MBWinnipeg4,652 1996QCSaguenay2,699 1997MBSouthern Manitoba1,230 1948ONSouthern Ontario706 1993MBWinnipeg618 2005ONSouthern Ontario1,587 2005ABHigh River, Southern AB1,519 1937ONSouthern Ontario470 1923NBSaint John River Basin463 1955SK/MBManitoba and Saskatchewan362 2004ABEdmonton303 1995ABSouthern Alberta285 1934NBPlaster Rock198 1936NBNew Brunswick188 1999MBMelita163 1916ONCentral Ontario161 1909NBChester149 1961NBSaint John River Basin148 1987QCMontréal147 1996QCMontréal and Mauricie Region145 1920ONSouthwestern Ontario132 1920BCPrince George131 2004ONPeterborough129 1972QCRichelieu River124 1983NFNewfoundland115 1974QCManiwaki103
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., City of Port Coquitlam website, Retrieved on March 31, 2013 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.Calgary Herald, 3 June 1929
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 struck the 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 to over $1,000,000,000 .
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 . University of Western Ontario Geography professor Dan Shrubsole estimated the costs at about $2,000,000,000 (2008). Environment Canada estimated the flood damages at $25,000,000 (1954) or $205 million (in 2008 dollars)