Abstract

Floods are part of the natural hydrological cycle (the seasonal fluctuation of water levels) and occur along rivers and streams somewhere in Canada every year. Flooding is a common natural hazard that has caused 260 known disasters since 1900, resulting in the loss of 235 lives and 8.7 billion dollars in damage.

Most flooding in Canada is caused by weather-related mechanisms, specifically runoff from snowmelt, storm rainfall, rainfall on snow and the obstruction of flow in rivers and streams by ice jams. Floods can also be caused by the formation and failure of natural dams, but this occurs far less frequently than weather-related flooding and is usually more localized. Floods from natural dams result from the blockage of drainage by landslides, glaciers and moraines, and, at a much smaller-scale, by snow and beaver dams.

Flooding causes loss of life and damages property. Water-damaged buildings can cause significant health problems to building occupants for years after the flood because of fungi growing within the walls and building contents. The damaging effects of flooding can be reduced by identifying and carefully managing lands that are prone to flooding. Many urban areas located on such lands are protected by flood -control structures, such as dykes.