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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..〔〔 Flooding is part of the natural environmental process.〔 Flooding used to be more frequent in spring, but take place in summer 〔 with flash floods from heavy rainfall. 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, 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)'s〔The 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 106 )〕〔The 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==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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