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- Annual exceedance probability (AEP)
The probability, expressed as a percentage, of a given flood flow or water level occurring or being exceeded in any given year.
Flood events are usually expressed in terms of an annual exceedance probability (AEP), probability ratio, or return period. For example, a 1% AEP flood event, a 1:100 flood event, and a 100-year flood event, are equivalent. However, the concept of return periods is sometimes misinterpreted as a period of time between events (e.g., 100 years until the next 100-year flood) rather than an annual exceedance probability.
- Coastal flooding
Where coastal and lakefront areas are flooded by storm surge, wave setup, wave runup, or a combination of all the above. Coastal flooding along the Atlantic, Arctic, and Pacific coasts can further be exacerbated by the occurrence of the flooding concurrently with high tide conditions.
- Design or regulatory flood
A specific flood magnitude or past flood event used as a benchmark for delineating the flood hazard areas that may be used for development regulation or long-term planning.
- Digital elevation model (DEM)
A file with terrain elevations recorded for the intersection of a fine-grained grid and organized by quadrangle as the digital equivalent of the elevation data on a topographic base map.
- Digital surface model (DSM)
A land surface, including buildings, vegetation, and other above-ground features, represented in digital form by an elevation grid or lists of three-dimensional coordinates.
- Digital terrain model (DTM)
A land surface, free of buildings and vegetation, represented in digital form by an elevation grid or lists of three-dimensional coordinates.
- Event
A singular or combination of natural processes (e.g., snowmelt, rainfall) which lead to flooding.
- Flood fringe areas
The remaining areas of the floodplain that are outside of the floodway.
- Flood hazard area
The area inundated by flood waters for the design or regulatory flood event, as determined by hydrologic and hydraulic procedures.
- Flood hazard delineation
The hydrologic and hydraulic procedures necessary to define the spatial extent, depths, and velocities of the design or regulatory flood for mapping within a study area.
- Flood mapping
The process of applying hydrologic, hydraulic, or hydrodynamic modelling outputs onto a base map to depict flood characteristics. This typically takes the form of flood lines or areas on a map that show the area that will be inundated by water, or the elevation that water would reach during a specified flood event. The data shown on the maps may also include flow velocities, depth, other risk parameters, and vulnerabilities.
- Flooding
The temporary inundation by water of normally dry land.
- Floodplain
Areas adjacent to the river channel, lake shoreline, or coastline that may be subject to flooding.
In some jurisdictions, the floodplain is referred to as the flood hazard area, which is divided into zones to support regulation and planning. These zones typically include the floodway and flood fringe, and may also contain sub-zones. Where this division exists, the terms are often defined as floodway or flood fringe areas.
- Floodway
The river channel and adjacent areas where water depths and velocities are typically greater and more hazardous.
- Hazard
A potentially damaging physical event, phenomenon, or human activity that may cause the loss of life or injury, property damage, social and economic disruption, or environmental degradation.
- Hydrometric
Relating to the monitoring and recording of water levels, velocities, and flows.
- Hydrotechnical
Relating to the technical aspects of water resources (e.g., flows, levels, extents, velocities).
- Pluvial flooding
Where extreme rainfall causes overland flooding separate from a waterway. This can include flooding in an urban setting, where the storm sewer system is overwhelmed by the rainfall, or in a rural setting where the rainfall exceeds the capacity of the ground and vegetation to absorb or store the water. Pluvial flooding can also trigger flash flood events.
- Probability ratio
A ratio used to express the likelihood of a given flood flow or water level occurring or being exceeded in any given year.
- Return period
Annual Exceedance Probability expressed in terms of years, rather than annual probability of a specific flood occurring. For example, the 0.01 annual exceedance probability is equivalent to the 100-year return period flood.
- Risk
The combination of the likelihood and the adverse consequences of a specified hazard being realized, including potential economic, social/cultural, environmental and human impacts.
- Riverine/fluvial flooding
Where high flow on a waterway exceeds the conveyance of the waterway, resulting in flooding extending into the floodplain. Fluvial flooding can also occur on lakes, where inflows raise water levels to the point where they flood adjacent land. Fluvial flooding can result from a number of causes, including abnormal snowpack, fast snowpack melt, rain-on-snow events, and heavy precipitation.
- Stream
A general term for a natural, continuously flowing watercourse.
- Streamflow
Also known as discharge, flow, or streamflow. The volume of water passing by a specific point in a stream at a defined interval. Often referred to as discharge (e.g., in cubic metres per second—m3/s).
- Study area
The location of the flood hazard delineation.
- Watershed
Also known as drainage area, drainage basin or watershed. It is the area of land draining to a particular location and includes the upstream drainage area of the main waterway as well as any tributary streams.
References
- Federal Hydrologic and Hydraulic Procedures for Flood Hazard Delineation Version 2.0 (Natural Resources Canada, 2023).
- Emergency Management Framework for Canada (Ministers Responsible for Emergency Management, 2017).
- National Disaster Mitigation Program (National Disaster Mitigation Program, 2021) literature.