October 29, 2015 9:21 am

Understanding urban runoff: Why cities flood

People wade through flood water on Lakeshore West during a storm in Toronto on Monday, July 8, 2013.


You see it every time there’s a heavy rainfall: torrents of water running down streets, large lake-like “puddles” pooling in the middle of roads, flooding streets. Sometimes it doesn’t even take that much rain to produce these things.

The reason we see these each time we get a storm is due to the concrete jungle.

Typically, when rain falls, most of it is absorbed into the ground. During heavy rains, some water won’t be absorbed, but will be carried away above ground to areas where it will be absorbed.


The problem is, with cities, there isn’t much natural ground to allow that absorption. Instead, there is mostly pavement, sidewalks and more that all cover up the ground so vital in taking in that water.

Since the water has nowhere to go, it runs off, causing pooling and flooding. And the flooding can be dangerous, sweeping away cars and people.

In order to mitigate flood risks and damage to homes and buildings, cities have implemented flood management practices, including more greenspace and redesign of areas most threatened by flooding.

© 2015 Shaw Media

Report an error


Want to discuss? Please read our Commenting Policy first.