What is flooding?

Types of flooding

Flooding is often used to describe a situation where there is more water than we want, or there is water in places we don’t expect it to be.

When precipitation (rain and snow) falls or melts, the water travels across the ground and other surfaces to places like lakes, rivers, forests, and stormwater infrastructure. Some of this water evaporates into the air, is absorbed by soil and plants, or move underground.

When there is more water than can be absorbed, evaporated, stored, or carried away, flooding can happen. Flood water is all of the extra water beyond what our natural systems and infrastructure can handle. This can look like:

• rivers overtopping their banks;
• water pooling on the ground when soil is fully saturated;
• water collecting on paved surfaces (like roads and parking lots) that can’t soak it up;
• water rushing into storm drains, underground pipes, and ditches;
• water backing up and spilling out of drainage systems when they’re over capacity;
• waves crashing onto shorelines; or
• coastal areas being flooded with sea water.

The technical term for when water spills out of lakes, river and stream banks is fluvial flooding.

Another type of flood is called pluvial flooding. This happens when heavy precipitation flows over land and collects in low spots. It’s sometimes called “flash flooding”, and water can move very quickly. It can happen anywhere, but especially in areas where drainage systems are overwhelmed by a lot of water in a short period of time. 

In the Halifax Regional Municipality, we also experience coastal flooding. Coastal flooding happens when ocean water is pushed onto land above its usual height during storms, hurricanes and high tides. It’s often worse when high tide and storm surges happen at the same time.

The terms pluvial, fluvial and coastal flooding are used on this website. To help you remember:

“Fluvial flows from the river, pluvial pours from the sky and coastal comes above the ocean’s high tide.”