Share this page Print

Flood-related Glossary of terms

Design Flood - The size of flood that flood-related policies and structures are designed to protect against. In Alberta, flood-related policies, such as Calgary bylaws, are based on a 1:100 year flood. The design flood for structural design depends on the structure, but it is often the 1:100 year flood.

Flood mitigation - Includes policies or structures that reduce the risk of floods to a community, either by preventing floodwater from entering the community or by reducing the potential damages or threats to public safety when flooding does occur.

Flood barrier - An earthen embankment (known as a berm or a dyke), flood wall, or a temporary wall constructed of sand bags or other materials built to provide protection from floods.

Flood hazard mapping - Mapping that shows flood hazard areas along streams and rivers.

Flood Hazard Area - In Alberta, the flood hazard area is the area that would be flooded in a 1:100 year flood. It is typically divided into two zones: floodway and flood fringe. In some areas, such as Calgary, there may also be a third zone, called the overland flow zone, which is considered a special part of the flood fringe.

Floodway - The floodway includes the channel of a river and, in some places, the land next to the river. The floodway carries the bulk of the floodwater downstream. Flow is usually fastest and deepest in the floodway.

Floodplain - The area next to a river which can flood when river flows are high. The floodway and flood fringe are within the floodplain.

Flood fringe - The area outside of the floodway that is flooded in a 1:100 year return period, but where flows are not as deep or fast as in the floodway.

Flow Rate - Flow is a measure of the amount of water traveling past a point in a given amount of time. In rivers, the flow of water is typically reported in cubic metres per second (m3/s). A cubic meter is the volume of water contained in a cube of one metre high, one metre wide, and one metre deep. It is equivalent to 1000 litres of water and weighs a metric tonne. Typical flow rates on the Bow River upstream of where it meets the Elbow River is ranges between 70 to 400m3/s.

Non-structural mitigation measures - Knowledge, practice, or agreements to reduce risk and improve resiliency. These measures include policies, land use planning, development regulations, emergency response and public training and awareness.

Recovery - The process of returning a community, organization, businesses, institutions back to normality after a disaster.

Resilience - The capacity of individuals, communities, institutions, businesses and systems to absorb stresses and maintain function during external stresses.

Structural mitigation measures - Keep river flood water out of communities to a specified water level, reduce property damage and increase public safety. Examples of physical structures are dams and reservoirs, as well as barriers.

  • Upstream physical measures such as dams and reservoirs are built to control or slow the flow of the river to reduce the risk of flooding to a community as a whole.
  • Local physical barriers, such as berms, dykes and flood walls are placed where the river banks need to be raised to mitigate flooding at specific locations and providing protection to specific communities/areas.

Watershed - The entire land area that drains to a river. The Elbow River watershed extends up into the Rocky Mountains beyond Bragg Creek. Calgary gets its water from both the Elbow River and Bow River watersheds.

1-in-100-year return period flood - A large flood that has a one per cent chance of occurring in any given year. It can also be called a 1 per cent flood or a 100-year flood, and is often written as "1:100 year flood". Although called a "1 in 100 year flood" there will not necessarily be one every 100 years. It is even possible to have more than one 1 in 100 year flood in the same year. On the Bow River, the estimated flow rate for a 1:100 year return period is about 2020 m3/s.