Report from the Expert Management Panel on River Flood Mitigation, June 2014

Watershed reports

Based on the Watershed Reports to date, several key national themes are emerging:

Canadian watersheds face a series of significant threats, which left unchecked will jeopardize the health of water resources that provide invaluable wealth across the country.

Pollution is one of the most significant threats to Canada’s rivers, with most watersheds scoring “high” or “very high.”

The meaning of 1-100

       Frequently the meaning of 1-100 year flood is misinterpreted as meaning a flood will occur only once every 100 years; 1-100 year is actually a statistical designation meaning that in any given year there is a 1% chance a flood risk area will flood. It is similar to rolling a 100 sided dice each year where the number “1” means the area will flood. Further, some areas have experienced more than one 1-100 year flood in the same year.
       If we further break down the statistics, a 1-50 year flood has a 86.7% probability of occuring in a 50 year period and the 1-100 year flood has a 63.4% probability of occuring in a 100 year time frame!

 “From City of Calgary Website”

“…this does not mean that if a 100-year flood happened this spring, it wouldn’t happen again for another 100 years. It could happen again in the following year or even twice or more in any given year”