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.