History of flooding in Canada

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.(Sandink & 2010 7). 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.(Sandink & 2010 6) Between 1900 and 2005 there were 241 flood disasters in Canada.(Sandink & 2010 6)

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.(NHC & 2008 21) 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.

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