Common Types of Flood in BC
Types of flood that occur in BC include:
- River (Fluvial or riverine): flooding that occurs when creeks or rivers overflow onto dry land, typically resulting from snowmelt or heavy rainfall
- Coastal: flooding that occurs when the ocean levels are higher than normal as a result of tide or storm activity
- Pluvial: flooding that occurs during and after heavy rain or snow when water ponds in low-lying areas, particularly in urban areas if streets and drainage systems are overwhelmed
- Atmospheric Rivers refer to flows of moisture-laden air, sometimes described as “rivers in the sky,” which carry and release large amounts of water in a short period of time as either snow or rain and lead to flooding
- Groundwater: flooding that occurs when groundwater tables are high (usually as a result of nearby riverine, coastal and/or pluvial flooding) and water is pushed up to the surface
- Tsunami: a type of coastal flood that occurs when large waves form as a result of geological activity (an earthquake or a landslide) in a large body of water
- Glacial outburst: the sudden, usually natural, release of impounded water held behind a glacier
- Dam or dike failure: the sudden release of water as a result of infrastructure failure (e.g., release of water previously stored in a reservoir).
Rotary Beach, Okanagan Lake during the 2017 flood
Major Floods Hazards in the Lower Mainland
Fraser River and Coastal Flooding
In the Lower Mainland, communities can experience local flooding from heavy rainfall or from nearby creeks or rivers that overflow their banks.
Two types of large-scale floods, however, are likely to create the most widespread impacts across the region.
Atmospheric River Flooding
Atmospheric rivers can deposit large amounts of water in the form of rain or snow over a short period. This type of sustained, heavy rain can cause waterways to overflow and have serious impacts, as in November 2021 when the Nooksack River in Washington State overtopped / breached dikes and flooded Sumas Prairie.