What is flood?

Flood is the presence of water on land that is normally dry. Flooding is a natural process that has shaped the earth’s landscapes and ecosystems for many thousands of years. When people develop floodplains for settlement, infrastructure, agriculture and other industries, flooding can cause adverse impacts.

Types of Flood

Pluvial, coastal, riverine — learn about the types of flood in British Columbia,
and the most serious flood hazards faced by BC Lower Mainland communities.

Learn About Types of Flood

Floods on The Fraser

The Fraser Valley and other parts of the Fraser Basin have experienced two major floods of written record, the largest in 1894 and the second largest in 1948.

How Would a Lower Mainland Flood Impact Us?

A large flood in the Lower Mainland may displace up to 300,000 people if there were multiple failures in diking systems. And disruptions would extend to those living outside the floodplain too. That’s because extensive flooding would impact transportation corridors, shipping routes and other critical infrastructure, and would disrupt social, cultural and economic activity. Look at the projected impacts.

Economic Losses

Critical Infrastructure and Service Disruptions

Impacts on Animals and the Environment

Affected People

Damage to or Loss of Cultural Assets

Knowing Who Does What

Flood risk reduction is a shared responsibility in BC – and as the risk grows, so does the importance of flood risk reduction. See who does what in flood risk reduction and emergency response.

Flood Glossary You Should Know

Looking to become Flood Wise? Here is some flood terminology to get you started.

The presence of water on land that is normally dry. Often used to describe a watercourse or body of water that overtops its natural or artificial confines. See Flood 101 for a look at different types of flooding. 

A floodplain is flat or nearly flat land that is susceptible to flooding from a watercourse, lake or other body of water.

Steps to reduce flood damage by structural measures (such as dikes), non-structural measures (such as keeping populations and assets away from flood-prone areas or requiring floodproofing), or a combination of these measures.

Floodplain management includes policies and regulations intended to reduce flood risks associated with land use and development in floodplains and flood hazard areas.

A flood of a given size that is estimated to recur once in 100 years on average. This is an older term — the probability of flood recurrence is now more often expressed in terms of Annual Exceedance Probability (AEP).

Natural process or phenomenon that may cause loss of life, injury, other health impacts, property damage, loss of livelihoods and services, social and economic disruption, or environmental damage.

The maximum rate of water discharge during a flood at a given location on a river or other watercourse.

The ability of a system (such as individual or multiple buildings or infrastructure assets), community, or society exposed to hazards to resist, absorb, accommodate, and recover from the effects of a hazard in a timely and efficient manner, including through the preservation and restoration of its essential basic structures and functions.

The increase (or decrease) in still water level at a coastal site due to meteorological conditions. To learn how storm surge contributes to coastal flood hazard, see Coastal Flood.


Check out the most Frequently Asked Questions on flood hazards and flood management


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