What is flooding?

Types of flooding

Flooding is often used to describe a situation when 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, water travels across the ground and other surfaces to different places – like lakes, rivers, forests and in and around our communities. Some of this water evaporates into the air, some of it absorbs into soil and moves underground and some is taken up by plants.

When there is more water than can be evaporated into the air, stored in our lakes and rivers, used by plants or absorbed into the ground, we have flooding. This can look like water overtopping the banks of a river, or soil that cannot hold any more water. In our urban environments, water flows quickly over paved surfaces that can’t absorb water. Some of this water makes its way into infrastructure like underground pipes or roadside ditches, but when there is too much water, these systems can also be overwhelmed.

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 flooding is related to surface water, where heavy precipitation or snowmelt flows over the ground and pools in low spots. This is often called “flash flooding”. Pluvial flooding can happen anywhere when our drainage system is overwhelmed, especially during very intense rainstorms, when a lot of rain falls in a short period of time.

In the Halifax Regional Municipality, we also experience coastal flooding. Coastal flooding happens on land along the coast when ocean water is pushed above its usual height. This can happen during high winds and hurricanes, and is much worse when it occurs at high tide.

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.”