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.1,740 m3/s (61,000 cu ft/s) when the flood reached its peak level on June 21, 2013.
Large flood disasters in Canada and estimated total costs
List of floods
1879 Fort Calgary flood The flood of 1879 had an estimated peak rate of 2,265 m3/s (80,000 cu ft/s) 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 14,700 m3/s (520,000 cu ft/s); 200 year daily maximum flow 15,600 m3/s (550,000 cu ft/s); 500 year daily maximum flow 16,800 m3/s (590,000 cu ft/s). The Fraser's highest recorded flow, in June 1894, is estimated to have been 17,000 cubic metres per second (600,000 cu ft/s) or within a range of about16,000 to 18,000 cubic metres per second (570,000 to 640,000 cu ft/s) 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 2,265 m3/s (80,000 cu ft/s) based on high-water marks. In comparison, 116 years later, in June 2013, the Bow River in Calgary peaked at c.1,740 m3/s (61,000 cu ft/s).
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 2.1 m (6.9 ft) 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 20 cm (7.9 in) when it rises to 2.9 m (9.5 ft). The Bow River, though it rises 1.5 m (4.9 ft) above normal, is still about .6 m (2.0 ft) under the 1915 record height.
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